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 Preprints BibTeX:  @unpublished{nowforever,, title = {Preprints}, year = 2030 }  Zhao Liu, Gunnar Möller and Emil J. Bergholtz Lattice Genons arXiv:1702.05115v1 [cond-mat.str-el]. Abstract: Topological degeneracy is, together with fractionalization, the hallmark of topological order. While fractionalization has been demonstrated both theoretically and in laboratories leading to deep insights into our basic understanding of matter, there has been no corresponding success in tracking the evolution of ground-state degeneracy due to the lack of tractable microscopic models with arbitrarily tunable topology of space. In this work however, by computer simulations, we show that lattice versions of multicomponent fractional quantum Hall systems are novel playgrounds to fill this void. With wormhole-like defects that connect separated "universes" of different components, thus changing the global topology of space, we observe a nontrivial dependence of ground-state degeneracy on the number of defects, equivalent to adding exotic non-Abelian quasiparticles called "genons" proposed recently in terms of effective topological field theory. We identify a number of different lattice genons in both Abelian and non-Abelian phases, with quantum dimensions exceeding those of fundamental quasiparticles in the host states, and provide a promising platform to study their intriguing behavior. BibTeX:  @unpublished{1702.05115v1, author = Zhao Liu, Gunnar Möller and Emil J. Bergholtz, title = Lattice Genons, year = 2017, note = arXiv:1702.05115v1 [cond-mat.str-el], url = http://arxiv.org/abs/1702.05115v1 }  Vir B. Bulchandani, Romain Vasseur, Christoph Karrasch and Joel E. Moore Bethe-Boltzmann Hydrodynamics and Spin Transport in the XXZ Chain arXiv:1702.06146v1 [cond-mat.stat-mech]. Abstract: Quantum integrable systems, such as the interacting Bose gas in one dimension and the XXZ quantum spin chain, have an extensive number of local conserved quantities that endow them with exotic thermalization and transport properties. We review recently introduced hydrodynamic approaches for such integrable systems in detail and extend them to finite times and arbitrary initial conditions. We then discuss how such methods can be applied to describe non-equilibrium steady states involving ballistic heat and spin currents. In particular, we show that the spin Drude weight in the XXZ chain, previously accessible only by heuristic Bethe ansatz techniques, may be evaluated from hydrodynamics in very good agreement with density-matrix renormalization group calculations. This agreement is a strong check on the equivalence between the generalized hydrodynamics resulting from the infinite set of conservation laws in this model on the one hand, and the Bethe-Boltzmann equation in terms of the pseudo-momentum distribution on the other. BibTeX:  @unpublished{1702.06146v1, author = Vir B. Bulchandani, Romain Vasseur, Christoph Karrasch and Joel E. Moore, title = Bethe-Boltzmann Hydrodynamics and Spin Transport in the XXZ Chain, year = 2017, note = arXiv:1702.06146v1 [cond-mat.stat-mech], url = http://arxiv.org/abs/1702.06146v1 }  Henrik Wilming, Rodrigo Gallego and Jens Eisert Axiomatic characterization of the quantum relative entropy and free energy arXiv:1702.08473v1 [quant-ph]. Abstract: Building upon work by Matsumoto, we show that the quantum relative entropy with full-rank second argument is determined by four simple axioms: i) Continuity in the first argument, ii) the validity of the data-processing inequality, iii) additivity under tensor products, and iv) super-additivity. This observation has immediate implications for quantum thermodynamics, which we discuss. Specifically, we demonstrate that, under reasonable restrictions, the free energy is singled out as a measure of athermality. In particular, we consider an extended class of Gibbs-preserving maps as free operations in a resource-theoretic framework, in which a catalyst is allowed to build up correlations with the system at hand. The free energy is the only extensive and continuous function that is monotonic under such free operations. BibTeX:  @unpublished{1702.08473v1, author = Henrik Wilming, Rodrigo Gallego and Jens Eisert, title = Axiomatic characterization of the quantum relative entropy and free energy, year = 2017, note = arXiv:1702.08473v1 [quant-ph], url = http://arxiv.org/abs/1702.08473v1 }  Manuel Laubach, Johannes Reuther, Ronny Thomale and Stephan Rachel Three-band Hubbard model for Na$_2$IrO$_3$: Topological insulator, zigzag antiferromagnet, and Kitaev-Heisenberg material arXiv:1701.04896v1 [cond-mat.str-el]. Abstract: Na$_2$IrO$_3$ was one of the first materials proposed to feature the Kane-Mele type topological insulator phase. Contemporaneously it was claimed that the very same material is in a Mott insulating phase which is described by the Kitaev-Heisenberg (KH) model. First experiments indeed revealed Mott insulating behavior in conjunction with antiferromagnetic long-range order. Further refined experiments established antiferromagnetic order of zigzag type which is not captured by the KH model. Since then several extensions and modifications of the KH model were proposed in order to describe the experimental findings. Here we suggest that adding charge fluctuations to the KH model represents an alternative explanation of zigzag antiferromagnetism. Moreover, a phenomenological three-band Hubbard model unifies all the pieces of the puzzle: topological insulator physics for weak and KH model for strong electron-electron interactions as well as a zigzag antiferromagnet at intermediate interaction strength. BibTeX:  @unpublished{1701.04896v1, author = Manuel Laubach, Johannes Reuther, Ronny Thomale and Stephan Rachel, title = Three-band Hubbard model for Na$_2$IrO$_3$: Topological insulator, zigzag antiferromagnet, and Kitaev-Heisenberg material, year = 2017, note = arXiv:1701.04896v1 [cond-mat.str-el], url = http://arxiv.org/abs/1701.04896v1 }  U. Las Heras, R. Di Candia, K. G. Fedorov, F. Deppe, M. Sanz and E. Solano Quantum Illumination Unveils Cloaking arXiv:1611.10280v1 [quant-ph]. Abstract: In quantum illumination entangled light is employed to enhance the detection accuracy of an object when compared with the best classical protocol. On the other hand, cloaking is a stealth technology based on covering a target with a material deflecting the light around the object to avoid its detection. Here, we propose a quantum illumination protocol especially adapted to quantum microwave technology which, by seizing weaknesses in current cloaking techniques, allows for a $3$ dB improvement in the detection of a cloaked target. Finally, we study the minimal efficiency required by the photocounter for which the quantum illumination protocol still shows a gain with respect to the classical protocol. BibTeX:  @unpublished{1611.10280v1, author = U. Las Heras, R. Di Candia, K. G. Fedorov, F. Deppe, M. Sanz and E. Solano, title = Quantum Illumination Unveils Cloaking, year = 2016, note = arXiv:1611.10280v1 [quant-ph], url = http://arxiv.org/abs/1611.10280v1 }  Daniel Litinski, Piet W. Brouwer and Michele Filippone The Interacting Mesoscopic Capacitor Out of Equilibrium arXiv:1612.04822v1 [cond-mat.mes-hall]. Abstract: We consider the full non-equilibrium response of a mesoscopic capacitor in the large transparency limit, exactly solving a model with electron-electron interactions appropriate for a cavity in the quantum Hall regime. For a cavity coupled to the electron reservoir via an ideal point contact, we show that the response to any time-dependent gate voltage $V_{\rm g}(t)$ is strictly linear in $V_{\rm g}$. We analyze the charge and current response to a sudden gate voltage shift, and find that this response is not captured by a simple circuit analogy. In particular, in the limit of strong interactions a sudden change in the gate voltage leads to the emission of a sequence of multiple charge pulses, the width and separation of which are controlled by the charge-relaxation time $\tau_{\rm c} = h C_{\rm g}/e^2$ and the time of flight $\tau_{\rm f}$. We also consider the effect of a finite reflection amplitude in the point contact, which leads to non-linear-in-gate-voltage corrections to the charge and current response. BibTeX:  @unpublished{1612.04822v1, author = Daniel Litinski, Piet W. Brouwer and Michele Filippone, title = The Interacting Mesoscopic Capacitor Out of Equilibrium, year = 2016, note = arXiv:1612.04822v1 [cond-mat.mes-hall], url = http://arxiv.org/abs/1612.04822v1 }  Elina Locane and Piet W. Brouwer Current-induced switching of magnetic molecules on topological insulator surfaces arXiv:1612.02711v1 [cond-mat.mes-hall]. Abstract: Electrical currents at the surface or edge of a topological insulator are intrinsically spin-polarized. We show that such surface/edge currents can be used to switch the orientation of a molecular magnet weakly coupled to the surface or edge of a topological insulator. For the edge of a two-dimensional topological insulator as well as for the surface of a three-dimensional topological insulator the application of a well-chosen surface/edge current can lead to a complete polarization of the molecule if the molecule's magnetic anisotropy axis is appropriately aligned with the current direction. For a generic orientation of the molecule a nonzero but incomplete polarization is obtained. We calculate the probability distribution of the magnetic states and the switching rates as a function of the applied current. BibTeX:  @unpublished{1612.02711v1, author = Elina Locane and Piet W. Brouwer, title = Current-induced switching of magnetic molecules on topological insulator surfaces, year = 2016, note = arXiv:1612.02711v1 [cond-mat.mes-hall], url = http://arxiv.org/abs/1612.02711v1 }  M. L. Baez and J. Reuther Numerical treatment of spin systems with unrestricted spin length $S$: A functional renormalization group study arXiv:1612.05074v2 [cond-mat.str-el]. Abstract: We develop a generalized pseudo-fermion functional renormalization group (PFFRG) approach that can be applied to arbitrary Heisenberg models with spins ranging from the quantum case $S=1/2$ to the classical limit $S\rightarrow\infty$. Within this framework, spins of magnitude $S$ are realized by implementing $M=2S$ copies of spin-1/2 degrees of freedom on each lattice site. We confirm that even without explicitly projecting onto the highest spin sector of the Hilbert space, ground states tend to select the largest possible local spin magnitude. This justifies the average treatment of the pseudo fermion constraint in previous spin-1/2 PFFRG studies. We apply this method to the antiferromagnetic $J_1$-$J_2$ honeycomb Heisenberg model with nearest neighbor $J_1>0$ and second neighbor $J_2>0$ interactions. Mapping out the phase diagram in the $J_2/J_1$-$S$ plane we find that upon increasing $S$ quantum fluctuations are rapidly decreasing. In particular, already at $S=1$ we find no indication for a magnetically disordered phase. In the limit $S\rightarrow\infty$, the known phase diagram of the classical system is exactly reproduced. More generally, we prove that for $S\rightarrow\infty$ the PFFRG approach is identical to the Luttinger-Tisza method. BibTeX:  @unpublished{1612.05074v2, author = M. L. Baez and J. Reuther, title = Numerical treatment of spin systems with unrestricted spin length $S$: A functional renormalization group study, year = 2016, note = arXiv:1612.05074v2 [cond-mat.str-el], url = http://arxiv.org/abs/1612.05074v2 }  A. Steffens, C. Riofrio, W. McCutcheon, B. A. Bell, A. McMillan, J. G. Rarity and J. Eisert Experimentally exploring compressed sensing quantum tomography arXiv:1611.01189 [quant-ph]. Abstract: In the light of the progress in quantum technologies, the task of verifying the correct functioning of processes and obtaining accurate tomographic information about quantum states becomes increasingly important. Compressed sensing, a machinery derived from the theory of signal processing, has emerged as a feasible tool to perform robust and significantly more resource-economical quantum state tomography for intermediate-sized quantum systems. In this work, we provide a comprehensive analysis of compressed sensing tomography in the regime in which tomographically complete data is available with reliable statistics from experimental observations of a multi-mode photonic architecture. Due to the fact that the data is known with high statistical significance, we are in a position to systematically explore the quality of reconstruction depending on the number of employed measurement settings, randomly selected from the complete set of data, and on different model assumptions. We present and test a complete prescription to perform efficient compressed sensing and are able to reliably use notions of model selection and cross-validation to account for experimental imperfections and finite counting statistics. Thus, we establish compressed sensing as an effective tool for quantum state tomography, specifically suited for photonic systems. BibTeX:  @unpublished{Steffens2016, author = A. Steffens, C. Riofrio, W. McCutcheon, B. A. Bell, A. McMillan, J. G. Rarity and J. Eisert, title = Experimentally exploring compressed sensing quantum tomography, year = 2016, note = arXiv:1611.01189 [quant-ph], url = https://arxiv.org/abs/1611.01189 }  Gleb Skorobagatko, Anton Bruch, Silvia Viola Kusminskiy and Alessandro Romito Effect of interactions on quantum limited detectors arXiv:1609.07281 [cond-mat.mes-hall]. Abstract: We consider the effect of electron-electron interactions on a voltage biased quantum point contact in the tunneling regime used as a detector of a nearby qubit. We model the leads of the quantum point contact as Luttinger liquids, incorporate the effects of finite temperature and analyze the detection-induced decoherence rate and the detector efficiency, $Q$. We find that interactions generically reduce the induced decoherence along with the detector's efficiency, and strongly affect the relative strength of the decoherence induced by tunneling and that induced by interactions with the local density. With increasing interaction strength, the regime of quantum limited detection ($Q=1$) is shifted to increasingly lower temperatures or higher bias voltages respectively. For small to moderate interaction strengths, $Q$ is a monotonously decreasing function of temperature as in the non-interacting case. Surprisingly, for sufficiently strong interactions we identify an intermediate temperature regime where the efficiency of the detector increases with rising temperature. BibTeX:  @unpublished{Skorobagatko2016, author = Gleb Skorobagatko, Anton Bruch, Silvia Viola Kusminskiy and Alessandro Romito, title = Effect of interactions on quantum limited detectors, year = 2016, note = arXiv:1609.07281 [cond-mat.mes-hall], url = https://arxiv.org/abs/1609.07281 }  Patrick Rebentrost, Adrian Steffens and Seth Lloyd Quantum singular value decomposition of non-sparse low-rank matrices arXiv:1607.05404v1 [quant-ph]. Abstract: In this work, we present a method to exponentiate non-sparse indefinite low-rank matrices on a quantum computer. Given an operation for accessing the elements of the matrix, our method allows singular values and associated singular vectors to be found quantum mechanically in a time exponentially faster in the dimension of the matrix than known classical algorithms. The method extends to non-Hermitian and non-square matrices via embedding matrices. In the context of the generic singular value decomposition of a matrix, we discuss the Procrustes problem of finding a closest isometry to a given matrix. BibTeX:  @unpublished{1607.05404v1, author = Patrick Rebentrost, Adrian Steffens and Seth Lloyd, title = Quantum singular value decomposition of non-sparse low-rank matrices, year = 2016, note = arXiv:1607.05404v1 [quant-ph], url = http://arxiv.org/abs/1607.05404v1 }  E. Onorati, O. Buerschaper, M. Kliesch, W. Brown, A. H. Werner and J. Eisert Mixing properties of stochastic quantum Hamiltonians arXiv:1606.01914 [quant-ph]. Abstract: Random quantum processes play a central role both in the study of fundamental mixing processes in quantum mechanics related to equilibration, thermalisation and fast scrambling by black holes, as well as in quantum process design and quantum information theory. In this work, we present a framework describing the mixing properties of continuous-time unitary evolutions originating from local Hamiltonians having time-fluctuating terms, reflecting a Brownian motion on the unitary group. The induced stochastic time evolution is shown to converge to a unitary design. As a first main result, we present bounds to the mixing time. By developing tools in representation theory, we analytically derive an expression for a local k-th moment operator that is entirely independent of k, giving rise to approximate unitary k-designs and quantum tensor product expanders. As a second main result, we introduce tools for proving bounds on the rate of decoupling from an environment with random quantum processes. By tying the mathematical description closely with the more established one of random quantum circuits, we present a unified picture for analysing local random quantum and classes of Markovian dissipative processes, for which we discuss applications. BibTeX:  @unpublished{Onorati2016, author = E. Onorati, O. Buerschaper, M. Kliesch, W. Brown, A. H. Werner and J. Eisert, title = Mixing properties of stochastic quantum Hamiltonians, year = 2016, note = arXiv:1606.01914 [quant-ph], url = https://arxiv.org/abs/1606.01914 }  Björn Sbierski, Maximilian Trescher, Emil J. Bergholtz and Piet W. Brouwer Disordered double Weyl node: Comparison of transport and density-of-states calculations arXiv:1606.06941 [cond-mat.mes-hall]. Abstract: Double Weyl nodes are topologically protected band crossing points which carry chiral charge $\pm2$. They are stabilized by $C_{4}$ point group symmetry and are predicted to occur in $\mathrm{SrSi_{2}}$ or $\mathrm{HgCr_{2}Se_{4}}$. We study their stability and physical properties in the presence of a disorder potential. We investigate the density of states and the quantum transport properties at the nodal point. We find that, in contrast to their counterparts with unit chiral charge, double Weyl nodes are unstable to any finite amount of disorder and give rise to a diffusive phase, in agreement with predictions of Goswami and Nevidomskyy [Phys. Rev. B 92, 214504 (2015)] and Bera, Sau, and Roy [Phys. Rev. B 93, 201302(R) (2016)]. However, for finite system sizes a crossover between pseudodiffusive and diffusive quantum transport can be observed. BibTeX:  @unpublished{Sbierski2016a, author = Björn Sbierski, Maximilian Trescher, Emil J. Bergholtz and Piet W. Brouwer, title = Disordered double Weyl node: Comparison of transport and density-of-states calculations, year = 2016, note = arXiv:1606.06941 [cond-mat.mes-hall], url = https://arxiv.org/abs/1606.06941 }  H. Wilming, M. J. Kastoryano, A. H. Werner and J. Eisert Emergence of spontaneous symmetry breaking in dissipative lattice systems arXiv:1602.01108 [quant-ph]. Abstract: A cornerstone of the theory of phase transitions is the observation that many-body systems exhibiting a spontaneous symmetry breaking in the thermodynamic limit generally show extensive fluctuations of an order parameter in large but finite systems. In this work, we introduce the dynamical analogue of such a theory. Specifically, we consider local dissipative dynamics preparing a steady-state of quantum spins on a lattice exhibiting a discrete or continuous symmetry but with extensive fluctuations in a local order parameter. We show that for all such processes satisfying detailed balance, there exist metastable symmetry-breaking states, i.e., states that become stationary in the thermodynamic limit and give a finite value to the order parameter. We give results both for discrete and continuous symmetries and explicitly show how to construct the symmetry-breaking states. Our results show in a simple way that, in large systems, local dissipative dynamics satisfying detailed balance cannot uniquely and efficiently prepare states with extensive fluctuations with respect to local operators. We discuss the implications of our results for quantum simulators and dissipative state preparation. BibTeX:  @unpublished{Wilming2016, author = H. Wilming, M. J. Kastoryano, A. H. Werner and J. Eisert, title = Emergence of spontaneous symmetry breaking in dissipative lattice systems, year = 2016, note = arXiv:1602.01108 [quant-ph], url = http://arxiv.org/abs/1602.01108 }  Juan Bermejo-Vega and Kevin C. Zatloukal Abelian Hypergroups and Quantum Computation arXiv:1509.05806 [quant-ph]. Abstract: Motivated by a connection, described here for the first time, between the hidden normal subgroup problem (HNSP) and abelian hypergroups (algebraic objects that model collisions of physical particles), we develop a stabilizer formalism using abelian hypergroups and an associated classical simulation theorem (a la Gottesman-Knill). Using these tools, we develop the first provably efficient quantum algorithm for finding hidden subhypergroups of nilpotent abelian hypergroups and, via the aforementioned connection, a new, hypergroup-based algorithm for the HNSP on nilpotent groups. We also give efficient methods for manipulating non-unitary, non-monomial stabilizers and an adaptive Fourier sampling technique of general interest. BibTeX:  @unpublished{Bermejo-Vega2015, author = Juan Bermejo-Vega and Kevin C. Zatloukal, title = Abelian Hypergroups and Quantum Computation, year = 2015, note = arXiv:1509.05806 [quant-ph], url = http://arxiv.org/abs/1509.05806 }  Netanel H. Lindner, Aaron Farrell, Eran Lustig, Gil Refael and Felix von Oppen Lighting up topological insulators: large surface photocurrents from magnetic superlattices arXiv:1403.0010v2 [cond-mat.mes-hall]. Abstract: The gapless surface states of topological insulators (TI) can potentially be used to detect and harvest low-frequency infrared light. Nonetheless, it was shown that significant surface photocurrents due to light with frequency below the bulk gap are rather hard to produce. Here we demonstrate that a periodic magnetic pattern added to the surface dramatically enhances surface photocurrents in TI's. Moreover, the sensitivity of this set-up to the wavelength of the incident light can be optimized by tuning the geometry of the magnetic pattern. The ability to produce substantial photocurrents on TI surfaces from mid-range and far-infrared light could be used in photovoltaic applications, as well as for detection of micrometer wavelength radiation. For light of wavelength greater than 15$\mu$m we estimate that at room temperature, a detector based on the effect we describe can have a specific detectivity as high as 10$^7$ cm$\sqrt{\text{Hz}}$/W (i.e. 10$^9$ Jones). The device can therefore operate at much larger wavelengths than existing infrared detectors, while maintaining a comparable figure of merit.er wavelength radiation. BibTeX:  @unpublished{1403.0010v2, author = Netanel H. Lindner, Aaron Farrell, Eran Lustig, Gil Refael and Felix von Oppen, title = Lighting up topological insulators: large surface photocurrents from magnetic superlattices, year = 2014, note = arXiv:1403.0010v2 [cond-mat.mes-hall], url = http://arxiv.org/abs/1403.0010v2 }  C. Gogolin, M. Kliesch, L. Aolita and J. Eisert Boson-Sampling in the light of sample complexity arXiv:1306.3995 [quant-ph]. Abstract: Boson-Sampling is a classically computationally hard problem that can - in principle - be efficiently solved with quantum linear optical networks. Very recently, a rush of experimental activity has ignited with the aim of developing such devices as feasible instances of quantum simulators. Even approximate Boson-Sampling is believed to be hard with high probability if the unitary describing the optical network is drawn from the Haar measure. In this work we show that in this setup, with probability exponentially close to one in the number of bosons, no symmetric algorithm can distinguish the Boson-Sampling distribution from the uniform one from fewer than exponentially many samples. This means that the two distributions are operationally indistinguishable without detailed a priori knowledge. We carefully discuss the prospects of efficiently using knowledge about the implemented unitary for devising non-symmetric algorithms that could potentially improve upon this. We conclude that due to the very fact that Boson-Sampling is believed to be hard, efficient classical certification of Boson-Sampling devices seems to be out of reach. BibTeX:  @unpublished{2013arXiv1306.3995G, author = C. Gogolin, M. Kliesch, L. Aolita and J. Eisert, title = Boson-Sampling in the light of sample complexity, year = 2013, note = arXiv:1306.3995 [quant-ph], url = http://arxiv.org/abs/1306.3995 }  F. Caravelli, F. Markopoulou, A. Riera and L. Sindoni Quenches and lattice simulators for particle creation arXiv:1212.1981 [gr-qc]. Abstract: In this paper we propose a framework for simulating thermal particle production in condensed matter systems. The procedure we describe can be realized by means of a quantum quench of a parameter in the model. In order to support this claim, we study quadratic fermionic systems in one and two dimensions by means of analytical and numerical techniques. In particular, we are able to show that a class of observables associated to Unruh--de Witt detectors are very relevant for this type of setup and that exhibit approximate thermalization. BibTeX:  @unpublished{2012arXiv1212.1981C, author = F. Caravelli, F. Markopoulou, A. Riera and L. Sindoni, title = Quenches and lattice simulators for particle creation, year = 2012, note = arXiv:1212.1981 [gr-qc], url = http://arxiv.org/abs/1212.1981 }  M. Ohliger, V. Nesme, D. Gross, Y.-K. Liu and J. Eisert Continuous-variable quantum compressed sensing arXiv:1111.0853v2 [quant-ph]. Abstract: We introduce a novel method to faithfully reconstruct unknown quantum states that are approximately low-rank, using only a few measurement settings. The method is general enough to allow for measurements from a continuous family, and is also applicable to continuous-variable states. As a technical result, this work generalizes quantum compressed sensing to the situation where the measured observables are taken from a so-called tight frame (rather than an orthonormal basis) --- hence covering most realistic measurement scenarios. As an application, we discuss the reconstruction of quantum states of light from homodyne detection and other types of measurements, and we present simulations that show the advantage of the proposed compressed sensing technique over present methods. Finally, we introduce a method to construct a certificate which guarantees the success of the reconstruction with no assumption on the state, and we show how slightly more measurements give rise to "universal" state reconstruction that is highly robust to noise. BibTeX:  @unpublished{Ohliger2011, author = M. Ohliger, V. Nesme, D. Gross, Y.-K. Liu and J. Eisert, title = Continuous-variable quantum compressed sensing, year = 2011, note = arXiv:1111.0853v2 [quant-ph], url = http://arxiv.org/abs/1111.0853 }  2017 BibTeX:  @unpublished{20172018,, title = {Preprints}, year = 2017 }  Adrian Steffens, Patrick Rebentrost, Iman Marvian, Jens Eisert and Seth Lloyd An efficient quantum algorithm for spectral estimation New Journal of Physics 19(3), 033005 (2017). Abstract: We develop an efficient quantum implementation of an important signal processing algorithm for line spectral estimation: the matrix pencil method , which determines the frequencies and damping factors of signals consisting of finite sums of exponentially damped sinusoids. Our algorithm provides a quantum speedup in a natural regime where the sampling rate is much higher than the number of sinusoid components. Along the way, we develop techniques that are expected to be useful for other quantum algorithms as well—consecutive phase estimations to efficiently make products of asymmetric low rank matrices classically accessible and an alternative method to efficiently exponentiate non-Hermitian matrices. Our algorithm features an efficient quantum–classical division of labor: the time-critical steps are implemented in quantum superposition, while an interjacent step, requiring much fewer parameters, can operate classically. We show that frequencies and damping factors can be obtained in time logarithmic in the number of sampling points, exponentially faster than known classical algorithms. BibTeX:  @article{1367-2630-19-3-033005, author = Adrian Steffens, Patrick Rebentrost, Iman Marvian, Jens Eisert and Seth Lloyd, title = An efficient quantum algorithm for spectral estimation, journal = New Journal of Physics, year = 2017, volume = 19, number = 3, pages = 033005, url = http://stacks.iop.org/1367-2630/19/i=3/a=033005, doi = http://dx.doi.org/10.1088/1367-2630/aa5e48 }  U. Alvarez-Rodriguez, R. Di Candia, J. Casanova, M. Sanz and E. Solano Algorithmic quantum simulation of memory effects Phys. Rev. A 95(2), 020301 (2017). Abstract: We propose a method for the algorithmic quantum simulation of memory effects described by integrodifferential evolution equations. It consists in the systematic use of perturbation theory techniques and a Markovian quantum simulator. Our method aims to efficiently simulate both completely positive and nonpositive dynamics without the requirement of engineering non-Markovian environments. Finally, we find that small error bounds can be reached with polynomially scaling resources, evaluated as the time required for the simulation. BibTeX:  @article{PhysRevA.95.020301, author = U. Alvarez-Rodriguez, R. Di Candia, J. Casanova, M. Sanz and E. Solano, title = Algorithmic quantum simulation of memory effects, journal = Phys. Rev. A, year = 2017, volume = 95, number = 2, pages = 020301, url = http://link.aps.org/doi/10.1103/PhysRevA.95.020301, doi = http://dx.doi.org/10.1103/PhysRevA.95.020301 }  Max Hering and Johannes Reuther Functional renormalization group analysis of Dzyaloshinsky-Moriya and Heisenberg spin interactions on the kagome lattice Phys. Rev. B 95(5), 054418 (2017). Abstract: We investigate the effects of Dzyaloshinsky-Moriya (DM) interactions on the frustrated J1−J2 kagome-Heisenberg model using the pseudofermion functional renormalization group (PFFRG) technique. In order to treat the off-diagonal nature of DM interactions, we develop an extended PFFRG scheme. We benchmark this approach in parameter regimes that have previously been studied with other methods and find good agreement of the magnetic phase diagram. Particularly, finite DM interactions are found to stabilize all types of noncollinear magnetic orders of the J1−J2 Heisenberg model (q=0, 3×3, and cuboc orders) and shrink the extents of magnetically disordered phases. We discuss our results in the light of the mineral herbertsmithite which has been experimentally predicted to host a quantum spin liquid at low temperatures. Our PFFRG data indicate that this material lies in close proximity to a quantum critical point. In parts of the experimentally relevant parameter regime for herbertsmithite, the spin-correlation profile is found to be in good qualitative agreement with recent inelastic-neutron-scattering data. BibTeX:  @article{PhysRevB.95.054418, author = Max Hering and Johannes Reuther, title = Functional renormalization group analysis of Dzyaloshinsky-Moriya and Heisenberg spin interactions on the kagome lattice, journal = Phys. Rev. B, year = 2017, volume = 95, number = 5, pages = 054418, url = http://link.aps.org/doi/10.1103/PhysRevB.95.054418, doi = http://dx.doi.org/10.1103/PhysRevB.95.054418 }  Kevin A. Madsen, Emil J. Bergholtz and Piet W. Brouwer Josephson effect in a Weyl SNS junction Phys. Rev. B 95(6), 064511 (2017). Abstract: We calculate the Josephson current density j(ϕ) for a Weyl superconductor–normal-metal–superconductor junction for which the outer terminals are superconducting Weyl metals and the normal layer is a Weyl (semi)metal. We describe the Weyl (semi)metal using a simple model with two Weyl points. The model has broken time-reversal symmetry, but inversion symmetry is present. We calculate the Josephson current for both zero and finite temperature for the two pairing mechanisms inside the superconductors that have been proposed in the literature, zero-momentum BCS-like pairing and finite-momentum FFLO-like pairing, and assuming the short-junction limit. For both pairing types we find that the current is proportional to the normal-state junction conductivity, with a proportionality coefficient that shows quantitative differences between the two pairing mechanisms. The current for the BCS-like pairing is found to be independent of the chemical potential, whereas the current for the FFLO-like pairing is not. BibTeX:  @article{PhysRevB.95.064511, author = Kevin A. Madsen, Emil J. Bergholtz and Piet W. Brouwer, title = Josephson effect in a Weyl SNS junction, journal = Phys. Rev. B, year = 2017, volume = 95, number = 6, pages = 064511, url = http://link.aps.org/doi/10.1103/PhysRevB.95.064511, doi = http://dx.doi.org/10.1103/PhysRevB.95.064511 }  M. Sanz, U. Las Heras, J. J. García-Ripoll, E. Solano and R. Di Candia Quantum Estimation Methods for Quantum Illumination Phys. Rev. Lett. 118(7), 070803 (2017). Abstract: Quantum illumination consists in shining quantum light on a target region immersed in a bright thermal bath with the aim of detecting the presence of a possible low-reflective object. If the signal is entangled with the receiver, then a suitable choice of the measurement offers a gain with respect to the optimal classical protocol employing coherent states. Here, we tackle this detection problem by using quantum estimation techniques to measure the reflectivity parameter of the object, showing an enhancement in the signal-to-noise ratio up to 3 dB with respect to the classical case when implementing only local measurements. Our approach employs the quantum Fisher information to provide an upper bound for the error probability, supplies the concrete estimator saturating the bound, and extends the quantum illumination protocol to non-Gaussian states. As an example, we show how Schrödinger’s cat states may be used for quantum illumination. BibTeX:  @article{PhysRevLett.118.070803, author = M. Sanz, U. Las Heras, J. J. García-Ripoll, E. Solano and R. Di Candia, title = Quantum Estimation Methods for Quantum Illumination, journal = Phys. Rev. Lett., year = 2017, volume = 118, number = 7, pages = 070803, url = http://link.aps.org/doi/10.1103/PhysRevLett.118.070803, doi = http://dx.doi.org/10.1103/PhysRevLett.118.070803 }  Maximilian Trescher, Björn Sbierski, Piet W. Brouwer and Emil J. Bergholtz Tilted disordered Weyl semimetals Phys. Rev. B 95(4), 045139 (2017). Abstract: Although Lorentz invariance forbids the presence of a term that tilts the energy-momentum relation in the Weyl Hamiltonian, a tilted dispersion is not forbidden and, in fact, generic for condensed matter realizations of Weyl semimetals. We here investigate the combined effect of such a tilted Weyl dispersion and the presence of potential disorder. In particular, we address the influence of a tilt on the disorder-induced phase transition between a quasiballistic phase at weak disorder, in which the disorder is an irrelevant perturbation, and a diffusive phase at strong disorder. Our main result is that the presence of a tilt leads to a reduction of the critical disorder strength for this transition or, equivalently, that increasing the tilt at fixed disorder strength drives the system through the phase transition to the diffusive strong-disorder phase. Notably this obscures the tilt-induced Lifshitz transition to an overtilted type II Weyl phase at any finite disorder strength. Our results are supported by analytical calculations using the self-consistent Born approximation and numerical calculations of the density of states and of transport properties. BibTeX:  @article{PhysRevB.95.045139, author = Maximilian Trescher, Björn Sbierski, Piet W. Brouwer and Emil J. Bergholtz, title = Tilted disordered Weyl semimetals, journal = Phys. Rev. B, year = 2017, volume = 95, number = 4, pages = 045139, url = http://link.aps.org/doi/10.1103/PhysRevB.95.045139, doi = http://dx.doi.org/10.1103/PhysRevB.95.045139 }  2016 BibTeX:  @unpublished{20162017,, title = {Preprints}, year = 2016 }  C. Cedzich, F. A. Grünbaum, C. Stahl, L. Velázquez, A. H. Werner and R. F. Werner Bulk-edge correspondence of one-dimensional quantum walks Journal of Physics A: Mathematical and Theoretical 49(21), 21LT01 (2016). Abstract: We outline a theory of symmetry protected topological phases of one-dimensional quantum walks. We assume spectral gaps around the symmetry-distinguished points +1 and −1, in which only discrete eigenvalues are allowed. The phase classification by integer or binary indices extends the classification known for translation invariant systems in terms of their band structure. However, our theory requires no translation invariance whatsoever, and the indices we define in this general setting are invariant under arbitrary symmetric local perturbations, even those that cannot be continuously contracted to the identity. More precisely we define two indices for every walk, characterizing the behavior far to the right and far to the left, respectively. Their sum is a lower bound on the number of eigenstates at +1 and −1. For a translation invariant system the indices add up to zero, so one of them already characterizes the phase. By joining two bulk phases with different indices we get a walk in which the right and left indices no longer cancel, so the theory predicts bound states at +1 or −1. This is a rigorous statement of bulk-edge correspondence. The results also apply to the Hamiltonian case with a single gap at zero. BibTeX:  @article{1751-8121-49-21-21LT01, author = C. Cedzich, F. A. Grünbaum, C. Stahl, L. Velázquez, A. H. Werner and R. F. Werner, title = Bulk-edge correspondence of one-dimensional quantum walks, journal = Journal of Physics A: Mathematical and Theoretical, year = 2016, volume = 49, number = 21, pages = 21LT01, url = http://stacks.iop.org/1751-8121/49/i=21/a=21LT01, doi = http://dx.doi.org/10.1088/1751-8113/49/21/21LT01 }  Yang Peng, Yuval Vinkler-Aviv, Piet W. Brouwer, Leonid I. Glazman and Felix von Oppen Parity Anomaly and Spin Transmutation in Quantum Spin Hall Josephson Junctions Phys. Rev. Lett. 117(26), 267001 (2016). Abstract: We study the Josephson effect in a quantum spin Hall system coupled to a localized magnetic impurity. As a consequence of the fermion parity anomaly, the spin of the combined system of impurity and spin-Hall edge alternates between half-integer and integer values when the superconducting phase difference across the junction advances by 2π. This leads to characteristic differences in the splittings of the spin multiplets by exchange coupling and single-ion anisotropy at phase differences, for which time-reversal symmetry is preserved. We discuss the resulting 8π-periodic (or Z4) fractional Josephson effect in the context of recent experiments. BibTeX:  @article{PhysRevLett.117.267001, author = Yang Peng, Yuval Vinkler-Aviv, Piet W. Brouwer, Leonid I. Glazman and Felix von Oppen, title = Parity Anomaly and Spin Transmutation in Quantum Spin Hall Josephson Junctions, journal = Phys. Rev. Lett., year = 2016, volume = 117, number = 26, pages = 267001, url = http://link.aps.org/doi/10.1103/PhysRevLett.117.267001, doi = http://dx.doi.org/10.1103/PhysRevLett.117.267001 }  W. Zhu, Zhao Liu, F. D. M. Haldane and D. N. Sheng Fractional quantum Hall bilayers at half filling: Tunneling-driven non-Abelian phase Phys. Rev. B 94(24), 245147 (2016). Abstract: Multicomponent quantum Hall systems with internal degrees of freedom provide a fertile ground for the emergence of exotic quantum liquids. Here, we investigate the possibility of non-Abelian topological order in the half-filled fractional quantum Hall (FQH) bilayer system driven by the tunneling effect between two layers. By means of the state-of-the-art density-matrix renormalization group, we unveil “fingerprint” evidence of the non-Abelian Moore-Read Pfaffian state emerging in the intermediate-tunneling regime, including the ground-state degeneracy on the torus geometry and the topological entanglement spectroscopy (entanglement spectrum and topological entanglement entropy) on the spherical geometry, respectively. Remarkably, the phase transition from the previously identified Abelian (331) Halperin state to the non-Abelian Moore-Read Pfaffian state is determined to be continuous, which is signaled by the continuous evolution of the universal part of the entanglement spectrum, and discontinuities in the excitation gap and the derivative of the ground-state energy. Our results not only provide a “proof-of-principle” demonstration of realizing a non-Abelian state through coupling different degrees of freedom, but also open up a possibility in FQH bilayer systems for detecting different chiral p−wave pairing states. BibTeX:  @article{PhysRevB.94.245147, author = W. Zhu, Zhao Liu, F. D. M. Haldane and D. N. Sheng, title = Fractional quantum Hall bilayers at half filling: Tunneling-driven non-Abelian phase, journal = Phys. Rev. B, year = 2016, volume = 94, number = 24, pages = 245147, url = http://link.aps.org/doi/10.1103/PhysRevB.94.245147, doi = http://dx.doi.org/10.1103/PhysRevB.94.245147 }  Michele Filippone and Piet W. Brouwer Tunneling into quantum wires: Regularization of the tunneling Hamiltonian and consistency between free and bosonized fermions Phys. Rev. B 94(23), 235426 (2016). Abstract: Tunneling between a point contact and a one-dimensional wire is usually described with the help of a tunneling Hamiltonian that contains a δ function in position space. Whereas the leading-order contribution to the tunneling current is independent of the way this δ function is regularized, higher-order corrections with respect to the tunneling amplitude are known to depend on the regularization. Instead of regularizing the δ function in the tunneling Hamiltonian, one may also obtain a finite tunneling current by invoking the ultraviolet cutoffs in a field-theoretic description of the electrons in the one-dimensional conductor, a procedure that is often used in the literature. For the latter case, we show that standard ultraviolet cutoffs lead to different results for the tunneling current in fermionic and bosonized formulations of the theory, when going beyond leading order in the tunneling amplitude. We show how to recover the standard fermionic result using the formalism of functional bosonization and revisit the tunneling current to leading order in the interacting case. BibTeX:  @article{PhysRevB.94.235426, author = Michele Filippone and Piet W. Brouwer, title = Tunneling into quantum wires: Regularization of the tunneling Hamiltonian and consistency between free and bosonized fermions, journal = Phys. Rev. B, year = 2016, volume = 94, number = 23, pages = 235426, url = http://link.aps.org/doi/10.1103/PhysRevB.94.235426, doi = http://dx.doi.org/10.1103/PhysRevB.94.235426 }  Yasir Iqbal, Pratyay Ghosh, Rajesh Narayanan, Brijesh Kumar, Johannes Reuther and Ronny Thomale Intertwined nematic orders in a frustrated ferromagnet Phys. Rev. B 94(22), 224403 (2016). Abstract: We investigate the quantum phases of the frustrated spin-12J1−J2−J3 Heisenberg model on the square lattice with ferromagnetic J1 and antiferromagnetic J2 and J3 interactions. Using the pseudofermion functional renormalization group technique, we find an intermediate paramagnetic phase located between classically ordered ferromagnetic, stripy antiferromagnetic, and incommensurate spiral phases. We observe that quantum fluctuations lead to significant shifts of the spiral pitch angles compared to the classical limit. By computing the response of the system with respect to various spin rotation and lattice symmetry-breaking perturbations, we identify a complex interplay between different nematic spin states in the paramagnetic phase. While retaining time-reversal invariance, these phases either break spin-rotation symmetry, lattice-rotation symmetry, or a combination of both. We therefore propose the J1−J2−J3 Heisenberg model on the square lattice as a paradigmatic example where different intimately connected types of nematic orders emerge in the same model. BibTeX:  @article{PhysRevB.94.224403, author = Yasir Iqbal, Pratyay Ghosh, Rajesh Narayanan, Brijesh Kumar, Johannes Reuther and Ronny Thomale, title = Intertwined nematic orders in a frustrated ferromagnet, journal = Phys. Rev. B, year = 2016, volume = 94, number = 22, pages = 224403, url = http://link.aps.org/doi/10.1103/PhysRevB.94.224403, doi = http://dx.doi.org/10.1103/PhysRevB.94.224403 }  Björn Sbierski, Kevin S. C. Decker and Piet W. Brouwer Weyl node with random vector potential Phys. Rev. B 94(22), 220202 (2016). Abstract: We study Weyl semimetals in the presence of generic disorder, consisting of a random vector potential as well as a random scalar potential. We derive renormalization group flow equations to second order in the disorder strength. These flow equations predict a disorder-induced phase transition between a pseudoballistic weak-disorder phase and a diffusive strong-disorder phase for a sufficiently strong random scalar potential or for a pure three-component random vector potential. We verify these predictions using a numerical study of the density of states near the Weyl point and of quantum transport properties at the Weyl point. In contrast, for a pure single-component random vector potential, the diffusive strong-disorder phase is absent. BibTeX:  @article{PhysRevB.94.220202, author = Björn Sbierski, Kevin S. C. Decker and Piet W. Brouwer, title = Weyl node with random vector potential, journal = Phys. Rev. B, year = 2016, volume = 94, number = 22, pages = 220202, url = http://link.aps.org/doi/10.1103/PhysRevB.94.220202, doi = http://dx.doi.org/10.1103/PhysRevB.94.220202 }  Zhao Liu and R. N. Bhatt Quantum Entanglement as a Diagnostic of Phase Transitions in Disordered Fractional Quantum Hall Liquids Physical Review Letters 117(20), (2016). Abstract: We investigate the disorder-driven phase transition from a fractional quantum Hall state to an Anderson insulator using quantum entanglement methods. We find that the transition is signaled by a sharp increase in the sensitivity of a suitably averaged entanglement entropy with respect to disorder—the magnitude of its disorder derivative appears to diverge in the thermodynamic limit. We also study the level statistics of the entanglement spectrum as a function of disorder. However, unlike the dramatic phase-transition signal in the entanglement entropy derivative, we find a gradual reduction of level repulsion only deep in the Anderson insulating phase. BibTeX:  @article{Liu2016, author = Zhao Liu and R. N. Bhatt, title = Quantum Entanglement as a Diagnostic of Phase Transitions in Disordered Fractional Quantum Hall Liquids, journal = Physical Review Letters, year = 2016, volume = 117, number = 20, pages = , url = http://dx.doi.org/10.1103/PhysRevLett.117.206801, doi = http://dx.doi.org/10.1103/physrevlett.117.206801 }  C. Krumnow, L. Veis, Ö. Legeza and J. Eisert Fermionic Orbital Optimization in Tensor Network States Phys. Rev. Lett. 117(21), 210402 (2016). Abstract: Tensor network states and specifically matrix-product states have proven to be a powerful tool for simulating ground states of strongly correlated spin models. Recently, they have also been applied to interacting fermionic problems, specifically in the context of quantum chemistry. A new freedom arising in such nonlocal fermionic systems is the choice of orbitals, it being far from clear what choice of fermionic orbitals to make. In this Letter, we propose a way to overcome this challenge. We suggest a method intertwining the optimization over matrix product states with suitable fermionic Gaussian mode transformations. The described algorithm generalizes basis changes in the spirit of the Hartree-Fock method to matrix-product states, and provides a black box tool for basis optimization in tensor network methods. BibTeX:  @article{PhysRevLett.117.210402, author = C. Krumnow, L. Veis, Ö. Legeza and J. Eisert, title = Fermionic Orbital Optimization in Tensor Network States, journal = Phys. Rev. Lett., year = 2016, volume = 117, number = 21, pages = 210402, url = http://link.aps.org/doi/10.1103/PhysRevLett.117.210402, doi = http://dx.doi.org/10.1103/PhysRevLett.117.210402 }  Michele Filippone, Piet W. Brouwer, Jens Eisert and Felix von Oppen Drude weight fluctuations in many-body localized systems Phys. Rev. B 94(20), 201112 (2016). Abstract: We numerically investigate the distribution of Drude weights D of many-body states in disordered one-dimensional interacting electron systems across the transition to a many-body localized phase. Drude weights are proportional to the spectral curvatures induced by magnetic fluxes in mesoscopic rings. They offer a method to relate the transition to the many-body localized phase to transport properties. In the delocalized regime, we find that the Drude weight distribution at a fixed disorder configuration agrees well with the random-matrix-theory prediction P(D)∝(γ2+D2)−3/2, although the distribution width γ strongly fluctuates between disorder realizations. A crossover is observed towards a distribution with different large-D asymptotics deep in the many-body localized phase, which however differs from the commonly expected Cauchy distribution. We show that the average distribution width γ, rescaled by LΔ,Δ being the average level spacing in the middle of the spectrum and L the systems size, is an efficient probe of the many-body localization transition, as it increases (vanishes) exponentially in the delocalized (localized) phase. BibTeX:  @article{PhysRevB.94.201112, author = Michele Filippone, Piet W. Brouwer, Jens Eisert and Felix von Oppen, title = Drude weight fluctuations in many-body localized systems, journal = Phys. Rev. B, year = 2016, volume = 94, number = 20, pages = 201112, url = http://link.aps.org/doi/10.1103/PhysRevB.94.201112, doi = http://dx.doi.org/10.1103/PhysRevB.94.201112 }  M. Gluza, C. Krumnow, M. Friesdorf, C. Gogolin and J. Eisert Equilibration via Gaussification in Fermionic Lattice Systems Phys. Rev. Lett. 117(19), 190602 (2016). Abstract: In this Letter, we present a result on the nonequilibrium dynamics causing equilibration and Gaussification of quadratic noninteracting fermionic Hamiltonians. Specifically, based on two basic assumptions—clustering of correlations in the initial state and the Hamiltonian exhibiting delocalizing transport—we prove that non-Gaussian initial states become locally indistinguishable from fermionic Gaussian states after a short and well controlled time. This relaxation dynamics is governed by a power-law independent of the system size. Our argument is general enough to allow for pure and mixed initial states, including thermal and ground states of interacting Hamiltonians on large classes of lattices as well as certain spin systems. The argument gives rise to rigorously proven instances of a convergence to a generalized Gibbs ensemble. Our results allow us to develop an intuition of equilibration that is expected to be more generally valid and relates to current experiments of cold atoms in optical lattices. BibTeX:  @article{PhysRevLett.117.190602, author = M. Gluza, C. Krumnow, M. Friesdorf, C. Gogolin and J. Eisert, title = Equilibration via Gaussification in Fermionic Lattice Systems, journal = Phys. Rev. Lett., year = 2016, volume = 117, number = 19, pages = 190602, url = http://link.aps.org/doi/10.1103/PhysRevLett.117.190602, doi = http://dx.doi.org/10.1103/PhysRevLett.117.190602 }  Frédéric Combes, Maximilian Trescher, Frédéric Piéchon and Jean-Noël Fuchs Statistical mechanics approach to the electric polarization and dielectric constant of band insulators Phys. Rev. B 94(15), 155109 (2016). Abstract: We develop a theory for the analytic computation of the free energy of band insulators in the presence of a uniform and constant electric field. The two key ingredients are a perturbation-like expression of the Wannier-Stark energy spectrum of electrons and a modified statistical mechanics approach involving a local chemical potential in order to deal with the unbounded spectrum and impose the physically relevant electronic filling. At first order in the field, we recover the result of King-Smith, Vanderbilt, and Resta for the electric polarization in terms of a Zak phase—albeit at finite temperature—and, at second order, deduce a general formula for the electric susceptibility, or equivalently for the dielectric constant. Advantages of our method are the validity of the formalism both at zero and finite temperature and the easy computation of higher order derivatives of the free energy. We verify our findings on two different one-dimensional tight-binding models. BibTeX:  @article{PhysRevB.94.155109, author = Frédéric Combes, Maximilian Trescher, Frédéric Piéchon and Jean-Noël Fuchs, title = Statistical mechanics approach to the electric polarization and dielectric constant of band insulators, journal = Phys. Rev. B, year = 2016, volume = 94, number = 15, pages = 155109, url = http://link.aps.org/doi/10.1103/PhysRevB.94.155109, doi = http://dx.doi.org/10.1103/PhysRevB.94.155109 }  R. Gallego, J. Eisert and H. Wilming Thermodynamic work from operational principles New Journal of Physics 18(10), 103017 (2016). Abstract: In recent years we have witnessed a concentrated effort to make sense of thermodynamics for small-scale systems. One of the main difficulties is to capture a suitable notion of work that models realistically the purpose of quantum machines, in an analogous way to the role played, for macroscopic machines, by the energy stored in the idealisation of a lifted weight. Despite several attempts to resolve this issue by putting forward specific models, these are far from realistically capturing the transitions that a quantum machine is expected to perform. In this work, we adopt a novel strategy by considering arbitrary kinds of systems that one can attach to a quantum thermal machine and defining work quantifiers . These are functions that measure the value of a transition and generalise the concept of work beyond those models familiar from phenomenological thermodynamics. We do so by imposing simple operational axioms that any reasonable work quantifier must fulfil and by deriving from them stringent mathematical condition with a clear physical interpretation. Our approach allows us to derive much of the structure of the theory of thermodynamics without taking the definition of work as a primitive. We can derive, for any work quantifier , a quantitative second law in the sense of bounding the work that can be performed using some non-equilibrium resource by the work that is needed to create it. We also discuss in detail the role of reversibility and correlations in connection with the second law. Furthermore, we recover the usual identification of work with energy in degrees of freedom with vanishing entropy as a particular case of our formalism. Our mathematical results can be formulated abstractly and are general enough to carry over to other resource theories than quantum thermodynamics. BibTeX:  @article{1367-2630-18-10-103017, author = R. Gallego, J. Eisert and H. Wilming, title = Thermodynamic work from operational principles, journal = New Journal of Physics, year = 2016, volume = 18, number = 10, pages = 103017, url = http://stacks.iop.org/1367-2630/18/i=10/a=103017, doi = http://dx.doi.org/10.1088/1367-2630/18/10/103017 }  Christian Balz, Bella Lake, Johannes Reuther, Hubertus Luetkens, Rico Schönemann, Thomas Herrmannsdörfer, Yogesh Singh, A. T. M. Nazmul Islam, Elisa M. Wheeler, Jose A. Rodriguez-Rivera, Tatiana Guidi, Giovanna G. Simeoni, Chris Baines and Hanjo Ryll Physical realization of a quantum spin liquid based on a complex frustration mechanism Nature Physics 12(10), (2016). Abstract: Unlike conventional magnets where the magnetic moments are partially or completely static in the ground state, in a quantum spin liquid they remain in collective motion down to the lowest temperatures. The importance of this state is that it is coherent and highly entangled without breaking local symmetries. In the case of magnets with isotropic interactions, spin-liquid behaviour is sought in simple lattices with antiferromagnetic interactions that favour antiparallel alignments of the magnetic moments and are incompatible with the lattice geometries. Despite an extensive search, experimental realizations remain very few. Here we investigate the novel, unexplored magnet Ca10Cr7O28, which has a complex Hamiltonian consisting of several different isotropic interactions and where the ferromagnetic couplings are stronger than the antiferromagnetic ones. We show both experimentally and theoretically that it displays all the features expected of a quantum spin liquid. Thus spin-liquid behaviour in isotropic magnets is not restricted to the simple idealized models currently investigated, but can be compatible with complex structures and ferromagnetic interactions. BibTeX:  @article{10.1038/nphys3826, author = Christian Balz, Bella Lake, Johannes Reuther, Hubertus Luetkens, Rico Schönemann, Thomas Herrmannsdörfer, Yogesh Singh, A. T. M. Nazmul Islam, Elisa M. Wheeler, Jose A. Rodriguez-Rivera, Tatiana Guidi, Giovanna G. Simeoni, Chris Baines and Hanjo Ryll, title = Physical realization of a quantum spin liquid based on a complex frustration mechanism, journal = Nature Physics, year = 2016, volume = 12, number = 10, pages = , url = http://dx.doi.org/10.1038/nphys3826, doi = http://dx.doi.org/10.1038/nphys3826 }  Yasir Iqbal, Ronny Thomale, Francesco Parisen Toldin, Stephan Rachel and Johannes Reuther Functional renormalization group for three-dimensional quantum magnetism Phys. Rev. B 94(14), 140408 (2016). Abstract: We formulate a pseudofermion functional renormalization group (PFFRG) scheme to address frustrated quantum magnetism in three dimensions. In a scenario where many numerical approaches fail due to sign problem or small system size, three-dimensional (3D) PFFRG allows for a quantitative investigation of the quantum spin problem and its observables. We illustrate 3D PFFRG for the simple cubic J1−J2−J3 quantum Heisenberg antiferromagnet, and benchmark it against other approaches, if available. BibTeX:  @article{PhysRevB.94.140408, author = Yasir Iqbal, Ronny Thomale, Francesco Parisen Toldin, Stephan Rachel and Johannes Reuther, title = Functional renormalization group for three-dimensional quantum magnetism, journal = Phys. Rev. B, year = 2016, volume = 94, number = 14, pages = 140408, url = http://link.aps.org/doi/10.1103/PhysRevB.94.140408, doi = http://dx.doi.org/10.1103/PhysRevB.94.140408 }  K. Meichanetzidis, M. Cirio, J. K. Pachos and V. Lahtinen Anatomy of fermionic entanglement and criticality in Kitaev spin liquids Phys. Rev. B 94(11), 115158 (2016). Abstract: We analyze in detail the effect of nontrivial band topology on the area-law behavior of the entanglement entropy in Kitaev's honeycomb model. By mapping the translationally invariant 2D spin model onto 1D fermionic subsystems, we identify those subsystems responsible for universal entanglement contributions in the gapped phases and those responsible for critical entanglement scaling in the gapless phases. For the gapped phases, we analytically show how the topological edge states contribute to the entanglement entropy and provide a universal lower bound for it. For the gapless semimetallic phases and topological phase transitions, the identification of the critical subsystems shows that they fall always into the Ising or the XY universality classes. As our study concerns the fermionic degrees of freedom in the honeycomb model, qualitatively similar results are expected to apply also to generic topological insulators and superconductors. BibTeX:  @article{PhysRevB.94.115158, author = K. Meichanetzidis, M. Cirio, J. K. Pachos and V. Lahtinen, title = Anatomy of fermionic entanglement and criticality in Kitaev spin liquids, journal = Phys. Rev. B, year = 2016, volume = 94, number = 11, pages = 115158, url = http://link.aps.org/doi/10.1103/PhysRevB.94.115158, doi = http://dx.doi.org/10.1103/PhysRevB.94.115158 }  Vaibhav Madhok, Carlos A. Riofrío and Ivan H. Deutsch Review: Characterizing and quantifying quantum chaos with quantum tomography Pramana 87(5), 65 (2016). Abstract: We explore quantum signatures of classical chaos by studying the rate of information gain in quantum tomography. The tomographic record consists of a time series of expectation values of a Hermitian operator evolving under the application of the Floquet operator of a quantum map that possesses (or lacks) time-reversal symmetry. We find that the rate of information gain, and hence the fidelity of quantum state reconstruction, depends on the symmetry class of the quantum map involved. Moreover, we find an increase in information gain and hence higher reconstruction fidelities when the Floquet maps employed increase in chaoticity. We make predictions for the information gain and show that these results are well described by random matrix theory in the fully chaotic regime. We derive analytical expressions for bounds on information gain using random matrix theory for different classes of maps and show that these bounds are realized by fully chaotic quantum systems. BibTeX:  @article{10.1007/s12043-016-1259-x, author = Vaibhav Madhok, Carlos A. Riofrío and Ivan H. Deutsch, title = Review: Characterizing and quantifying quantum chaos with quantum tomography, journal = Pramana, year = 2016, volume = 87, number = 5, pages = 65, url = https://link.springer.com/article/10.1007%2Fs12043-016-1259-x, doi = http://dx.doi.org/10.1007/s12043-016-1259-x }  M. Udagawa and E. J. Bergholtz Field-Selective Anomaly and Chiral Mode Reversal in Type-II Weyl Materials Phys. Rev. Lett. 117(8), 086401 (2016). Abstract: Three-dimensional condensed matter incarnations of Weyl fermions generically have a tilted dispersion—in sharp contrast to their elusive high-energy relatives where a tilt is forbidden by Lorentz invariance, and with the low-energy excitations of two-dimensional graphene sheets where a tilt is forbidden by either crystalline or particle-hole symmetry. Very recently, a number of materials (MoTe2, LaAlGe, and WTe2) have been identified as hosts of so-called type-II Weyl fermions whose dispersion is so strongly tilted that a Fermi surface is formed, whereby the Weyl node becomes a singular point connecting electron and hole pockets. We here predict that these systems have remarkable properties in the presence of magnetic fields. Most saliently, we show that the nature of the chiral anomaly depends crucially on the relative angle between the applied field and the tilt, and that an inversion-asymmetric overtilting creates an imbalance in the number of chiral modes with positive and negative slopes. The field-selective anomaly gives a novel magneto-optical resonance, providing an experimental way to detect concealed Weyl nodes. BibTeX:  @article{PhysRevLett.117.086401, author = M. Udagawa and E. J. Bergholtz, title = Field-Selective Anomaly and Chiral Mode Reversal in Type-II Weyl Materials, journal = Phys. Rev. Lett., year = 2016, volume = 117, number = 8, pages = 086401, url = http://link.aps.org/doi/10.1103/PhysRevLett.117.086401, doi = http://dx.doi.org/10.1103/PhysRevLett.117.086401 }  Yimin Ge and Jens Eisert Area laws and efficient descriptions of quantum many-body states New Journal of Physics 18(8), 083026 (2016). Abstract: It is commonly believed that area laws for entanglement entropies imply that a quantum many-body state can be faithfully represented by efficient tensor network states—a conjecture frequently stated in the context of numerical simulations and analytical considerations. In this work, we show that this is in general not the case, except in one-dimension. We prove that the set of quantum many-body states that satisfy an area law for all Renyi entropies contains a subspace of exponential dimension. We then show that there are states satisfying area laws for all Renyi entropies but cannot be approximated by states with a classical description of small Kolmogorov complexity, including polynomial projected entangled pair states or states of multi-scale entanglement renormalisation. Not even a quantum computer with post-selection can efficiently prepare all quantum states fulfilling an area law, and we show that not all area law states can be eigenstates of local Hamiltonians. We also prove translationally and rotationally invariant instances of these results, and show a variation with decaying correlations using quantum error-correcting codes. BibTeX:  @article{1367-2630-18-8-083026, author = Yimin Ge and Jens Eisert, title = Area laws and efficient descriptions of quantum many-body states, journal = New Journal of Physics, year = 2016, volume = 18, number = 8, pages = 083026, url = http://stacks.iop.org/1367-2630/18/i=8/a=083026, doi = http://dx.doi.org/10.1088/1367-2630/18/8/083026 }  Yang Peng, Falko Pientka, Erez Berg, Yuval Oreg and Felix von Oppen Signatures of topological Josephson junctions Phys. Rev. B 94(8), 085409 (2016). Abstract: Quasiparticle poisoning and diabatic transitions may significantly narrow the window for the experimental observation of the $4\pi$-periodic $\text{dc}$ Josephson effect predicted for topological Josephson junctions. Here, we show that switching-current measurements provide accessible and robust signatures for topological superconductivity which persist in the presence of quasiparticle poisoning processes. Such measurements provide access to the phase-dependent subgap spectrum and Josephson currents of the topological junction when incorporating it into an asymmetric SQUID together with a conventional Josephson junction with large critical current. We also argue that pump-probe experiments with multiple current pulses can be used to measure the quasiparticle poisoning rates of the topological junction. The proposed signatures are particularly robust, even in the presence of Zeeman fields and spin-orbit coupling, when focusing on short Josephson junctions. Finally, we also consider microwave excitations of short topological Josephson junctions which may complement switching-current measurements. BibTeX:  @article{PhysRevB.94.085409, author = Yang Peng, Falko Pientka, Erez Berg, Yuval Oreg and Felix von Oppen, title = Signatures of topological Josephson junctions, journal = Phys. Rev. B, year = 2016, volume = 94, number = 8, pages = 085409, url = http://link.aps.org/doi/10.1103/PhysRevB.94.085409, doi = http://dx.doi.org/10.1103/PhysRevB.94.085409 }  Robert-Jan Slager, Vladimir Juričić, Ville Lahtinen and Jan Zaanen Self-organized pseudo-graphene on grain boundaries in topological band insulators Phys. Rev. B 93(24), 245406 (2016). Abstract: Semimetals are characterized by nodal band structures that give rise to exotic electronic properties. The stability of Dirac semimetals, such as graphene in two spatial dimensions, requires the presence of lattice symmetries, while akin to the surface states of topological band insulators, Weyl semimetals in three spatial dimensions are protected by band topology. Here we show that in the bulk of topological band insulators, self-organized topologically protected semimetals can emerge along a grain boundary, a ubiquitous extended lattice defect in any crystalline material. In addition to experimentally accessible electronic transport measurements, these states exhibit a valley anomaly in two dimensions influencing edge spin transport, whereas in three dimensions they appear as graphenelike states that may exhibit an odd-integer quantum Hall effect. The general mechanism underlying these semimetals—the hybridization of spinon modes bound to the grain boundary—suggests that topological semimetals can emerge in any topological material where lattice dislocations bind localized topological modes. BibTeX:  @article{PhysRevB.93.245406, author = Robert-Jan Slager, Vladimir Juričić, Ville Lahtinen and Jan Zaanen, title = Self-organized pseudo-graphene on grain boundaries in topological band insulators, journal = Phys. Rev. B, year = 2016, volume = 93, number = 24, pages = 245406, url = http://link.aps.org/doi/10.1103/PhysRevB.93.245406, doi = http://dx.doi.org/10.1103/PhysRevB.93.245406 }  A. H. Werner, D. Jaschke, P. Silvi, M. Kliesch, T. Calarco, J. Eisert and S. Montangero Positive Tensor Network Approach for Simulating Open Quantum Many-Body Systems Phys. Rev. Lett. 116(23), 237201 (2016). Abstract: Open quantum many-body systems play an important role in quantum optics and condensed matter physics, and capture phenomena like transport, the interplay between Hamiltonian and incoherent dynamics, and topological order generated by dissipation. We introduce a versatile and practical method to numerically simulate one-dimensional open quantum many-body dynamics using tensor networks. It is based on representing mixed quantum states in a locally purified form, which guarantees that positivity is preserved at all times. Moreover, the approximation error is controlled with respect to the trace norm. Hence, this scheme overcomes various obstacles of the known numerical open-system evolution schemes. To exemplify the functioning of the approach, we study both stationary states and transient dissipative behavior, for various open quantum systems ranging from few to many bodies. BibTeX:  @article{PhysRevLett.116.237201, author = A. H. Werner, D. Jaschke, P. Silvi, M. Kliesch, T. Calarco, J. Eisert and S. Montangero, title = Positive Tensor Network Approach for Simulating Open Quantum Many-Body Systems, journal = Phys. Rev. Lett., year = 2016, volume = 116, number = 23, pages = 237201, url = http://link.aps.org/doi/10.1103/PhysRevLett.116.237201, doi = http://dx.doi.org/10.1103/PhysRevLett.116.237201 }  P. G. Silvestrov, P. Recher and P. W. Brouwer Noiseless manipulation of helical edge state transport by a quantum magnet Phys. Rev. B 93(20), 205130 (2016). Abstract: The current through a helical edge state of a quantum spin Hall insulator may be fully transmitted through a magnetically gapped region due to a combination of spin-transfer torque and spin pumping [Meng et al., Phys. Rev. B 90, 205403 (2014)]. Using a scattering approach, we here argue that in such a system the current is effectively carried by electrons with energies below the magnet-induced gap and well below the Fermi energy. This has striking consequences, such as the absence of shot noise, an exponential suppression of thermal noise, and an obstruction of thermal transport. For two helical edges covered by the same quantum magnet, the device can act as a robust noiseless current splitter. BibTeX:  @article{PhysRevB.93.205130, author = P. G. Silvestrov, P. Recher and P. W. Brouwer, title = Noiseless manipulation of helical edge state transport by a quantum magnet, journal = Phys. Rev. B, year = 2016, volume = 93, number = 20, pages = 205130, url = http://link.aps.org/doi/10.1103/PhysRevB.93.205130, doi = http://dx.doi.org/10.1103/PhysRevB.93.205130 }  Jörg Behrmann, Zhao Liu and Emil J. Bergholtz Model Fractional Chern Insulators Phys. Rev. Lett. 116(21), 216802 (2016). Abstract: We devise local lattice models whose ground states are model fractional Chern insulators—Abelian and non-Abelian topologically ordered states characterized by exact ground state degeneracies at any finite size and infinite entanglement gaps. Most saliently, we construct exact parent Hamiltonians for two distinct families of bosonic lattice generalizations of the ${\mathcal{Z}}_{k}$ parafermion quantum Hall states: (i) color-entangled fractional Chern insulators at band filling fractions $\nu =k/\left(\mathcal{C}+1\right)$ and (ii) nematic states at $\nu =k/2$, where $\mathcal{C}$ is the Chern number of the lowest band. In spite of a fluctuating Berry curvature, our construction is partially frustration free: the ground states reside entirely within the lowest band and exactly minimize a local ($k+1$) body repulsion term by term. In addition to providing the first known models hosting intriguing states such as higher Chern number generalizations of the Fibonacci anyon quantum Hall states, the remarkable stability and finite-size properties make our models particularly well suited for the study of novel phenomena involving, e.g., twist defects and proximity induced superconductivity, as well as being a guide for designing experiments. BibTeX:  @article{PhysRevLett.116.216802, author = Jörg Behrmann, Zhao Liu and Emil J. Bergholtz, title = Model Fractional Chern Insulators, journal = Phys. Rev. Lett., year = 2016, volume = 116, number = 21, pages = 216802, url = http://link.aps.org/doi/10.1103/PhysRevLett.116.216802, doi = http://dx.doi.org/10.1103/PhysRevLett.116.216802 }  Michael J. Kastoryano and Fernando G. S. L. Brandão Quantum Gibbs Samplers: The Commuting Case Communications in Mathematical Physics 344(3), 915--957 (2016). Abstract: We analyze the problem of preparing quantum Gibbs states of lattice spin Hamiltonians with local and commuting terms on a quantum computer and in nature. Our central result is an equivalence between the behavior of correlations in the Gibbs state and the mixing time of the semigroup which drives the system to thermal equilibrium (the Gibbs sampler). We introduce a framework for analyzing the correlation and mixing properties of quantum Gibbs states and quantum Gibbs samplers, which is rooted in the theory of non-commutative L_p spaces. We consider two distinct classes of Gibbs samplers, one of them being the well-studied Davies generator modelling the dynamics of a system due to weak-coupling with a large Markovian environment. We show that their spectral gap is independent of system size if, and only if, a certain strong form of clustering of correlations holds in the Gibbs state. Therefore every Gibbs state of a commuting Hamiltonian that satisfies clustering of correlations in this strong sense can be prepared efficiently on a quantum computer. As concrete applications of our formalism, we show that for every one-dimensional lattice system, or for systems in lattices of any dimension at temperatures above a certain threshold, the Gibbs samplers of commuting Hamiltonians are always gapped, giving an efficient way of preparing the associated Gibbs states on a quantum computer. BibTeX:  @article{10.1007/s00220-016-2641-8, author = Michael J. Kastoryano and Fernando G. S. L. Brandão, title = Quantum Gibbs Samplers: The Commuting Case, journal = Communications in Mathematical Physics, year = 2016, volume = 344, number = 3, pages = 915--957, url = https://link.springer.com/article/10.1007%2Fs00220-016-2641-8, doi = http://dx.doi.org/10.1007/s00220-016-2641-8 }  Björn Sbierski, Martin Schneider and Piet W. Brouwer Weak side of strong topological insulators Phys. Rev. B 93(16), 161105 (2016). Abstract: Strong topological insulators may have nonzero weak indices. The nonzero weak indices allow for the existence of topologically protected helical states along line defects of the lattice. If the lattice admits line defects that connect opposite surfaces of a slab of such a “weak-and-strong” topological insulator, these states effectively connect the surface states at opposite surfaces. Depending on the phases accumulated along the dislocation lines, this connection results in a suppression of in-plane transport and the opening of a spectral gap or in an enhanced density of states and an increased conductivity. BibTeX:  @article{PhysRevB.93.161105, author = Björn Sbierski, Martin Schneider and Piet W. Brouwer, title = Weak side of strong topological insulators, journal = Phys. Rev. B, year = 2016, volume = 93, number = 16, pages = 161105, url = http://link.aps.org/doi/10.1103/PhysRevB.93.161105, doi = http://dx.doi.org/10.1103/PhysRevB.93.161105 }  H. Wilming, R. Gallego and J. Eisert Second law of thermodynamics under control restrictions Phys. Rev. E 93(4), 042126 (2016). Abstract: The second law of thermodynamics, formulated as an ultimate bound on the maximum extractable work, has been rigorously derived in multiple scenarios. However, the unavoidable limitations that emerge due to the lack of control on small systems are often disregarded when deriving such bounds, which is specifically important in the context of quantum thermodynamics. Here we study the maximum extractable work with limited control over the working system and its interaction with the heat bath. We derive a general second law when the set of accessible Hamiltonians of the working system is arbitrarily restricted. We then apply our bound to particular scenarios that are important in realistic implementations: limitations on the maximum energy gap and local control over many-body systems. We hence demonstrate in what precise way the lack of control affects the second law. In particular, contrary to the unrestricted case, we show that the optimal work extraction is not achieved by simple thermal contacts. Our results not only generalize the second law to scenarios of practical relevance, but also take first steps in the direction of local thermodynamics. BibTeX:  @article{PhysRevE.93.042126, author = H. Wilming, R. Gallego and J. Eisert, title = Second law of thermodynamics under control restrictions, journal = Phys. Rev. E, year = 2016, volume = 93, number = 4, pages = 042126, url = http://link.aps.org/doi/10.1103/PhysRevE.93.042126, doi = http://dx.doi.org/10.1103/PhysRevE.93.042126 }  Dganit Meidan, Alessandro Romito and Piet W. Brouwer Transport signatures of interacting fermions in quasi-one-dimensional topological superconductors Phys. Rev. B 93(12), 125433 (2016). Abstract: A topological superconducting wire with an effective time-reversal symmetry is known to have a Z8 topological classification in the presence of interactions. The topological index |n|≤4 counts the number of Majorana end states, negative n corresponding to end states that are odd under time reversal. If such a wire is weakly coupled to a normal-metal lead, interactions induce a Kondo-like correlated state if |n|=4. We show that the Kondo-like state manifests itself in an anomalous temperature dependence of the zero-bias conductance and by an anomalous Fano factor for the zero-temperature normally reflected current at finite bias. We also consider the splitting of the effective Kondo resonance for weak symmetry-breaking perturbations. BibTeX:  @article{PhysRevB.93.125433, author = Dganit Meidan, Alessandro Romito and Piet W. Brouwer, title = Transport signatures of interacting fermions in quasi-one-dimensional topological superconductors, journal = Phys. Rev. B, year = 2016, volume = 93, number = 12, pages = 125433, url = http://link.aps.org/doi/10.1103/PhysRevB.93.125433, doi = http://dx.doi.org/10.1103/PhysRevB.93.125433 }  K. Meichanetzidis, J. Eisert, M. Cirio, V. Lahtinen and J. K. Pachos Diagnosing Topological Edge States via Entanglement Monogamy Phys. Rev. Lett. 116(13), 130501 (2016). Abstract: Topological phases of matter possess intricate correlation patterns typically probed by entanglement entropies or entanglement spectra. In this Letter, we propose an alternative approach to assessing topologically induced edge states in free and interacting fermionic systems. We do so by focussing on the fermionic covariance matrix. This matrix is often tractable either analytically or numerically, and it precisely captures the relevant correlations of the system. By invoking the concept of monogamy of entanglement, we show that highly entangled states supported across a system bipartition are largely disentangled from the rest of the system, thus, usually appearing as gapless edge states. We then define an entanglement qualifier that identifies the presence of topological edge states based purely on correlations present in the ground states. We demonstrate the versatility of this qualifier by applying it to various free and interacting fermionic topological systems. BibTeX:  @article{PhysRevLett.116.130501, author = K. Meichanetzidis, J. Eisert, M. Cirio, V. Lahtinen and J. K. Pachos, title = Diagnosing Topological Edge States via Entanglement Monogamy, journal = Phys. Rev. Lett., year = 2016, volume = 116, number = 13, pages = 130501, url = http://link.aps.org/doi/10.1103/PhysRevLett.116.130501, doi = http://dx.doi.org/10.1103/PhysRevLett.116.130501 }  Oded Zilberberg, Alessandro Romito and Yuval Gefen Many-body manifestation of interaction-free measurement: The Elitzur-Vaidman bomb Phys. Rev. B 93(11), 115411 (2016). Abstract: We consider an implementation of the Elitzur-Vaidman bomb experiment in a dc-biased electronic Mach-Zehnder interferometer with a leakage port on one of its arms playing the role of a “lousy bomb.” Many-body correlations tend to screen out manifestations of interaction-free measurement. Analyzing the correlations between the current at the interferometer's drains and at the leakage port, we identify the limit where the originally proposed single-particle effect is recovered. Specifically, we find that in the regime of sufficiently diluted injected electron beam and short measurement times, effects of quantum-mechanical wave-particle duality emerge in the cross-current correlations. BibTeX:  @article{PhysRevB.93.115411, author = Oded Zilberberg, Alessandro Romito and Yuval Gefen, title = Many-body manifestation of interaction-free measurement: The Elitzur-Vaidman bomb, journal = Phys. Rev. B, year = 2016, volume = 93, number = 11, pages = 115411, url = http://link.aps.org/doi/10.1103/PhysRevB.93.115411, doi = http://dx.doi.org/10.1103/PhysRevB.93.115411 }  Anton Bruch, Mark Thomas, Silvia Viola Kusminskiy, Felix von Oppen and Abraham Nitzan Quantum thermodynamics of the driven resonant level model Phys. Rev. B 93(11), 115318 (2016). Abstract: We present a consistent thermodynamic theory for the resonant level model in the wide-band limit, whose level energy is driven slowly by an external force. The problem of defining “system” and “bath” in the strong-coupling regime is circumvented by considering as the system everything that is influenced by the externally driven level. The thermodynamic functions that are obtained to first order beyond the quasistatic limit fulfill the first and second law with a positive entropy production, successfully connect to the forces experienced by the external driving, and reproduce the correct weak-coupling limit of stochastic thermodynamics. BibTeX:  @article{PhysRevB.93.115318, author = Anton Bruch, Mark Thomas, Silvia Viola Kusminskiy, Felix von Oppen and Abraham Nitzan, title = Quantum thermodynamics of the driven resonant level model, journal = Phys. Rev. B, year = 2016, volume = 93, number = 11, pages = 115318, url = http://link.aps.org/doi/10.1103/PhysRevB.93.115318, doi = http://dx.doi.org/10.1103/PhysRevB.93.115318 }  Michael E. Beverland, Oliver Buerschaper, Robert Koenig, Fernando Pastawski, John Preskill and Sumit Sijher Protected gates for topological quantum field theories Journal of Mathematical Physics 57(2), 022201 (2016). Abstract: We study restrictions on locality-preserving unitary logical gates for topological quantum codes in two spatial dimensions. A locality-preserving operation is one which maps local operators to local operators — for example, a constant-depth quantum circuit of geometrically local gates, or evolution for a constant time governed by a geometrically local bounded-strength Hamiltonian. Locality-preserving logical gates of topological codes are intrinsically fault tolerant because spatially localized errors remain localized, and hence sufficiently dilute errors remain correctable. By invoking general properties of two-dimensional topological field theories, we find that the locality-preserving logical gates are severely limited for codes which admit non-abelian anyons, in particular, there are no locality-preserving logical gates on the torus or the sphere with M punctures if the braiding of anyons is computationally universal. Furthermore, for Ising anyons on the M-punctured sphere, locality-preserving gates must be elements of the logical Pauli group. We derive these results by relating logical gates of a topological code to automorphisms of the Verlinde algebra of the corresponding anyon model, and by requiring the logical gates to be compatible with basis changes in the logical Hilbert space arising from local F-moves and the mapping class group. BibTeX:  @article{Beverland2016, author = Michael E. Beverland, Oliver Buerschaper, Robert Koenig, Fernando Pastawski, John Preskill and Sumit Sijher, title = Protected gates for topological quantum field theories, journal = Journal of Mathematical Physics, year = 2016, volume = 57, number = 2, pages = 022201, url = http://dx.doi.org/10.1063/1.4939783, doi = http://dx.doi.org/10.1063/1.4939783 }  María Florencia Ludovico, Francesca Battista, Felix von Oppen and Liliana Arrachea Adiabatic response and quantum thermoelectrics for ac-driven quantum systems Physical Review B 93(7), (2016). Abstract: We generalize the theory of thermoelectrics to include coherent electron systems under adiabatic ac driving, accounting for quantum pumping of charge and heat, as well as for the work exchanged between the electron system and driving potentials. We derive the relevant response coefficients in the adiabatic regime and show that they obey generalized Onsager reciprocity relations. We analyze the consequences of our generalized thermoelectric framework for quantum motors, generators, heat engines, and heat pumps, characterizing them in terms of efficiencies and figures of merit. We illustrate these concepts in a model for a quantum pump. BibTeX:  @article{Ludovico2016, author = María Florencia Ludovico, Francesca Battista, Felix von Oppen and Liliana Arrachea, title = Adiabatic response and quantum thermoelectrics for ac-driven quantum systems, journal = Physical Review B, year = 2016, volume = 93, number = 7, pages = , url = http://dx.doi.org/10.1103/PhysRevB.93.075136, doi = http://dx.doi.org/10.1103/physrevb.93.075136 }  Yuval Ronen, Yonatan Cohen, Jung-Hyun Kang, Arbel Haim, Maria-Theresa Rieder, Moty Heiblum, Diana Mahalu and Hadas Shtrikman Charge of a quasiparticle in a superconductor Proc Natl Acad Sci USA 113(7), 1743–1748 (2016). Abstract: Non-linear charge transport in SIS Josephson junctions has a unique signature in the shuttled charge quantum between the two superconductors. In the zero-bias limit Cooper pairs, each with twice the electron charge, carry the Josephson current. An applied bias VSD leads to multiple Andreev reflections (MAR), which in the limit of weak tunneling probability should lead to integer multiples of the electron charge ne traversing the junction, with n integer larger than 2Δ/eVSD and Δ the superconducting order parameter. Exceptionally, just above the gap, eVSD>2Δ, with Andreev reflections suppressed, one would expect the current to be carried by partitioned quasiparticles; each with energy dependent charge, being a superposition of an electron and a hole. Employing shot noise measurements in an SIS junction induced in an InAs nanowire (with noise proportional to the partitioned charge), we first observed quantization of the partitioned charge q=e∗/e=n, with n=1−4; thus reaffirming the validity of our charge interpretation. Concentrating next on the bias region eVSD≈2Δ, we found a reproducible and clear dip in the extracted charge to q≈0.6, which, after excluding other possibilities, we attribute to the partitioned quasiparticle charge. Such dip is supported by numerical simulations of our SIS structure. BibTeX:  @article{Ronen2016, author = Yuval Ronen, Yonatan Cohen, Jung-Hyun Kang, Arbel Haim, Maria-Theresa Rieder, Moty Heiblum, Diana Mahalu and Hadas Shtrikman, title = Charge of a quasiparticle in a superconductor, journal = Proc Natl Acad Sci USA, year = 2016, volume = 113, number = 7, pages = 1743–1748, url = http://dx.doi.org/10.1073/pnas.1515173113, doi = http://dx.doi.org/10.1073/pnas.1515173113 }  Zhao Liu, Abolhassan Vaezi, Cécile Repellin and Nicolas Regnault Phase diagram of ν=1/2+1/2 bilayer bosons with interlayer couplings Phys. Rev. B 93(8), 085115 (2016). Abstract: We present the quantitative phase diagram of the bilayer bosonic fractional quantum Hall system on the torus geometry at total filling factor ν=1 in the lowest Landau level. We consider short-range interactions within and between the two layers, as well as the interlayer tunneling. In the fully polarized regime, we provide an updated detailed numerical analysis to establish the presence of the Moore-Read phase of both even and odd numbers of particles. In the actual bilayer situation, we find that both interlayer interactions and tunneling can provide the physical mechanism necessary for the low-energy physics to be driven by the fully polarized regime, thus leading to the emergence of the Moore-Read phase. Interlayer interactions favor a ferromagnetic phase when the system is SU(2) symmetric, while the interlayer tunneling acts as a Zeeman field polarizing the system. Besides the Moore-Read phase, the (220) Halperin state and the coupled Moore-Read state are also realized in this model. We study their stability against each other. BibTeX:  @article{PhysRevB.93.085115, author = Zhao Liu, Abolhassan Vaezi, Cécile Repellin and Nicolas Regnault, title = Phase diagram of ν=1/2+1/2 bilayer bosons with interlayer couplings, journal = Phys. Rev. B, year = 2016, volume = 93, number = 8, pages = 085115, url = http://link.aps.org/doi/10.1103/PhysRevB.93.085115, doi = http://dx.doi.org/10.1103/PhysRevB.93.085115 }  Iliya Esin, Alessandro Romito, Ya M. Blanter and Yuval Gefen Crossover between strong and weak measurement in interacting many-body systems New Journal of Physics 18(1), 013016 (2016). Abstract: Measurements with variable system–detector interaction strength, ranging from weak to strong, have been recently reported in a number of electronic nanosystems. In several such instances many-body effects play a significant role. Here we consider the weak-to-strong crossover for a setup consisting of an electronic Mach–Zehnder interferometer, where a second interferometer is employed as a detector. In the context of a conditional which-path protocol, we define a generalized conditional value (GCV), and determine its full crossover between the regimes of weak and strong (projective) measurement. We find that the GCV has an oscillatory dependence on the system–detector interaction strength. These oscillations are a genuine many-body effect, and can be experimentally observed through the voltage dependence of cross current correlations. BibTeX:  @article{1367-2630-18-1-013016, author = Iliya Esin, Alessandro Romito, Ya M. Blanter and Yuval Gefen, title = Crossover between strong and weak measurement in interacting many-body systems, journal = New Journal of Physics, year = 2016, volume = 18, number = 1, pages = 013016, url = http://stacks.iop.org/1367-2630/18/i=1/a=013016, doi = http://dx.doi.org/1367-2630/18/1/013016 }  Michele Filippone, Frank Hekking and Anna Minguzzi Violation of the Wiedemann-Franz law for one-dimensional ultracold atomic gases Physical Review A 93(1), 011602 (2016). Abstract: We study energy and particle transport for one-dimensional strongly interacting bosons through a ballistic single channel connecting two atomic reservoirs. We show the emergence of particle- and energy-current separation, leading to the violation of the Wiedemann-Franz law. As a consequence, we predict different time scales for the equilibration of temperature and particle imbalances between the reservoirs. Going beyond the linear spectrum approximation, we show the emergence of thermoelectric effects, which could be controlled by either tuning interactions or the temperature. Our results describe, in a unified picture, fermions in condensed-matter devices and bosons in ultracold atom setups. We conclude by discussing the effects of a controllable disorder. BibTeX:  @article{Filippone2016, author = Michele Filippone, Frank Hekking and Anna Minguzzi, title = Violation of the Wiedemann-Franz law for one-dimensional ultracold atomic gases, journal = Physical Review A, year = 2016, volume = 93, number = 1, pages = 011602, url = http://dx.doi.org/10.1103/PhysRevA.93.011602, doi = http://dx.doi.org/10.1103/physreva.93.011602 }  Manuel Laubach, Darshan G. Joshi, Johannes Reuther, Ronny Thomale, Matthias Vojta and Stephan Rachel Quantum disordered insulating phase in the frustrated cubic-lattice Hubbard model Physical Review B 93(4), (2016). Abstract: In the quest for quantum spin liquids in three spatial dimensions (3D), we study the half-filled Hubbard model on the simple cubic lattice with hopping processes up to third neighbors. Employing the variational cluster approach (VCA), we determine the zero-temperature phase diagram: In addition to a paramagnetic metal at small interaction strength U and various antiferromagnetic insulators at large U, we find an intermediate-U antiferromagnetic metal. Most interestingly, we also identify a nonmagnetic insulating region, extending from intermediate to strong U. Using VCA results in the large-U limit, we establish the phase diagram of the corresponding J1−J2−J3 Heisenberg model. This is qualitatively confirmed—including the nonmagnetic region—using spin-wave theory. Further analysis reveals a striking similarity to the behavior of the J1−J2 square-lattice Heisenberg model, suggesting that the nonmagnetic region may host a 3D spin-liquid phase. BibTeX:  @article{Laubach2016, author = Manuel Laubach, Darshan G. Joshi, Johannes Reuther, Ronny Thomale, Matthias Vojta and Stephan Rachel, title = Quantum disordered insulating phase in the frustrated cubic-lattice Hubbard model, journal = Physical Review B, year = 2016, volume = 93, number = 4, pages = , url = http://dx.doi.org/10.1103/PhysRevB.93.041106, doi = http://dx.doi.org/10.1103/physrevb.93.041106 }  Stephan Waeldchen, Janina Gertis, Earl T. Campbell and Jens Eisert Renormalizing Entanglement Distillation Physical Review Letters 116(2), (2016). Abstract: Entanglement distillation refers to the task of transforming a collection of weakly entangled pairs into fewer highly entangled ones. It is a core ingredient in quantum repeater protocols, which are needed to transmit entanglement over arbitrary distances in order to realize quantum key distribution schemes. Usually, it is assumed that the initial entangled pairs are identically and independently distributed and are uncorrelated with each other, an assumption that might not be reasonable at all in any entanglement generation process involving memory channels. Here, we introduce a framework that captures entanglement distillation in the presence of natural correlations arising from memory channels. Conceptually, we bring together ideas from condensed-matter physics—ideas from renormalization and matrix-product states and operators—with those of local entanglement manipulation, Markov chain mixing, and quantum error correction. We identify meaningful parameter regions for which we prove convergence to maximally entangled states, arising as the fixed points of a matrix-product operator renormalization flow. BibTeX:  @article{Waeldchen2016, author = Stephan Waeldchen, Janina Gertis, Earl T. Campbell and Jens Eisert, title = Renormalizing Entanglement Distillation, journal = Physical Review Letters, year = 2016, volume = 116, number = 2, pages = , url = http://dx.doi.org/10.1103/PhysRevLett.116.020502, doi = http://dx.doi.org/10.1103/physrevlett.116.020502 }  Alessandro Romito, Andrew N. Jordan, Yakir Aharonov and Yuval Gefen Weak values are quantum: you can bet on it Quantum Studies: Mathematics and Foundations 3(1), 1--4 (2016). Abstract: The outcome of a weak quantum measurement conditioned to a subsequent post-selection (a weak value protocol) can assume peculiar values. These results cannot be explained in terms of conditional probabilistic outcomes of projective measurements. However, a classical model has been recently put forward that can reproduce peculiar expectation values, reminiscent of weak values. This led the authors of that work to claim that weak values have an entirely classical explanation. Here we discuss what is quantum about weak values with the help of a simple model based on basic quantum mechanics. We first demonstrate how a classical theory can indeed give rise to non-trivial conditional values, and explain what features of weak values are genuinely quantum. We finally use our model to outline some main issues under current research. BibTeX:  @article{10.1007/s40509-015-0069-z, author = Alessandro Romito, Andrew N. Jordan, Yakir Aharonov and Yuval Gefen, title = Weak values are quantum: you can bet on it, journal = Quantum Studies: Mathematics and Foundations, year = 2016, volume = 3, number = 1, pages = 1--4, url = https://link.springer.com/article/10.1007%2Fs40509-015-0069-z, doi = http://dx.doi.org/10.1007/s40509-015-0069-z }  2015 BibTeX:  @unpublished{20152016,, title = {Preprints}, year = 2015 }  Yasir Iqbal, Harald O. Jeschke, Johannes Reuther, Roser Valentí, I. I. Mazin, Martin Greiter and Ronny Thomale Paramagnetism in the kagome compounds (Zn,Mg,Cd )Cu3(OH)6Cl2 Physical Review B 92(22), 220404 (2015). Abstract: Frustrated magnetism on the kagome lattice has been a fertile ground for rich and fascinating physics, ranging from experimental evidence of a spin liquid to theoretical predictions of exotic superconductivity. Among experimentally realized spin-12 kagome magnets, herbertsmithite, kapellasite, and haydeeite [(Zn,Mg)Cu3(OH)6Cl2] are all well described by a three-parameter Heisenberg model, but they exhibit distinctly different physics. We address the problem using a pseudofermion functional renormalization-group approach and analyze the low-energy physics in the experimentally accessible parameter range. Our analysis places kapellasite and haydeeite near the boundaries between magnetically ordered and disordered phases, implying that slight modifications could dramatically affect their magnetic properties. Inspired by this, we perform ab initio density functional theory calculations of (Zn,Mg,Cd)Cu3 (OH)6Cl2 at various pressures. Our results suggest that by varying pressure and composition one can traverse a paramagnetic regime between different magnetically ordered phases. BibTeX:  @article{Iqbal2015, author = Yasir Iqbal, Harald O. Jeschke, Johannes Reuther, Roser Valentí, I. I. Mazin, Martin Greiter and Ronny Thomale, title = Paramagnetism in the kagome compounds (Zn,Mg,Cd )Cu3(OH)6Cl2, journal = Physical Review B, year = 2015, volume = 92, number = 22, pages = 220404, url = http://dx.doi.org/10.1103/PhysRevB.92.220404, doi = http://dx.doi.org/10.1103/physrevb.92.220404 }  Ville Lahtinen and Eddy Ardonne Realizing All so(N)_1 Quantum Criticalities in Symmetry Protected Cluster Models Physical Review Letters 115(23), 237203 (2015). Abstract: We show that all so(N)1 universality class quantum criticalities emerge when one-dimensional generalized cluster models are perturbed with Ising or Zeeman terms. Each critical point is described by a low-energy theory of N linearly dispersing fermions, whose spectrum we show to precisely match the prediction by so(N)1 conformal field theory. Furthermore, by an explicit construction we show that all the cluster models are dual to nonlocally coupled transverse field Ising chains, with the universality of the so(N)1 criticality manifesting itself as N of these chains becoming critical. This duality also reveals that the symmetry protection of cluster models arises from the underlying Ising symmetries and it enables the identification of local representations for the primary fields of the so(N)1 conformal field theories. For the simplest and experimentally most realistic case that corresponds to the original one-dimensional cluster model with local three-spin interactions, our results show that the su(2)2≃so(3)1 Wess-Zumino-Witten model can emerge in a local, translationally invariant, and Jordan-Wigner solvable spin-1/2 model. BibTeX:  @article{Lahtinen2015, author = Ville Lahtinen and Eddy Ardonne, title = Realizing All so(N)_1 Quantum Criticalities in Symmetry Protected Cluster Models, journal = Physical Review Letters, year = 2015, volume = 115, number = 23, pages = 237203, url = http://dx.doi.org/10.1103/PhysRevLett.115.237203, doi = http://dx.doi.org/10.1103/physrevlett.115.237203 }  Yang Peng, Falko Pientka, Yuval Vinkler-Aviv, Leonid I. Glazman and Felix von Oppen Robust Majorana Conductance Peaks for a Superconducting Lead Physical Review Letters 115(26), 266804 (2015). Abstract: Experimental evidence for Majorana bound states largely relies on measurements of the tunneling conductance. While the conductance into a Majorana state is in principle quantized to 2e2/h, observation of this quantization has been elusive, presumably due to temperature broadening in the normal-metal lead. Here, we propose to use a superconducting lead instead, whose gap strongly suppresses thermal excitations. For a wide range of tunneling strengths and temperatures, a Majorana state is then signaled by symmetric conductance peaks at eV=±Δ of a universal height G=(4−π)2e2/h. For a superconducting scanning tunneling microscope tip, Majorana states appear as spatial conductance plateaus while the conductance varies with the local wave function for trivial Andreev bound states. We discuss effects of nonresonant (bulk) Andreev reflections and quasiparticle poisoning. BibTeX:  @article{Peng2015, author = Yang Peng, Falko Pientka, Yuval Vinkler-Aviv, Leonid I. Glazman and Felix von Oppen, title = Robust Majorana Conductance Peaks for a Superconducting Lead, journal = Physical Review Letters, year = 2015, volume = 115, number = 26, pages = 266804, url = http://dx.doi.org/10.1103/PhysRevLett.115.266804, doi = http://dx.doi.org/10.1103/physrevlett.115.266804 }  Ioannis Rousochatzakis, Johannes Reuther, Ronny Thomale, Stephan Rachel and N. B. Perkins Phase Diagram and Quantum Order by Disorder in the Kitaev K 1 − K 2~{H}oneycomb Magnet Physical Review X 5(4), (2015). Abstract: We show that the topological Kitaev spin liquid on the honeycomb lattice is extremely fragile against the second-neighbor Kitaev coupling K2, which has recently been shown to be the dominant perturbation away from the nearest-neighbor model in iridate Na2IrO3, and may also play a role in α−RuCl3 and Li2IrO3. This coupling naturally explains the zigzag ordering (without introducing unrealistically large longer-range Heisenberg exchange terms) and the special entanglement between real and spin space observed recently in Na2IrO3. Moreover, the minimal K1−K2 model that we present here holds the unique property that the classical and quantum phase diagrams and their respective order-by-disorder mechanisms are qualitatively different due to the fundamentally different symmetries of the classical and quantum counterparts. BibTeX:  @article{Rousochatzakis2015, author = Ioannis Rousochatzakis, Johannes Reuther, Ronny Thomale, Stephan Rachel and N. B. Perkins, title = Phase Diagram and Quantum Order by Disorder in the Kitaev K 1 − K 2~{H}oneycomb Magnet, journal = Physical Review X, year = 2015, volume = 5, number = 4, pages = , url = http://dx.doi.org/10.1103/PhysRevX.5.041035, doi = http://dx.doi.org/10.1103/physrevx.5.041035 }  Niko Säkkinen, Yang Peng, Heiko Appel and Robert van Leeuwen Many-body Green’s function theory for electron-phonon interactions: Ground state properties of the Holstein dimer J. Chem. Phys. 143(23), 234101 (2015). Abstract: We study ground-state properties of a two-site, two-electron Holstein model describing two molecules coupled indirectly via electron-phonon interaction by using both exact diagonalization and self-consistent diagrammatic many-body perturbation theory. The Hartree and self-consistent Born approximations used in the present work are studied at different levels of self-consistency. The governing equations are shown to exhibit multiple solutions when the electron-phonon interaction is sufficiently strong, whereas at smaller interactions, only a single solution is found. The additional solutions at larger electron-phonon couplings correspond to symmetry-broken states with inhomogeneous electron densities. A comparison to exact results indicates that this symmetry breaking is strongly correlated with the formation of a bipolaron state in which the two electrons prefer to reside on the same molecule. The results further show that the Hartree and partially self-consistent Born solutions obtained by enforcing symmetry do not compare well with exact energetics, while the fully self-consistent Born approximation improves the qualitative and quantitative agreement with exact results in the same symmetric case. This together with a presented natural occupation number analysis supports the conclusion that the fully self-consistent approximation describes partially the bipolaron crossover. These results contribute to better understanding how these approximations cope with the strong localizing effect of the electron-phonon interaction. BibTeX:  @article{Saekkinen2015, author = Niko Säkkinen, Yang Peng, Heiko Appel and Robert van Leeuwen, title = Many-body Green’s function theory for electron-phonon interactions: Ground state properties of the Holstein dimer, journal = J. Chem. Phys., year = 2015, volume = 143, number = 23, pages = 234101, url = http://dx.doi.org/10.1063/1.4936142, doi = http://dx.doi.org/10.1063/1.4936142 }  Mark Thomas, Torsten Karzig and Silvia Viola Kusminskiy Langevin dynamics of a heavy particle and orthogonality effects Physical Review B 92(24), 245404 (2015). Abstract: The dynamics of a classical heavy particle moving in a quantum environment is determined by a Langevin equation which encapsulates the effect of the environment-induced reaction forces on the particle. For an open quantum system, these include a Born-Oppenheimer force, a dissipative force, and a stochastic force due to shot and thermal noise. Recently, it was shown that these forces can be expressed in terms of the scattering matrix of the system by considering the classical heavy particle as a time-dependent scattering center, allowing to demonstrate interesting features of these forces when the system is driven out of equilibrium. At the same time, it is well known that small changes in a scattering potential can have a profound impact on a fermionic system due to the Anderson orthogonality catastrophe. In this work, by calculating the Loschmidt echo, we relate Anderson orthogonality effects with the mesoscopic reaction forces for an environment that can be taken out of equilibrium. In particular, we show how the decay of the Loschmidt echo is characterized by fluctuations and dissipation in the system and discuss different quench protocols. BibTeX:  @article{Thomas2015, author = Mark Thomas, Torsten Karzig and Silvia Viola Kusminskiy, title = Langevin dynamics of a heavy particle and orthogonality effects, journal = Physical Review B, year = 2015, volume = 92, number = 24, pages = 245404, url = http://dx.doi.org/10.1103/PhysRevB.92.245404, doi = http://dx.doi.org/10.1103/physrevb.92.245404 }  Leandro Aolita, Christian Gogolin, Martin Kliesch and Jens Eisert Reliable quantum certification of photonic state preparations Nat Comms 6(8498), 8498 (2015). Abstract: Quantum technologies promise a variety of exciting applications. Even though impressive progress has been achieved recently, a major bottleneck currently is the lack of practical certification techniques. The challenge consists of ensuring that classically intractable quantum devices perform as expected. Here we present an experimentally friendly and reliable certification tool for photonic quantum technologies: an efficient certification test for experimental preparations of multimode pure Gaussian states, pure non-Gaussian states generated by linear-optical circuits with Fock-basis states of constant boson number as inputs, and pure states generated from the latter class by post-selecting with Fock-basis measurements on ancillary modes. Only classical computing capabilities and homodyne or hetorodyne detection are required. Minimal assumptions are made on the noise or experimental capabilities of the preparation. The method constitutes a step forward in many-body quantum certification, which is ultimately about testing quantum mechanics at large scales. BibTeX:  @article{Aolita2015a, author = Leandro Aolita, Christian Gogolin, Martin Kliesch and Jens Eisert, title = Reliable quantum certification of photonic state preparations, journal = Nat Comms, year = 2015, volume = 6, number = 8498, pages = 8498, url = http://dx.doi.org/10.1038/ncomms9498, doi = http://dx.doi.org/10.1038/ncomms9498 }  M. Friesdorf, A. H. Werner, M. Goihl, J. Eisert and W. Brown Local constants of motion imply information propagation New J. Phys. 17(11), 113054 (2015). Abstract: Interacting quantum many-body systems are expected to thermalize, in the sense that the evolution of local expectation values approaches a stationary value resembling a thermal ensemble. This intuition is notably contradicted in systems exhibiting many-body localisation (MBL). In stark contrast to the non-interacting case of Anderson localisation, the entanglement of states grows without limit over time, albeit slowly. In this work, we establish a novel link between quantum information theory and notions of condensed matter physics, capturing this phenomenon in the Heisenberg picture. We show that the mere existence of local constants of motion, often taken as the defining property of MBL, together with a generic spectrum of the Hamiltonian, is already sufficient to rigorously prove information propagation: these systems can be used to send a classical bit over arbitrary distances, in that the impact of a local perturbation can be detected arbitrarily far away. This counterintuitive result is compatible with and further corroborates the intuition of a slow entanglement growth following global quenches in MBL systems. We perform a detailed perturbation analysis of quasi-local constants of motion and also show that they indeed can be used to construct efficient spectral tensor networks, as recently suggested. Our results provide a detailed and at the same time model-independent picture of information propagation in MBL systems. BibTeX:  @article{Friesdorf2015a, author = M. Friesdorf, A. H. Werner, M. Goihl, J. Eisert and W. Brown, title = Local constants of motion imply information propagation, journal = New J. Phys., year = 2015, volume = 17, number = 11, pages = 113054, url = http://dx.doi.org/10.1088/1367-2630/17/11/113054, doi = http://dx.doi.org/10.1088/1367-2630/17/11/113054 }  G. Haack, A. Steffens, J. Eisert and R. Hübener Continuous matrix product state tomography of quantum transport experiments New Journal of Physics 17(11), 113024 (2015). Abstract: In recent years, a close connection between the description of open quantum systems, the input–output formalism of quantum optics, and continuous matrix product states (cMPS) in quantum field theory has been established. The latter constitute a variational class of one-dimensional quantum field states and have been shown to provide an efficient ansatz for performing tomography of open quantum systems. So far, however, the connection between cMPS and open quantum systems has not yet been developed for quantum transport experiments in the condensed-matter context. In this work, we first present an extension of the tomographic possibilities of cMPS by demonstrating the validity of reconstruction schemes based on low-order counting probabilities compared to previous schemes based on low-order correlation functions. We then show how fermionic quantum transport settings can be formulated within the cMPS framework. Our procedure, via the measurements of low-order correlation functions only, allows us to gain access to quantities that are not directly measurable with present technology. Emblematic examples are high-order correlations functions and waiting time distributions (WTD). The latter are of particular interest since they offer insights into short-time scale physics. We demonstrate the functioning of the method with actual data, opening up the way to accessing WTD within the quantum regime. BibTeX:  @article{1367-2630-17-11-113024, author = G. Haack, A. Steffens, J. Eisert and R. Hübener, title = Continuous matrix product state tomography of quantum transport experiments, journal = New Journal of Physics, year = 2015, volume = 17, number = 11, pages = 113024, url = http://stacks.iop.org/1367-2630/17/i=11/a=113024, doi = }  Michael Ruby, Falko Pientka, Yang Peng, Felix von Oppen, Benjamin W. Heinrich and Katharina J. Franke End States and Subgap Structure in Proximity-Coupled Chains of Magnetic Adatoms Physical Review Letters 115(19), 197204 (2015). Abstract: A recent experiment [Nadj-Perge et al., Science 346, 602 (2014)] provides evidence for Majorana zero modes in iron (Fe) chains on the superconducting Pb(110) surface. Here, we study this system by scanning tunneling microscopy using superconducting tips. This high-resolution technique resolves a rich subgap structure, including zero-energy excitations in some chains. We compare the symmetry properties of the data under voltage reversal against theoretical expectations and provide evidence that the putative Majorana signature overlaps with a previously unresolved low-energy resonance. Interpreting the data within a Majorana framework suggests that the topological gap is smaller than previously extracted from experiment. Aided by model calculations, we also analyze higher-energy features of the subgap spectrum and their relation to high-bias peaks which we associate with the Fe d bands. BibTeX:  @article{Ruby2015, author = Michael Ruby, Falko Pientka, Yang Peng, Felix von Oppen, Benjamin W. Heinrich and Katharina J. Franke, title = End States and Subgap Structure in Proximity-Coupled Chains of Magnetic Adatoms, journal = Physical Review Letters, year = 2015, volume = 115, number = 19, pages = 197204, url = http://dx.doi.org/10.1103/PhysRevLett.115.197204, doi = http://dx.doi.org/10.1103/physrevlett.115.197204 }  Rodrigo Gallego and Leandro Aolita Resource Theory of Steering Physical Review X 5(4), (2015). Abstract: We present an operational framework for Einstein-Podolsky-Rosen steering as a physical resource. For arbitrary-dimensional bipartite systems composed of a quantum subsystem and a black-box device, we show that local operations assisted by one-way classical communication (1W-LOCCs) from the quantum part to the black box cannot create steering. Based on this, we build a resource theory of steering with 1W-LOCCs as the free operations. We introduce the notion of convex steering monotones as the fundamental axiomatic quantifiers of steering. As a convenient example thereof, we present the relative entropy of steering. In addition, we prove that two previously proposed quantifiers, the steerable weight and the robustness of steering, are also convex steering monotones. To end up with for minimal-dimensional systems, we establish, on the one hand, necessary and sufficient conditions for pure-state steering conversions under stochastic 1W-LOCCs and prove, on the other hand, the nonexistence of steering bits, i.e., measure-independent maximally steerable states from which all states can be obtained by means of the free operations. Our findings reveal unexpected aspects of steering and lay the foundations for further research, with potential implications in Bell nonlocality. BibTeX:  @article{Gallego2015a, author = Rodrigo Gallego and Leandro Aolita, title = Resource Theory of Steering, journal = Physical Review X, year = 2015, volume = 5, number = 4, pages = , url = http://dx.doi.org/10.1103/PhysRevX.5.041008, doi = http://dx.doi.org/10.1103/physrevx.5.041008 }  Michael Herold, Earl T. Campbell, Jens Eisert and Michael J. Kastoryano Cellular-automaton decoders for topological quantum memories npj Quantum Inf. 1(), 15010 (2015). Abstract: We introduce a new framework for constructing topological quantum memories, by recasting error recovery as a dynamical process on a field generating cellular automaton. We envisage quantum systems controlled by a classical hardware composed of small local memories, communicating with neighbours and repeatedly performing identical simple update rules. This approach does not require any global operations or complex decoding algorithms. Our cellular automata draw inspiration from classical field theories, with a Coulomb-like potential naturally emerging from the local dynamics. For a 3D automaton coupled to a 2D toric code, we present evidence of an error correction threshold above 6.1% for uncorrelated noise. A 2D automaton equipped with a more complex update rule yields a threshold above 8.2%. Our framework provides decisive new tools in the quest for realising a passive dissipative quantum memory. BibTeX:  @article{Herold2015, author = Michael Herold, Earl T. Campbell, Jens Eisert and Michael J. Kastoryano, title = Cellular-automaton decoders for topological quantum memories, journal = npj Quantum Inf., year = 2015, volume = 1, number = , pages = 15010, url = http://dx.doi.org/10.1038/npjqi.2015.10, doi = http://dx.doi.org/10.1038/npjqi.2015.10 }  Flore K. Kunst, Christophe Delerue, Cristiane Morais Smith and Vladimir Juričić Kekule versus hidden superconducting order in graphene-like systems: Competition and coexistence Phys. Rev. B 92(16), 165423 (2015). Abstract: We theoretically study the competition between two possible exotic superconducting orders that may occur in graphene-like systems, assuming dominant nearest-neighbor attraction: the gapless hidden superconducting order, which renormalizes the Fermi velocity, and the Kekule order, which opens a superconducting gap. We perform an analysis within the mean-field theory for Dirac electrons, at finite temperature and finite chemical potential, as well as at half filling and zero temperature, first excluding the possibility of the coexistence of the two orders. In that case, we find the dependence of the critical (more precisely, crossover) temperature and the critical interaction on the chemical potential. As a result of this analysis, we find that the Kekule order is preferred over the hidden order at both finite temperature and finite chemical potential. However, when the coexistence of the two superconducting orders is allowed, by solving the coupled mean-field gap equations, we find that above a critical value of the attractive interaction a mixed phase sets in, in which these orders coexist. We show that the critical value of the interaction for this transition is greater than the critical coupling for the hidden superconducting state in the absence of the Kekule order, implying that there is a region in the phase diagram where the Kekule order is favored as a result of the competition with the hidden superconducting order. The latter, however, eventually sets in and coexists with the Kekule state. According to our mean-field calculations, the transition from the Kekule to the mixed phase is of the second order, but it may become first order when fluctuations are considered. Finally, we investigate whether these phases could be possible in honeycomb superlattices of self-assembled semiconducting nanocrystals, which have been recently experimentally realized with CdSe and PbSe. BibTeX:  @article{PhysRevB.92.165423, author = Flore K. Kunst, Christophe Delerue, Cristiane Morais Smith and Vladimir Juričić, title = Kekule versus hidden superconducting order in graphene-like systems: Competition and coexistence, journal = Phys. Rev. B, year = 2015, volume = 92, number = 16, pages = 165423, url = http://link.aps.org/doi/10.1103/PhysRevB.92.165423, doi = http://dx.doi.org/10.1103/PhysRevB.92.165423 }  Dario Bercioux and Procolo Lucignano Quantum transport in Rashba spin–orbit materials: a review Reports on Progress in Physics 78(10), 106001 (2015). Abstract: In this review article we describe spin-dependent transport in materials with spin–orbit interaction of Rashba type. We mainly focus on semiconductor heterostructures, however we consider topological insulators, graphene and hybrid structures involving superconductors as well. We start from the Rashba Hamiltonian in a two dimensional electron gas and then describe transport properties of two- and quasi-one-dimensional systems. The problem of spin current generation and interference effects in mesoscopic devices is described in detail. We address also the role of Rashba interaction on localisation effects in lattices with nontrivial topology, as well as on the Ahronov–Casher effect in ring structures. A brief section, in the end, describes also some related topics including the spin-Hall effect, the transition from weak localisation to weak anti localisation and the physics of Majorana fermions in hybrid heterostructures involving Rashba materials in the presence of superconductivity. BibTeX:  @article{0034-4885-78-10-106001, author = Dario Bercioux and Procolo Lucignano, title = Quantum transport in Rashba spin–orbit materials: a review, journal = Reports on Progress in Physics, year = 2015, volume = 78, number = 10, pages = 106001, url = http://stacks.iop.org/0034-4885/78/i=10/a=106001, doi = http://dx.doi.org/10.1088/0034-4885/78/10/106001 }  S. Pirandola, J. Eisert, C. Weedbrook, A. Furusawa and S. L. Braunstein Advances in quantum teleportation Nature Photon 9(10), 641–652 (2015). Abstract: Quantum teleportation is one of the most important protocols in quantum information. By exploiting the physical resource of entanglement, quantum teleportation serves as a key primitive across a variety of quantum information tasks and represents an important building block for quantum technologies, with a pivotal role in the continuing progress of quantum communication, quantum computing and quantum networks. Here we summarize the basic theoretical ideas behind quantum teleportation and its variant protocols. We focus on the main experiments, together with the technical advantages and disadvantages associated with the use of the various technologies, from photonic qubits and optical modes to atomic ensembles, trapped atoms and solid-state systems. After analysing the current state-of-the-art, we finish by discussing open issues, challenges and potential future implementations. BibTeX:  @article{Pirandola2015, author = S. Pirandola, J. Eisert, C. Weedbrook, A. Furusawa and S. L. Braunstein, title = Advances in quantum teleportation, journal = Nature Photon, year = 2015, volume = 9, number = 10, pages = 641–652, url = http://dx.doi.org/10.1038/nphoton.2015.154, doi = http://dx.doi.org/10.1038/nphoton.2015.154 }  Björn Sbierski, Emil J. Bergholtz and Piet W. Brouwer Quantum critical exponents for a disordered three-dimensional Weyl node Phys. Rev. B 92(11), 115145 (2015). Abstract: Three-dimensional Dirac and Weyl semimetals exhibit a disorder-induced quantum phase transition between a semimetallic phase at weak disorder and a diffusive-metallic phase at strong disorder. Despite considerable effort, both numerically and analytically, the critical exponents ν and z of this phase transition are not known precisely. Here we report a numerical calculation of the critical exponent ν=1.47±0.03 using a minimal single-Weyl node model and a finite-size scaling analysis of conductance. Our high-precision numerical value for ν is incompatible with previous numerical studies on tight-binding models and with one- and two-loop calculations in an ε-expansion scheme. We further obtain z=1.49±0.02 from the scaling of the conductivity with chemical potential. BibTeX:  @article{PhysRevB.92.115145, author = Björn Sbierski, Emil J. Bergholtz and Piet W. Brouwer, title = Quantum critical exponents for a disordered three-dimensional Weyl node, journal = Phys. Rev. B, year = 2015, volume = 92, number = 11, pages = 115145, url = http://link.aps.org/doi/10.1103/PhysRevB.92.115145, doi = http://dx.doi.org/10.1103/PhysRevB.92.115145 }  Piet W. Brouwer and Jeroen Danon Semiclassical theory of persistent current fluctuations in ballistic chaotic rings Physica E: Low-dimensional Systems and Nanostructures 74(), 644 - 650 (2015). Abstract: Abstract The persistent current in a mesoscopic ring has a Gaussian distribution with small non-Gaussian corrections. Here we report a semiclassical calculation of the leading non-Gaussian correction, which is described by the three-point correlation function. The semiclassical approach is applicable to systems in which the electron dynamics is ballistic and chaotic, and includes the dependence on the Ehrenfest time. At small but finite Ehrenfest times, the non-Gaussian fluctuations are enhanced with respect to the limit of zero Ehrenfest time. BibTeX:  @article{Brouwer2015644, author = Piet W. Brouwer and Jeroen Danon, title = Semiclassical theory of persistent current fluctuations in ballistic chaotic rings, journal = Physica E: Low-dimensional Systems and Nanostructures, year = 2015, volume = 74, number = , pages = 644 - 650, url = http://www.sciencedirect.com/science/article/pii/S138694771530148X, doi = http://dx.doi.org/http://dx.doi.org/10.1016/j.physe.2015.08.004 }  Max Hering, Martin Schneider and Piet W. Brouwer Electronic transport in graphene with particle-hole-asymmetric disorder Phys. Rev. B 92(7), 075415 (2015). Abstract: We study the conductivity of graphene with a smooth but particle-hole-asymmetric disorder potential. Using perturbation theory for the weak-disorder regime and numerical calculations, we investigate how the particle-hole asymmetry shifts the position of the minimal conductivity away from the Dirac point ɛ=0. We find that the conductivity minimum is shifted in opposite directions for weak and strong disorder. For large disorder strengths, the conductivity minimum appears close to the doping level for which electron and hole doped regions (“puddles”) are equal in size. BibTeX:  @article{PhysRevB.92.075415, author = Max Hering, Martin Schneider and Piet W. Brouwer, title = Electronic transport in graphene with particle-hole-asymmetric disorder, journal = Phys. Rev. B, year = 2015, volume = 92, number = 7, pages = 075415, url = http://link.aps.org/doi/10.1103/PhysRevB.92.075415, doi = http://dx.doi.org/10.1103/PhysRevB.92.075415 }  N. H. Y. Ng, L. Mančinska, C. Cirstoiu, J. Eisert and S. Wehner Limits to catalysis in quantum thermodynamics New J. Phys. 17(8), 085004 (2015). Abstract: Quantum thermodynamics is a research field that aims at fleshing out the ultimate limits of thermodynamic processes in the deep quantum regime. A complete picture of thermodynamical processes naturally allows for auxiliary systems dubbed 'catalysts', i.e., any physical systems facilitating state transformations while remaining essentially intact in their state, like an auxiliary system, a clock, or an actual catalyst. In this work, we present a comprehensive analysis of the power and limitation of such thermal catalysis. Specifically, we provide a family of optimal catalysts that can be returned with minimal trace distance error after facilitating a state transformation process. To incorporate the genuine physical role of a catalyst, we identify very significant restrictions on arbitrary state transformations under dimension or mean energy bounds, using methods of convex relaxations. We discuss the implication of these findings on possible thermodynamic state transformations in the quantum regime. BibTeX:  @article{Ng2015, author = N. H. Y. Ng, L. Mančinska, C. Cirstoiu, J. Eisert and S. Wehner, title = Limits to catalysis in quantum thermodynamics, journal = New J. Phys., year = 2015, volume = 17, number = 8, pages = 085004, url = http://dx.doi.org/10.1088/1367-2630/17/8/085004, doi = http://dx.doi.org/10.1088/1367-2630/17/8/085004 }  Falko Pientka, Yang Peng, Leonid Glazman and Felix von Oppen Topological superconducting phase and Majorana bound states in Shiba chains Physica Scripta 2015(T164), 014008 (2015). Abstract: Chains of magnetic adatoms on a conventional superconducting substrate constitute a promising venue for realizing topological superconductivity and Majorana end states. Here, we give a brief overview over recent attempts to describe these systems theoretically, emphasizing how the topological phase emerges from the physics of individual magnetic impurities and their associated Shiba states. BibTeX:  @article{Pientka2015, author = Falko Pientka, Yang Peng, Leonid Glazman and Felix von Oppen, title = Topological superconducting phase and Majorana bound states in Shiba chains, journal = Physica Scripta, year = 2015, volume = 2015, number = T164, pages = 014008, url = http://dx.doi.org/10.1088/0031-8949/2015/T164/014008, doi = http://dx.doi.org/10.1088/0031-8949/2015/t164/014008 }  Michael Ruby, Falko Pientka, Yang Peng, Felix von Oppen, Benjamin W. Heinrich and Katharina J. Franke Tunneling Processes into Localized Subgap States in Superconductors Physical Review Letters 115(8), (2015). Abstract: We combine scanning-tunneling-spectroscopy experiments probing magnetic impurities on a superconducting surface with a theoretical analysis of the tunneling processes between (superconducting) tip and substrate. We show that the current through impurity-induced Shiba bound states is carried by single-electron tunneling at large tip-substrate distances and Andreev reflections at smaller distances. The single-electron current requires relaxation processes, allowing us to extract information on quasiparticle transitions and lifetimes. BibTeX:  @article{Ruby2015a, author = Michael Ruby, Falko Pientka, Yang Peng, Felix von Oppen, Benjamin W. Heinrich and Katharina J. Franke, title = Tunneling Processes into Localized Subgap States in Superconductors, journal = Physical Review Letters, year = 2015, volume = 115, number = 8, pages = , url = http://dx.doi.org/10.1103/PhysRevLett.115.087001, doi = http://dx.doi.org/10.1103/physrevlett.115.087001 }  S. Gröblacher, A. Trubarov, N. Prigge, G. D. Cole, M. Aspelmeyer and J. Eisert Observation of non-{Markov}ian micromechanical Brownian motion Nat Comms 6(), 7606 (2015). Abstract: All physical systems are to some extent open and interacting with their environment. This insight, basic as it may seem, gives rise to the necessity of protecting quantum systems from decoherence in quantum technologies and is at the heart of the emergence of classical properties in quantum physics. The precise decoherence mechanisms, however, are often unknown for a given system. In this work, we make use of an opto-mechanical resonator to obtain key information about spectral densities of its condensed-matter heat bath. In sharp contrast to what is commonly assumed in high-temperature quantum Brownian motion describing the dynamics of the mechanical degree of freedom, based on a statistical analysis of the emitted light, it is shown that this spectral density is highly non-Ohmic, reflected by non-Markovian dynamics, which we quantify. We conclude by elaborating on further applications of opto-mechanical systems in open system identification. BibTeX:  @article{Groeblacher2015, author = S. Gröblacher, A. Trubarov, N. Prigge, G. D. Cole, M. Aspelmeyer and J. Eisert, title = Observation of non-{Markov}ian micromechanical Brownian motion, journal = Nat Comms, year = 2015, volume = 6, number = , pages = 7606, url = http://dx.doi.org/10.1038/ncomms8606, doi = http://dx.doi.org/10.1038/ncomms8606 }  Jesús Martínez-Blanco, Christophe Nacci, Steven C. Erwin, Kiyoshi Kanisawa, Elina Locane, Mark Thomas, Felix von Oppen, Piet W. Brouwer and Stefan Fölsch Gating a single-molecule transistor with individual atoms Nature Physics 11(8), 640–644 (2015). Abstract: Transistors, regardless of their size, rely on electrical gates to control the conductance between source and drain contacts. In atomic-scale transistors, this conductance is sensitive to single electrons hopping via individual orbitals1, 2. Single-electron transport in molecular transistors has been previously studied using top-down approaches to gating, such as lithography and break junctions1, 3, 4, 5, 6, 7, 8, 9, 10, 11. But atomically precise control of the gate—which is crucial to transistor action at the smallest size scales—is not possible with these approaches. Here, we used individual charged atoms, manipulated by a scanning tunnelling microscope12, to create the electrical gates for a single-molecule transistor. This degree of control allowed us to tune the molecule into the regime of sequential single-electron tunnelling, albeit with a conductance gap more than one order of magnitude larger than observed previously8, 11, 13, 14. This unexpected behaviour arises from the existence of two different orientational conformations of the molecule, depending on its charge state. Our results show that strong coupling between these charge and conformational degrees of freedom leads to new behaviour beyond the established picture of single-electron transport in atomic-scale transistors. BibTeX:  @article{Martinez-Blanco2015, author = Jesús Martínez-Blanco, Christophe Nacci, Steven C. Erwin, Kiyoshi Kanisawa, Elina Locane, Mark Thomas, Felix von Oppen, Piet W. Brouwer and Stefan Fölsch, title = Gating a single-molecule transistor with individual atoms, journal = Nature Physics, year = 2015, volume = 11, number = 8, pages = 640–644, url = http://dx.doi.org/10.1038/nphys3385, doi = http://dx.doi.org/10.1038/nphys3385 }  A. Steffens, M. Friesdorf, T. Langen, B. Rauer, T. Schweigler, R. Hübener, J. Schmiedmayer, C.A. Riofrío and J. Eisert Towards experimental quantum-field tomography with ultracold atoms Nat Comms 6(), 7663 (2015). Abstract: The experimental realization of large-scale many-body systems in atomic-optical architectures has seen immense progress in recent years, rendering full tomography tools for state identification inefficient, especially for continuous systems. To work with these emerging physical platforms, new technologies for state identification are required. Here we present first steps towards efficient experimental quantum-field tomography. Our procedure is based on the continuous analogues of matrix-product states, ubiquitous in condensed-matter theory. These states naturally incorporate the locality present in realistic physical settings and are thus prime candidates for describing the physics of locally interacting quantum fields. To experimentally demonstrate the power of our procedure, we quench a one-dimensional Bose gas by a transversal split and use our method for a partial quantum-field reconstruction of the far-from-equilibrium states of this system. We expect our technique to play an important role in future studies of continuous quantum many-body systems. BibTeX:  @article{Steffens2015, author = A. Steffens, M. Friesdorf, T. Langen, B. Rauer, T. Schweigler, R. Hübener, J. Schmiedmayer, C.A. Riofrío and J. Eisert, title = Towards experimental quantum-field tomography with ultracold atoms, journal = Nat Comms, year = 2015, volume = 6, number = , pages = 7663, url = http://dx.doi.org/10.1038/ncomms8663, doi = http://dx.doi.org/10.1038/ncomms8663 }  M. Friesdorf, A. H. Werner, W. Brown, V. B. Scholz and J. Eisert Many-Body Localization Implies that Eigenvectors are Matrix-Product States Physical Review Letters 114(17), (2015). Abstract: The phenomenon of many-body localization has received a lot of attention recently, both for its implications in condensed-matter physics of allowing systems to be an insulator even at nonzero temperature as well as in the context of the foundations of quantum statistical mechanics, providing examples of systems showing the absence of thermalization following out-of-equilibrium dynamics. In this work, we establish a novel link between dynamical properties—a vanishing group velocity and the absence of transport—with entanglement properties of individual eigenvectors. For systems with a generic spectrum, we prove that strong dynamical localization implies that all of its many-body eigenvectors have clustering correlations. The same is true for parts of the spectrum, thus allowing for the existence of a mobility edge above which transport is possible. In one dimension these results directly imply an entanglement area law; hence, the eigenvectors can be efficiently approximated by matrix-product states. BibTeX:  @article{Friesdorf2015, author = M. Friesdorf, A. H. Werner, W. Brown, V. B. Scholz and J. Eisert, title = Many-Body Localization Implies that Eigenvectors are Matrix-Product States, journal = Physical Review Letters, year = 2015, volume = 114, number = 17, pages = , url = http://dx.doi.org/10.1103/PhysRevLett.114.170505, doi = http://dx.doi.org/10.1103/physrevlett.114.170505 }  Torsten Karzig, Falko Pientka, Gil Refael and Felix von Oppen Shortcuts to non-Abelian braiding Phys. Rev. B 91(20), (2015). Abstract: Topological quantum information processing relies on adiabatic braiding of non-Abelian quasiparticles. Performing the braiding operations in finite time introduces transitions out of the ground-state manifold and deviations from the non-Abelian Berry phase. We show that these errors can be eliminated by suitably designed counterdiabatic correction terms in the Hamiltonian. We implement the resulting shortcuts to adiabaticity for simple protocols of non-Abelian braiding and show that the error suppression can be substantial even for approximate realizations of the counterdiabatic terms. BibTeX:  @article{Karzig2015, author = Torsten Karzig, Falko Pientka, Gil Refael and Felix von Oppen, title = Shortcuts to non-Abelian braiding, journal = Phys. Rev. B, year = 2015, volume = 91, number = 20, pages = , url = http://dx.doi.org/10.1103/PhysRevB.91.201102, doi = http://dx.doi.org/10.1103/physrevb.91.201102 }  Torsten Karzig, Armin Rahmani, Felix von Oppen and Gil Refael Optimal control of Majorana zero modes Phys. Rev. B 91(20), (2015). Abstract: Braiding of Majorana zero modes provides a promising platform for quantum information processing, which is topologically protected against errors. Strictly speaking, however, the scheme relies on infinite braiding times as it utilizes the adiabatic limit. Here we show how to minimize nonadiabatic errors for finite braiding times by finding an optimal protocol for the Majorana movement. Interestingly, these protocols are characterized by sharp transitions between Majorana motion at maximal and minimal velocities. We find that these so-called bang-bang protocols can minimize the nonadiabatic transitions of the system by orders of magnitude in comparison with naive protocols. BibTeX:  @article{Karzig2015a, author = Torsten Karzig, Armin Rahmani, Felix von Oppen and Gil Refael, title = Optimal control of Majorana zero modes, journal = Phys. Rev. B, year = 2015, volume = 91, number = 20, pages = , url = http://dx.doi.org/10.1103/PhysRevB.91.201404, doi = http://dx.doi.org/10.1103/physrevb.91.201404 }  Arbel Haim, Erez Berg, Felix von Oppen and Yuval Oreg Signatures of Majorana Zero Modes in Spin-Resolved Current Correlations Physical Review Letters 114(16), (2015). Abstract: We consider a normal lead coupled to a Majorana bound state. We show that the spin-resolved current correlations exhibit unique features which distinguish Majorana bound states from other low-energy resonances. In particular, the spin-up and spin-down currents from a Majorana bound state are anticorrelated at low bias voltages, and become uncorrelated at higher voltages. This behavior is independent of the exact form of coupling to the lead, and of the direction of the spin polarization. In contrast, an ordinary low-energy Andreev bound state gives rise to a positive correlation between the spin-up and spin-down currents, and this spin-resolved current-current correlation approaches a nonzero constant at high bias voltages. We discuss experimental setups in which this effect can be measured. BibTeX:  @article{Haim2015, author = Arbel Haim, Erez Berg, Felix von Oppen and Yuval Oreg, title = Signatures of Majorana Zero Modes in Spin-Resolved Current Correlations, journal = Physical Review Letters, year = 2015, volume = 114, number = 16, pages = , url = http://dx.doi.org/10.1103/PhysRevLett.114.166406, doi = http://dx.doi.org/10.1103/physrevlett.114.166406 }  R. Hübener, Y. Sekino and J. Eisert Equilibration in low-dimensional quantum matrix models J. High Energ. Phys. 2015(4), (2015). Abstract: Matrix models play an important role in studies of quantum gravity, being candidates for a formulation of M-theory, but are notoriously difficult to solve. In this work, we present a fresh approach by introducing a novel exact model, provably equivalent with a low-dimensional bosonic matrix model, which is on its own a well-known, unsolved model of quantum chaos. In our equivalent reformulation local structure becomes apparent, facilitating analytical and precise numerical study. We derive a substantial part of the low energy spectrum, find a conserved charge, and are able to derive numerically the Regge trajectories. To exemplify the usefulness of the approach, we address questions of equilibration starting from a non-equilibrium situation, building upon an intuition from quantum information. We finally discuss possible generalisations of the approach. BibTeX:  @article{Huebener2015, author = R. Hübener, Y. Sekino and J. Eisert, title = Equilibration in low-dimensional quantum matrix models, journal = J. High Energ. Phys., year = 2015, volume = 2015, number = 4, pages = , url = http://dx.doi.org/10.1007/JHEP04(2015)166, doi = http://dx.doi.org/10.1007/jhep04(2015)166 }  Stephan Rachel, Manuel Laubach, Johannes Reuther and Ronny Thomale Quantum Paramagnet in a π Flux Triangular Lattice Hubbard Model Physical Review Letters 114(16), (2015). Abstract: We propose the π flux triangular lattice Hubbard model (π THM) as a prototypical setup to stabilize magnetically disordered quantum states of matter in the presence of charge fluctuations. The quantum paramagnetic domain of the π THM that we identify for intermediate Hubbard U is framed by a Dirac semimetal for weak coupling and by 120° Néel order for strong coupling. Generalizing the Klein duality from spin Hamiltonians to tight-binding models, the π THM maps to a Hubbard model which corresponds to the (JH,JK)=(−1,2) Heisenberg-Kitaev model in its strong coupling limit. The π THM provides a promising microscopic testing ground for exotic finite-U spin liquid ground states amenable to numerical investigation. BibTeX:  @article{Rachel2015, author = Stephan Rachel, Manuel Laubach, Johannes Reuther and Ronny Thomale, title = Quantum Paramagnet in a π Flux Triangular Lattice Hubbard Model, journal = Physical Review Letters, year = 2015, volume = 114, number = 16, pages = , url = http://dx.doi.org/10.1103/PhysRevLett.114.167201, doi = http://dx.doi.org/10.1103/physrevlett.114.167201 }  M. Schneider, D. Faria, S. Viola Kusminskiy and N. Sandler Local sublattice symmetry breaking for graphene with a centrosymmetric deformation Phys. Rev. B 91(16), (2015). Abstract: We calculate the local density of states (LDOS) for an infinite graphene sheet with a single centrosymmetric out-of-plane deformation, in order to investigate measurable strain signatures on graphene. We focus on the regime of small deformations and show that the strain-induced pseudomagnetic field induces an imbalance of the LDOS between the two triangular graphene sublattices in the region of the deformation. Real-space imaging reveals a characteristic sixfold symmetry pattern where the sublattice symmetry is broken within each fold, consistent with experimental and tight-binding observations. The open geometry we study allows us to make use of the usual continuum model of graphene and to obtain results independent of boundary conditions. We provide an analytic perturbative expression for the contrast between the LDOS of each sublattice, showing a scaling law as a function of the amplitude and width of the deformation. We confirm our results by a numerically exact iterative scattering matrix method. BibTeX:  @article{Schneider2015, author = M. Schneider, D. Faria, S. Viola Kusminskiy and N. Sandler, title = Local sublattice symmetry breaking for graphene with a centrosymmetric deformation, journal = Phys. Rev. B, year = 2015, volume = 91, number = 16, pages = , url = http://dx.doi.org/10.1103/PhysRevB.91.161407, doi = http://dx.doi.org/10.1103/physrevb.91.161407 }  Leandro Aolita, Fernando de Melo and Luiz Davidovich Open-system dynamics of entanglement:a key issues review Reports on Progress in Physics 78(4), 042001 (2015). Abstract: One of the greatest challenges in the fields of quantum information processing and quantum technologies is the detailed coherent control over each and every constituent of quantum systems with an ever increasing number of particles. Within this endeavor, harnessing of many-body entanglement against the detrimental effects of the environment is a major pressing issue. Besides being an important concept from a fundamental standpoint, entanglement has been recognized as a crucial resource for quantum speed-ups or performance enhancements over classical methods. Understanding and controlling many-body entanglement in open systems may have strong implications in quantum computing, quantum simulations of many-body systems, secure quantum communication or cryptography, quantum metrology, our understanding of the quantum-to-classical transition, and other important questions of quantum foundations. In this paper we present an overview of recent theoretical and experimental efforts to underpin the dynamics of entanglement under the influence of noise. Entanglement is thus taken as a dynamic quantity on its own, and we survey how it evolves due to the unavoidable interaction of the entangled system with its surroundings. We analyze several scenarios, corresponding to different families of states and environments, which render a very rich diversity of dynamical behaviors. In contrast to single-particle quantities, like populations and coherences, which typically vanish only asymptotically in time, entanglement may disappear at a finite time. In addition, important classes of entanglement display an exponential decay with the number of particles when subject to local noise, which poses yet another threat to the already-challenging scaling of quantum technologies. Other classes, however, turn out to be extremely robust against local noise. Theoretical results and recent experiments regarding the difference between local and global decoherence are summarized. Control and robustness-enhancement techniques, scaling laws, statistical and geometrical aspects of multipartite-entanglement decay are also reviewed; all in order to give a broad picture of entanglement dynamics in open quantum systems addressed to both theorists and experimentalists inside and outside the field of quantum information. BibTeX:  @article{Aolita2015, author = Leandro Aolita, Fernando de Melo and Luiz Davidovich, title = Open-system dynamics of entanglement:a key issues review, journal = Reports on Progress in Physics, year = 2015, volume = 78, number = 4, pages = 042001, url = http://dx.doi.org/10.1088/0034-4885/78/4/042001, doi = http://dx.doi.org/10.1088/0034-4885/78/4/042001 }  Simon Braun, Mathis Friesdorf, Sean S. Hodgman, Michael Schreiber, Jens Philipp Ronzheimer, Arnau Riera, Marco del Rey, Immanuel Bloch, Jens Eisert and Ulrich Schneider Emergence of coherence and the dynamics of quantum phase transitions Proceedings of the National Academy of Sciences 112(12), 201408861 (2015). Abstract: The dynamics of quantum phase transitions pose one of the most challenging problems in modern many-body physics. Here, we study a prototypical example in a clean and well-controlled ultracold atom setup by observing the emergence of coherence when crossing the Mott insulator to superfluid quantum phase transition. In the 1D Bose–Hubbard model, we find perfect agreement between experimental observations and numerical simulations for the resulting coherence length. We, thereby, perform a largely certified analog quantum simulation of this strongly correlated system reaching beyond the regime of free quasiparticles. Experimentally, we additionally explore the emergence of coherence in higher dimensions, where no classical simulations are available, as well as for negative temperatures. For intermediate quench velocities, we observe a power-law behavior of the coherence length, reminiscent of the Kibble–Zurek mechanism. However, we find nonuniversal exponents that cannot be captured by this mechanism or any other known model. BibTeX:  @article{Braun2015, author = Simon Braun, Mathis Friesdorf, Sean S. Hodgman, Michael Schreiber, Jens Philipp Ronzheimer, Arnau Riera, Marco del Rey, Immanuel Bloch, Jens Eisert and Ulrich Schneider, title = Emergence of coherence and the dynamics of quantum phase transitions, journal = Proceedings of the National Academy of Sciences, year = 2015, volume = 112, number = 12, pages = 201408861, url = http://dx.doi.org/10.1073/pnas.1408861112, doi = http://dx.doi.org/10.1073/pnas.1408861112 }  Yang Peng, Falko Pientka, Leonid I. Glazman and Felix von Oppen Strong Localization of Majorana End States in Chains of Magnetic Adatoms Physical Review Letters 114(10), (2015). Abstract: A recent experiment [Nadj-Perge et al, Science 346, 602 (2014)] gives possible evidence for Majorana bound states in chains of magnetic adatoms placed on a superconductor. While many features of the observed end states are naturally interpreted in terms of Majorana states, their strong localization remained puzzling. We consider a linear chain of Anderson impurities on a superconductor as a minimal model and treat it largely analytically within mean-field theory. We explore the phase diagram, the subgap excitation spectrum, and the Majorana wave functions. Owing to a strong velocity renormalization, the latter are localized on a scale which is parametrically small compared to the coherence length of the host superconductor. BibTeX:  @article{physRevLett.114.106801, author = Yang Peng, Falko Pientka, Leonid I. Glazman and Felix von Oppen, title = Strong Localization of Majorana End States in Chains of Magnetic Adatoms, journal = Physical Review Letters, year = 2015, volume = 114, number = 10, pages = , url = http://dx.doi.org/10.1103/PhysRevLett.114.106801, doi = http://dx.doi.org/10.1103/physrevlett.114.106801 }  Maximilian Trescher, Björn Sbierski, Piet W. Brouwer and Emil J. Bergholtz Quantum transport in Dirac materials: Signatures of tilted and anisotropic Dirac and Weyl cones Phys. Rev. B 91(11), (2015). Abstract: We calculate conductance and noise for quantum transport at the nodal point for arbitrarily tilted and anisotropic Dirac or Weyl cones. Tilted and anisotropic dispersions are generic in the absence of certain discrete symmetries, such as particle-hole and lattice point group symmetries. Whereas anisotropy affects the conductance g, but leaves the Fano factor F (the ratio of shot noise power and current) unchanged, a tilt affects both g and F. Since F is a universal number in many other situations, this finding is remarkable. We apply our general considerations to specific lattice models of strained graphene and a pyrochlore Weyl semimetal. BibTeX:  @article{Trescher2015, author = Maximilian Trescher, Björn Sbierski, Piet W. Brouwer and Emil J. Bergholtz, title = Quantum transport in Dirac materials: Signatures of tilted and anisotropic Dirac and Weyl cones, journal = Phys. Rev. B, year = 2015, volume = 91, number = 11, pages = , url = http://dx.doi.org/10.1103/PhysRevB.91.115135, doi = http://dx.doi.org/10.1103/physrevb.91.115135 }  Miklós Antal Werner, Arne Brataas, Felix von Oppen and Gergely Zaránd Anderson localization and quantum Hall effect: Numerical observation of two-parameter scaling Phys. Rev. B 91(12), (2015). Abstract: A two-dimensional disordered system of noninteracting fermions in a homogeneous magnetic field is investigated numerically. By using a modified Landau gauge, we explore the renormalization group flow of the longitudinal and Hall conductances and find that the flow is consistent with the predictions of Pruisken and Khmelnitskii. The extracted critical exponents agree with the results obtained by using transfer matrix methods. The necessity of a second scaling parameter is also demonstrated in the level curvature distribution. Near the critical point the distribution slightly differs from the prediction of random matrix theory, in agreement with previous works. Close to the quantum Hall fixed points the distribution is lognormal since here states are strongly localized. BibTeX:  @article{Werner2015, author = Miklós Antal Werner, Arne Brataas, Felix von Oppen and Gergely Zaránd, title = Anderson localization and quantum Hall effect: Numerical observation of two-parameter scaling, journal = Phys. Rev. B, year = 2015, volume = 91, number = 12, pages = , url = http://dx.doi.org/10.1103/PhysRevB.91.125418, doi = http://dx.doi.org/10.1103/physrevb.91.125418 }  H. Bernigau, M. J. Kastoryano and J. Eisert Mutual information area laws for thermal free fermions J. Stat. Mech. P 02008(2), P02008 (2015). Abstract: We provide a rigorous and asymptotically exact expression of the mutual information of translationally invariant free fermionic lattice systems in a Gibbs state. In order to arrive at this result, we introduce a novel frameworkfor computing determinants of Toeplitz operators with smooth symbols, and for treating Toeplitz matrices with system size dependent entries. The asymptotically exact mutual information for a partition of the one-dimensional lattice satisfies an area law, with a prefactor which we compute explicitly. As examples, we discuss the fermionic XX model in one dimension and free fermionic models on the torus in higher dimensions in detail. Special emphasis is put onto the discussion of the temperature dependence of the mutual information, scaling like the logarithm of the inverse temperature, hence confirming an expression suggested by conformal field theory. We also comment on the applicability of the formalism to treat open systems driven by quantum noise. In the appendix, we derive useful bounds to the mutual information in terms of purities. Finally, we provide a detailed error analysis for finite system sizes. This analysis is valuable in its own right for the abstract theory of Toeplitz determinants. BibTeX:  @article{Bernigau2013a12345, author = H. Bernigau, M. J. Kastoryano and J. Eisert, title = Mutual information area laws for thermal free fermions, journal = J. Stat. Mech. P, year = 2015, volume = 02008, number = 2, pages = P02008, url = http://iopscience.iop.org/1742-5468/2015/2/P02008/article?fromSearchPage=true, doi = http://dx.doi.org/10.1088/1742-5468/2015/02/P02008 }  J. Eisert, M. Friesdorf and C. Gogolin Quantum many-body systems out of equilibrium Nature Physics 11(2), 124–130 (2015). Abstract: How do closed quantum many-body systems driven out of equilibrium eventually achieve equilibration? And how do these systems thermalize, given that they comprise so many degrees of freedom? Progress in answering these—and related—questions has accelerated in recent years—a trend that can be partially attributed to success with experiments performing quantum simulations using ultracold atoms and trapped ions. Here we provide an overview of this progress, specifically in studies probing dynamical equilibration and thermalization of systems driven out of equilibrium by quenches, ramps and periodic driving. In doing so, we also address topics such as the eigenstate thermalization hypothesis, typicality, transport, many-body localization and universality near phase transitions, as well as future prospects for quantum simulation. BibTeX:  @article{Eisert2015, author = J. Eisert, M. Friesdorf and C. Gogolin, title = Quantum many-body systems out of equilibrium, journal = Nature Physics, year = 2015, volume = 11, number = 2, pages = 124–130, url = http://dx.doi.org/10.1038/nphys3215, doi = http://dx.doi.org/10.1038/nphys3215 }  Osvaldo Jiménez Farías, Vincenzo D’Ambrosio, Caterina Taballione, Fabrizio Bisesto, Sergei Slussarenko, Leandro Aolita, Lorenzo Marrucci, Stephen P. Walborn and Fabio Sciarrino Resilience of hybrid optical angular momentum qubits to turbulence Sci. Rep. 5(8424), 8424 (2015). Abstract: Recent schemes to encode quantum information into the total angular momentum of light, defining rotation-invariant hybrid qubits composed of the polarization and orbital angular momentum degrees of freedom, present interesting applications for quantum information technology. However, there remains the question as to how detrimental effects such as random spatial perturbations affect these encodings. Here, we demonstrate that alignment-free quantum communication through a turbulent channel based on hybrid qubits can be achieved with unit transmission fidelity. In our experiment, alignment-free qubits are produced with q-plates and sent through a homemade turbulence chamber. The decoding procedure, also realized with q-plates, relies on both degrees of freedom and renders an intrinsic error-filtering mechanism that maps errors into losses. BibTeX:  @article{Farias2015, author = Osvaldo Jiménez Farías, Vincenzo D’Ambrosio, Caterina Taballione, Fabrizio Bisesto, Sergei Slussarenko, Leandro Aolita, Lorenzo Marrucci, Stephen P. Walborn and Fabio Sciarrino, title = Resilience of hybrid optical angular momentum qubits to turbulence, journal = Sci. Rep., year = 2015, volume = 5, number = 8424, pages = 8424, url = http://dx.doi.org/10.1038/srep08424, doi = http://dx.doi.org/10.1038/srep08424 }  Piotr Mironowicz, Rodrigo Gallego and Marcin Pawłowski Robust amplification of Santha-Vazirani sources with three devices Phys. Rev. A 91(3), (2015). Abstract: We demonstrate that amplification of arbitrarily weak randomness is possible using quantum resources. We present a randomness amplification protocol that involves Bell experiments. We find a Bell inequality that can amplify arbitrarily weak randomness and give a detailed analysis of the protocol involving it. Our analysis includes finding a sufficient violation of the Bell inequality as a function of the initial quality of randomness. It has a very important property that for any quality the required violation is strictly lower than possible to obtain using quantum resources. Among other things, this means that the protocol takes a finite amount of time to amplify arbitrarily weak randomness. BibTeX:  @article{Mironowicz2015, author = Piotr Mironowicz, Rodrigo Gallego and Marcin Pawłowski, title = Robust amplification of Santha-Vazirani sources with three devices, journal = Phys. Rev. A, year = 2015, volume = 91, number = 3, pages = , url = http://dx.doi.org/10.1103/PhysRevA.91.032317, doi = http://dx.doi.org/10.1103/physreva.91.032317 }  E. J. Bergholtz, Zhao Liu, M. Trescher, R. Moessner and M. Udagawa Topology and Interactions in a Frustrated Slab: Tuning from Weyl Semimetals to $\mathcal{C}\>1$ Fractional Chern Insulators Phys. Rev. Lett. 114(1), 016806 (2015). Abstract: We show that, quite generically, a [111] slab of spin-orbit coupled pyrochlore lattice exhibits surface states whose constant energy curves take the shape of Fermi arcs, localized to different surfaces depending on their quasimomentum. Remarkably, these persist independently of the existence of Weyl points in the bulk. Considering interacting electrons in slabs of finite thickness, we find a plethora of known fractional Chern insulating phases, to which we add the discovery of a new higher Chern number state which is likely a generalization of the Moore-Read fermionic fractional quantum Hall state. By contrast, in the three-dimensional limit, we argue for the absence of gapped states of the flat surface band due to a topologically protected coupling of the surface to gapless states in the bulk. We comment on generalizations as well as experimental perspectives in thin slabs of pyrochlore iridates. BibTeX:  @article{PhysRevLett.114.016806, author = E. J. Bergholtz, Zhao Liu, M. Trescher, R. Moessner and M. Udagawa, title = Topology and Interactions in a Frustrated Slab: Tuning from Weyl Semimetals to $\mathcal{C}\>1$ Fractional Chern Insulators, journal = Phys. Rev. Lett., year = 2015, volume = 114, number = 1, pages = 016806, url = http://link.aps.org/doi/10.1103/PhysRevLett.114.016806, doi = http://dx.doi.org/10.1103/PhysRevLett.114.016806 }  M. Dall'Arno, E. Passaro, R. Gallego, M. Pawlowski and A. Acin Detection loophole attacks on semi-device-independent quantum and classical protocols Quantum Information and Computation 15(1\&2), 0037--0049 (2015). Abstract: Semi-device-independent quantum protocols realize information tasks - e.g. secure key distribution, random access coding, and randomness generation - in a scenario where no assumption on the internal working of the devices used in the protocol is made, except their dimension. These protocols offer two main advantages: first, their implementation is often less demanding than fully-device-independent protocols. Second, they are more secure than their device-dependent counterparts. Their classical analogous is represented by random access codes, which provide a general framework for describing one-sided classical communication tasks. We discuss conditions under which detection inefficiencies can be exploited by a malicious provider to fake the performance of semi-device-independent quantum and classical protocols - and how to prevent it. BibTeX:  @article{gallego20151, author = M. Dall'Arno, E. Passaro, R. Gallego, M. Pawlowski and A. Acin, title = Detection loophole attacks on semi-device-independent quantum and classical protocols, journal = Quantum Information and Computation, year = 2015, volume = 15, number = 1\&2, pages = 0037--0049, url = http://www.rintonpress.com/xxqic15/qic-15-12/0037-0049.pdf, doi = }  2014 BibTeX:  @unpublished{20142015,, title = {Preprints}, year = 2014 }  and Earl T. Campbell Enhanced Fault-Tolerant Quantum Computing in $d$-Level Systems Phys. Rev. Lett. 113(23), 230501 (2014). Abstract: Error-correcting codes protect quantum information and form the basis of fault-tolerant quantum computing. Leading proposals for fault-tolerant quantum computation require codes with an exceedingly rare property, a transversal non-Clifford gate. Codes with the desired property are presented for d-level qudit systems with prime d. The codes use n=d−1 qudits and can detect up to ∼d/3 errors. We quantify the performance of these codes for one approach to quantum computation known as magic-state distillation. Unlike prior work, we find performance is always enhanced by increasing d. BibTeX:  @article{PhysRevLett.113.230501, author = and Earl T. Campbell, title = Enhanced Fault-Tolerant Quantum Computing in $d$-Level Systems, journal = Phys. Rev. Lett., year = 2014, volume = 113, number = 23, pages = 230501, url = http://link.aps.org/doi/10.1103/PhysRevLett.113.230501, doi = http://dx.doi.org/10.1103/PhysRevLett.113.230501 }  R. Gallego, A. Riera and J. Eisert Thermal machines beyond the weak coupling regime New Journal of Physics 16(12), 125009 (2014). Abstract: How much work can be extracted from a heat bath using a thermal machine? The study of this question has a very long history in statistical physics in the weak-coupling limit, when applied to macroscopic systems. However, the assumption that thermal heat baths remain uncorrelated with associated physical systems is less reasonable on the nano-scale and in the quantum setting. In this work, we establish a framework of work extraction in the presence of quantum correlations. We show in a mathematically rigorous and quantitative fashion that quantum correlations and entanglement emerge as limitations to work extraction compared to what would be allowed by the second law of thermodynamics. At the heart of the approach are operations that capture the naturally non-equilibrium dynamics encountered when putting physical systems into contact with each other. We discuss various limits that relate to known results and put our work into the context of approaches to finite-time quantum thermodynamics. BibTeX:  @article{1367-2630-16-12-125009, author = R. Gallego, A. Riera and J. Eisert, title = Thermal machines beyond the weak coupling regime, journal = New Journal of Physics, year = 2014, volume = 16, number = 12, pages = 125009, url = http://stacks.iop.org/1367-2630/16/i=12/a=125009, doi = http://dx.doi.org/10.1088/1367-2630/16/12/125009 }  Alexandra Junck, Gil Refael and Felix von Oppen Current amplification and relaxation in Dirac systems Phys. Rev. B 90(24), 245110 (2014). Abstract: Recent experiments provide evidence for photocurrent generation in Dirac systems such as topological-insulator surface states and graphene. Within the simplest picture, the magnitude of the photocurrents is governed by the competition between photoexcitation of particle-hole pairs and current relaxation by scattering. Here, we study the relaxation of photocurrents by electron-electron (e−e) collisions, which should dominate in clean systems. We compute the current relaxation rate as a function of the initial energies of the photoexcited carriers and the Fermi energy. For a positive Fermi energy, we find that collisions of a single excited electron with the Fermi sea can substantially increase the current, while for a single excited hole the current initially decreases. Together these processes partially cancel leading to a relative suppression of the relaxation of the total photocurrent carried by an electron-hole pair. We also analyze the limit of many scattering events and find that while e−e collisions initially reduce the current associated with a single hole, the current eventually reverses sign and becomes as large in magnitude as in the electron case. Thus, for photoexcited electron-hole pairs, the current ultimately relaxes to zero. We discuss schemes which may allow one to probe the nontrivial current amplification physics for individual carriers in experiment. BibTeX:  @article{PhysRevB.90.245110, author = Alexandra Junck, Gil Refael and Felix von Oppen, title = Current amplification and relaxation in Dirac systems, journal = Phys. Rev. B, year = 2014, volume = 90, number = 24, pages = 245110, url = http://link.aps.org/doi/10.1103/PhysRevB.90.245110, doi = http://dx.doi.org/10.1103/PhysRevB.90.245110 }  M.-T. Rieder, A. Levchenko and T. Micklitz Brownian scattering of a spinon in a Luttinger liquid Phys. Rev. B 90(24), 245434 (2014). Abstract: We consider strongly interacting one-dimensional electron liquids where elementary excitations carry either spin or charge. At small temperatures a spinon created at the bottom of its band scatters off low-energy spin and charge excitations and follows the diffusive motion of a Brownian particle in momentum space. We calculate the mobility characterizing these processes and show that the resulting diffusion coefficient of the spinon is parametrically enhanced at low temperatures compared to that of a mobile impurity in a spinless Luttinger liquid. We briefly discuss that this hints at the relevance of spin in the process of equilibration of strongly interacting one-dimensional electrons, and comment on implications for transport in clean single-channel quantum wires. BibTeX:  @article{PhysRevB.90.245434, author = M.-T. Rieder, A. Levchenko and T. Micklitz, title = Brownian scattering of a spinon in a Luttinger liquid, journal = Phys. Rev. B, year = 2014, volume = 90, number = 24, pages = 245434, url = http://link.aps.org/doi/10.1103/PhysRevB.90.245434, doi = http://dx.doi.org/10.1103/PhysRevB.90.245434 }  and P. G. Silvestrov Functionalized graphene in quantizing magnetic field: The case of bunched impurities Phys. Rev. B 90(23), 235130 (2014). Abstract: Resonant scattering at the atomic absorbates in graphene was investigated recently in relation with the transport and gap opening problems. Attaching an impurity atom to graphene is believed to lead to the creation of unusual zero-energy localized electron states. This paper aims to describe the behavior of the localized impurity-induced levels in graphene in a quantizing magnetic field. It is shown that in the magnetic field the impurity level effectively hybridizes with one of the n=0 Landau level states and splits into two opposite-energy states. The new hybridized state is doubly occupied, forming a spin singlet and reducing the polarization of a quantum Hall ferromagnet in undoped graphene. Taking into account the electron-electron interaction changes radically the spectrum of the electrons surrounding the impurity, which should be seen experimentally. While existing publications investigate graphene uniformly covered by adatoms, here we address a possibly even more experimentally relevant case of the clusterized impurity distribution. The limit of a dense bunch of the impurity atoms is considered, and it is shown how such a bunch changes the spectrum and spin polarization of a large dense electron droplet surrounding it. The droplet is encircled by an edge state carrying a persistent current. BibTeX:  @article{PhysRevB.90.235130, author = and P. G. Silvestrov, title = Functionalized graphene in quantizing magnetic field: The case of bunched impurities, journal = Phys. Rev. B, year = 2014, volume = 90, number = 23, pages = 235130, url = http://link.aps.org/doi/10.1103/PhysRevB.90.235130, doi = http://dx.doi.org/10.1103/PhysRevB.90.235130 }  A. Steffens, C. A. Riofrío, R. Hübener and J. Eisert Quantum field tomography New Journal of Physics 16(12), 123010 (2014). Abstract: We introduce the concept of quantum field tomography, the efficient and reliable reconstruction of unknown quantum fields based on data of correlation functions. At the basis of the analysis is the concept of continuous matrix product states (cMPS), a complete set of variational states grasping states in one-dimensional quantum field theory. We innovate a practical method, making use of and developing tools in estimation theory used in the context of compressed sensing such as Prony methods and matrix pencils, allowing us to faithfully reconstruct quantum field states based on low-order correlation functions. In the absence of a phase reference, we highlight how specific higher order correlation functions can still be predicted. We exemplify the functioning of the approach by reconstructing randomized cMPS from their correlation data and study the robustness of the reconstruction for different noise models. Furthermore, we apply the method to data generated by simulations based on cMPS and using the time-dependent variational principle. The presented approach is expected to open up a new window into experimentally studying continuous quantum systems, such as those encountered in experiments with ultra-cold atoms on top of atom chips. By virtue of the analogy with the input–output formalism in quantum optics, it also allows for studying open quantum systems. BibTeX:  @article{1367-2630-16-12-123010, author = A. Steffens, C. A. Riofrío, R. Hübener and J. Eisert, title = Quantum field tomography, journal = New Journal of Physics, year = 2014, volume = 16, number = 12, pages = 123010, url = http://stacks.iop.org/1367-2630/16/i=12/a=123010, doi = http://dx.doi.org/10.1088/1367-2630/16/12/123010 }  Géraldine Haack, Mathias Albert and Christian Flindt Distributions of electron waiting times in quantum-coherent conductors Phys. Rev. B 90(20), 205429 (2014). Abstract: The distribution of electron waiting times is useful to characterize quantum transport in mesoscopic structures. Here we consider a generic quantum-coherent conductor consisting of a mesoscopic scatterer in a two-terminal setup. We extend earlier results for single-channel conductors to setups with several (possibly spin degenerate) conduction channels and we discuss the effect of a finite electronic temperature. We present detailed investigations of the electron waiting times in a quantum point contact as well as in two mesoscopic interferometers with energy-dependent transmissions: a Fabry–Pérot interferometer and a Mach–Zehnder interferometer. We show that the waiting time distributions allow us to determine characteristic features of the scatterers, for instance, the number of resonant levels in the Fabry–Pérot interferometer that contribute to the electronic transport. BibTeX:  @article{PhysRevB.90.205429, author = Géraldine Haack, Mathias Albert and Christian Flindt, title = Distributions of electron waiting times in quantum-coherent conductors, journal = Phys. Rev. B, year = 2014, volume = 90, number = 20, pages = 205429, url = http://link.aps.org/doi/10.1103/PhysRevB.90.205429, doi = http://dx.doi.org/10.1103/PhysRevB.90.205429 }  Emanuela Margapoti, Philipp Strobel, Mahmoud M. Asmar, Max Seifert, Juan Li, Matthias Sachsenhauser, Özlem Ceylan, Carlos-Andres Palma, Johannes V. Barth, Jose A. Garrido, Anna Cattani-Scholz, Sergio E. Ulloa and Jonathan J. Finley Emergence of Photoswitchable States in a Graphene–Azobenzene–Au Platform Nano Letters 14(12), 6823-6827 (2014). Abstract: The perfect transmission of charge carriers through potential barriers in graphene (Klein tunneling) is a direct consequence of the Dirac equation that governs the low-energy carrier dynamics. As a result, localized states do not exist in unpatterned graphene, but quasibound states can occur for potentials with closed integrable dynamics. Here, we report the observation of resonance states in photoswitchable self-assembled molecular(SAM)-graphene hybrid. Conductive AFM measurements performed at room temperature reveal strong current resonances, the strength of which can be reversibly gated on- and off- by optically switching the molecular conformation of the mSAM. Comparisons of the voltage separation between current resonances (∼70–120 mV) with solutions of the Dirac equation indicate that the radius of the gating potential is ∼7 ± 2 nm with a strength ≥0.5 eV. Our results and methods might provide a route toward optically programmable carrier dynamics and transport in graphene nanomaterials. BibTeX:  @article{doi:10.1021/nl503681z, author = Emanuela Margapoti, Philipp Strobel, Mahmoud M. Asmar, Max Seifert, Juan Li, Matthias Sachsenhauser, Özlem Ceylan, Carlos-Andres Palma, Johannes V. Barth, Jose A. Garrido, Anna Cattani-Scholz, Sergio E. Ulloa and Jonathan J. Finley, title = Emergence of Photoswitchable States in a Graphene–Azobenzene–Au Platform, journal = Nano Letters, year = 2014, volume = 14, number = 12, pages = 6823-6827, url = http://dx.doi.org/10.1021/nl503681z, doi = http://dx.doi.org/10.1021/nl503681z }  Oded Zilberberg, Assaf Carmi and Alessandro Romito Measuring cotunneling in its wake Phys. Rev. B 90(20), 205413 (2014). Abstract: We introduce a rate formalism to treat classically forbidden electron transport through a quantum dot (cotunneling) in the presence of a coupled measurement device. We demonstrate this formalism for a toy model case of cotunneling through a single-level dot while being coupled to a strongly pinched-off quantum point contact (QPC). We find that the detector generates three types of back-action: the measurement collapses the coherent transport through the virtual state, but at the same time allows for QPC-assisted incoherent transport, and widens the dot level. Last, we obtain the measured cotunneling time from the cross correlation between dot and QPC currents. BibTeX:  @article{PhysRevB.90.205413, author = Oded Zilberberg, Assaf Carmi and Alessandro Romito, title = Measuring cotunneling in its wake, journal = Phys. Rev. B, year = 2014, volume = 90, number = 20, pages = 205413, url = http://link.aps.org/doi/10.1103/PhysRevB.90.205413, doi = http://dx.doi.org/10.1103/PhysRevB.90.205413 }  Ingemar Bengtsson, Kate Blanchfield, Earl Campbell and Mark Howard Order 3 symmetry in the Clifford hierarchy Journal of Physics A: Mathematical and Theoretical 47(45), 455302 (2014). Abstract: We investigate the action of the first three levels of the Clifford hierarchy on sets of mutually unbiased bases comprising the Ivanovic mutually unbiased base (MUB) and the Alltop MUBs. Vectors in the Alltop MUBs exhibit additional symmetries when the dimension is a prime number equal to 1 modulo 3 and thus the set of all Alltop vectors splits into three Clifford orbits. These vectors form configurations with so-called Zauner subspaces, eigenspaces of order 3 elements of the Clifford group highly relevant to the SIC problem. We identify Alltop vectors as the magic states that appear in the context of fault-tolerant universal quantum computing, wherein the appearance of distinct Clifford orbits implies a surprising inequivalence between some magic states. BibTeX:  @article{1751-8121-47-45-455302, author = Ingemar Bengtsson, Kate Blanchfield, Earl Campbell and Mark Howard, title = Order 3 symmetry in the Clifford hierarchy, journal = Journal of Physics A: Mathematical and Theoretical, year = 2014, volume = 47, number = 45, pages = 455302, url = http://stacks.iop.org/1751-8121/47/i=45/a=455302, doi = http://dx.doi.org/10.1088/1751-8113/47/45/455302https://dudle.inf.tu-dresden.de/9lqibjnc/ }  M. Kliesch, D. Gross and J. Eisert Matrix-Product Operators and States: NP-Hardness and Undecidability Phys. Rev. Lett. 113(16), 160503 (2014). Abstract: Tensor network states constitute an important variational set of quantum states for numerical studies of strongly correlated systems in condensed-matter physics, as well as in mathematical physics. This is specifically true for finitely correlated states or matrix-product operators, designed to capture mixed states of one-dimensional quantum systems. It is a well-known open problem to find an efficient algorithm that decides whether a given matrix-product operator actually represents a physical state that in particular has no negative eigenvalues. We address and answer this question by showing that the problem is provably undecidable in the thermodynamic limit and that the bounded version of the problem is NP-hard (nondeterministic-polynomial-time hard) in the system size. Furthermore, we discuss numerous connections between tensor network methods and (seemingly) different concepts treated before in the literature, such as hidden Markov models and tensor trains. BibTeX:  @article{PhysRevLett.113.160503, author = M. Kliesch, D. Gross and J. Eisert, title = Matrix-Product Operators and States: NP-Hardness and Undecidability, journal = Phys. Rev. Lett., year = 2014, volume = 113, number = 16, pages = 160503, url = http://link.aps.org/doi/10.1103/PhysRevLett.113.160503, doi = http://dx.doi.org/10.1103/PhysRevLett.113.160503 }  Clemens Meyer zu Rheda, Géraldine Haack and Alessandro Romito On-demand maximally entangled states with a parity meter and continuous feedback Phys. Rev. B 90(15), 155438 (2014). Abstract: Generating on-demand maximally entangled states is one of the cornerstones for quantum information processing. Parity measurements can serve to create Bell states and have been implemented via an electronic Mach-Zehnder interferometer among others. However, the entanglement generation is necessarily harmed by measurement-induced dephasing processes in one of the two parity subspaces. In this work, we propose two different schemes of continuous feedback for a parity measurement. They enable us to avoid both the measurement-induced dephasing process and the experimentally unavoidable dephasing, e.g., due to fluctuations of the gate voltages controlling the initialization of the qubits. We show that we can generate maximally entangled steady states in both parity subspaces. Importantly, the measurement scheme we propose is valid for implementation of parity measurements with feedback loops in various solid-state environments. BibTeX:  @article{PhysRevB.90.155438, author = Clemens Meyer zu Rheda, Géraldine Haack and Alessandro Romito, title = On-demand maximally entangled states with a parity meter and continuous feedback, journal = Phys. Rev. B, year = 2014, volume = 90, number = 15, pages = 155438, url = http://link.aps.org/doi/10.1103/PhysRevB.90.155438, doi = http://dx.doi.org/10.1103/PhysRevB.90.155438 }  M.-T. Rieder, T. Micklitz, A. Levchenko and K. A. Matveev Interaction-induced backscattering in short quantum wires Phys. Rev. B 90(16), 165405 (2014). Abstract: We study interaction-induced backscattering in clean quantum wires with adiabatic contacts exposed to a voltage bias. Particle backscattering relaxes such systems to a fully equilibrated steady state only on length scales exponentially large in the ratio of bandwidth of excitations and temperature. Here we focus on shorter wires in which full equilibration is not accomplished. Signatures of relaxation then are due to backscattering of hole excitations close to the band bottom which perform a diffusive motion in momentum space while scattering from excitations at the Fermi level. This is reminiscent to the first passage problem of a Brownian particle and, regardless of the interaction strength, can be described by an inhomogeneous Fokker-Planck equation. From general solutions of the latter we calculate the hole backscattering rate for different wire lengths and discuss the resulting length dependence of interaction-induced correction to the conductance of a clean single channel quantum wire. BibTeX:  @article{PhysRevB.90.165405, author = M.-T. Rieder, T. Micklitz, A. Levchenko and K. A. Matveev, title = Interaction-induced backscattering in short quantum wires, journal = Phys. Rev. B, year = 2014, volume = 90, number = 16, pages = 165405, url = http://link.aps.org/doi/10.1103/PhysRevB.90.165405, doi = http://dx.doi.org/10.1103/PhysRevB.90.165405 }  G. Schwiete and A. M. Finkel’stein Renormalization group analysis of thermal transport in the disordered Fermi liquid Phys. Rev. B 90(15), (2014). Abstract: We present a detailed study of thermal transport in the disordered Fermi liquid with short-range interactions. At temperatures smaller than the impurity scattering rate, i.e., in the diffusive regime, thermal conductivity acquires nonanalytic quantum corrections. When these quantum corrections become large at low temperatures, the calculation of thermal conductivity demands a theoretical approach that treats disorder and interactions on an equal footing. In this paper, we develop such an approach by merging Luttinger's idea of using gravitational potentials for the analysis of thermal phenomena with a renormalization group calculation based on the Keldysh nonlinear sigma model. The gravitational potentials are introduced in the action as auxiliary sources that couple to the heat density. These sources are a convenient tool for generating expressions for the heat density and its correlation function from the partition function. Already in the absence of the gravitational potentials, the nonlinear sigma model contains several temperature-dependent renormalization group charges. When the gravitational potentials are introduced into the model, they acquire an independent renormalization group flow. We show that this flow preserves the phenomenological form of the correlation function, reflecting its relation to the specific heat and the constraints imposed by energy conservation. The main result of our analysis is that the Wiedemann-Franz law holds down to the lowest temperatures even in the presence of disorder and interactions and despite the quantum corrections that arise for both the electric and thermal conductivities. BibTeX:  @article{physrevb.90.155441, author = G. Schwiete and A. M. Finkel’stein, title = Renormalization group analysis of thermal transport in the disordered Fermi liquid, journal = Phys. Rev. B, year = 2014, volume = 90, number = 15, pages = , url = http://dx.doi.org/10.1103/PhysRevB.90.155441, doi = http://dx.doi.org/10.1103/physrevb.90.155441 }  Masafumi Udagawa and Emil J. Bergholtz Correlations and entanglement in flat band models with variable Chern numbers Journal of Statistical Mechanics: Theory and Experiment 2014(10), P10012 (2014). Abstract: We discuss a number of illuminating results for tight-binding models supporting a band with variable Chern numbers and illustrate them explicitly for a simple class of two-banded models. First, for models with a fixed number of bands, we show that the minimal hopping range needed to achieve a given Chern number C increases with C and that the band flattening requires an exponential tail of long-range processes. We further verify that the entanglement spectrum corresponding to a real space partitioning contains C chiral modes and thereby complies with the archetypal correspondence between the bulk entanglement and the edge energetics. Finally, we address the issue of interactions and study the problem of two interacting particles projected to the flattened band as a function of the Chern number. Our results provide valuable insights for the full interacting problem of a partially filled Chern band at variable filling fractions and Chern numbers. BibTeX:  @article{1742-5468-2014-10-P10012, author = Masafumi Udagawa and Emil J. Bergholtz, title = Correlations and entanglement in flat band models with variable Chern numbers, journal = Journal of Statistical Mechanics: Theory and Experiment, year = 2014, volume = 2014, number = 10, pages = P10012, url = http://stacks.iop.org/1742-5468/2014/i=10/a=P10012, doi = http://dx.doi.org/10.1088/1742-5468/2014/10/P10012 }  Liliana Arrachea, Niels Bode and Felix von Oppen Vibrational cooling and thermoelectric response of nanoelectromechanical systems Phys. Rev. B 90(12), 125450 (2014). Abstract: An important goal in nanoelectromechanics is to cool the vibrational motion, ideally to its quantum ground state. Cooling by an applied charge current is a particularly simple and hence attractive strategy to this effect. Here we explore this phenomenon in the context of the general theory of thermoelectrics. In linear response, this theory describes thermoelectric refrigerators in terms of their cooling efficiency η and figure of merit ZT. We show that both concepts carry over to phonon cooling in nanoelectromechanical systems. As an important consequence, this allows us to discuss the efficiency of phonon refrigerators in relation to the fundamental Carnot efficiency. We illustrate these general concepts by thoroughly investigating a simple double-quantum-dot model with the dual advantage of being quite realistic experimentally and amenable to a largely analytical analysis theoretically. Specifically, we obtain results for the efficiency, the figure of merit, and the effective temperature of the vibrational motion in two regimes. In the quantum regime in which the vibrational motion is fast compared to the electronic degrees of freedom, we can describe the electronic and phononic dynamics of the model in terms of master equations. In the complementary classical regime of slow vibrational motion, the dynamics is described in terms of an appropriate Langevin equation. Remarkably, we find that the efficiency can approach the maximal Carnot value in the quantum regime, with large associated figures of merit. In contrast, the efficiencies are typically far from the Carnot limit in the classical regime. Our theoretical results should provide guidance to implementing efficient vibrational cooling of nanoelectromechanical systems in the laboratory. BibTeX:  @article{PhysRevB.90.125450, author = Liliana Arrachea, Niels Bode and Felix von Oppen, title = Vibrational cooling and thermoelectric response of nanoelectromechanical systems, journal = Phys. Rev. B, year = 2014, volume = 90, number = 12, pages = 125450, url = http://link.aps.org/doi/10.1103/PhysRevB.90.125450, doi = http://dx.doi.org/10.1103/PhysRevB.90.125450 }  J. C. Budich, J. Eisert, E. J. Bergholtz, S. Diehl and P. Zoller Search for localized Wannier functions of topological band structures via compressed sensing Phys. Rev. B 90(11), 115110 (2014). Abstract: We investigate the interplay of band structure topology and localization properties of Wannier functions. To this end, we extend a recently proposed compressed sensing based paradigm for the search for maximally localized Wannier functions [Ozolins et al., Proc. Natl. Acad. Sci. USA 110, 18368 (2013)]. We develop a practical toolbox that enables the search for maximally localized Wannier functions which exactly obey the underlying physical symmetries of a translationally invariant quantum lattice system under investigation. Most saliently, this allows us to systematically identify the most localized representative of a topological equivalence class of band structures, i.e., the most localized set of Wannier functions that is adiabatically connected to a generic initial representative. We also elaborate on the compressed sensing scheme and find a particularly simple and efficient implementation in which each step of the iteration is an O(NlogN) algorithm in the number of lattice sites N. We present benchmark results on one-dimensional topological superconductors demonstrating the power of these tools. Furthermore, we employ our method to address the open question of whether compact Wannier functions can exist for symmetry-protected topological states such as topological insulators in two dimensions. The existence of such functions would imply exact flat-band models with finite range hopping. Here, we find numerical evidence for the absence of such functions. We briefly discuss applications in dissipative-state preparation and in devising variational sets of states for tensor network methods. BibTeX:  @article{PhysRevB.90.115110, author = J. C. Budich, J. Eisert, E. J. Bergholtz, S. Diehl and P. Zoller, title = Search for localized Wannier functions of topological band structures via compressed sensing, journal = Phys. Rev. B, year = 2014, volume = 90, number = 11, pages = 115110, url = http://link.aps.org/doi/10.1103/PhysRevB.90.115110, doi = http://dx.doi.org/10.1103/PhysRevB.90.115110 }  Michele Filippone, Cătălin Paşcu Moca, Gergely Zaránd and Christophe Mora Kondo temperature of SU(4) symmetric quantum dots Phys. Rev. B 90(12), 121406 (2014). Abstract: A path integral approach is used to derive a closed analytical expression for the Kondo temperature of the SU(4) symmetrical Anderson model. In contrast to the SU(2) case, the prefactor of the Kondo temperature is found to display a peculiar orbital-energy (gate voltage) dependence, reflecting the presence of various SU(4) mixed valence fixed points. Our analytical expressions are tested against and confirmed by numerical renormalization group computations. BibTeX:  @article{PhysRevB.90.121406, author = Michele Filippone, Cătălin Paşcu Moca, Gergely Zaránd and Christophe Mora, title = Kondo temperature of SU(4) symmetric quantum dots, journal = Phys. Rev. B, year = 2014, volume = 90, number = 12, pages = 121406, url = http://link.aps.org/doi/10.1103/PhysRevB.90.121406, doi = http://dx.doi.org/10.1103/PhysRevB.90.121406 }  Maria-Theresa Rieder and Piet W. Brouwer Density of states at disorder-induced phase transitions in a multichannel Majorana wire Phys. Rev. B 90(20), 205404 (2014). Abstract: An N-channel spinless p-wave superconducting wire is known to go through a series of N topological phase transitions upon increasing the disorder strength. Here, we show that at each of those transitions the density of states shows a Dyson singularity ν(ɛ)∝ɛ−1∣∣lnɛ∣∣−3, whereas ν(ɛ)∝ɛ|α|−1 has a power-law singularity for small energies ɛ away from the critical points. Using the concept of “superuniversality” [Gruzberg et al., Phys. Rev. B 71, 245124 (2005)], we are able to relate the exponent α to the wire's transport properties at zero energy and, hence, to the mean free path l and the superconducting coherence length ξ. BibTeX:  @article{PhysRevB.90.205404, author = Maria-Theresa Rieder and Piet W. Brouwer, title = Density of states at disorder-induced phase transitions in a multichannel Majorana wire, journal = Phys. Rev. B, year = 2014, volume = 90, number = 20, pages = 205404, url = http://link.aps.org/doi/10.1103/PhysRevB.90.205404, doi = http://dx.doi.org/10.1103/PhysRevB.90.205404 }  Kristan Temme, Fernando Pastawski and Michael J. Kastoryano Hypercontractivity of quasi-free quantum semigroups Journal of Physics A: Mathematical and Theoretical 47(40), 405303 (2014). Abstract: Hypercontractivity of a quantum dynamical semigroup has strong implications for its convergence behavior and entropy decay rate. A logarithmic Sobolev inequality and the corresponding logarithmic Sobolev constant can be inferred from the semigroupʼs hypercontractive norm bound. We consider completely-positive quantum mechanical semigroups described by a Lindblad master equation. To prove the norm bound, we follow an approach which has its roots in the study of classical rate equations. We use interpolation theorems for non-commutative ${{\mathbb{L}}_{p}}$ spaces to obtain a general hypercontractive inequality from a particular #"IMG"# [http://ej.iop.org/images/1751-8121/47/40/405303/jpa501301ieqn2.gif] $p\to q$ -norm bound. Then, we derive a bound on the $2\to 4$-norm from an analysis of the block diagonal structure of the semigroupʼs spectrum. We show that the dynamics of an N -qubit graph state Hamiltonian weakly coupled to a thermal environment is hypercontractive. As a consequence this allows for the efficient preparation of graph states in time ${\rm poly}({\rm log} (N))$ by coupling at sufficiently low temperature. Furthermore, we extend our results to gapped Liouvillians arising from a weak linear coupling of a free-fermion systems. BibTeX:  @article{1751-8121-47-40-405303, author = Kristan Temme, Fernando Pastawski and Michael J. Kastoryano, title = Hypercontractivity of quasi-free quantum semigroups, journal = Journal of Physics A: Mathematical and Theoretical, year = 2014, volume = 47, number = 40, pages = 405303, url = http://stacks.iop.org/1751-8121/47/i=40/a=405303, doi = http://dx.doi.org/10.1088/1751-8113/47/40/405303 }  Dganit Meidan, Alessandro Romito and Piet W. Brouwer Scattering Matrix Formulation of the Topological Index of Interacting Fermions in One-Dimensional Superconductors Phys. Rev. Lett. 113(5), 057003 (2014). Abstract: We construct a scattering matrix formulation for the topological classification of one-dimensional superconductors with effective time-reversal symmetry in the presence of interactions. For an isolated system, Fidkowski and Kitaev have shown that such systems have a ℤ8 topological classification. We here show that these systems have a unitary scattering matrix at zero temperature when weakly coupled to a normal-metal lead, with a topological index given by the trace of the Andreev-reflection matrix, trrhe. With interactions, trrhe generically takes on the finite set of values 0, ±1, ±2, ±3, and ±4. We show that the two topologically equivalent phases with trrhe=±4 support emergent many-body end states, which we identify to be a topologically protected Kondo-like resonance. The path in phase space that connects these equivalent phases crosses a non-Fermi-liquid fixed point where a multiple-channel Kondo effect develops. Our results connect the topological index to transport properties, thereby highlighting the experimental signatures of interacting topological phases in one dimension. BibTeX:  @article{PhysRevLett.113.057003, author = Dganit Meidan, Alessandro Romito and Piet W. Brouwer, title = Scattering Matrix Formulation of the Topological Index of Interacting Fermions in One-Dimensional Superconductors, journal = Phys. Rev. Lett., year = 2014, volume = 113, number = 5, pages = 057003, url = http://link.aps.org/doi/10.1103/PhysRevLett.113.057003, doi = http://dx.doi.org/10.1103/PhysRevLett.113.057003 }  Alessandro Romito and Yuval Gefen Weak measurement of cotunneling time Phys. Rev. B 90(8), 085417 (2014). Abstract: Quantum mechanics allows the existence of “virtual states” that have no classical analog. Such virtual states defy direct observation through strong measurement, which would destroy the volatile virtual state. Here, we show how a virtual state of an interacting many-body system can be detected employing a weak measurement protocol with post-selection. We employ this protocol for the measurement of the time it takes an electron to tunnel through a virtual state of a quantum dot (cotunneling). Contrary to classical intuition, this cotunneling time is independent of the strength of the dot-lead coupling and may deviate from that predicted by time-energy uncertainty relation. Our approach, amenable to experimental verification, may elucidate an important facet of quantum mechanics which hitherto was not accessible by direct measurements. BibTeX:  @article{PhysRevB.90.085417, author = Alessandro Romito and Yuval Gefen, title = Weak measurement of cotunneling time, journal = Phys. Rev. B, year = 2014, volume = 90, number = 8, pages = 085417, url = http://link.aps.org/doi/10.1103/PhysRevB.90.085417, doi = http://dx.doi.org/10.1103/PhysRevB.90.085417 }  G. Schwiete and A. M. Finkel'stein Thermal transport and Wiedemann-Franz law in the disordered Fermi liquid Phys. Rev. B 90(6), 060201 (2014). Abstract: We study thermal transport at low temperatures in the disordered Fermi liquid with short-range interactions. Gravitational potentials are used as sources for finding the heat density and its correlation function. For a comprehensive study, we extend the renormalization group (RG) analysis developed for electric transport by including the gravitational potentials into the RG scheme. Our analysis reveals that the Wiedemann-Franz law remains valid even in the presence of quantum corrections caused by the interplay of diffusion modes and the electron-electron interaction. In the present scheme this fundamental relation is closely connected with a fixed point in the multiparametric RG flow of the gravitational potentials. BibTeX:  @article{PhysRevB.90.060201, author = G. Schwiete and A. M. Finkel'stein, title = Thermal transport and Wiedemann-Franz law in the disordered Fermi liquid, journal = Phys. Rev. B, year = 2014, volume = 90, number = 6, pages = 060201, url = http://link.aps.org/doi/10.1103/PhysRevB.90.060201, doi = http://dx.doi.org/10.1103/PhysRevB.90.060201 }  J. Danon, A. Ricottone and P. W. Brouwer Spin-wave-induced correction to the conductivity of ferromagnets Phys. Rev. B 90(2), 024405 (2014). Abstract: We calculate the correction to the conductivity of a disordered ferromagnetic metal due to spin-wave-mediated electron-electron interactions. This correction is the generalization of the Altshuler-Aronov correction to spin-wave-mediated interactions. We derive a general expression for the conductivity correction to lowest order in the spin-wave-mediated interaction and for the limit that the exchange splitting Δ is much smaller than the Fermi energy. For a “clean” ferromagnet with Δτel/ℏ≫1, with τel being the mean time for impurity scattering, we find a correction δσ∝−T5/2 at temperatures T above the spin-wave gap. In the opposite, “dirty” limit, Δτel/ℏ≪1, the correction is a nonmonotonous function of temperature. BibTeX:  @article{PhysRevB.90.024405, author = J. Danon, A. Ricottone and P. W. Brouwer, title = Spin-wave-induced correction to the conductivity of ferromagnets, journal = Phys. Rev. B, year = 2014, volume = 90, number = 2, pages = 024405, url = http://link.aps.org/doi/10.1103/PhysRevB.90.024405, doi = http://dx.doi.org/10.1103/PhysRevB.90.024405 }  Martin Kliesch, Christian Gogolin and Jens Eisert Lieb-Robinson bounds and the simulation of time evolution of local observables in lattice systems (Book Chapter) Many-Electron Approaches in Physics, Chemistry and Mathematics: A Multidisciplinary View Part IV(), 301--320 (2014). Abstract: This is an introductory text reviewing Lieb-Robinson bounds for open and closed quantum many-body systems. We introduce the Heisenberg picture for time-dependent local Liouvillians and state a Lieb-Robinson bound. Finally we discuss a number of important consequences in quantum many-body theory. BibTeX:  @article{arxiv13060716inbook, author = Martin Kliesch, Christian Gogolin and Jens Eisert, title = Lieb-Robinson bounds and the simulation of time evolution of local observables in lattice systems (Book Chapter), journal = Many-Electron Approaches in Physics, Chemistry and Mathematics: A Multidisciplinary View, year = 2014, volume = Part IV, number = , pages = 301--320, url = http://arxiv.org/pdf/1306.0716v1.pdf, doi = }  M. Kliesch, C. Gogolin, M. J. Kastoryano, A. Riera and J. Eisert Locality of Temperature Phys. Rev. X 4(3), 031019 (2014). Abstract: This work is concerned with thermal quantum states of Hamiltonians on spin- and fermionic-lattice systems with short-range interactions. We provide results leading to a local definition of temperature, thereby extending the notion of “intensivity of temperature” to interacting quantum models. More precisely, we derive a perturbation formula for thermal states. The influence of the perturbation is exactly given in terms of a generalized covariance. For this covariance, we prove exponential clustering of correlations above a universal critical temperature that upper bounds physical critical temperatures such as the Curie temperature. As a corollary, we obtain that above the critical temperature, thermal states are stable against distant Hamiltonian perturbations. Moreover, our results imply that above the critical temperature, local expectation values can be approximated efficiently in the error and the system size. BibTeX:  @article{PhysRevX.4.031019, author = M. Kliesch, C. Gogolin, M. J. Kastoryano, A. Riera and J. Eisert, title = Locality of Temperature, journal = Phys. Rev. X, year = 2014, volume = 4, number = 3, pages = 031019, url = http://link.aps.org/doi/10.1103/PhysRevX.4.031019, doi = http://dx.doi.org/10.1103/PhysRevX.4.031019 }  M. Marciani, P. W. Brouwer and C. W. J. Beenakker Time-delay matrix, midgap spectral peak, and thermopower of an Andreev billiard Phys. Rev. B 90(4), 045403 (2014). Abstract: We derive the statistics of the time-delay matrix (energy derivative of the scattering matrix) in an ensemble of superconducting quantum dots with chaotic scattering (Andreev billiards), coupled ballistically to M conducting modes (electron-hole modes in a normal metal or Majorana edge modes in a superconductor). As a first application we calculate the density of states ρ0 at the Fermi level. The ensemble average ⟨ρ0⟩=δ−10M[max(0,M+2α/β)]−1 deviates from the bulk value 1/δ0 by an amount depending on the Altland-Zirnbauer symmetry indices α,β. The divergent average for M=1,2 in symmetry class D (α=−1, β=1) originates from the midgap spectral peak of a closed quantum dot, but now no longer depends on the presence or absence of a Majorana zero mode. As a second application we calculate the probability distribution of the thermopower, contrasting the difference for paired and unpaired Majorana edge modes. BibTeX:  @article{PhysRevB.90.045403, author = M. Marciani, P. W. Brouwer and C. W. J. Beenakker, title = Time-delay matrix, midgap spectral peak, and thermopower of an Andreev billiard, journal = Phys. Rev. B, year = 2014, volume = 90, number = 4, pages = 045403, url = http://link.aps.org/doi/10.1103/PhysRevB.90.045403, doi = http://dx.doi.org/10.1103/PhysRevB.90.045403 }  D. Mastrogiuseppe, A. Wong, K. Ingersent, S. E. Ulloa and N. Sandler Kondo effect in graphene with Rashba spin-orbit coupling Phys. Rev. B 90(3), 035426 (2014). Abstract: We study the Kondo screening of a magnetic impurity adsorbed in graphene in the presence of Rashba spin-orbit interaction. The system is described by an effective single-channel Anderson impurity model, which we analyze using the numerical renormalization group. The nontrivial energy dependence of the host density of states gives rise to interesting behaviors under variation of the chemical potential or the spin-orbit coupling. Varying the Rashba coupling produces strong changes in the Kondo temperature characterizing the many-body screening of the impurity spin, and at half filling allows an approach to a quantum phase transition separating the strong-coupling Kondo phase from a free-moment phase. Tuning the chemical potential close to sharp features of the hybridization function results in striking features in the temperature dependencies of thermodynamic quantities and in the frequency dependence of the impurity spectral function. BibTeX:  @article{PhysRevB.90.035426, author = D. Mastrogiuseppe, A. Wong, K. Ingersent, S. E. Ulloa and N. Sandler, title = Kondo effect in graphene with Rashba spin-orbit coupling, journal = Phys. Rev. B, year = 2014, volume = 90, number = 3, pages = 035426, url = http://link.aps.org/doi/10.1103/PhysRevB.90.035426, doi = http://dx.doi.org/10.1103/PhysRevB.90.035426 }  David A. Ruiz-Tijerina, E. Vernek and Sergio E. Ulloa Capacitive interactions and Kondo effect tuning in double quantum impurity systems Phys. Rev. B 90(3), 035119 (2014). Abstract: We present a study of the correlated transport regimes of a double quantum impurity system with mutual capacitive interactions. Such system can be implemented by a double quantum dot arrangement or by a quantum dot and nearby quantum point contact, with independently connected sets of metallic terminals. Many-body spin correlations arising within each dot-lead subsystem give rise to the Kondo effect under appropriate conditions. The otherwise independent Kondo ground states may be modified by the capacitive coupling, decisively modifying the ground state of the double quantum impurity system. We analyze this coupled system through variational methods and the numerical renormalization group technique. Our results reveal a strong dependence of the coupled system ground state on the electron-hole asymmetries of the individual subsystems, as well as on their hybridization strengths to the respective reservoirs. The electrostatic repulsion produced by the capacitive coupling produces an effective shift of the individual energy levels toward higher energies, with a stronger effect on the “shallower” subsystem (that closer to resonance with the Fermi level), potentially pushing it out of the Kondo regime and dramatically changing the transport properties of the system. The effective remote gating that this entails is found to depend nonlinearly on the capacitive coupling strength, as well as on the independent subsystem levels. The analysis we present here of this mutual interaction should be important to fully characterize transport through such coupled systems. BibTeX:  @article{PhysRevB.90.035119, author = David A. Ruiz-Tijerina, E. Vernek and Sergio E. Ulloa, title = Capacitive interactions and Kondo effect tuning in double quantum impurity systems, journal = Phys. Rev. B, year = 2014, volume = 90, number = 3, pages = 035119, url = http://link.aps.org/doi/10.1103/PhysRevB.90.035119, doi = http://dx.doi.org/10.1103/PhysRevB.90.035119 }  Björn Sbierski, Gregor Pohl, Emil J. Bergholtz and Piet W. Brouwer Quantum Transport of Disordered Weyl Semimetals at the Nodal Point Phys. Rev. Lett. 113(2), 026602 (2014). Abstract: Weyl semimetals are paradigmatic topological gapless phases in three dimensions. We here address the effect of disorder on charge transport in Weyl semimetals. For a single Weyl node with energy at the degeneracy point and without interactions, theory predicts the existence of a critical disorder strength beyond which the density of states takes on a nonzero value. Predictions for the conductivity are divergent, however. In this work, we present a numerical study of transport properties for a disordered Weyl cone at zero energy. For weak disorder, our results are consistent with a renormalization group flow towards an attractive pseudoballistic fixed point with zero conductivity and a scale-independent conductance; for stronger disorder, diffusive behavior is reached. We identify the Fano factor as a signature that discriminates between these two regimes. BibTeX:  @article{PhysRevLett.113.026602, author = Björn Sbierski, Gregor Pohl, Emil J. Bergholtz and Piet W. Brouwer, title = Quantum Transport of Disordered Weyl Semimetals at the Nodal Point, journal = Phys. Rev. Lett., year = 2014, volume = 113, number = 2, pages = 026602, url = http://link.aps.org/doi/10.1103/PhysRevLett.113.026602, doi = http://dx.doi.org/10.1103/PhysRevLett.113.026602 }  Martin Schneider and Piet W. Brouwer Quantum corrections to transport in graphene: a trajectory-based semiclassical analysis New Journal of Physics 16(7), 073015 (2014). Abstract: We review a calculation of the quantum corrections to electrical transport in graphene, using the trajectory-based semiclassical method. Compared to conventional metals, for graphene the semiclassical propagator contains an additional pseudospin structure that influences the results for weak localization, and interaction-induced effects, such as the Altshuler–Aronov correction and dephasing. Our results apply to a sample of graphene that is doped away from the Dirac point and subject to a smooth disorder potential, such that electrons follow classical trajectories. In such a system, the Ehrenfest time enters as an additional timescale. BibTeX:  @article{1367-2630-16-7-073015, author = Martin Schneider and Piet W. Brouwer, title = Quantum corrections to transport in graphene: a trajectory-based semiclassical analysis, journal = New Journal of Physics, year = 2014, volume = 16, number = 7, pages = 073015, url = http://stacks.iop.org/1367-2630/16/i=7/a=073015, doi = http://dx.doi.org/10.1088/1367-2630/16/7/073015 }  Hussain Anwar, Benjamin J. Brown, Earl T. Campbell and Dan E. Browne Fast decoders for qudit topological codes New Journal of Physics 16(6), 063038 (2014). Abstract: Qudit toric codes are a natural higher-dimensional generalization of the well-studied qubit toric code. However, standard methods for error correction of the qubit toric code are not applicable to them. Novel decoders are needed. In this paper we introduce two renormalization group decoders for qudit codes and analyse their error correction thresholds and efficiency. The first decoder is a generalization of a 'hard-decisions' decoder due to Bravyi and Haah (arXiv:1112.3252). We modify this decoder to overcome a percolation effect which limits its threshold performance for many-level quantum systems. The second decoder is a generalization of a 'soft-decisions' decoder due to Poulin and Duclos-Cianci (2010 Phys. Rev. Lett. 104 050504), with a small cell size to optimize the efficiency of implementation in the high dimensional case. In each case, we estimate thresholds for the uncorrelated bit-flip error model and provide a comparative analysis of the performance of both these approaches to error correction of qudit toric codes. BibTeX:  @article{1367-2630-16-6-063038, author = Hussain Anwar, Benjamin J. Brown, Earl T. Campbell and Dan E. Browne, title = Fast decoders for qudit topological codes, journal = New Journal of Physics, year = 2014, volume = 16, number = 6, pages = 063038, url = http://stacks.iop.org/1367-2630/16/i=6/a=063038, doi = http://dx.doi.org/10.1088/1367-2630/16/6/063038 }  G. Kells, D. Sen, J. K. Slingerland and S. Vishveshwara Topological blocking in quantum quench dynamics Phys. Rev. B 89(23), 235130 (2014). Abstract: We study the nonequilibrium dynamics of quenching through a quantum critical point in topological systems, focusing on one of their defining features: ground-state degeneracies and associated topological sectors. We present the notion of “topological blocking,” experienced by the dynamics due to a mismatch in degeneracies between two phases, and we argue that the dynamic evolution of the quench depends strongly on the topological sector being probed. We demonstrate this interplay between quench and topology in models stemming from two extensively studied systems, the transverse Ising chain and the Kitaev honeycomb model. Through nonlocal maps of each of these systems, we effectively study spinless fermionic p-wave paired topological superconductors. Confining the systems to ring and toroidal geometries, respectively, enables us to cleanly address degeneracies, subtle issues of fermion occupation and parity, and mismatches between topological sectors. We show that various features of the quench, which are related to Kibble-Zurek physics, are sensitive to the topological sector being probed, in particular, the overlap between the time-evolved initial ground state and an appropriate low-energy state of the final Hamiltonian. While most of our study is confined to translationally invariant systems, where momentum is a convenient quantum number, we briefly consider the effect of disorder and illustrate how this can influence the quench in a qualitatively different way depending on the topological sector considered. BibTeX:  @article{PhysRevB.89.235130, author = G. Kells, D. Sen, J. K. Slingerland and S. Vishveshwara, title = Topological blocking in quantum quench dynamics, journal = Phys. Rev. B, year = 2014, volume = 89, number = 23, pages = 235130, url = http://link.aps.org/doi/10.1103/PhysRevB.89.235130, doi = http://dx.doi.org/10.1103/PhysRevB.89.235130 }  J. C. Budich, J. Eisert and E. J. Bergholtz Topological insulators with arbitrarily tunable entanglement Phys. Rev. B 89(19), 195120 (2014). Abstract: We elucidate how Chern and topological insulators fulfill an area law for the entanglement entropy. By explicit construction of a family of lattice Hamiltonians, we are able to demonstrate that the area law contribution can be tuned to an arbitrarily small value but is topologically protected from vanishing exactly. We prove this by introducing novel methods to bound entanglement entropies from correlations using perturbation bounds, drawing intuition from ideas of quantum information theory. This rigorous approach is complemented by an intuitive understanding in terms of entanglement edge states. These insights have a number of important consequences: The area law has no universal component, no matter how small, and the entanglement scaling cannot be used as a faithful diagnostic of topological insulators. This holds for all Renyi entropies which uniquely determine the entanglement spectrum, which is hence also nonuniversal. The existence of arbitrarily weakly entangled topological insulators furthermore opens up possibilities of devising correlated topological phases in which the entanglement entropy is small and which are thereby numerically tractable, specifically in tensor network approaches. BibTeX:  @article{PhysRevB.89.195120, author = J. C. Budich, J. Eisert and E. J. Bergholtz, title = Topological insulators with arbitrarily tunable entanglement, journal = Phys. Rev. B, year = 2014, volume = 89, number = 19, pages = 195120, url = http://link.aps.org/doi/10.1103/PhysRevB.89.195120, doi = http://dx.doi.org/10.1103/PhysRevB.89.195120 }  Falko Pientka, Leonid I. Glazman and Felix von Oppen Unconventional topological phase transitions in helical Shiba chains Phys. Rev. B 89(18), 180505 (2014). Abstract: Chains of magnetic impurities placed on a superconducting substrate and forming helical spin order provide a promising venue for realizing a topological superconducting phase. An effective tight-binding description of such helical Shiba chains involves long-range (power-law) hopping and pairing amplitudes which induce an unconventional topological critical point. At the critical point, we find exponentially localized Majorana bound states with a short localization length unrelated to a topological gap. Away from the critical point, this exponential decay develops a power-law tail. Our analytical results have encouraging implications for experiment. BibTeX:  @article{PhysRevB.89.180505, author = Falko Pientka, Leonid I. Glazman and Felix von Oppen, title = Unconventional topological phase transitions in helical Shiba chains, journal = Phys. Rev. B, year = 2014, volume = 89, number = 18, pages = 180505, url = http://link.aps.org/doi/10.1103/PhysRevB.89.180505, doi = http://dx.doi.org/10.1103/PhysRevB.89.180505 }  Martin Schneider and Piet W. Brouwer Density of states as a probe of electrostatic confinement in graphene Phys. Rev. B 89(20), 205437 (2014). Abstract: We theoretically analyze the possibility to confine electrons in single-layer graphene with the help of metallic gates, via the evaluation of the density of states of such a gate-defined quantum dot in the presence of a ring-shaped metallic contact. The possibility to electrostatically confine electrons in a gate-defined “quantum dot” with finite-carrier density, surrounded by an undoped graphene sheet, strongly depends on the integrability of the electron dynamics in the quantum dot. With the present calculations, we can quantitatively compare confinement in dots with integrable and chaotic dynamics, and verify the prediction that the Berry phase associated with the pseudospin leads to partial confinement in situations where no confinement is expected according to the arguments relying on the classical dynamics only. BibTeX:  @article{PhysRevB.89.205437, author = Martin Schneider and Piet W. Brouwer, title = Density of states as a probe of electrostatic confinement in graphene, journal = Phys. Rev. B, year = 2014, volume = 89, number = 20, pages = 205437, url = http://link.aps.org/doi/10.1103/PhysRevB.89.205437, doi = http://dx.doi.org/10.1103/PhysRevB.89.205437 }  G. H. Aguilar, T. Kolb, D. Cavalcanti, L. Aolita, R. Chaves, S. P. Walborn and P. H. Souto Ribeiro Linear-Optical Simulation of the Cooling of a Cluster-State Hamiltonian System Phys. Rev. Lett. 112(16), 160501 (2014). Abstract: A measurement-based quantum computer could consist of a local-gapped Hamiltonian system, whose thermal states—at sufficiently low temperature—are universal resources for the computation. Initialization of the computer would correspond to cooling the system. We perform an experimental quantum simulation of such a cooling process with entangled photons. We prepare three-qubit thermal cluster states exploiting the equivalence between local dephasing and thermalization for these states. This allows us to tune the system’s temperature by changing the dephasing strength. We monitor the entanglement as the system cools down and observe the transitions from separability to bound entanglement, and then to free entanglement. We also analyze the performance of the system for measurement-based single-qubit state preparation. These studies constitute a basic characterization of experimental cluster-state computation under imperfect conditions. BibTeX:  @article{PhysRevLett.112.160501, author = G. H. Aguilar, T. Kolb, D. Cavalcanti, L. Aolita, R. Chaves, S. P. Walborn and P. H. Souto Ribeiro, title = Linear-Optical Simulation of the Cooling of a Cluster-State Hamiltonian System, journal = Phys. Rev. Lett., year = 2014, volume = 112, number = 16, pages = 160501, url = http://link.aps.org/doi/10.1103/PhysRevLett.112.160501, doi = http://dx.doi.org/10.1103/PhysRevLett.112.160501 }  Mahmoud M. Asmar and Sergio E. Ulloa Spin-Orbit Interaction and Isotropic Electronic Transport in Graphene Phys. Rev. Lett. 112(13), 136602 (2014). Abstract: Broken symmetries in graphene affect the massless nature of its charge carriers. We present an analysis of scattering by defects in graphene in the presence of spin-orbit interactions (SOIs). A characteristic constant ratio (≃2) of the transport to elastic times for massless electrons signals the anisotropy of the scattering. We show that SOIs lead to a drastic decrease of this ratio, especially at low carrier concentrations, while the scattering becomes increasingly isotropic. As the strength of the SOI determines the energy (carrier concentration) where this drop is more evident, this effect could help evaluate these interactions through transport measurements in graphene systems with enhanced spin-orbit coupling. BibTeX:  @article{PhysRevLett.112.136602, author = Mahmoud M. Asmar and Sergio E. Ulloa, title = Spin-Orbit Interaction and Isotropic Electronic Transport in Graphene, journal = Phys. Rev. Lett., year = 2014, volume = 112, number = 13, pages = 136602, url = http://link.aps.org/doi/10.1103/PhysRevLett.112.136602, doi = http://dx.doi.org/10.1103/PhysRevLett.112.136602 }  Rafael Chaves, Antonio Ac\'\in, Leandro Aolita and Daniel Cavalcanti Detecting nonlocality of noisy multipartite states with the Clauser-Horne-Shimony-Holt inequality Phys. Rev. A 89(4), 042106 (2014). Abstract: The Clauser-Horne-Shimony-Holt inequality was originally proposed as a Bell inequality to detect nonlocality in bipartite systems. However, it can also be used to certify the nonlocality of multipartite quantum states. We apply this to study the nonlocality of multipartite Greenberger-Horne-Zeilinger (GHZ), W, and graph states under local decoherence processes. We derive lower bounds on the critical local-noise strength tolerated by the states before becoming local. In addition, for the whole noisy dynamics, we derive lower bounds on the corresponding nonlocal content for the three classes of states. All the bounds presented can be calculated efficiently and, in some cases, provide significantly tighter estimates than with any other known method. For example, they reveal that N-qubit GHZ states undergoing local dephasing are, for all N, nonlocal throughout all the dephasing dynamics. BibTeX:  @article{PhysRevA.89.042106, author = Rafael Chaves, Antonio Ac\'\in, Leandro Aolita and Daniel Cavalcanti, title = Detecting nonlocality of noisy multipartite states with the Clauser-Horne-Shimony-Holt inequality, journal = Phys. Rev. A, year = 2014, volume = 89, number = 4, pages = 042106, url = http://link.aps.org/doi/10.1103/PhysRevA.89.042106, doi = http://dx.doi.org/10.1103/PhysRevA.89.042106 }  M. Rebello Sousa Dias, V. Lopez-Richard, G. E. Marques and S. Ulloa Spin filtering in nanowire directional coupler EPL (Europhysics Letters) 106(1), 17002 (2014). Abstract: The spin transport characteristics of a nanowire directional electronic coupler have been evaluated theoretically via a transfer matrix approach. The application of a gate field in the region of mixing allows for control of spin current through the different leads of the coupler via the Rashba spin-orbit interaction. The combination of spin-orbit interaction and applied gate voltages on different legs of the coupler give rise to a controllable modulation of the spin polarization. Both structural factors and field strength tuning lead to a rich phenomenology that could be exploited in spintronic devices. BibTeX:  @article{0295-5075-106-1-17002, author = M. Rebello Sousa Dias, V. Lopez-Richard, G. E. Marques and S. Ulloa, title = Spin filtering in nanowire directional coupler, journal = EPL (Europhysics Letters), year = 2014, volume = 106, number = 1, pages = 17002, url = http://stacks.iop.org/0295-5075/106/i=1/a=17002, doi = http://dx.doi.org/10.1209/0295-5075/106/17002 }  Björn Sbierski and Piet W. Brouwer Z2 phase diagram of three-dimensional disordered topological insulators via a scattering matrix approach Phys. Rev. B 89(15), 155311 (2014). Abstract: The role of disorder in the field of three-dimensional time-reversal-invariant topological insulators has become an active field of research recently. However, the computation of ℤ2 invariants for large, disordered systems still poses a considerable challenge. In this paper, we apply and extend a recently proposed method based on the scattering matrix approach, which allows the study of large systems at reasonable computational effort with few-channel leads. By computing the ℤ2 invariant directly for the disordered topological Anderson insulator, we unambiguously identify the topological nature of this phase without resorting to its connection with the clean case. We are able to efficiently compute the ℤ2 phase diagram in the mass-disorder plane. The topological phase boundaries are found to be well described by the self-consistent Born approximation, both for vanishing and finite chemical potentials. BibTeX:  @article{PhysRevB.89.155311, author = Björn Sbierski and Piet W. Brouwer, title = Z2 phase diagram of three-dimensional disordered topological insulators via a scattering matrix approach, journal = Phys. Rev. B, year = 2014, volume = 89, number = 15, pages = 155311, url = http://link.aps.org/doi/10.1103/PhysRevB.89.155311, doi = http://dx.doi.org/10.1103/PhysRevB.89.155311 }  P. G. Silvestrov and O. Entin-Wohlman Wigner crystal of a two-dimensional electron gas with a strong spin-orbit interaction Phys. Rev. B 89(15), 155103 (2014). Abstract: The Wigner-crystal phase of two-dimensional electrons interacting via the Coulomb repulsion and subject to a strong Rashba spin-orbit coupling is investigated. For low enough electronic densities the spin-orbit band splitting can be larger than the zero-point energy of the lattice vibrations. Then the degeneracy of the lower subband results in a spontaneous symmetry breaking of the vibrational ground state. The 60∘ rotational symmetry of the triangular (spin-orbit coupling free) structure is lost, and the unit cell of the new lattice contains two electrons. Breaking the rotational symmetry also leads to a (slight) squeezing of the underlying triangular lattice. BibTeX:  @article{PhysRevB.89.155103, author = P. G. Silvestrov and O. Entin-Wohlman, title = Wigner crystal of a two-dimensional electron gas with a strong spin-orbit interaction, journal = Phys. Rev. B, year = 2014, volume = 89, number = 15, pages = 155103, url = http://link.aps.org/doi/10.1103/PhysRevB.89.155103, doi = http://dx.doi.org/10.1103/PhysRevB.89.155103 }  R. Steinigeweg, A. Khodja, H. Niemeyer, C. Gogolin and J. Gemmer Pushing the Limits of the Eigenstate Thermalization Hypothesis towards Mesoscopic Quantum Systems Phys. Rev. Lett. 112(13), 130403 (2014). Abstract: In the ongoing discussion on thermalization in closed quantum many-body systems, the eigenstate thermalization hypothesis has recently been proposed as a universal concept and has attracted considerable attention. So far this concept is, as the name states, hypothetical. The majority of attempts to overcome this hypothetical character are based on exact diagonalization, which implies for, e.g., spin systems a limitation of roughly 15 spins. In this Letter we present an approach that pushes this limit up to system sizes of roughly 35 spins, thereby going significantly beyond what is possible with exact diagonalization. A concrete application to a Heisenberg spin ladder which yields conclusive results is demonstrated. BibTeX:  @article{PhysRevLett.112.130403, author = R. Steinigeweg, A. Khodja, H. Niemeyer, C. Gogolin and J. Gemmer, title = Pushing the Limits of the Eigenstate Thermalization Hypothesis towards Mesoscopic Quantum Systems, journal = Phys. Rev. Lett., year = 2014, volume = 112, number = 13, pages = 130403, url = http://link.aps.org/doi/10.1103/PhysRevLett.112.130403, doi = http://dx.doi.org/10.1103/PhysRevLett.112.130403 }  Rodrigo Gallego, Lars Erik Würflinger, Rafael Chaves, Antonio Acín and Miguel Navascués Nonlocality in sequential correlation scenarios New Journal of Physics 16(3), 033037 (2014). Abstract: As first shown by Popescu (1995 Phys. Rev. Lett. 74 2619), some quantum states only reveal their nonlocality when subjected to a sequence of measurements while giving rise to local correlations in standard Bell tests. Motivated by this manifestation of ‘hidden nonlocality’ we set out to develop a general framework for the study of nonlocality when sequences of measurements are performed. Similar to Gallego et al (2013 Phys. Rev. Lett. 109 070401) our approach is operational, i.e. the task is to identify the set of allowed operations in sequential correlation scenarios and define nonlocality as the resource that cannot be created by these operations. This leads to a characterization of sequential nonlocality that contains as particular cases standard nonlocality and hidden nonlocality. BibTeX:  @article{1367-2630-16-3-033037, author = Rodrigo Gallego, Lars Erik Würflinger, Rafael Chaves, Antonio Acín and Miguel Navascués, title = Nonlocality in sequential correlation scenarios, journal = New Journal of Physics, year = 2014, volume = 16, number = 3, pages = 033037, url = http://stacks.iop.org/1367-2630/16/i=3/a=033037, doi = http://dx.doi.org/10.1088/1367-2630/16/3/033037 }  A. Benyamini, A. Hamo, S. Viola Kusminskiy, F. von Oppen and S. Ilani Real-space tailoring of the electron-phonon coupling in ultraclean nanotube mechanical resonators Nature Physics 10(2), 151--156 (2014). Abstract: The coupling between electrons and phonons is at the heart of many fundamental phenomena in nature. Despite tremendous advances in controlling electrons or phonons in engineered nanosystems, control over their coupling is still widely lacking. Here we demonstrate the ability to fully tailor electron–phonon interactions using a new class of suspended carbon nanotube devices, in which we can form highly tunable single and double quantum dots at arbitrary locations along a nanotube mechanical resonator. We find that electron–phonon coupling can be turned on and off by controlling the position of a quantum dot along the resonator. Using double quantum dots we structure the interactions in real space to couple specific electronic and phononic modes. This tailored coupling allows measurement of the phonons’ spatial parity and imaging of their mode shapes. Finally, we demonstrate coupling between phonons and internal electrons in an isolated system, decoupled from the random environment of the electronic leads, a crucial step towards fully engineered quantum-coherent electron–phonon systems. BibTeX:  @article{benyamini2014, author = A. Benyamini, A. Hamo, S. Viola Kusminskiy, F. von Oppen and S. Ilani, title = Real-space tailoring of the electron-phonon coupling in ultraclean nanotube mechanical resonators, journal = Nature Physics, year = 2014, volume = 10, number = 2, pages = 151--156, url = http://www.nature.com/nphys/journal/v10/n2/full/nphys2842.html, doi = http://dx.doi.org/10.1038/nphys2842 }  A. Dechant, E. Lutz, D. A. Kessler and E. Barkai Scaling Green-Kubo Relation and Application to Three Aging Systems Phys. Rev. X 4(1), 011022 (2014). Abstract: The Green-Kubo formula relates the spatial diffusion coefficient to the stationary velocity autocorrelation function. We derive a generalization of the Green-Kubo formula that is valid for systems with long-range or nonstationary correlations for which the standard approach is no longer valid. For the systems under consideration, the velocity autocorrelation function ⟨v(t+τ)v(t)⟩ asymptotically exhibits a certain scaling behavior and the diffusion is anomalous, ⟨x2(t)⟩≃2D_ν t^ν. We show how both the anomalous diffusion coefficient Dν and the exponent ν can be extracted from this scaling form. Our scaling Green-Kubo relation thus extends an important relation between transport properties and correlation functions to generic systems with scale-invariant dynamics. This includes stationary systems with slowly decaying power-law correlations, as well as aging systems, systems whose properties depend on the age of the system. Even for systems that are stationary in the long-time limit, we find that the long-time diffusive behavior can strongly depend on the initial preparation of the system. In these cases, the diffusivity Dν is not unique, and we determine its values, respectively, for a stationary or nonstationary initial state. We discuss three applications of the scaling Green-Kubo relation: free diffusion with nonlinear friction corresponding to cold atoms diffusing in optical lattices, the fractional Langevin equation with external noise recently suggested to model active transport in cells, and the Lévy walk with numerous applications, in particular, blinking quantum dots. These examples underline the wide applicability of our approach, which is able to treat very different mechanisms of anomalous diffusion. BibTeX:  @article{PhysRevX.4.011022, author = A. Dechant, E. Lutz, D. A. Kessler and E. Barkai, title = Scaling Green-Kubo Relation and Application to Three Aging Systems, journal = Phys. Rev. X, year = 2014, volume = 4, number = 1, pages = 011022, url = http://link.aps.org/doi/10.1103/PhysRevX.4.011022, doi = http://dx.doi.org/10.1103/PhysRevX.4.011022 }  G. Kells, V. Lahtinen and J. Vala Kitaev spin models from topological nanowire networks Phys. Rev. B 89(7), 075122 (2014). Abstract: We show that networks of superconducting topological nanowires can realize the physics of exactly solvable Kitaev spin models on trivalent lattices. This connection arises from the low-energy theory of both systems being described by a tight-binding model of Majorana modes. In Kitaev spin models the Majorana description provides a convenient representation to solve the model, whereas in an array of Josephson junctions of topological nanowires it arises from localized physical Majorana modes tunneling between the wire ends. We explicitly show that an array of junctions of three wires—a setup relevant to topological quantum computing with nanowires—can realize the Yao-Kivelson model, a variant of Kitaev spin models on a decorated honeycomb lattice. Employing properties of the latter, we show that the network can be constructed to give rise to two-dimensional collective topological states characterized by Chern numbers ν=0,±1, and ±2, and that defects in the array can be associated with vortex-like quasiparticle excitations. In addition we show that the collective states are stable in the presence of disorder and superconducting phase fluctuations. When the network is operated as a quantum information processor, the connection to Kitaev spin models implies that decoherence mechanisms can in general be understood in terms of proliferation of the vortex-like quasiparticles. BibTeX:  @article{PhysRevB.89.075122, author = G. Kells, V. Lahtinen and J. Vala, title = Kitaev spin models from topological nanowire networks, journal = Phys. Rev. B, year = 2014, volume = 89, number = 7, pages = 075122, url = http://link.aps.org/doi/10.1103/PhysRevB.89.075122, doi = http://dx.doi.org/10.1103/PhysRevB.89.075122 }  Diego Mastrogiuseppe, Arturo Wong, Kevin Ingersent, Sergio E. Ulloa and Nancy Sandler Quantum phase transitions into Kondo states in bilayer graphene Phys. Rev. B 89(8), 081101 (2014). Abstract: We study a magnetic impurity intercalated in bilayer graphene. A representative configuration generates a hybridization function with strong dependence on the conduction-electron energy, including a full gap with one hard and one soft edge. Shifts of the chemical potential via gating or doping drive the system between non-Kondo (free-moment) and Kondo-screened phases, with strong variation of the Kondo scale. Quantum phase transitions near the soft edge are of Kosterlitz-Thouless type, while others are first order. Near the hard edge, a bound-state singlet appears inside the gap; although of single-particle character, its signatures in scanning tunneling spectroscopy are very similar to those arising from a many-body Kondo resonance. BibTeX:  @article{PhysRevB.89.081101, author = Diego Mastrogiuseppe, Arturo Wong, Kevin Ingersent, Sergio E. Ulloa and Nancy Sandler, title = Quantum phase transitions into Kondo states in bilayer graphene, journal = Phys. Rev. B, year = 2014, volume = 89, number = 8, pages = 081101, url = http://link.aps.org/doi/10.1103/PhysRevB.89.081101, doi = http://dx.doi.org/10.1103/PhysRevB.89.081101 }  G. Schwiete and A. M. Finkel'stein Keldysh approach to the renormalization group analysis of the disordered electron liquid Phys. Rev. B 89(7), 075437 (2014). Abstract: We present a Keldysh nonlinear sigma-model approach to the renormalization group analysis of the disordered electron liquid. We include both the Coulomb interaction and Fermi-liquid type interactions in the singlet and triplet channels into the formalism. Based on this model, we reproduce the coupled renormalization group equations for the diffusion coefficient, the frequency, and interaction constants previously derived with the replica model in the imaginary time technique. With the help of source fields coupling to the particle-number and spin densities, we study the density-density and spin density-spin density correlation functions in the diffusive regime. This allows us to obtain results for the electric conductivity and the spin susceptibility and thereby to rederive the main results of the one-loop renormalization group analysis of the disordered electron liquid in the Keldysh formalism. BibTeX:  @article{PhysRevB.89.075437, author = G. Schwiete and A. M. Finkel'stein, title = Keldysh approach to the renormalization group analysis of the disordered electron liquid, journal = Phys. Rev. B, year = 2014, volume = 89, number = 7, pages = 075437, url = http://link.aps.org/doi/10.1103/PhysRevB.89.075437, doi = http://dx.doi.org/10.1103/PhysRevB.89.075437 }  Vaibhav Madhok, Carlos A. Riofrío, Shohini Ghose and Ivan H. Deutsch Information Gain in Tomography–A Quantum Signature of Chaos Phys. Rev. Lett. 112(1), 014102 (2014). Abstract: We find quantum signatures of chaos in various metrics of information gain in quantum tomography. We employ a quantum state estimator based on weak collective measurements of an ensemble of identically prepared systems. The tomographic measurement record consists of a sequence of expectation values of a Hermitian operator that evolves under repeated application of the Floquet map of the quantum kicked top. We find an increase in information gain and, hence, higher fidelities in the reconstruction algorithm when the chaoticity parameter map increases. The results are well predicted by random matrix theory. BibTeX:  @article{PhysRevLett.112.014102, author = Vaibhav Madhok, Carlos A. Riofrío, Shohini Ghose and Ivan H. Deutsch, title = Information Gain in Tomography–A Quantum Signature of Chaos, journal = Phys. Rev. Lett., year = 2014, volume = 112, number = 1, pages = 014102, url = http://link.aps.org/doi/10.1103/PhysRevLett.112.014102, doi = http://dx.doi.org/10.1103/PhysRevLett.112.014102 }  2013 BibTeX:  @unpublished{20132014,, title = {Preprints}, year = 2013 }  Maxim Breitkreiz and Piet W. Brouwer Semiclassical theory of speckle correlations Phys. Rev. E 88(6), 062905 (2013). Abstract: Coherent wave propagation in random media results in a characteristic speckle pattern, with spatial intensity correlations with short-range and long-range behavior. Here, we show how the speckle correlation function can be obtained from a ray picture for two representative geometries, namely a chaotic cavity and a random waveguide. Our calculation allows us to study the crossover between a “ray limit” and a “wave limit,” in which the Ehrenfest time τE is larger or smaller than the typical transmission time τD, respectively. Remarkably, long-range speckle correlations persist in the ray limit τE≫τD. BibTeX:  @article{PhysRevE.88.062905, author = Maxim Breitkreiz and Piet W. Brouwer, title = Semiclassical theory of speckle correlations, journal = Phys. Rev. E, year = 2013, volume = 88, number = 6, pages = 062905, url = http://link.aps.org/doi/10.1103/PhysRevE.88.062905, doi = http://dx.doi.org/10.1103/PhysRevE.88.062905 }  Jens Eisert, Mauritz van den Worm, Salvatore R. Manmana and Michael Kastner Breakdown of Quasilocality in Long-Range Quantum Lattice Models Phys. Rev. Lett. 111(26), 260401 (2013). Abstract: We study the nonequilibrium dynamics of correlations in quantum lattice models in the presence of long-range interactions decaying asymptotically as a power law. For exponents larger than the lattice dimensionality, a Lieb-Robinson-type bound effectively restricts the spreading of correlations to a causal region, but allows supersonic propagation. We show that this decay is not only sufficient but also necessary. Using tools of quantum metrology, for any exponents smaller than the lattice dimension, we construct Hamiltonians giving rise to quantum channels with capacities not restricted to a causal region. An analytical analysis of long-range Ising models illustrates the disappearance of the causal region and the creation of correlations becoming distance independent. Numerical results obtained using matrix product state methods for the XXZ spin chain reveal the presence of a sound cone for large exponents and supersonic propagation for small ones. In all models we analyzed, the fast spreading of correlations follows a power law, but not the exponential increase of the long-range Lieb-Robinson bound. BibTeX:  @article{PhysRevLett.111.260401, author = Jens Eisert, Mauritz van den Worm, Salvatore R. Manmana and Michael Kastner, title = Breakdown of Quasilocality in Long-Range Quantum Lattice Models, journal = Phys. Rev. Lett., year = 2013, volume = 111, number = 26, pages = 260401, url = http://link.aps.org/doi/10.1103/PhysRevLett.111.260401, doi = http://dx.doi.org/10.1103/PhysRevLett.111.260401 }  Andreas Inhofer and Dario Bercioux Proposal for an on-demand source of polarized electrons into the edges of a topological insulator Phys. Rev. B 88(23), 235412 (2013). Abstract: We propose a device that allows for the emission of pairs of spin-polarized electrons into the edge states of a two-dimensional topological insulator. Charge and spin emission is achieved using a periodically driven quantum dot weakly coupled to the edge states of the host topological insulator. We present calculations of the emitted time-dependent charge and spin currents of such a dynamical scatterer using the Floquet scattering matrix approach. Experimental signatures of spin-polarized two-particle emission can be found in noise measurements. Here a new form of noise suppression, named Z2 antibunching, is introduced. Additionally, we propose a setup in which entanglement of the emitted electrons is generated. This entanglement is based on a postselection procedure and becomes manifest in a violation of a Clauser-Horne-Shimony-Holt inequality. BibTeX:  @article{PhysRevB.88.235412, author = Andreas Inhofer and Dario Bercioux, title = Proposal for an on-demand source of polarized electrons into the edges of a topological insulator, journal = Phys. Rev. B, year = 2013, volume = 88, number = 23, pages = 235412, url = http://link.aps.org/doi/10.1103/PhysRevB.88.235412, doi = http://dx.doi.org/10.1103/PhysRevB.88.235412 }  Lucia Lenz, DanielF. Urban and Dario Bercioux Rashba spin-orbit interaction in graphene armchair nanoribbons The European Physical Journal B 86(12), 1-9 (2013). Abstract: We study graphene nanoribbons (GNRs) with armchair edges in the presence of Rashba spin- orbit interactions (RSOI). We impose the boundary conditions on the tight binding Hamiltonians for bulk graphene with RSOI by means of a sine transform and study the influence of RSOI on the spectra and the spin polarization in detail. We derive the low energy approximation of the RSOI Hamiltonian for the zeroth and first order in momentum and test their ranges of validity. The choice of a basis appropriate for armchair boundaries is important in the case of mode-coupling effects and leads to results that are easy to work with. BibTeX:  @article{bercioux20131, author = Lucia Lenz, DanielF. Urban and Dario Bercioux, title = Rashba spin-orbit interaction in graphene armchair nanoribbons, journal = The European Physical Journal B, year = 2013, volume = 86, number = 12, pages = 1-9, url = http://dx.doi.org/10.1140/epjb/e2013-40760-4, doi = http://dx.doi.org/10.1140/epjb/e2013-40760-4 }  A. Ricottone, J. Danon and P. W. Brouwer Spin-wave-induced corrections to the electronic density of states in metallic ferromagnets New Journal of Physics 15(12), 123036 (2013). Abstract: We calculate the correction to the electronic density of states in a disordered ferromagnetic metal induced by spin-wave mediated interaction between the electrons. Our calculation is valid for the case that the exchange splitting Δ in the ferromagnet is much smaller than the Fermi energy, but we make no assumption on the relative magnitude of Δ and the elastic electronic scattering time τ el . In the ‘clean limit’ Δ τ el /ℏ ≫ 1 we find a correction with a T d /2 temperature dependence, where d is the effective dimensionality of the ferromagnet. In the ‘dirty limit’ Δ τ el /ℏ ≪ 1, the density-of-states correction is a non-monotonous function of energy and temperature. BibTeX:  @article{1367-2630-15-12-123036, author = A. Ricottone, J. Danon and P. W. Brouwer, title = Spin-wave-induced corrections to the electronic density of states in metallic ferromagnets, journal = New Journal of Physics, year = 2013, volume = 15, number = 12, pages = 123036, url = http://stacks.iop.org/1367-2630/15/i=12/a=123036, doi = http://dx.doi.org/10.1088/1367-2630/15/12/123036 }  Barbara Bravo, Ariel Dobry, Diego Mastrogiuseppe and Claudio Gazza Generation of chiral solitons in antiferromagnetic chains by a quantum quench Phys. Rev. B 88(19), 195125 (2013). Abstract: We analyze the time evolution of a magnetic excitation in a spin-1/2 antiferromagnetic Heisenberg chain after a quantum quench. By a proper modulation of the magnetic exchange coupling, we prepare a static soliton of total spin 1/2 as an initial spin state. Using bosonization and a numerical time-dependent density matrix renormalization group algorithm, we show that the initial excitation evolves to a state composed of two counterpropagating chiral states, which interfere to yield ⟨S_z⟩=1/4 for each mode. We find that these dynamically generated states remain considerably stable as time evolution is carried out. We propose spin-Peierls materials and ultracold-atom systems as suitable experimental scenarios in which to conduct and observe this mechanism. BibTeX:  @article{PhysRevB.88.195125, author = Barbara Bravo, Ariel Dobry, Diego Mastrogiuseppe and Claudio Gazza, title = Generation of chiral solitons in antiferromagnetic chains by a quantum quench, journal = Phys. Rev. B, year = 2013, volume = 88, number = 19, pages = 195125, url = http://link.aps.org/doi/10.1103/PhysRevB.88.195125, doi = http://dx.doi.org/10.1103/PhysRevB.88.195125 }  Torsten Karzig, Gil Refael and Felix von Oppen Boosting Majorana Zero Modes Phys. Rev. X 3(4), 041017 (2013). Abstract: One-dimensional topological superconductors are known to host Majorana zero modes at domain walls terminating the topological phase. Their non-Abelian nature allows for processing quantum information by braiding operations that are insensitive to local perturbations, making Majorana zero modes a promising platform for topological quantum computation. Motivated by the ultimate goal of executing quantum-information processing on a finite time scale, we study domain walls moving at a constant velocity. We exploit an effective Lorentz invariance of the Hamiltonian to obtain an exact solution of the associated quasiparticle spectrum and wave functions for arbitrary velocities. Essential features of the solution have a natural interpretation in terms of the familiar relativistic effects of Lorentz contraction and time dilation. We find that the Majorana zero modes remain stable as long as the domain wall moves at subluminal velocities with respect to the effective speed of light of the system. However, the Majorana bound state dissolves into a continuous quasiparticle spectrum after the domain wall propagates at luminal or even superluminal velocities. This relativistic catastrophe implies that there is an upper limit for possible braiding frequencies even in a perfectly clean system with an arbitrarily large topological gap. We also exploit our exact solution to consider domain walls moving past static impurities present in the system. BibTeX:  @article{PhysRevX.3.041017, author = Torsten Karzig, Gil Refael and Felix von Oppen, title = Boosting Majorana Zero Modes, journal = Phys. Rev. X, year = 2013, volume = 3, number = 4, pages = 041017, url = http://link.aps.org/doi/10.1103/PhysRevX.3.041017, doi = http://dx.doi.org/10.1103/PhysRevX.3.041017 }  Zhao Liu, Emil J. Bergholtz and Eliot Kapit Non-Abelian fractional Chern insulators from long-range interactions Phys. Rev. B 88(20), 205101 (2013). Abstract: The recent theoretical discovery of fractional Chern insulators (FCIs) has provided an important new way to realize topologically ordered states in lattice models. In earlier works, on-site and nearest-neighbor Hubbard-like interactions have been used extensively to stabilize Abelian FCIs in systems with nearly flat, topologically nontrivial bands. However, attempts to use two-body interactions to stabilize non-Abelian FCIs, where the ground state in the presence of impurities can be massively degenerate and manipulated through anyon braiding, have proven very difficult in uniform lattice systems. Here, we study the remarkable effect of long-range interactions in a lattice model that possesses an exactly flat lowest band with a unit Chern number. When spinless bosons with two-body long-range interactions partially fill the lowest Chern band, we find convincing evidence of gapped, bosonic Read-Rezayi (RR) phases with non-Abelian anyon statistics. We characterize these states through studying topological degeneracies, the overlap between the ground states of two-body interactions and the exact RR ground states of three- and four-body interactions, and state counting in the particle-cut entanglement spectrum. Moreover, we demonstrate how an approximate lattice form of Haldane's pseudopotentials, analogous to that in the continuum, can be used as an efficient guiding principle in the search for lattice models with stable non-Abelian phases. BibTeX:  @article{PhysRevB.88.205101, author = Zhao Liu, Emil J. Bergholtz and Eliot Kapit, title = Non-Abelian fractional Chern insulators from long-range interactions, journal = Phys. Rev. B, year = 2013, volume = 88, number = 20, pages = 205101, url = http://link.aps.org/doi/10.1103/PhysRevB.88.205101, doi = http://dx.doi.org/10.1103/PhysRevB.88.205101 }  Falko Pientka, Liang Jiang, David Pekker, Jason Alicea, Gil Refael, Yuval Oreg and Felix von Oppen Magneto-Josephson effects and Majorana bound states in quantum wires New Journal of Physics 15(11), 115001 (2013). Abstract: A prominent signature of Majorana bound states is the exotic Josephson effects they produce, the classic example being a fractional Josephson current with 4 π periodicity in the phase difference across the junction. Recent work established that topological insulator edges support a novel ‘magneto-Josephson effect’, whereby a dissipationless current exhibits 4 π -periodic dependence also on the relative orientation of the Zeeman fields in the two banks of the junction. Here, we explore the magneto-Josephson effect in junctions based on spin–orbit-coupled quantum wires. In contrast to the topological insulator case, the periodicities of the magneto-Josephson effect no longer follow from an exact superconductor–magnetism duality of the Hamiltonian. We employ numerical calculations as well as analytical arguments to identify the domain configurations that display exotic Josephson physics for quantum-wire junctions, and elucidate the characteristic differences with the corresponding setups for topological insulators edges. To provide guidance to experiments, we also estimate the magnitude of the magneto-Josephson effects in realistic parameter regimes, and compare the Majorana-related contribution to the coexisting 2 π -periodic effects emerging from non-Majorana states. BibTeX:  @article{1367-2630-15-11-115001, author = Falko Pientka, Liang Jiang, David Pekker, Jason Alicea, Gil Refael, Yuval Oreg and Felix von Oppen, title = Magneto-Josephson effects and Majorana bound states in quantum wires, journal = New Journal of Physics, year = 2013, volume = 15, number = 11, pages = 115001, url = http://stacks.iop.org/1367-2630/15/i=11/a=115001, doi = http://dx.doi.org/10.1088/1367-2630/15/11/115001 }  G. Schwiete and A. M. Finkel'stein Kinetics of disordered Bose gas with collisions Phys. Rev. A 88(5), 053611 (2013). Abstract: We discuss the kinetics of the disordered interacting Bose gas using the Boltzmann transport equation. The theory may serve as a unifying framework for studying questions of dynamics of the expanding Bose gas at different stages of the expansion. We show that the transport theory allows us to straightforwardly reproduce and generalize a number of results previously obtained from microscopic models in different formalisms. Based on estimates for the interparticle scattering rates, we discuss the relevance of interaction effects for the localization problem in the interacting disordered Bose gas. We argue that, if the number of particles is large enough, the size of the expanding cloud may exceed the localization length. We describe the spreading of the wave packet in this regime as collision-induced diffusion and compare the obtained rate of expansion to known results on subdiffusive spreading in nonlinear disordered lattices. BibTeX:  @article{PhysRevA.88.053611, author = G. Schwiete and A. M. Finkel'stein, title = Kinetics of disordered Bose gas with collisions, journal = Phys. Rev. A, year = 2013, volume = 88, number = 5, pages = 053611, url = http://link.aps.org/doi/10.1103/PhysRevA.88.053611, doi = http://dx.doi.org/10.1103/PhysRevA.88.053611 }  Christian F. Hermanns, Matthias Bernien, Alex Krüger, Christian Schmidt, Sören T. Waßerroth, Gelavizh Ahmadi, Benjamin W. Heinrich, Martin Schneider, Piet W. Brouwer, Katharina J. Franke, Eugen Weschke and Wolfgang Kuch Magnetic Coupling of Gd_3 N@C_80 Endohedral Fullerenes to a Substrate Phys. Rev. Lett. 111(16), 167203 (2013). Abstract: Using magnetic endohedral fullerenes for molecular spintronics requires control over their encapsulated magnetic moments. We show by field-dependent x-ray magnetic circular dichroism measurements of Gd3N@C80 endohedral fullerenes adsorbed on a Cu surface that the magnetic moments of the encapsulated Gd atoms lie in a 4f7 ground state and couple ferromagnetically to each other. When the molecules are in contact with a ferromagnetic Ni substrate, we detect two different Gd species. The more abundant one couples antiferromagnetically to the Ni, whereas the other one exhibits a stronger and ferromagnetic coupling to the substrate. Both of these couplings to the substrate can be explained by an indirect exchange mechanism mediated by the carbon cage. The origin of the distinctly different behavior may be attributed to different orientations and thus electronic coupling of the carbon cage to the substrate, as revealed by scanning tunneling microscopy of the fullerenes on Cu. BibTeX:  @article{PhysRevLett.111.167203, author = Christian F. Hermanns, Matthias Bernien, Alex Krüger, Christian Schmidt, Sören T. Waßerroth, Gelavizh Ahmadi, Benjamin W. Heinrich, Martin Schneider, Piet W. Brouwer, Katharina J. Franke, Eugen Weschke and Wolfgang Kuch, title = Magnetic Coupling of Gd_3 N@C_80 Endohedral Fullerenes to a Substrate, journal = Phys. Rev. Lett., year = 2013, volume = 111, number = 16, pages = 167203, url = http://link.aps.org/doi/10.1103/PhysRevLett.111.167203, doi = http://dx.doi.org/10.1103/PhysRevLett.111.167203 }  Michael J. Kastoryano and Jens Eisert Rapid mixing implies exponential decay of correlations Journal of Mathematical Physics 54(10), - (2013). Abstract: We provide an analysis of the correlation properties of spin and fermionic systems on a lattice evolving according to open system dynamics generated by a local primitive Liouvillian. We show that if the Liouvillian has a spectral gap which is independent of the system size, then the correlations between local observables decay exponentially as a function of the distance between their supports. We prove, furthermore, that if the Log-Sobolev constant is independent of the system size, then the system satisfies clustering of correlations in the mutual information—a much more stringent form of correlation decay. As a consequence, in the latter case we get an area law (with logarithmic corrections) for the mutual information. As a further corollary, we obtain a stability theorem for local distant perturbations. We also demonstrate that gapped free-fermionic systems exhibit clustering of correlations in the covariance and in the mutual information. We conclude with a discussion of the implications of these results for the classical simulation of open quantum systems with matrix-product operators and the robust dissipative preparation of topologically ordered states of lattice spin systems. BibTeX:  @article{:/content/aip/journal/jmp/54/10/10.1063/1.4822481, author = Michael J. Kastoryano and Jens Eisert, title = Rapid mixing implies exponential decay of correlations, journal = Journal of Mathematical Physics, year = 2013, volume = 54, number = 10, pages = -, url = http://scitation.aip.org/content/aip/journal/jmp/54/10/10.1063/1.4822481, doi = http://dx.doi.org/http://dx.doi.org/10.1063/1.4822481 }  Falko Pientka, Leonid I. Glazman and Felix von Oppen Topological superconducting phase in helical Shiba chains Phys. Rev. B 88(15), 155420 (2013). Abstract: Recently, it has been suggested that topological superconductivity and Majorana end states can be realized in a chain of magnetic impurities on the surface of an s-wave superconductor when the magnetic moments form a spin helix as a result of the RKKY interaction mediated by the superconducting substrate. Here, we investigate this scenario theoretically by developing a tight-binding Bogoliubov-de Gennes description starting from the Shiba bound states induced by the individual magnetic impurities. While the resulting model Hamiltonian has similarities with the Kitaev model for one-dimensional spinless p-wave superconductors, there are also important differences, most notably the long-range nature of hopping and pairing as well as the complex hopping amplitudes. We use both analytical and numerical approaches to explore the consequences of these differences for the phase diagram and the localization properties of the Majorana end states when the Shiba chain is in a topological superconducting phase. BibTeX:  @article{PhysRevB.88.155420, author = Falko Pientka, Leonid I. Glazman and Felix von Oppen, title = Topological superconducting phase in helical Shiba chains, journal = Phys. Rev. B, year = 2013, volume = 88, number = 15, pages = 155420, url = http://link.aps.org/doi/10.1103/PhysRevB.88.155420, doi = http://dx.doi.org/10.1103/PhysRevB.88.155420 }  B. Sbierski, M. Hanl, A. Weichselbaum, H. E. Türeci, M. Goldstein, L. I. Glazman, J. von Delft and A. Imamoglu Proposed Rabi-Kondo Correlated State in a Laser-Driven Semiconductor Quantum Dot Phys. Rev. Lett. 111(15), 157402 (2013). Abstract: Spin exchange between a single-electron charged quantum dot and itinerant electrons leads to an emergence of Kondo correlations. When the quantum dot is driven resonantly by weak laser light, the resulting emission spectrum allows for a direct probe of these correlations. In the opposite limit of vanishing exchange interaction and strong laser drive, the quantum dot exhibits coherent oscillations between the single-spin and optically excited states. Here, we show that the interplay between strong exchange and nonperturbative laser coupling leads to the formation of a new nonequilibrium quantum-correlated state, characterized by the emergence of a laser-induced secondary spin screening cloud, and examine the implications for the emission spectrum. BibTeX:  @article{PhysRevLett.111.157402, author = B. Sbierski, M. Hanl, A. Weichselbaum, H. E. Türeci, M. Goldstein, L. I. Glazman, J. von Delft and A. Imamoglu, title = Proposed Rabi-Kondo Correlated State in a Laser-Driven Semiconductor Quantum Dot, journal = Phys. Rev. Lett., year = 2013, volume = 111, number = 15, pages = 157402, url = http://link.aps.org/doi/10.1103/PhysRevLett.111.157402, doi = http://dx.doi.org/10.1103/PhysRevLett.111.157402 }  Emil J. Bergholtz and Zhao Liu Topological Flat Band Models and Fractional Chern Insulators International Journal of Modern Physics B 27(24), 1330017 (2013). Abstract: Topological insulators and their intriguing edge states can be understood in a single-particle picture and can as such be exhaustively classified. Interactions significantly complicate this picture and can lead to entirely new insulating phases, with an altogether much richer and less explored phenomenology. Most saliently, lattice generalizations of fractional quantum Hall states, dubbed fractional Chern insulators, have recently been predicted to be stabilized by interactions within nearly dispersionless bands with nonzero Chern number, C. Contrary to their continuum analogues, these states do not require an external magnetic field and may potentially persist even at room temperature, which make these systems very attractive for possible applications such as topological quantum computation. This review recapitulates the basics of tight-binding models hosting nearly flat bands with nontrivial topology, C≠0, and summarizes the present understanding of interactions and strongly correlated phases within these bands. Emphasis is made on microscopic models, highlighting the analogy with continuum Landau level physics, as well as qualitatively new, lattice specific, aspects including Berry curvature fluctuations, competing instabilities as well as novel collective states of matter emerging in bands with |C|>1. Possible experimental realizations, including oxide interfaces and cold atom implementations as well as generalizations to flat bands characterized by other topological invariants are also discussed. BibTeX:  @article{emilzhao2013, author = Emil J. Bergholtz and Zhao Liu, title = Topological Flat Band Models and Fractional Chern Insulators, journal = International Journal of Modern Physics B, year = 2013, volume = 27, number = 24, pages = 1330017, url = http://www.worldscientific.com/doi/abs/10.1142/S021797921330017X, doi = http://dx.doi.org/10.1142/S021797921330017X }  Vincenzo D'Ambrosio, Nicolò Spagnolo, Lorenzo Del Re, Sergei Slussarenko, Ying Li, Leon Chuan Kwek, Lorenzo Marruci, Leandro Aolita and Fabio Scriarrino Photonic polarization gears for ultra-sensitive angular measurements Nature Communications 4(), 8 (2013). Abstract: Quantum metrology bears a great promise in enhancing measurement precision, but is unlikely to become practical in the near future. Its concepts can nevertheless inspire classical or hybrid methods of immediate value. Here we demonstrate NOON-like photonic states of m quanta of angular momentum up to m=100, in a setup that acts as a ‘photonic gear’, converting, for each photon, a mechanical rotation of an angle θ into an amplified rotation of the optical polarization by mθ, corresponding to a ‘super-resolving’ Malus’ law. We show that this effect leads to single-photon angular measurements with the same precision of polarization-only quantum strategies with m photons, but robust to photon losses. Moreover, we combine the gear effect with the quantum enhancement due to entanglement, thus exploiting the advantages of both approaches. The high ‘gear ratio’ m boosts the current state of the art of optical non-contact angular measurements by almost two orders of magnitude. BibTeX:  @article{aolita2013_1, author = Vincenzo D'Ambrosio, Nicolò Spagnolo, Lorenzo Del Re, Sergei Slussarenko, Ying Li, Leon Chuan Kwek, Lorenzo Marruci, Leandro Aolita and Fabio Scriarrino, title = Photonic polarization gears for ultra-sensitive angular measurements, journal = Nature Communications, year = 2013, volume = 4, number = , pages = 8, url = http://www.nature.com/ncomms/2013/130918/ncomms3432/full/ncomms3432.html, doi = http://dx.doi.org/10.1038/ncomms3432 }  and J. Eisert Entanglement and Tensor Network States (Book Chapter) Emergent Phenomena in Correlated Matter (Eds. E. Pavarini, E. Koch, and U. Schollwöck) Ch. 17(), 17.1--17.41 (2013). Abstract: These lecture notes provide a brief overview of methods of entanglement theory applied to the study of quantum many-body systems, as well as of tensor network states capturing quantum states naturally appearing in condensed-matter systems. BibTeX:  @article{arxiv13083318inbook, author = and J. Eisert, title = Entanglement and Tensor Network States (Book Chapter), journal = Emergent Phenomena in Correlated Matter (Eds. E. Pavarini, E. Koch, and U. Schollwöck), year = 2013, volume = Ch. 17, number = , pages = 17.1--17.41, url = http://www.cond-mat.de/events/correl13/manuscripts/eisert.pdf, doi = }  A. M. Läuchli, Zhao Liu, E. J. Bergholtz and R. Moessner Hierarchy of Fractional Chern Insulators and Competing Compressible States Phys. Rev. Lett. 111(12), 126802 (2013). Abstract: We study the phase diagram of interacting electrons in a dispersionless Chern band as a function of their filling. We find hierarchy multiplets of incompressible states at fillings ν=1/3, 2/5, 3/7, 4/9, 5/9, 4/7, 3/5 as well as ν=1/5, 2/7. These are accounted for by an analogy to Haldane pseudopotentials extracted from an analysis of the two-particle problem. Important distinctions to standard fractional quantum Hall physics are striking: in the absence of particle-hole symmetry in a single band, an interaction-induced single-hole dispersion appears, which perturbs and eventually destabilizes incompressible states as ν increases. For this reason, the nature of the state at ν=2/3 is hard to pin down, while ν=5/7, 4/5 do not seem to be incompressible in our system. BibTeX:  @article{PhysRevLett.111.126802, author = A. M. Läuchli, Zhao Liu, E. J. Bergholtz and R. Moessner, title = Hierarchy of Fractional Chern Insulators and Competing Compressible States, journal = Phys. Rev. Lett., year = 2013, volume = 111, number = 12, pages = 126802, url = http://link.aps.org/doi/10.1103/PhysRevLett.111.126802, doi = http://dx.doi.org/10.1103/PhysRevLett.111.126802 }  Kevin A. Madsen, Emil J. Bergholtz and Piet W. Brouwer Topological equivalence of crystal and quasicrystal band structures Phys. Rev. B 88(12), 125118 (2013). Abstract: A number of recent articles have reported the existence of topologically nontrivial states and associated end states in one-dimensional incommensurate lattice models that would usually only be expected in higher dimensions. Using an explicit construction, we here argue that the end states have precisely the same origin as their counterparts in commensurate models and that incommensurability does not in fact provide a meaningful connection to the topological classification of systems in higher dimensions. In particular, we show that it is possible to smoothly interpolate between states with commensurate and incommensurate modulation parameters without closing the band gap and without states crossing the band gap. BibTeX:  @article{PhysRevB.88.125118, author = Kevin A. Madsen, Emil J. Bergholtz and Piet W. Brouwer, title = Topological equivalence of crystal and quasicrystal band structures, journal = Phys. Rev. B, year = 2013, volume = 88, number = 12, pages = 125118, url = http://link.aps.org/doi/10.1103/PhysRevB.88.125118, doi = http://dx.doi.org/10.1103/PhysRevB.88.125118 }  Raúl Bustos-Marún, Gil Refael and Felix von Oppen Adiabatic Quantum Motors Phys. Rev. Lett. 111(6), 060802 (2013). Abstract: When parameters are varied periodically, charge can be pumped through a mesoscopic conductor without applied bias. Here, we consider the inverse effect in which a transport current drives a periodic variation of an adiabatic degree of freedom. This provides a general operating principle for adiabatic quantum motors which we discuss here in general terms. We relate the work performed per cycle on the motor degree of freedom to characteristics of the underlying quantum pump and discuss the motors' efficiency. Quantum motors based on chaotic quantum dots operate solely due to quantum interference, and motors based on Thouless pumps have ideal efficiency. BibTeX:  @article{Bustos-Mar'un2013, author = Raúl Bustos-Marún, Gil Refael and Felix von Oppen, title = Adiabatic Quantum Motors, journal = Phys. Rev. Lett., year = 2013, volume = 111, number = 6, pages = 060802, url = http://link.aps.org/doi/10.1103/PhysRevLett.111.060802, doi = http://dx.doi.org/10.1103/PhysRevLett.111.060802 }  and J. Danon Spin-flip phonon-mediated charge relaxation in double quantum dots Phys. Rev. B 88(7), 075306 (2013). Abstract: We theoretically study the (1,1) triplet to (0,2) singlet relaxation rate in a lateral gate-defined double quantum dot tuned to the regime of Pauli spin blockade. We present a detailed derivation of the effective phonon density of states for this specific charge transition, keeping track of the contribution from piezoelectric as well as deformation potential electron-phonon coupling. We further investigate two different spin-mixing mechanisms which can couple the triplet and singlet states: a magnetic field gradient over the double dot (relevant at low external magnetic field) and spin-orbit interaction (relevant at high field), and we also indicate how the two processes could interfere at intermediate magnetic field. Finally, we show how to combine all results and evaluate the relaxation rate for realistic system parameters. BibTeX:  @article{PhysRevB.88.075306, author = and J. Danon, title = Spin-flip phonon-mediated charge relaxation in double quantum dots, journal = Phys. Rev. B, year = 2013, volume = 88, number = 7, pages = 075306, url = http://link.aps.org/doi/10.1103/PhysRevB.88.075306, doi = http://dx.doi.org/10.1103/PhysRevB.88.075306 }  Alexandra Junck, Gil Refael and Felix von Oppen Photocurrent response of topological insulator surface states Phys. Rev. B 88(7), 075144 (2013). Abstract: We study the photocurrent response of topological insulator surface states to circularly polarized light for arbitrary oblique incidence. We describe the surface states within a Dirac model, including several perturbations such as hexagonal warping, nonlinear corrections to the mode velocity, and applied magnetic fields. We find that the photogalvanic current is strongly suppressed for the usual orbital coupling, prompting us to include the weaker Zeeman coupling. We find that the helicity-independent photocurrent dominates over the helicity-dependent contributions. BibTeX:  @article{PhysRevB.88.075144, author = Alexandra Junck, Gil Refael and Felix von Oppen, title = Photocurrent response of topological insulator surface states, journal = Phys. Rev. B, year = 2013, volume = 88, number = 7, pages = 075144, url = http://link.aps.org/doi/10.1103/PhysRevB.88.075144, doi = http://dx.doi.org/10.1103/PhysRevB.88.075144 }  Zhao Liu, D. L. Kovrizhin and Emil J. Bergholtz Bulk-edge correspondence in fractional Chern insulators Phys. Rev. B 88(8), 081106 (2013). Abstract: It has been recently realized that strong interactions in topological Bloch bands give rise to the appearance of novel states of matter. Here we study connections between these systems—fractional Chern insulators and the fractional quantum Hall states—via generalization of a gauge-fixed Wannier-Qi construction in the cylinder geometry. Our setup offers a number of important advantages compared to the earlier exact diagonalization studies on a torus. Most notably, it gives access to edge states and to a single-cut orbital entanglement spectrum, hence to the physics of bulk-edge correspondence. It is also readily implemented in the state-of-the-art density matrix renormalization group method that allows for numerical simulations of significantly larger systems. We demonstrate our general approach on examples of flat-band models on ruby and kagome lattices at bosonic filling fractions ν=1/2 and ν=1, which show the signatures of (non)-Abelian phases, and establish the correspondence between the physics of edge states and the entanglement in the bulk. Notably, we find that the non-Abelian ν=1 phase can be stabilized by purely on-site interactions in the presence of a confining potential. BibTeX:  @article{PhysRevB.88.081106, author = Zhao Liu, D. L. Kovrizhin and Emil J. Bergholtz, title = Bulk-edge correspondence in fractional Chern insulators, journal = Phys. Rev. B, year = 2013, volume = 88, number = 8, pages = 081106, url = http://link.aps.org/doi/10.1103/PhysRevB.88.081106, doi = http://dx.doi.org/10.1103/PhysRevB.88.081106 }  V. Parente, A. Tagliacozzo, F. von Oppen and F. Guinea Electron-phonon interaction on the surface of a three-dimensional topological insulator Phys. Rev. B 88(7), 075432 (2013). Abstract: We analyze the interaction at the surface of a three-dimensional (3D) topological insulator among 2D electron states belonging to the Dirac cone close to the point of the Brillouin zone and the Rayleigh surface phonon mode. The model deals with an elastic continuum in the long-wavelength limit, in Random Phase Approximation (RPA). Screening of the electronic polarization is quite effective at small wave vectors. On the other hand, the absence of backscattering for the Dirac electrons at the Fermi surface is partly responsible for the reduced influence of the electron-phonon interaction in renormalizing the phonon dispersion at finite wave vectors. We infer that softening of the Rayleigh mode appears as unlikely, at least for the case of a clean and defect-free surface to which our approximate treatment applies. The dielectric response to virtual excitation of the Rayleigh phonon could drive the electron-electron interaction attractive at low frequencies, but the average weak coupling pairing interaction is found to be too small to induce a surface superconducting instability. BibTeX:  @article{PhysRevB.88.075432, author = V. Parente, A. Tagliacozzo, F. von Oppen and F. Guinea, title = Electron-phonon interaction on the surface of a three-dimensional topological insulator, journal = Phys. Rev. B, year = 2013, volume = 88, number = 7, pages = 075432, url = http://link.aps.org/doi/10.1103/PhysRevB.88.075432, doi = http://dx.doi.org/10.1103/PhysRevB.88.075432 }  Maria-Theresa Rieder, Piet W. Brouwer and İnanç Adagideli Reentrant topological phase transitions in a disordered spinless superconducting wire Phys. Rev. B 88(6), 060509(R) (2013). Abstract: In a one-dimensional spinless p-wave superconductor with coherence length ξ, disorder induces a phase transition between a topologically nontrivial phase and a trivial insulating phase at the critical mean-free path l=ξ/2. Here, we show that a multichannel spinless p-wave superconductor goes through an alternation of topologically trivial and nontrivial phases upon increasing the disorder strength, the number of phase transitions being equal to the channel number N. The last phase transition, from a nontrivial phase into the trivial phase, takes place at a mean-free path l=ξ/(N+1), parametrically smaller than the critical mean-free path in one dimension. Our result is valid in the limit that the wire width W is much smaller than the superconducting coherence length ξ. BibTeX:  @article{PhysRevB.88.060509, author = Maria-Theresa Rieder, Piet W. Brouwer and İnanç Adagideli, title = Reentrant topological phase transitions in a disordered spinless superconducting wire, journal = Phys. Rev. B, year = 2013, volume = 88, number = 6, pages = 060509(R), url = http://link.aps.org/doi/10.1103/PhysRevB.88.060509, doi = http://dx.doi.org/10.1103/PhysRevB.88.060509 }  Sebastian Deffner and Eric Lutz Quantum Speed Limit for Non-Markovian Dynamics Phys. Rev. Lett. 111(1), 010402 (2013). Abstract: We derive a Margolus-Levitin-type bound on the minimal evolution time of an arbitrarily driven open quantum system. We express this quantum speed limit time in terms of the operator norm of the nonunitary generator of the dynamics. We apply these results to the damped Jaynes-Cummings model and demonstrate that the corresponding bound is tight. We further show that non-Markovian effects can speed up quantum evolution and therefore lead to a smaller quantum speed limit time. BibTeX:  @article{Deffner2013, author = Sebastian Deffner and Eric Lutz, title = Quantum Speed Limit for Non-Markovian Dynamics, journal = Phys. Rev. Lett., year = 2013, volume = 111, number = 1, pages = 010402, url = http://link.aps.org/doi/10.1103/PhysRevLett.111.010402, doi = http://dx.doi.org/10.1103/PhysRevLett.111.010402 }  Brian Tarasinski and Georg Schwiete Fluctuation conductivity of disordered superconductors in magnetic fields Phys. Rev. B 88(1), 014518 (2013). Abstract: We calculate fluctuation corrections to the longitudinal conductivity of disordered superconductors subject to an external magnetic field. We derive analytic expressions that are valid in the entire metallic part of the temperature–magnetic field phase diagram as long as the effect of the magnetic field on the spin degrees of freedom of the electrons may be neglected. Our calculations are based on a kinetic equation approach. For the special case of superconducting films and wires in parallel magnetic fields, we perform a detailed comparison with results that were previously obtained with diagrammatic perturbation theory in the imaginary-time formalism. As an application, we study the fluctuation conductivity of films in tilted magnetic fields with a special focus on the low-temperature regime. We present a detailed discussion of the phenomenon of the nonmonotonic magnetoresistance and find that it displays a pronounced dependence on the tilting angle. BibTeX:  @article{PhysRevB.88.014518, author = Brian Tarasinski and Georg Schwiete, title = Fluctuation conductivity of disordered superconductors in magnetic fields, journal = Phys. Rev. B, year = 2013, volume = 88, number = 1, pages = 014518, url = http://link.aps.org/doi/10.1103/PhysRevB.88.014518, doi = http://dx.doi.org/10.1103/PhysRevB.88.014518 }  Stefan Walter, Jan Carl Budich, Jens Eisert and Björn Trauzettel Entanglement of nanoelectromechanical oscillators by Cooper-pair tunneling Phys. Rev. B 88(3), 035441 (2013). Abstract: We demonstrate that entanglement of two macroscopic nanoelectromechanical resonators—coupled to each other via a common detector, a tunnel junction—can be generated by running a current through the device. We introduce a setup that overcomes generic limitations of proposals suggesting to entangle systems via a shared bath. At the heart of the proposal is an Andreev entangler setup, representing an experimentally feasible way of entangling two nanomechanical oscillators. Instead of relying on the coherence of a (fermionic) bath, in the Andreev entangler setup, a split Cooper pair that coherently tunnels to each oscillator mediates their coupling and thereby induces entanglement between them. Since entanglement is in each instance generated by Markovian and non-Markovian noisy open system dynamics in an out-of-equilibrium situation, we argue that the present scheme also opens up perspectives to observe dissipation-driven entanglement in a condensed-matter system. BibTeX:  @article{PhysRevB.88.035441, author = Stefan Walter, Jan Carl Budich, Jens Eisert and Björn Trauzettel, title = Entanglement of nanoelectromechanical oscillators by Cooper-pair tunneling, journal = Phys. Rev. B, year = 2013, volume = 88, number = 3, pages = 035441, url = http://link.aps.org/doi/10.1103/PhysRevB.88.035441, doi = http://dx.doi.org/10.1103/PhysRevB.88.035441 }  D. Faria, A. Latgé, S. E. Ulloa and N. Sandler Currents and pseudomagnetic fields in strained graphene rings Phys. Rev. B 87(24), 241403 (2013). Abstract: We study the effects of strain on the electronic properties and persistent current characteristics of a graphene ring using the Dirac representation. For a slightly deformed graphene ring flake, one obtains sizable pseudomagnetic (gauge) fields that may effectively reduce or enhance locally the applied magnetic flux through the ring. Flux-induced persistent currents in a flat ring have full rotational symmetry throughout the structure; in contrast, we show that currents in the presence of a \emph{circularly symmetric} deformation are strongly inhomogeneous, due to the underlying symmetries of graphene. This result illustrates the inherent \emph{competition} between the real'' magnetic field and the pseudo'' field arising from strains, and suggests an alternative way to probe the strength and symmetries of pseudomagnetic fields on graphene systems. BibTeX:  @article{Faria2013, author = D. Faria, A. Latgé, S. E. Ulloa and N. Sandler, title = Currents and pseudomagnetic fields in strained graphene rings, journal = Phys. Rev. B, year = 2013, volume = 87, number = 24, pages = 241403, url = http://link.aps.org/doi/10.1103/PhysRevB.87.241403, doi = http://dx.doi.org/10.1103/PhysRevB.87.241403 }  Julia Heinl, Martin Schneider and Piet W. Brouwer Interplay of Aharonov-Bohm and Berry phases in gate-defined graphene quantum dots Phys. Rev. B 87(24), 245426 (2013). Abstract: We study the influence of a magnetic flux tube on the possibility to electrostatically confine electrons in a graphene quantum dot. Without a magnetic flux tube, the graphene pseudospin is responsible for a quantization of the total angular momentum to half-integer values. On the other hand, with a flux tube containing half a flux quantum, the Aharonov-Bohm phase and Berry phase precisely cancel, and we find a state at zero angular momentum that cannot be confined electrostatically. In this case, true bound states only exist in regular geometries for which states without zero-angular-momentum component exist, while nonintegrable geometries lack confinement. We support these arguments with a calculation of the two-terminal conductance of a gate-defined graphene quantum dot, which shows resonances for a disk-shaped geometry and for a stadium-shaped geometry without flux tube, but no resonances for a stadium-shaped quantum dot with a Ï-flux tube. BibTeX:  @article{Heinl2013, author = Julia Heinl, Martin Schneider and Piet W. Brouwer, title = Interplay of Aharonov-Bohm and Berry phases in gate-defined graphene quantum dots, journal = Phys. Rev. B, year = 2013, volume = 87, number = 24, pages = 245426, url = http://link.aps.org/doi/10.1103/PhysRevB.87.245426, doi = http://dx.doi.org/10.1103/PhysRevB.87.245426 }  Alexandra Junck, Kun W. Kim, Doron L. Bergman, T. Pereg-Barnea and Gil Refael Transport through a disordered topological-metal strip Phys. Rev. B 87(23), 235114 (2013). Abstract: Features of a topological phase, and edge states in particular, may be obscured by overlapping in energy with a trivial conduction band. The topological nature of such a conductor, however, is revealed in its transport properties, especially in the presence of disorder. In this work, we explore the conductance behavior of such a system with disorder present, and contrast it with the quantized conductance in an ideal two-dimensional topological insulator. Our analysis relies on numerics on a lattice system and analytics on a simple toy model. Interestingly, we find that as disorder is increased from zero, the edge conductivity initially falls from its quantized value; yet, as disorder continues to increase, the conductivity recovers, and saturates at a value slightly below the quantized value of the clean system. We discuss how this effect can be understood from the tendency of the bulk states to localize, while the edge states remain delocalized. BibTeX:  @article{PhysRevB.87.235114, author = Alexandra Junck, Kun W. Kim, Doron L. Bergman, T. Pereg-Barnea and Gil Refael, title = Transport through a disordered topological-metal strip, journal = Phys. Rev. B, year = 2013, volume = 87, number = 23, pages = 235114, url = http://link.aps.org/doi/10.1103/PhysRevB.87.235114, doi = http://dx.doi.org/10.1103/PhysRevB.87.235114 }  E. T. Campbell, M. J. Hoban and J. Eisert Majorana fermions and non-locality Quantum Information and Computation 14(11\&12), 0981--0995 (2013). Abstract: Localized Majorana fermions emerge in many topologically ordered systems and exhibit exchange statistics of Ising anyons. This enables noise-resistant implementation of a limited set of operations by braiding and fusing Majorana fermions. Unfortunately, these operations are incapable of implementing universal quantum computation. We show that, regardless of these limitations, Majorana fermions could be used to demonstrate non-locality (correlations incompatible with a local hidden variable theory) in experiments using only topologically protected operations. We also demonstrate that our proposal is optimal in terms of resources, with 10 Majorana fermions shown to be both necessary and sufficient for demonstrating bipartite non-locality. Furthermore, we identify severe restrictions on the possibility of tripartite non-locality. We comment on the potential of such entangled systems to be used in quantum information protocols. BibTeX:  @article{2013arXiv1305.1953C, author = E. T. Campbell, M. J. Hoban and J. Eisert, title = Majorana fermions and non-locality, journal = Quantum Information and Computation, year = 2013, volume = 14, number = 11\&12, pages = 0981--0995, url = http://www.rintonpress.com/xxqic14/qic-14-1112/0981-0995.pdf, doi = }  Luis G. G. V. Dias da Silva, E. Vernek, K. Ingersent, N. Sandler and S. E. Ulloa Spin-polarized conductance in double quantum dots: Interplay of Kondo, Zeeman, and interference effects Phys. Rev. B 87(20), 205313 (2013). Abstract: We study the effect of a magnetic field in the Kondo regime of a double-quantum-dot system consisting of a strongly correlated dot (the side dot'') coupled to a second, noninteracting dot that also connects two external leads. We show, using the numerical renormalization group, that application of an in-plane magnetic field sets up a subtle interplay between electronic interference, Kondo physics, and Zeeman splitting with nontrivial consequences for spectral and transport properties. The value of the side-dot spectral function at the Fermi level exhibits a nonuniversal field dependence that can be understood using a form of the Friedel sum rule that appropriately accounts for the presence of an energy- and spin-dependent hybridization function. The applied field also accentuates the exchange-mediated interdot coupling, which dominates the ground state at intermediate fields leading to the formation of antiparallel magnetic moments on the dots. By tuning gate voltages and the magnetic field, one can achieve complete spin polarization of the linear conductance between the leads, raising the prospect of applications of the device as a highly tunable spin filter. The system's low-energy properties are qualitatively unchanged by the presence of weak on-site Coulomb repulsion within the second dot. BibTeX:  @article{Dias2013, author = Luis G. G. V. Dias da Silva, E. Vernek, K. Ingersent, N. Sandler and S. E. Ulloa, title = Spin-polarized conductance in double quantum dots: Interplay of Kondo, Zeeman, and interference effects, journal = Phys. Rev. B, year = 2013, volume = 87, number = 20, pages = 205313, url = http://link.aps.org/doi/10.1103/PhysRevB.87.205313, doi = http://dx.doi.org/10.1103/PhysRevB.87.205313 }  G. Haack, M. Moskalets and M. Büttiker Glauber coherence of single-electron sources Phys. Rev. B 87(20), 201302(R) (2013). Abstract: Recently demonstrated solid-state single-electron sources generate different quantum states depending on their operation condition. For adiabatic and nonadiabatic sources, we determine the Glauber correlation function in terms of the Floquet scattering matrix of the source. The correlation function provides full information on the shape of the state and on its time-dependent amplitude and phase. The coherence properties of single-electron states are therefore essential for the production of quantum multiparticle states. BibTeX:  @article{PhysRevB.87.201302, author = G. Haack, M. Moskalets and M. Büttiker, title = Glauber coherence of single-electron sources, journal = Phys. Rev. B, year = 2013, volume = 87, number = 20, pages = 201302(R), url = http://link.aps.org/doi/10.1103/PhysRevB.87.201302, doi = http://dx.doi.org/10.1103/PhysRevB.87.201302 }  Michael J. Kastoryano and Kristan Temme Quantum logarithmic Sobolev inequalities and rapid mixing Journal of Mathematical Physics 54(5), 052202 (2013). Abstract: A family of logarithmic Sobolev inequalities on finite dimensional quantum state spaces is introduced. The framework of non-commutative mathp-spaces is reviewed and the relationship between quantum logarithmic Sobolev inequalities and the hypercontractivity of quantum semigroups is discussed. This relationship is central for the derivation of lower bounds for the logarithmic Sobolev (LS) constants. Essential results for the family of inequalities are proved, and we show an upper bound to the generalized LS constant in terms of the spectral gap of the generator of the semigroup. These inequalities provide a framework for the derivation of improved bounds on the convergence time of quantum dynamical semigroups, when the LS constant and the spectral gap are of the same order. Convergence bounds on finite dimensional state spaces are particularly relevant for the field of quantum information theory. We provide a number of examples, where improved bounds on the mixing time of several semigroups are obtained, including the depolarizing semigroup and quantum expanders. BibTeX:  @article{Kastoryano2013a, author = Michael J. Kastoryano and Kristan Temme, title = Quantum logarithmic Sobolev inequalities and rapid mixing, journal = Journal of Mathematical Physics, year = 2013, volume = 54, number = 5, pages = 052202, url = http://link.aip.org/link/?JMP/54/052202/1, doi = http://dx.doi.org/10.1063/1.4804995 }  Martin Schneider, Georg Schwiete and Piet W. Brouwer Semiclassical theory of the interaction correction to the conductance of antidot arrays Phys. Rev. B 87(19), 195406 (2013). Abstract: Electron-electron interactions are responsible for a correction to the conductance of a diffusive metal, the Altshuler-Aronov correctionâ'' $\delta G_{AA}$. Here, we study the counterpart of this correction for a ballistic conductor, in which the electron motion is governed by chaotic classical dynamics. In the ballistic conductance, the Ehrenfest time $\tau E$ enters as an additional time scale that determines the magnitude of quantum interference effects. The Ehrenfest time effectively poses a short-time threshold for the trajectories contributing to the interaction correction. As a consequence, $\delta G_{AA}$ becomes exponentially suppressed if the Ehrenfest time is larger than the dwell time or the inverse temperature. We discuss the explicit dependence on Ehrenfest time in quasi-one- and two-dimensional antidot arrays. For strong interactions, the sign of $\delta G_{AA}$ may change as a function of temperature for temperatures in the vicinity of $\tfrac{\hbar}{\tau E}$. BibTeX:  @article{Schneider2013, author = Martin Schneider, Georg Schwiete and Piet W. Brouwer, title = Semiclassical theory of the interaction correction to the conductance of antidot arrays, journal = Phys. Rev. B, year = 2013, volume = 87, number = 19, pages = 195406, url = http://link.aps.org/doi/10.1103/PhysRevB.87.195406, doi = http://dx.doi.org/10.1103/PhysRevB.87.195406 }  Earl T. Campbell, Marco G. Genoni and Jens Eisert Continuous-variable entanglement distillation and noncommutative central limit theorems Phys. Rev. A 87(4), 042330 (2013). Abstract: Entanglement distillation transforms weakly entangled noisy states into highly entangled states, a primitive to be used in quantum repeater schemes and other protocols designed for quantum communication and key distribution. In this work, we present a comprehensive framework for continuous-variable entanglement distillation schemes that convert noisy non-Gaussian states into Gaussian ones in many iterations of the protocol. Instances of these protocols include (a) the recursive-Gaussifier protocol, (b) the temporally reordered recursive-Gaussifier protocol, and (c) the pumping-Gaussifier protocol. The flexibility of these protocols gives rise to several beneficial trade-offs related to success probabilities or memory requirements, which can be adjusted to reflect experimental demands. Despite these protocols involving measurements, we relate the convergence in this protocol to new instances of noncommutative central limit theorems, in a formalism that we lay out in great detail. Implications of the findings for quantum repeater schemes are discussed. BibTeX:  @article{PhysRevA.87.042330, author = Earl T. Campbell, Marco G. Genoni and Jens Eisert, title = Continuous-variable entanglement distillation and noncommutative central limit theorems, journal = Phys. Rev. A, year = 2013, volume = 87, number = 4, pages = 042330, url = http://link.aps.org/doi/10.1103/PhysRevA.87.042330, doi = http://dx.doi.org/10.1103/PhysRevA.87.042330 }  Alan A. Dzhioev, Daniel S. Kosov and Felix von Oppen Out-of-equilibrium catalysis of chemical reactions by electronic tunnel currents The Journal of Chemical Physics 138(13), 134103 (2013). Abstract: We present an escape rate theory for current-induced chemical reactions. We use Keldysh nonequilibrium Green's functions to derive a Langevin equation for the reaction coordinate. Due to the out of equilibrium electronic degrees of freedom, the friction, noise, and effective temperature in the Langevin equation depend locally on the reaction coordinate. As an example, we consider the dissociation of diatomic molecules induced by the electronic current from a scanning tunnelling microscope tip. In the resonant tunnelling regime, the molecular dissociation involves two processes which are intricately interconnected: a modification of the potential energy barrier and heating of the molecule. The decrease of the molecular barrier (i.e., the current induced catalytic reduction of the barrier) accompanied by the appearance of the effective, reaction-coordinate-dependent temperature is an alternative mechanism for current-induced chemical reactions, which is distinctly different from the usual paradigm of pumping vibrational degrees of freedom. BibTeX:  @article{Dzhioev2013, author = Alan A. Dzhioev, Daniel S. Kosov and Felix von Oppen, title = Out-of-equilibrium catalysis of chemical reactions by electronic tunnel currents, journal = The Journal of Chemical Physics, year = 2013, volume = 138, number = 13, pages = 134103, url = http://link.aip.org/link/?JCP/138/134103/1, doi = http://dx.doi.org/10.1063/1.4797495 }  Thomas Iadecola, David Campbell, Claudio Chamon, Chang-Yu Hou, Roman Jackiw, So-Young Pi and Silvia Viola Kusminskiy Materials Design from Nonequilibrium Steady States: Driven Graphene as a Tunable Semiconductor with Topological Properties Phys. Rev. Lett. 110(17), 176603 (2013). Abstract: Controlling the properties of materials by driving them out of equilibrium is an exciting prospect that has only recently begun to be explored. In this Letter we give a striking theoretical example of such materials design: a tunable gap in monolayer graphene is generated by exciting a particular optical phonon. We show that the system reaches a steady state whose transport properties are the same as if the system had a static electronic gap, controllable by the driving amplitude. Moreover, the steady state displays topological phenomena: there are chiral edge currents, which circulate a fractional charge e/2 per rotation cycle, with the frequency set by the optical phonon frequency. BibTeX:  @article{Iadecola2013, author = Thomas Iadecola, David Campbell, Claudio Chamon, Chang-Yu Hou, Roman Jackiw, So-Young Pi and Silvia Viola Kusminskiy, title = Materials Design from Nonequilibrium Steady States: Driven Graphene as a Tunable Semiconductor with Topological Properties, journal = Phys. Rev. Lett., year = 2013, volume = 110, number = 17, pages = 176603, url = http://link.aps.org/doi/10.1103/PhysRevLett.110.176603, doi = http://dx.doi.org/10.1103/PhysRevLett.110.176603 }  G. Schwiete and A. M. Finkel'stein Effective theory for the propagation of a wave packet in a disordered and nonlinear medium Phys. Rev. A 87(4), 043636 (2013). Abstract: The propagation of a wave packet in a nonlinear disordered medium exhibits interesting dynamics. Here, we present an analysis based on the nonlinear Schrödinger equation (Gross-Pitaevskii equation). This problem is directly connected to experiments on expanding Bose gases and to studies of transverse localization in nonlinear optical media. In a nonlinear medium, the energy of the wave packet is stored both in the kinetic and potential parts, and details of its propagation are to a large extent determined by the transfer from one form of energy to the other. A theory describing the evolution of the wave packet has been formulated [ Schwiete and Finkel'stein Phys. Rev. Lett. 104 103904 (2010)] in terms of a nonlinear kinetic equation. In this paper, we present details of the derivation of the kinetic equation and of its analysis. As an important new ingredient, we study interparticle collisions induced by the nonlinearity and derive the corresponding collision integral. We restrict ourselves to the weakly nonlinear limit, for which disorder scattering is the dominant scattering mechanism. We find that in the special case of a white-noise impurity potential, the mean-squared radius in a two-dimensional system scales linearly with t. This result has previously been obtained in the collisionless limit, but it also holds in the presence of collisions. Finally, we indicate different mechanisms through which the nonlinearity may influence localization of the expanding wave packet. BibTeX:  @article{PhysRevA.87.043636, author = G. Schwiete and A. M. Finkel'stein, title = Effective theory for the propagation of a wave packet in a disordered and nonlinear medium, journal = Phys. Rev. A, year = 2013, volume = 87, number = 4, pages = 043636, url = http://link.aps.org/doi/10.1103/PhysRevA.87.043636, doi = http://dx.doi.org/10.1103/PhysRevA.87.043636 }  Oded Zilberberg, Alessandro Romito, David J. Starling, Gregory A. Howland, Curtis J. Broadbent, John C. Howell and Yuval Gefen Null Values and Quantum State Discrimination Phys. Rev. Lett. 110(5), 170405 (2013). Abstract: We present a measurement protocol for discriminating between two different quantum states of a qubit with high fidelity. The protocol, called null value, is comprised of a projective measurement performed on the system with a small probability (also known as partial collapse), followed by a tuned postselection. We report on an optical experimental implementation of the scheme. We show that our protocol leads to an amplified signal-to-noise ratio (as compared with a straightforward strong measurement) when discerning between the two quantum states. BibTeX:  @article{Zilberberg2013, author = Oded Zilberberg, Alessandro Romito, David J. Starling, Gregory A. Howland, Curtis J. Broadbent, John C. Howell and Yuval Gefen, title = Null Values and Quantum State Discrimination, journal = Phys. Rev. Lett., year = 2013, volume = 110, number = 5, pages = 170405, url = http://link.aps.org/doi/10.1103/PhysRevLett.110.170405, doi = http://dx.doi.org/10.1103/PhysRevLett.110.170405 }  M. J. Kastoryano, M. M. Wolf and J. Eisert Precisely Timing Dissipative Quantum Information Processing Phys. Rev. Lett. 110(11), 110501 (2013). Abstract: Dissipative engineering constitutes a framework within which quantum information processing protocols are powered by system-environment interaction rather than by unitary dynamics alone. This framework embraces noise as a resource and, consequently, offers a number of advantages compared to one based on unitary dynamics alone, e.g., that the protocols are typically independent of the initial state of the system. However, the time independent nature of this scheme makes it difficult to imagine precisely timed sequential operations, conditional measurements, or error correction. In this work, we provide a path around these challenges, by introducing basic dissipative gadgets which allow us to precisely initiate, trigger, and time dissipative operations while keeping the system Liouvillian time independent. These gadgets open up novel perspectives for thinking of timed dissipative quantum information processing. As an example, we sketch how measurement-based computation can be simulated in the dissipative setting. BibTeX:  @article{Kastoryano2013, author = M. J. Kastoryano, M. M. Wolf and J. Eisert, title = Precisely Timing Dissipative Quantum Information Processing, journal = Phys. Rev. Lett., year = 2013, volume = 110, number = 11, pages = 110501, url = http://link.aps.org/doi/10.1103/PhysRevLett.110.110501, doi = http://dx.doi.org/10.1103/PhysRevLett.110.110501 }  Matthias C. Lüffe, Jeroen Danon and Tamara S. Nunner Evolution of the persistent spin helix in the presence of Hartree-Fock fields Phys. Rev. B 87(12), 125416 (2013). Abstract: We derive a spin diffusion equation for a spin-orbit coupled two-dimensional electron gas including the Hartree-Fock field resulting from first order electron-electron interactions. We find that the lifetime of the persistent spin helix, which emerges for equal linear Rashba and Dresselhaus spin-orbit interactions, can be enhanced considerably for large initial spin polarizations due to the Hartree-Fock field. The reason is a reduction of the symmetry-breaking cubic Dresselhaus scattering rate by the Hartree-Fock field. Also higher harmonics are generated and the polarization of the persistent spin helix rotates out of the (S_y,S_z) plane acquiring a finite S_x component. This effect becomes more pronounced when the cubic Dresselhaus spin-orbit interaction is large. BibTeX:  @article{Luffe2013, author = Matthias C. Lüffe, Jeroen Danon and Tamara S. Nunner, title = Evolution of the persistent spin helix in the presence of Hartree-Fock fields, journal = Phys. Rev. B, year = 2013, volume = 87, number = 12, pages = 125416, url = http://link.aps.org/doi/10.1103/PhysRevB.87.125416, doi = http://dx.doi.org/10.1103/PhysRevB.87.125416 }  Julia S. Meyer and Gil Refael Disordered topological metals Phys. Rev. B 87(10), 104202 (2013). Abstract: Topological behavior can be masked when disorder is present. A topological insulator, either intrinsic or interaction induced, may turn gapless when sufficiently disordered. Nevertheless, the metallic phase that emerges once a topological gap closes retains several topological characteristics. By considering the self-consistent disorder-averaged Green function of a topological insulator, we derive the condition for gaplessness. We show that the edge states survive in the gapless phase as edge resonances and that, similar to a doped topological insulator, the disordered topological metal also has a finite, but nonquantized topological index. We then consider the disordered Mott topological insulator. We show that within mean-field theory, the disordered Mott topological insulator admits a phase where the symmetry-breaking order parameter remains nonzero but the gap is closed, in complete analogy to âgapless superconductivityâ due to magnetic disorder. BibTeX:  @article{Meyer2013, author = Julia S. Meyer and Gil Refael, title = Disordered topological metals, journal = Phys. Rev. B, year = 2013, volume = 87, number = 10, pages = 104202, url = http://link.aps.org/doi/10.1103/PhysRevB.87.104202, doi = http://dx.doi.org/10.1103/PhysRevB.87.104202 }  T. Micklitz and A. Altland Semiclassical theory of chaotic quantum resonances Phys. Rev. E 87(3), 032918 (2013). Abstract: States supported by chaotic open quantum systems fall into two categories: a majority showing instantaneous ballistic decay, and a set of quantum resonances of classically vanishing support in phase space. We present a theory describing these structures within a unified semiclassical framework. Emphasis is put on the quantum diffraction mechanism which introduces an element of probability and is crucial for the formation of resonances. Our main result is boundary conditions on the semiclassical propagation along system trajectories. Depending on whether the trajectory propagation time is shorter or longer than the Ehrenfest time, these conditions describe deterministic escape, or probabilistic quantum decay. BibTeX:  @article{Micklitz2013, author = T. Micklitz and A. Altland, title = Semiclassical theory of chaotic quantum resonances, journal = Phys. Rev. E, year = 2013, volume = 87, number = 3, pages = 032918, url = http://link.aps.org/doi/10.1103/PhysRevE.87.032918, doi = http://dx.doi.org/10.1103/PhysRevE.87.032918 }  Michael Moskalets, Géraldine Haack and Markus Büttiker Single-electron source: Adiabatic versus nonadiabatic emission Phys. Rev. B 87(12), 125429 (2013). Abstract: We investigate adiabatic and nonadiabatic emission of single particles into an edge state using an analytically solvable dynamical scattering matrix model of an on-demand source. We compare adiabatic and nonadiabatic emissions by considering two geometries: a collider geometry where two emitters are coupled to two different edge states and a series geometry where two emitters are coupled to the same edge state. Most effects observed for adiabatic emitters also occur for nonadiabatic emitters. In particular this applies to effects arising due to the overlap of wave packets colliding at a quantum point contact. Specifically we compare the Pauli peak (the fermionic analog of the bosonic Hong-Ou-Mandel dip) for the adiabatic and nonadiabatic collider and find them to be similar. In contrast we find a striking difference between the two operating conditions in the series geometry in which particles are emitted into the same edge state. Whereas the squared average charge current can be nullified for both operating conditions, the heat current can be made to vanish only with adiabatic emitters. BibTeX:  @article{PhysRevB.87.125429, author = Michael Moskalets, Géraldine Haack and Markus Büttiker, title = Single-electron source: Adiabatic versus nonadiabatic emission, journal = Phys. Rev. B, year = 2013, volume = 87, number = 12, pages = 125429, url = http://link.aps.org/doi/10.1103/PhysRevB.87.125429, doi = http://dx.doi.org/10.1103/PhysRevB.87.125429 }  Sebastian Deffner and Eric Lutz Thermodynamic length for far-from-equilibrium quantum systems Phys. Rev. E 87(2), 022143 (2013). Abstract: We consider a closed quantum system initially at thermal equilibrium and driven by arbitrary external parameters. We derive a lower bound on the entropy production which we express in terms of the Bures angle between the nonequilibrium and the corresponding equilibrium state of the system. The Bures angle is an angle between mixed quantum states and defines a thermodynamic length valid arbitrarily far from equilibrium. As an illustration, we treat the case of a time-dependent harmonic oscillator for which we obtain analytic expressions for generic driving protocols. BibTeX:  @article{Deffner2013a, author = Sebastian Deffner and Eric Lutz, title = Thermodynamic length for far-from-equilibrium quantum systems, journal = Phys. Rev. E, year = 2013, volume = 87, number = 2, pages = 022143, url = http://link.aps.org/doi/10.1103/PhysRevE.87.022143, doi = http://dx.doi.org/10.1103/PhysRevE.87.022143 }  Liang Jiang, David Pekker, Jason Alicea, Gil Refael, Yuval Oreg, Arne Brataas and Felix von Oppen Magneto-Josephson effects in junctions with Majorana bound states Phys. Rev. B 87(7), 075438 (2013). Abstract: We investigate 1D quantum systems that support Majorana bound states at interfaces between topologically distinct regions. In particular, we show that there exists a duality between particle-hole and spin degrees of freedom in certain spin-orbit-coupled 1D platforms such as topological insulator edges. This duality results in a spin analog of previously explored fractional Josephson effects''âthat is, the spin current flowing across a magnetic junction exhibits 4\pi periodicity in the relative magnetic field angle across the junction. Furthermore, the interplay between the particle-hole and spin degrees of freedom results in unconventional magneto-Josephson effects, such that the Josephson charge current is a function of the magnetic field orientation with periodicity 4\pi. BibTeX:  @article{Jiang2013, author = Liang Jiang, David Pekker, Jason Alicea, Gil Refael, Yuval Oreg, Arne Brataas and Felix von Oppen, title = Magneto-Josephson effects in junctions with Majorana bound states, journal = Phys. Rev. B, year = 2013, volume = 87, number = 7, pages = 075438, url = http://link.aps.org/doi/10.1103/PhysRevB.87.075438, doi = http://dx.doi.org/10.1103/PhysRevB.87.075438 }  Falko Pientka, Alessandro Romito, Mathias Duckheim, Yuval Oreg and Felix von Oppen Signatures of topological phase transitions in mesoscopic superconducting rings New Journal of Physics 15(2), 025001 (2013). Abstract: We investigate Josephson currents in mesoscopic rings with a weak link which are in or near a topological superconducting phase. As a paradigmatic example, we consider the Kitaev model of a spinless p-wave superconductor in one dimension, emphasizing how this model emerges from more realistic settings based on semiconductor nanowires. We show that the flux periodicity of the Josephson current provides signatures of the topological phase transition and the emergence of Majorana fermions (MF) situated on both sides of the weak link even when fermion parity is not a good quantum number. In large rings, the MF hybridize only across the weak link. In this case, the Josephson current is h / e periodic in the flux threading the loop when fermion parity is a good quantum number but reverts to the more conventional h /2 e periodicity in the presence of fermion-parity changing relaxation processes. In mesoscopic rings, the MF also hybridize through their overlap in the interior of the superconducting ring. We find that in the topological superconducting phase, this gives rise to an h / e -periodic contribution even when fermion parity is not conserved and that this contribution exhibits a peak near the topological phase transition. This signature of the topological phase transition is robust to the effects of disorder. As a byproduct, we find that close to the topological phase transition, disorder drives the system deeper into the topological phase. This is in stark contrast to the known behavior far from the phase transition, where disorder tends to suppress the topological phase. BibTeX:  @article{Pientka2013, author = Falko Pientka, Alessandro Romito, Mathias Duckheim, Yuval Oreg and Felix von Oppen, title = Signatures of topological phase transitions in mesoscopic superconducting rings, journal = New Journal of Physics, year = 2013, volume = 15, number = 2, pages = 025001, url = http://stacks.iop.org/1367-2630/15/i=2/a=025001, doi = http://dx.doi.org/10.1088/1367-2630/15/2/025001 }  and Jens Eisert Pauli Principle, Reloaded (Viewpoint) Physics 6(), 8 (2013). Abstract: A generalized form of the Pauli exclusion principle gives insight into the quantum wave function describing multiple electrons. BibTeX:  @article{hysics.6.8, author = and Jens Eisert, title = Pauli Principle, Reloaded (Viewpoint), journal = Physics, year = 2013, volume = 6, number = , pages = 8, url = http://link.aps.org/doi/10.1103/Physics.6.8, doi = http://dx.doi.org/10.1103/Physics.6.8 }  R. Hübener, A. Mari and J. Eisert Wick's Theorem for Matrix Product States Phys. Rev. Lett. 110(4), 040401 (2013). Abstract: Matrix product states and their continuous analogues are variational classes of states that capture quantum many-body systems or quantum fields with low entanglement; they are at the basis of the density-matrix renormalization group method and continuous variants thereof. In this work we show that, generically, N-point functions of arbitrary operators in discrete and continuous translation invariant matrix product states are completely characterized by the corresponding two- and three-point functions. Aside from having important consequences for the structure of correlations in quantum states with low entanglement, this result provides a new way of reconstructing unknown states from correlation measurements, e.g., for one-dimensional continuous systems of cold atoms. We argue that such a relation of correlation functions may help in devising perturbative approaches to interacting theories. BibTeX:  @article{Hubener2013, author = R. Hübener, A. Mari and J. Eisert, title = Wick's Theorem for Matrix Product States, journal = Phys. Rev. Lett., year = 2013, volume = 110, number = 4, pages = 040401, url = http://link.aps.org/doi/10.1103/PhysRevLett.110.040401, doi = http://dx.doi.org/10.1103/PhysRevLett.110.040401 }  Zhao Liu and Emil J. Bergholtz From fractional Chern insulators to Abelian and non-Abelian fractional quantum Hall states: Adiabatic continuity and orbital entanglement spectrum Phys. Rev. B 87(3), 035306 (2013). Abstract: The possibility of realizing lattice analogs of fractional quantum Hall (FQH) states, so-called fractional Chern insulators (FCIs), in nearly flat topological (Chern) bands has attracted a lot of recent interest. Here, we make the connection between Abelian as well as non-Abelian FQH states and FCIs more precise. Using a gauge-fixed version of Qi's Wannier basis representation of a Chern band, we demonstrate that the interpolation between several FCI states, obtained by short-range lattice interactions in a spin-orbit-coupled kagome lattice model, and the corresponding continuum FQH states is smooth: the gap remains approximately constant and extrapolates to a finite value in the thermodynamic limit, while the low-lying part of the orbital entanglement spectrum remains qualitatively unaltered. The orbital entanglement spectra also provide a first glimpse of the edge physics of FCIs via the bulk-boundary correspondence. Corroborating these results, we find that the squared overlaps between the FCI and FQH ground states are as large as 98.7\% for the 8-electron Laughlin state at ν=1/3 (consistent with an earlier study) and 97.8\% for the 10-electron Moore-Read state at ν=1/2. For the bosonic analogs of these states, the adiabatic continuity is also shown to hold, albeit with somewhat smaller associated overlaps, etc. Although going between the Chern bands to the Landau-level problem is often smooth, we show that this is not always the case by considering fermions at filling fraction ν=4/5, where the interpolation between Hamiltonians describing the two systems results in a phase transition. BibTeX:  @article{Liu2013, author = Zhao Liu and Emil J. Bergholtz, title = From fractional Chern insulators to Abelian and non-Abelian fractional quantum Hall states: Adiabatic continuity and orbital entanglement spectrum, journal = Phys. Rev. B, year = 2013, volume = 87, number = 3, pages = 035306, url = http://link.aps.org/doi/10.1103/PhysRevB.87.035306, doi = http://dx.doi.org/10.1103/PhysRevB.87.035306 }  T. Micklitz, A. Levchenko and M. R. Norman Incoherent pair tunneling in the pseudogap phase of cuprates Phys. Rev. B 87(2), 024503 (2013). Abstract: Motivated by a recent experiment by Bergeal et al., we reconsider incoherent pair tunneling in a cuprate junction formed from an optimally doped superconducting lead and an underdoped normal-metallic lead. We study the impact of the pseudogap on the pair tunneling by describing fermions in the underdoped lead with a model self-energy that has been developed to reproduce photoemission data. We find that the pseudogap causes an additional temperature-dependent suppression of the pair contribution to the tunneling current. We discuss consistency with available experimental data and propose future experimental directions. BibTeX:  @article{PhysRevB.87.024503, author = T. Micklitz, A. Levchenko and M. R. Norman, title = Incoherent pair tunneling in the pseudogap phase of cuprates, journal = Phys. Rev. B, year = 2013, volume = 87, number = 2, pages = 024503, url = http://link.aps.org/doi/10.1103/PhysRevB.87.024503, doi = http://dx.doi.org/10.1103/PhysRevB.87.024503 }  2012 BibTeX:  @unpublished{20122013,, title = {Preprints}, year = 2012 }  Earl T. Campbell, Hussain Anwar and Dan E. Browne Magic-State Distillation in All Prime Dimensions Using Quantum Reed-Muller Codes Phys. Rev. X 2(4), 041021 (2012). Abstract: We propose families of protocols for magic-state distillation -- important components of fault-tolerance schemes -- for systems of odd prime dimension. Our protocols utilize quantum Reed-Muller codes with transversal non-Clifford gates. We find that, in higher dimensions, small and effective codes can be used that have no direct analogue in qubit (two-dimensional) systems. We present several concrete protocols, including schemes for three-dimensional (qutrit) and five-dimensional (ququint) systems. The five-dimensional protocol is, by many measures, the best magic-state-distillation scheme yet discovered. It excels both in terms of error threshold with respect to depolarizing noise (36.3\%) and the efficiency measure known as yield, where, for a large region of parameters, it outperforms its qubit counterpart by many orders of magnitude. BibTeX:  @article{Campbell2012b, author = Earl T. Campbell, Hussain Anwar and Dan E. Browne, title = Magic-State Distillation in All Prime Dimensions Using Quantum Reed-Muller Codes, journal = Phys. Rev. X, year = 2012, volume = 2, number = 4, pages = 041021, url = http://link.aps.org/doi/10.1103/PhysRevX.2.041021, doi = http://dx.doi.org/10.1103/PhysRevX.2.041021 }  S. M. Frolov, J. Danon, S. Nadj-Perge, K. Zuo, J. W. W. van Tilburg, V. S. Pribiag, J. W. G. van den Berg, E. P. A. M. Bakkers and L. P. Kouwenhoven Suppression of Zeeman Gradients by Nuclear Polarization in Double Quantum Dots Phys. Rev. Lett. 109(23), 236805 (2012). Abstract: We use electric dipole spin resonance to measure dynamic nuclear polarization in InAs nanowire quantum dots. The resonance shifts in frequency when the system transitions between metastable high and low current states, indicating the presence of nuclear polarization. We propose that the low and the high current states correspond to different total Zeeman energy gradients between the two quantum dots. In the low current state, dynamic nuclear polarization efficiently compensates the Zeeman gradient due to the g-factor mismatch, resulting in a suppressed total Zeeman gradient. We present a theoretical model of electron-nuclear feedback that demonstrates a fixed point in nuclear polarization for nearly equal Zeeman splittings in the two dots and predicts a narrowed hyperfine gradient distribution. BibTeX:  @article{Frolov2012, author = S. M. Frolov, J. Danon, S. Nadj-Perge, K. Zuo, J. W. W. van Tilburg, V. S. Pribiag, J. W. G. van den Berg, E. P. A. M. Bakkers and L. P. Kouwenhoven, title = Suppression of Zeeman Gradients by Nuclear Polarization in Double Quantum Dots, journal = Phys. Rev. Lett., year = 2012, volume = 109, number = 23, pages = 236805, url = http://link.aps.org/doi/10.1103/PhysRevLett.109.236805, doi = http://dx.doi.org/10.1103/PhysRevLett.109.236805 }  A. Mari and J. Eisert Positive Wigner Functions Render Classical Simulation of Quantum Computation Efficient Phys. Rev. Lett. 109(23), 230503 (2012). Abstract: We show that quantum circuits where the initial state and all the following quantum operations can be represented by positive Wigner functions can be classically efficiently simulated. This is true both for continuous-variable as well as discrete variable systems in odd prime dimensions, two cases which will be treated on entirely the same footing. Noting the fact that Clifford and Gaussian operations preserve the positivity of the Wigner function, our result generalizes the Gottesman-Knill theorem. Our algorithm provides a way of sampling from the output distribution of a computation or a simulation, including the efficient sampling from an approximate output distribution in the case of sampling imperfections for initial states, gates, or measurements. In this sense, this work highlights the role of the positive Wigner function as separating classically efficiently simulable systems from those that are potentially universal for quantum computing and simulation, and it emphasizes the role of negativity of the Wigner function as a computational resource. BibTeX:  @article{Mari2012b, author = A. Mari and J. Eisert, title = Positive Wigner Functions Render Classical Simulation of Quantum Computation Efficient, journal = Phys. Rev. Lett., year = 2012, volume = 109, number = 23, pages = 230503, url = http://link.aps.org/doi/10.1103/PhysRevLett.109.230503, doi = http://dx.doi.org/10.1103/PhysRevLett.109.230503 }  Mark Thomas and Alessandro Romito Decoherence effects on weak value measurements in double quantum dots Phys. Rev. B 86(23), 235419 (2012). Abstract: We study the effect of decoherence on a weak value measurement in a paradigm system consisting of a double quantum dot continuously measured by a quantum point contact. Fluctuations of the parameters controlling the dot state induce decoherence. We find that, for measurements longer than the decoherence time, weak values are always reduced within the range of the eigenvalues of the measured observable. For measurements at shorter time scales, the measured weak value strongly depends on the interplay between the decoherence dynamics of the system and the detector backaction. In particular, depending on the postselected state and the strength of the decoherence, a more frequent classical readout of the detector might lead to an enhancement of weak values. BibTeX:  @article{Thomas2012, author = Mark Thomas and Alessandro Romito, title = Decoherence effects on weak value measurements in double quantum dots, journal = Phys. Rev. B, year = 2012, volume = 86, number = 23, pages = 235419, url = http://link.aps.org/doi/10.1103/PhysRevB.86.235419, doi = http://dx.doi.org/10.1103/PhysRevB.86.235419 }  Maximilian Trescher and Emil J. Bergholtz Flat bands with higher Chern number in pyrochlore slabs Phys. Rev. B 86(24), 241111 (2012). Abstract: A large number of recent works point to the emergence of intriguing analogs of fractional quantum Hall states in lattice models due to effective interactions in nearly flat bands with Chern number C=1. Here, we provide an intuitive and efficient construction of almost dispersionless bands with higher Chern numbers. Inspired by the physics of quantum Hall multilayers and pyrochlore-based transition-metal oxides, we study a tight-binding model describing spin-orbit coupled electrons in N parallel kagome layers connected by apical sites forming Nâ1 intermediate triangular layers (as in the pyrochlore lattice). For each N, we find finite regions in parameter space giving a virtually flat band with C=N. We analytically express the states within these topological bands in terms of single-layer states and thereby explicitly demonstrate that the C=N wave functions have an appealing structure in which layer index and translations in reciprocal space are intricately coupled. This provides a promising arena for new collective states of matter. BibTeX:  @article{Trescher2012, author = Maximilian Trescher and Emil J. Bergholtz, title = Flat bands with higher Chern number in pyrochlore slabs, journal = Phys. Rev. B, year = 2012, volume = 86, number = 24, pages = 241111, url = http://link.aps.org/doi/10.1103/PhysRevB.86.241111, doi = http://dx.doi.org/10.1103/PhysRevB.86.241111 }  O. Abah, J. Roßnagel, G. Jacob, S. Deffner, F. Schmidt-Kaler, K. Singer and E. Lutz Single-Ion Heat Engine at Maximum Power Phys. Rev. Lett. 109(20), 203006 (2012). Abstract: We propose an experimental scheme to realize a nanoheat engine with a single ion. An Otto cycle may be implemented by confining the ion in a linear Paul trap with tapered geometry and coupling it to engineered laser reservoirs. The quantum efficiency at maximum power is analytically determined in various regimes. Moreover, Monte Carlo simulations of the engine are performed that demonstrate its feasibility and its ability to operate at a maximum efficiency of 30\% under realistic conditions. BibTeX:  @article{Abah2012, author = O. Abah, J. Roßnagel, G. Jacob, S. Deffner, F. Schmidt-Kaler, K. Singer and E. Lutz, title = Single-Ion Heat Engine at Maximum Power, journal = Phys. Rev. Lett., year = 2012, volume = 109, number = 20, pages = 203006, url = http://link.aps.org/doi/10.1103/PhysRevLett.109.203006, doi = http://dx.doi.org/10.1103/PhysRevLett.109.203006 }  Zhao Liu, Emil J. Bergholtz, Heng Fan and Andreas M. Läuchli Fractional Chern Insulators in Topological Flat Bands with Higher Chern Number Phys. Rev. Lett. 109(18), 186805 (2012). Abstract: Lattice models forming bands with higher Chern number offer an intriguing possibility for new phases of matter with no analogue in continuum Landau levels. Here, we establish the existence of a number of new bulk insulating states at fractional filling in flat bands with a Chern number C=N>1, forming in a recently proposed pyrochlore model with strong spin-orbit coupling. In particular, we find compelling evidence for a series of stable states at ν=1/(2N+1) for fermions as well as bosonic states at ν=1/(N+1). By examining the topological ground state degeneracies and the excitation structure as well as the entanglement spectrum, we conclude that these states are Abelian. We also explicitly demonstrate that these states are nevertheless qualitatively different from conventional quantum Hall (multilayer) states due to the novel properties of the underlying band structure. BibTeX:  @article{Liu2012, author = Zhao Liu, Emil J. Bergholtz, Heng Fan and Andreas M. Läuchli, title = Fractional Chern Insulators in Topological Flat Bands with Higher Chern Number, journal = Phys. Rev. Lett., year = 2012, volume = 109, number = 18, pages = 186805, url = http://link.aps.org/doi/10.1103/PhysRevLett.109.186805, doi = http://dx.doi.org/10.1103/PhysRevLett.109.186805 }  Falko Pientka, Graham Kells, Alessandro Romito, Piet W. Brouwer and Felix von Oppen Enhanced Zero-Bias Majorana Peak in the Differential Tunneling Conductance of Disordered Multisubband Quantum-Wire/Superconductor Junctions Phys. Rev. Lett. 109(22), 227006 (2012). Abstract: A recent experiment Mourik et al. [ Science 336 1003 (2012)] on InSb quantum wires provides possible evidence for the realization of a topological superconducting phase and the formation of Majorana bound states. Motivated by this experiment, we consider the signature of Majorana bound states in the differential tunneling conductance of multisubband wires. We show that the weight of the Majorana-induced zero-bias peak is strongly enhanced by mixing of subbands, when disorder is added to the end of the quantum wire. We also consider how the topological phase transition is reflected in the gap structure of the current-voltage characteristic. BibTeX:  @article{Pientka2012, author = Falko Pientka, Graham Kells, Alessandro Romito, Piet W. Brouwer and Felix von Oppen, title = Enhanced Zero-Bias Majorana Peak in the Differential Tunneling Conductance of Disordered Multisubband Quantum-Wire/Superconductor Junctions, journal = Phys. Rev. Lett., year = 2012, volume = 109, number = 22, pages = 227006, url = http://link.aps.org/doi/10.1103/PhysRevLett.109.227006, doi = http://dx.doi.org/10.1103/PhysRevLett.109.227006 }  Mark Thomas, Torsten Karzig, Silvia Viola Kusminskiy, Gergely Zaránd and Felix von Oppen Scattering theory of adiabatic reaction forces due to out-of-equilibrium quantum environments Phys. Rev. B 86(19), 195419 (2012). Abstract: The Landauer-B\"uttiker theory of mesoscopic conductors was recently extended to nanoelectromechanical systems. In this extension, the adiabatic reaction forces exerted by the electronic degrees of freedom on the mechanical modes were expressed in terms of the electronic S matrix and its first nonadiabatic correction, the A matrix. Here, we provide a more natural and efficient derivation of these results within the setting and solely with the methods of scattering theory. Our derivation is based on a generic model of a slow classical degree of freedom coupled to a quantum-mechanical scattering system, extending previous work on adiabatic reaction forces for closed quantum systems. BibTeX:  @article{Thomas2012a, author = Mark Thomas, Torsten Karzig, Silvia Viola Kusminskiy, Gergely Zaránd and Felix von Oppen, title = Scattering theory of adiabatic reaction forces due to out-of-equilibrium quantum environments, journal = Phys. Rev. B, year = 2012, volume = 86, number = 19, pages = 195419, url = http://link.aps.org/doi/10.1103/PhysRevB.86.195419, doi = http://dx.doi.org/10.1103/PhysRevB.86.195419 }  Niels Bode, Eros Mariani and Felix von Oppen Transport properties of graphene functionalized with molecular switches Journal of Physics: Condensed Matter 24(39), 394017 (2012). Abstract: We provide a theory of the electronic transport properties of a graphene layer functionalized with molecular switches. Our considerations are motivated by the spiropyranâmerocyanine system which is non-polar in its ring-closed spiropyran form and zwitterionic in its ring-open merocyanine form. The reversible switching between these two isomers affects the carriers in graphene through the associated change in the molecular dipole moment, turning the graphene layer into a sensor of the molecular switching state. We present results for both the quasiclassical (Boltzmann) and the quantum coherent regimes of transport. Quite generally, we find a linear sensitivity of the conductance on the molecular dipole moment whenever quantum interference effects play an essential role which contrasts with a quadratic (and typically weaker) dependence when quantum interference is absent. BibTeX:  @article{Bode2012b, author = Niels Bode, Eros Mariani and Felix von Oppen, title = Transport properties of graphene functionalized with molecular switches, journal = Journal of Physics: Condensed Matter, year = 2012, volume = 24, number = 39, pages = 394017, url = http://stacks.iop.org/0953-8984/24/i=39/a=394017, doi = http://dx.doi.org/10.1088/0953-8984/24/39/394017 }  Torsten Karzig, Alex Levchenko, Leonid I. Glazman and Felix von Oppen Relaxation and edge reconstruction in integer quantum Hall systems New Journal of Physics 14(10), 105009 (2012). Abstract: The interplay between the confinement potential and the electronâelectron interactions causes reconstructions of quantum Hall edges. We study the consequences of this edge reconstruction for the relaxation of hot electrons injected into integer quantum Hall edge states. In translationally invariant edges, the relaxation of hot electrons is governed by three-body collisions, which are sensitive to the electron dispersion and thus to reconstruction effects. We show that the relaxation rates are significantly altered in different reconstruction scenarios. BibTeX:  @article{Karzig2012, author = Torsten Karzig, Alex Levchenko, Leonid I. Glazman and Felix von Oppen, title = Relaxation and edge reconstruction in integer quantum Hall systems, journal = New Journal of Physics, year = 2012, volume = 14, number = 10, pages = 105009, url = http://stacks.iop.org/1367-2630/14/i=10/a=105009, doi = http://dx.doi.org/10.1088/1367-2630/14/10/105009 }  Eros Mariani, Alexander J. Pearce and Felix von Oppen Fictitious gauge fields in bilayer graphene Phys. Rev. B 86(16), 165448 (2012). Abstract: We discuss the effect of elastic deformations on the electronic properties of bilayer graphene membranes. Distortions of the lattice translate into fictitious gauge fields in the electronic Dirac Hamiltonian that are explicitly derived here for arbitrary elastic deformations, including in-plane as well as flexural (out-of-plane) distortions. We include gauge fields associated to intra- as well as interlayer hopping terms and discuss their effects on the electronic band structure and on the transport properties of suspended bilayer membranes. In particular, we consider the electron-phonon coupling induced by the fictitious gauge fields and analyze its contribution to the electrical resistivity. Of special interest is the appearance of a linear coupling for flexural modes, in stark contrast to the case of monolayer graphene. This new coupling channel is shown to dominate the temperature-dependent resistivity in suspended samples with low tension. BibTeX:  @article{Mariani2012, author = Eros Mariani, Alexander J. Pearce and Felix von Oppen, title = Fictitious gauge fields in bilayer graphene, journal = Phys. Rev. B, year = 2012, volume = 86, number = 16, pages = 165448, url = http://link.aps.org/doi/10.1103/PhysRevB.86.165448, doi = http://dx.doi.org/10.1103/PhysRevB.86.165448 }  G. Kells, D. Meidan and P. W. Brouwer Near-zero-energy end states in topologically trivial spin-orbit coupled superconducting nanowires with a smooth confinement Phys. Rev. B 86(10), 100503 (2012). Abstract: A one-dimensional spin-orbit coupled nanowire with proximity-induced pairing from a nearby s-wave superconductor may be in a topological nontrivial state, in which it has a zero-energy Majorana bound state at each end. We find that the topological trivial phase may have fermionic end states with an exponentially small energy, if the confinement potential at the wire's ends is smooth. The possible existence of such near-zero-energy levels implies that the mere observation of a zero-bias peak in the tunneling conductance is not an exclusive signature of a topological superconducting phase, even in the ideal clean single channel limit. BibTeX:  @article{Kells2012a, author = G. Kells, D. Meidan and P. W. Brouwer, title = Near-zero-energy end states in topologically trivial spin-orbit coupled superconducting nanowires with a smooth confinement, journal = Phys. Rev. B, year = 2012, volume = 86, number = 10, pages = 100503, url = http://link.aps.org/doi/10.1103/PhysRevB.86.100503, doi = http://dx.doi.org/10.1103/PhysRevB.86.100503 }  M.-T. Rieder, G. Kells, M. Duckheim, D. Meidan and P. W. Brouwer Endstates in multichannel spinless $p$-wave superconducting wires Phys. Rev. B 86(12), 125423 (2012). Abstract: Multimode spinless p-wave superconducting wires with a width W much smaller than the superconducting coherence length Î¾ are known to have multiple low-energy subgap states localized near the wire's ends. Here we compare the typical energies of such endstates for various terminations of the wire: A superconducting wire coupled to a normal-metal stub, a weakly disordered superconductor wire and a wire with smooth confinement. Depending on the termination, we find that the energies of the subgap states can be higher or lower than for the case of a rectangular wire with hard-wall boundaries. BibTeX:  @article{Rieder2012, author = M.-T. Rieder, G. Kells, M. Duckheim, D. Meidan and P. W. Brouwer, title = Endstates in multichannel spinless $p$-wave superconducting wires, journal = Phys. Rev. B, year = 2012, volume = 86, number = 12, pages = 125423, url = http://link.aps.org/doi/10.1103/PhysRevB.86.125423, doi = http://dx.doi.org/10.1103/PhysRevB.86.125423 }  F. Pientka, M. Gradhand, D. V. Fedorov, I. Mertig and B. L. Györffy Gauge freedom for degenerate Bloch states Phys. Rev. B 86(5), 054413 (2012). Abstract: In nonmagnetic crystals with inversion symmetry the electronic bands are twofold degenerate. As a consequence, any orthonormalized linear combination of the two corresponding eigenfunctions can represent the electron wave function. A priori it is not obvious which superposition, gauge, should be chosen to calculate a quantity which is not gauge invariant within a certain approximation. Here we consider gauge options appropriate under particular physical conditions. BibTeX:  @article{fp2012d, author = F. Pientka, M. Gradhand, D. V. Fedorov, I. Mertig and B. L. Györffy, title = Gauge freedom for degenerate Bloch states, journal = Phys. Rev. B, year = 2012, volume = 86, number = 5, pages = 054413, url = http://link.aps.org/doi/10.1103/PhysRevB.86.054413, doi = http://dx.doi.org/10.1103/PhysRevB.86.054413 }  A. T. Rømer, S. Graser, T. S. Nunner, P. J. Hirschfeld and B. M. Andersen Local modulations of the spin-fluctuation-mediated pairing interaction by impurities in $d$-wave superconductors Phys. Rev. B 86(5), 054507 (2012). Abstract: We present a self-consistent real space formulation of spin-fluctuation mediated d-wave pairing. By calculating all relevant inhomogeneous spin and charge susceptibilities in real space within the random phase approximation (RPA), we obtain the effective pairing interaction and study its spatial dependence near both local potential and hopping impurities. A remarkably large enhancement of the pairing interaction may be obtained near the impurity site. We discuss the relevance of our result to inhomogeneities observed by scanning tunneling spectroscopy on the surface of cuprate superconductors. BibTeX:  @article{Romer2012, author = A. T. Rømer, S. Graser, T. S. Nunner, P. J. Hirschfeld and B. M. Andersen, title = Local modulations of the spin-fluctuation-mediated pairing interaction by impurities in $d$-wave superconductors, journal = Phys. Rev. B, year = 2012, volume = 86, number = 5, pages = 054507, url = http://link.aps.org/doi/10.1103/PhysRevB.86.054507, doi = http://dx.doi.org/10.1103/PhysRevB.86.054507 }  P. G. Silvestrov, P. W. Brouwer and E. G. Mishchenko Spin and charge structure of the surface states in topological insulators Phys. Rev. B 86(7), 075302 (2012). Abstract: We investigate the spin and charge densities of surface states of the three-dimensional topological insulator Bi2Se3, starting from the continuum description of the material [ Zhang et al. Nat. Phys. 5 438 (2009)]. The spin structure on surfaces other than the (111) surface has additional complexity because of a misalignment of the contributions coming from the two sublattices of the crystal. For these surfaces we expect new features to be seen in the spin-resolved angular resolved photoemission spectroscopy (ARPES) experiments, caused by a nonhelical spin polarization of electrons at the individual sublattices as well as by the interference of the electron waves emitted coherently from two sublattices. We also show that the position of the Dirac crossing in the spectrum of the surface states depends on the orientation of the interface. This leads to contact potentials and surface charge redistribution at edges between different facets of the crystal. BibTeX:  @article{Silvestrov2012, author = P. G. Silvestrov, P. W. Brouwer and E. G. Mishchenko, title = Spin and charge structure of the surface states in topological insulators, journal = Phys. Rev. B, year = 2012, volume = 86, number = 7, pages = 075302, url = http://link.aps.org/doi/10.1103/PhysRevB.86.075302, doi = http://dx.doi.org/10.1103/PhysRevB.86.075302 }  Toby Cubitt, Jens Eisert and Michael Wolf The Complexity of Relating Quantum Channels to Master Equations Communications in Mathematical Physics 310(2), 383-418 (2012). Abstract: Completely positive, trace preserving (CPT) maps and Lindblad master equations are both widely used to describe the dynamics of open quantum systems. The connection between these two descriptions is a classic topic in mathematical physics. One direction was solved by the now famous result due to Lindblad, Kossakowski, Gorini and Sudarshan, who gave a complete characterisation of the master equations that generate completely positive semi-groups. However, the other direction has remained open: given a CPT map, is there a Lindblad master equation that generates it (and if so, can we find its form)? This is sometimes known as the Markovianity problem. Physically, it is asking how one can deduce underlying physical processes from experimental observations. We give a complexity theoretic answer to this problem: it is NP-hard. We also give an explicit algorithm that reduces the problem to integer semi-definite programming, a well-known NP problem. Together, these results imply that resolving the question of which CPT maps can be generated by master equations is tantamount to solving P = NP: any efficiently computable criterion for Markovianity would imply P = NP; whereas a proof that P = NP would imply that our algorithm already gives an efficiently computable criterion. Thus, unless P does equal NP, there cannot exist any simple criterion for determining when a CPT map has a master equation description. However, we also show that if the system dimension is fixed (relevant for current quantum process tomography experiments), then our algorithm scales efficiently in the required precision, allowing an underlying Lindblad master equation to be determined efficiently from even a single snapshot in this case. Our work also leads to similar complexity-theoretic answers to a related long-standing open problem in probability theory. BibTeX:  @article{Cubitt2012, author = Toby Cubitt, Jens Eisert and Michael Wolf, title = The Complexity of Relating Quantum Channels to Master Equations, journal = Communications in Mathematical Physics, year = 2012, volume = 310, number = 2, pages = 383-418, url = http://dx.doi.org/10.1007/s00220-011-1402-y, doi = http://dx.doi.org/10.1007/s00220-011-1402-y }  A. Mari and J. Eisert Opto- and electro-mechanical entanglement improved by modulation New Journal of Physics 14(7), 075014 (2012). Abstract: One of the main milestones in the study of opto- and electro-mechanical systems is to certify entanglement between a mechanical resonator and an optical or microwave mode of a cavity field. In this work, we show how a suitable time-periodic modulation can help to achieve large degrees of entanglement, building upon the framework introduced in Mari and Eisert (2009 Phys. Rev. Lett. 103 213603). It is demonstrated that with suitable driving, the maximum degree of entanglement can be significantly enhanced, in a way exhibiting a nontrivial dependence on the specifics of the modulation. Such time-dependent driving might help to experimentally achieve entangled mechanical systems also in situations when quantum correlations are otherwise suppressed by thermal noise. BibTeX:  @article{Mari2012a, author = A. Mari and J. Eisert, title = Opto- and electro-mechanical entanglement improved by modulation, journal = New Journal of Physics, year = 2012, volume = 14, number = 7, pages = 075014, url = http://stacks.iop.org/1367-2630/14/i=7/a=075014, doi = http://dx.doi.org/10.1088/1367-2630/14/7/075014 }  T. Micklitz, A. Levchenko and A. Rosch Nonlinear Conductance of Long Quantum Wires at a Conductance Plateau Transition: Where Does the Voltage Drop? Phys. Rev. Lett. 109(3), 036405 (2012). Abstract: We calculate the linear and nonlinear conductance of spinless fermions in clean, long quantum wires, where short-ranged interactions lead locally to equilibration. Close to the quantum phase transition, where the conductance jumps from zero to one conductance quantum, the conductance obtains a universal form governed by the ratios of temperature, bias voltage, and gate voltage. Asymptotic analytic results are compared to solutions of a Boltzmann equation which includes the effects of three-particle scattering. Surprisingly, we find that for long wires the voltage predominantly drops close to one end of the quantum wire due to a thermoelectric effect. BibTeX:  @article{Micklitz2012a, author = T. Micklitz, A. Levchenko and A. Rosch, title = Nonlinear Conductance of Long Quantum Wires at a Conductance Plateau Transition: Where Does the Voltage Drop?, journal = Phys. Rev. Lett., year = 2012, volume = 109, number = 3, pages = 036405, url = http://link.aps.org/doi/10.1103/PhysRevLett.109.036405, doi = http://dx.doi.org/10.1103/PhysRevLett.109.036405 }  Masaaki Nakamura, Zheng-Yuan Wang and Emil J. Bergholtz Exactly Solvable Fermion Chain Describing a $$\nu{}=1/3 Fractional Quantum Hall State Phys. Rev. Lett. 109(1), 016401 (2012). Abstract: We introduce an exactly solvable fermion chain that describes a ν=1/3 fractional quantum Hall (FQH) state beyond the thin-torus limit. The ground state of our model is shown to be unique for each center-of-mass sector, and it has a matrix product representation that enables us to exactly calculate order parameters, correlation functions, and entanglement spectra. The ground state of our model shows striking similarities with the BCS wave functions and quantum spin-1 chains. Using the variational method with matrix product ansatz, we analytically calculate excitation gaps and vanishing of the compressibility expected in the FQH state. We also show that the above results can be related to a ν=1/2 bosonic FQH state. BibTeX:  @article{Nakamura2012, author = Masaaki Nakamura, Zheng-Yuan Wang and Emil J. Bergholtz, title = Exactly Solvable Fermion Chain Describing a$$\nu${}=1/3$ Fractional Quantum Hall State, journal = Phys. Rev. Lett., year = 2012, volume = 109, number = 1, pages = 016401, url = http://link.aps.org/doi/10.1103/PhysRevLett.109.016401, doi = http://dx.doi.org/10.1103/PhysRevLett.109.016401 }  Hussain Anwar, Earl T. Campbell and Dan E. Browne Qutrit magic state distillation New Journal of Physics 14(6), 063006 (2012). Abstract: Magic state distillation (MSD) is a purification protocol that plays an important role in fault-tolerant quantum computation. Repeated iteration of the steps of an MSD protocol generates pure single non-stabilizer states, or magic states, from multiple copies of a mixed resource state using stabilizer operations only. Thus mixed resource states promote the stabilizer operations to full universality. MSD was introduced for qubit-based quantum computation, but little has been known concerning MSD in higher-dimensional qudit-based computation. Here, we describe a general approach for studying MSD in higher dimensions. We use it to investigate the features of a qutrit MSD protocol based on the five-qutrit stabilizer code. We show that this protocol distils non-stabilizer magic states, and identify two types of states that are attractors of this iteration map. Finally, we show how these states may be converted, via stabilizer circuits alone, into a state suitable for state-injected implementation of a non-Clifford phase gate, enabling non-Clifford unitary computation. BibTeX:  @article{Anwar2012, author = Hussain Anwar, Earl T. Campbell and Dan E. Browne, title = Qutrit magic state distillation, journal = New Journal of Physics, year = 2012, volume = 14, number = 6, pages = 063006, url = http://stacks.iop.org/1367-2630/14/i=6/a=063006, doi = http://dx.doi.org/10.1088/1367-2630/14/6/063006 }  Thomas Barthel and Martin Kliesch Quasilocality and Efficient Simulation of Markovian Quantum Dynamics Phys. Rev. Lett. 108(23), 230504 (2012). Abstract: We consider open many-body systems governed by a time-dependent quantum master equation with short-range interactions. With a generalized Lieb-Robinson bound, we show that the evolution in this very generic framework is quasilocal; i.e., the evolution of observables can be approximated by implementing the dynamics only in a vicinity of the observables’ support. The precision increases exponentially with the diameter of the considered subsystem. Hence, time evolution can be simulated on classical computers with a cost that is independent of the system size. Providing error bounds for Trotter decompositions, we conclude that the simulation on a quantum computer is additionally efficient in time. For experiments and simulations in the Schrödinger picture, our result can be used to rigorously bound finite-size effects. BibTeX:  @article{Barthel2012a, author = Thomas Barthel and Martin Kliesch, title = Quasilocality and Efficient Simulation of Markovian Quantum Dynamics, journal = Phys. Rev. Lett., year = 2012, volume = 108, number = 23, pages = 230504, url = http://link.aps.org/doi/10.1103/PhysRevLett.108.230504, doi = http://dx.doi.org/10.1103/PhysRevLett.108.230504 }  Andreas Dechant and Eric Lutz Anomalous Spatial Diffusion and Multifractality in Optical Lattices Phys. Rev. Lett. 108(23), 230601 (2012). Abstract: The transport of cold atoms in shallow optical lattices is characterized by slow, nonstationary momentum relaxation. We develop a projector operator method able to derive, in this case, a generalized Smoluchowski equation for the position variable. We show that this explicitly non-Markovian equation can be written as a systematic expansion involving higher-order derivatives. We use the latter to compute arbitrary moments of the spatial distribution and analyze their multifractal properties. BibTeX:  @article{Dechant2012a, author = Andreas Dechant and Eric Lutz, title = Anomalous Spatial Diffusion and Multifractality in Optical Lattices, journal = Phys. Rev. Lett., year = 2012, volume = 108, number = 23, pages = 230601, url = http://link.aps.org/doi/10.1103/PhysRevLett.108.230601, doi = http://dx.doi.org/10.1103/PhysRevLett.108.230601 }  J. Eisert, M. P. Müller and C. Gogolin Quantum measurement occurrence is undecidable Phys. Rev. Lett. 108(26), 260501 (2012). Abstract: In this work, we show that very natural, apparently simple problems in quantum measurement theory can be undecidable even if their classical analogues are decidable. Undecidability hence appears as a genuine quantum property here. Formally, an undecidable problem is a decision problem for which one cannot construct a single algorithm that will always provide a correct answer in finite time. The problem we consider is to determine whether sequentially used identical Stern-Gerlach-type measurement devices, giving rise to a tree of possible outcomes, have outcomes that never occur. Finally, we point out implications for measurement-based quantum computing and studies of quantum many-body models and suggest that a plethora of problems may indeed be undecidable. BibTeX:  @article{Eisert2012, author = J. Eisert, M. P. Müller and C. Gogolin, title = Quantum measurement occurrence is undecidable, journal = Phys. Rev. Lett., year = 2012, volume = 108, number = 26, pages = 260501, url = http://link.aps.org/doi/10.1103/PhysRevLett.108.260501, doi = http://dx.doi.org/10.1103/PhysRevLett.108.260501 }  M. Ohliger and J. Eisert Efficient measurement-based quantum computing with continuous-variable systems Phys. Rev. A 85(6), 062318 (2012). Abstract: We present strictly efficient schemes for scalable measurement-based quantum computing using continuous-variable systems: These schemes are based on suitable non-Gaussian resource states, ones that can be prepared using interactions of light with matter systems or even purely optically. Merely Gaussian measurements such as optical homodyning as well as photon counting measurements are required, on individual sites. These schemes overcome limitations posed by Gaussian cluster states, which are known not to be universal for quantum computations of unbounded length, unless one is willing to scale the degree of squeezing with the total system size. We establish a framework derived from tensor networks and matrix product states with infinite physical dimension and finite auxiliary dimension general enough to provide a framework for such schemes. Since in the discussed schemes the logical encoding is finite dimensional, tools of error correction are applicable. We also identify some further limitations for any continuous-variable computing scheme from which one can argue that no substantially easier ways of continuous-variable measurement-based computing than the presented one can exist. BibTeX:  @article{Ohliger2012, author = M. Ohliger and J. Eisert, title = Efficient measurement-based quantum computing with continuous-variable systems, journal = Phys. Rev. A, year = 2012, volume = 85, number = 6, pages = 062318, url = http://link.aps.org/doi/10.1103/PhysRevA.85.062318, doi = http://dx.doi.org/10.1103/PhysRevA.85.062318 }  Thomas Barthel and Robert Hübener Solving Condensed-Matter Ground-State Problems by Semidefinite Relaxations Phys. Rev. Lett. 108(20), 200404 (2012). Abstract: We present a generic approach to the condensed-matter ground-state problem which is complementary to variational techniques and works directly in the thermodynamic limit. Relaxing the ground-state problem, we obtain semidefinite programs (SDP). These can be solved efficiently, yielding strict lower bounds to the ground-state energy and approximations to the few-particle Greenâs functions. As the method is applicable for all particle statistics, it represents, in particular, a novel route for the study of strongly correlated fermionic and frustrated spin systems in D>1 spatial dimensions. It is demonstrated for the XXZ model and the Hubbard model of spinless fermions. The results are compared against exact solutions, quantum Monte Carlo calculations, and Anderson bounds, showing the competitiveness of the SDP method. BibTeX:  @article{Barthel2012, author = Thomas Barthel and Robert Hübener, title = Solving Condensed-Matter Ground-State Problems by Semidefinite Relaxations, journal = Phys. Rev. Lett., year = 2012, volume = 108, number = 20, pages = 200404, url = http://link.aps.org/doi/10.1103/PhysRevLett.108.200404, doi = http://dx.doi.org/10.1103/PhysRevLett.108.200404 }  and P. W. Brouwer Enter the Majorana Fermion (Perspective) Science 336(6084), 989--990 (2012). Abstract: All known fundamental particles are either bosons or fermions. Fermions are subject to the Pauli principle, which forbids two particles being in the same quantum state; bosons, by contrast, tend to bunch together in the same state. The same rule applies to the excitations of most solid-state systems, such as metals and semiconductors, which can be classified as fermionic or bosonic. However, sometimes excitationsâquasiparticlesâof a fundamentally different type emerge that resemble particles that hitherto have been considered only as a mathematical possibility. BibTeX:  @article{Brouwer2012, author = and P. W. Brouwer, title = Enter the Majorana Fermion (Perspective), journal = Science, year = 2012, volume = 336, number = 6084, pages = 989--990, url = https://www.sciencemag.org/content/336/6084/989, doi = http://dx.doi.org/10.1126/science.1223302 }  A. Dechant, E. Lutz, D. A. Kessler and E. Barkai Superaging correlation function and ergodicity breaking for Brownian motion in logarithmic potentials Phys. Rev. E 85(5), 051124 (2012). Abstract: We consider an overdamped Brownian particle moving in a confining asymptotically logarithmic potential, which supports a normalized Boltzmann equilibrium density. We derive analytical expressions for the two-time correlation function and the fluctuations of the time-averaged position of the particle for large but finite times. We characterize the occurrence of aging and nonergodic behavior as a function of the depth of the potential, and we support our predictions with extensive Langevin simulations. While the Boltzmann measure is used to obtain stationary correlation functions, we show how the non-normalizable infinite covariant density is related to the superaging behavior. BibTeX:  @article{Dechant2012, author = A. Dechant, E. Lutz, D. A. Kessler and E. Barkai, title = Superaging correlation function and ergodicity breaking for Brownian motion in logarithmic potentials, journal = Phys. Rev. E, year = 2012, volume = 85, number = 5, pages = 051124, url = http://link.aps.org/doi/10.1103/PhysRevE.85.051124, doi = http://dx.doi.org/10.1103/PhysRevE.85.051124 }  M. Gradhand, D. V. Fedorov, F. Pientka, P. Zahn, I. Mertig and B. L. Györffy First-principle calculations of the Berry curvature of Bloch states for charge and spin transport of electrons Journal of Physics: Condensed Matter 24(21), 213202 (2012). Abstract: Recent progress in wave packet dynamics based on the insight of Berry pertaining to adiabatic evolution of quantum systems has led to theneed for a new property of a Bloch state, the Berry curvature, to be calculated from first principles. We report here on the response to this challenge by the ab initio community during the past decade. First we give a tutorial introduction of the conceptual developments we mentioned above. Then we describe four methodologies which havebeen developed for first-principle calculations of the Berry curvature. Finally, to illustrate the significance of the new developments, we report some results of calculations of interesting physical properties such as the anomalous and spin Hall conductivity as well as the anomalous Nernst conductivity and discuss the influence of the Berry curvature on the de Haas-van Alphen oscillation. BibTeX:  @article{Gradhand2012, author = M. Gradhand, D. V. Fedorov, F. Pientka, P. Zahn, I. Mertig and B. L. Györffy, title = First-principle calculations of the Berry curvature of Bloch states for charge and spin transport of electrons, journal = Journal of Physics: Condensed Matter, year = 2012, volume = 24, number = 21, pages = 213202, url = http://stacks.iop.org/0953-8984/24/i=21/a=213202, doi = http://dx.doi.org/10.1088/0953-8984/24/21/213202 }  Konstantin S. Tikhonov, Georg Schwiete and Alexander M. Finkel'stein Fluctuation conductivity in disordered superconducting films Phys. Rev. B 85(17), 174527 (2012). Abstract: We study the effect of superconducting fluctuations on the longitudinal and the transverse (Hall) conductivity in homogeneously disordered films. Our calculation is based on the Usadel equation in the real-time formulation. We adjust this approach to derive analytic expressions for the fluctuation corrections in the entire metallic part of the temperature-magnetic field phase diagram, including the effects of both classical and quantum fluctuations. This method allows us to obtain fluctuation corrections in a compact and effective way, establishing a direct connection between phenomenological and microscopic calculations. BibTeX:  @article{Tikhonov2012, author = Konstantin S. Tikhonov, Georg Schwiete and Alexander M. Finkel'stein, title = Fluctuation conductivity in disordered superconducting films, journal = Phys. Rev. B, year = 2012, volume = 85, number = 17, pages = 174527, url = http://link.aps.org/doi/10.1103/PhysRevB.85.174527, doi = http://dx.doi.org/10.1103/PhysRevB.85.174527 }  Bertrand I. Halperin, Yuval Oreg, Ady Stern, Gil Refael, Jason Alicea and Felix von Oppen Adiabatic manipulations of Majorana fermions in a three-dimensional network of quantum wires Phys. Rev. B 85(14), 144501 (2012). Abstract: It has been proposed that localized zero-energy Majorana states can be realized in a two-dimensional network of quasi-one-dimensional semiconductor wires that are proximity coupled to a bulk superconductor. The wires should have strong spin-orbit coupling with appropriate symmetry, and their electrons should be partially polarized by a strong Zeeman field. Then, if the Fermi level is in an appropriate range, the wire can be in a topological superconducting phase, with Majorana states that occur at wire ends and at Y junctions, where three topological superconductor segments may be joined. Here we generalize these ideas to consider a three-dimensional network. The positions of Majorana states can be manipulated, and their non-Abelian properties made visible, by using external gates to selectively deplete portions of the network or by physically connecting and redividing wire segments. Majorana states can also be manipulated by reorientations of the Zeeman field on a wire segment, by physically rotating the wire about almost any axis, or by evolution of the phase of the order parameter in the proximity-coupled superconductor. We show how to keep track of sign changes in the zero-energy Hilbert space during adiabatic manipulations by monitoring the evolution of each Majorana state separately, rather than keeping track of the braiding of all possible pairs. This has conceptual advantages in the case of a three-dimensional network, and may be computationally useful even in two dimensions, if large numbers of Majorana sites are involved. BibTeX:  @article{Halperin2012, author = Bertrand I. Halperin, Yuval Oreg, Ady Stern, Gil Refael, Jason Alicea and Felix von Oppen, title = Adiabatic manipulations of Majorana fermions in a three-dimensional network of quantum wires, journal = Phys. Rev. B, year = 2012, volume = 85, number = 14, pages = 144501, url = http://link.aps.org/doi/10.1103/PhysRevB.85.144501, doi = http://dx.doi.org/10.1103/PhysRevB.85.144501 }  Endre Kajari, Alexander Wolf, Eric Lutz and Giovanna Morigi Statistical mechanics of entanglement mediated by a thermal reservoir Phys. Rev. A 85(4), 042318 (2012). Abstract: Two defect particles that couple to a harmonic chain, acting as common reservoir, can become entangled even when the two defects do not directly interact and the harmonic chain is effectively a thermal reservoir for each individual defect. This dynamics is encountered for sufficiently low temperatures of the chain and depends on the initial state of the two oscillators. In particular, when each defect is prepared in a squeezed state, entanglement can be found at time scales at which the steady state of a single defect is reached. We provide a microscopic description of the coupled quantum dynamics of chain and defects. By means of numerical simulations, we explore the parameter regimes for which entanglement is found under the specific assumption that both particles couple to the same ion of the chain. This model provides the microscopic setting where bath-induced entanglement can be observed. BibTeX:  @article{Kajari2012, author = Endre Kajari, Alexander Wolf, Eric Lutz and Giovanna Morigi, title = Statistical mechanics of entanglement mediated by a thermal reservoir, journal = Phys. Rev. A, year = 2012, volume = 85, number = 4, pages = 042318, url = http://link.aps.org/doi/10.1103/PhysRevA.85.042318, doi = http://dx.doi.org/10.1103/PhysRevA.85.042318 }  Thomas L. Schmidt, Stephan Rachel, Felix von Oppen and Leonid I. Glazman Inelastic Electron Backscattering in a Generic Helical Edge Channel Phys. Rev. Lett. 108(15), 156402 (2012). Abstract: We evaluate the low-temperature conductance of a weakly interacting one-dimensional helical liquid without axial spin symmetry. The lack of that symmetry allows for inelastic backscattering of a single electron, accompanied by forward scattering of another. This joint effect of weak interactions and potential scattering off impurities results in a temperature-dependent deviation from the quantized conductance, \delta{}G\propto{}T4. In addition, \delta{}G is sensitive to the position of the Fermi level. We determine numerically the parameters entering our generic model for the Bernevig-Hughes-Zhang Hamiltonian of a HgTe/CdTe quantum well in the presence of Rashba spin-orbit coupling. BibTeX:  @article{Schmidt2012, author = Thomas L. Schmidt, Stephan Rachel, Felix von Oppen and Leonid I. Glazman, title = Inelastic Electron Backscattering in a Generic Helical Edge Channel, journal = Phys. Rev. Lett., year = 2012, volume = 108, number = 15, pages = 156402, url = http://link.aps.org/doi/10.1103/PhysRevLett.108.156402, doi = http://dx.doi.org/10.1103/PhysRevLett.108.156402 }  Francis B. Wilken and Piet W. Brouwer Impurity-assisted Andreev reflection at a spin-active half metal-superconductor interface Phys. Rev. B 85(13), 134531 (2012). Abstract: The Andreev reflection amplitude at a clean interface between a half-metallic ferromagnet (H) and a superconductor (S) for which the half metal's magnetization has a gradient perpendicular to the interface is proportional to the excitation energy ɛ and vanishes at ɛ=0 [ Béri et al. Phys. Rev. B 79 024517 (2009)]. Here we show that the presence of impurities at or in the immediate vicinity of the HS interface leads to a finite Andreev reflection amplitude at ɛ=0. This impurity-assisted Andreev reflection dominates the low-bias conductance of an HS junction and the Josephson current of an SHS junction in the long-junction limit. BibTeX:  @article{Wilken2012, author = Francis B. Wilken and Piet W. Brouwer, title = Impurity-assisted Andreev reflection at a spin-active half metal-superconductor interface, journal = Phys. Rev. B, year = 2012, volume = 85, number = 13, pages = 134531, url = http://link.aps.org/doi/10.1103/PhysRevB.85.134531, doi = http://dx.doi.org/10.1103/PhysRevB.85.134531 }  Antoine Berut, Artak Arakelyan, Artyom Petrosyan, Sergio Ciliberto, Raoul Dillenschneider and Eric Lutz Experimental verification of Landauer's principle linking information and thermodynamics Nature 483(7388), 187--189 (2012). Abstract: In 1961, Rolf Landauer argued that the erasure of information is a dissipative process1. A minimal quantity of heat, proportional to the thermal energy and called the Landauer bound, is necessarily produced when a classical bit of information is deleted. A direct consequence of this logically irreversible transformation is that the entropy of the environment increases by a finite amount. Despite its fundamental importance for information theory and computer science the erasure principle has not been verified experimentally so far, the main obstacle being the difficulty of doing single-particle experiments in the low-dissipation regime. Here we experimentally show the existence of the Landauer bound in a generic model of a one-bit memory. Using a system of a single colloidal particle trapped in a modulated double-well potential, we establish that the mean dissipated heat saturates at the Landauer bound in the limit of long erasure cycles. This result demonstrates the intimate link between information theory and thermodynamics. It further highlights the ultimate physical limit of irreversible computation. BibTeX:  @article{eriknature101038, author = Antoine Berut, Artak Arakelyan, Artyom Petrosyan, Sergio Ciliberto, Raoul Dillenschneider and Eric Lutz, title = Experimental verification of Landauer's principle linking information and thermodynamics, journal = Nature, year = 2012, volume = 483, number = 7388, pages = 187--189, url = http://dx.doi.org/10.1038/nature10872, doi = http://dx.doi.org/10.1038/nature10872 }  Niels Bode, Liliana Arrachea, Gustavo S. Lozano, Tamara S. Nunner and Felix von Oppen Current-induced switching in transport through anisotropic magnetic molecules Phys. Rev. B 85(11), 115440 (2012). Abstract: Anisotropic single-molecule magnets may be thought of as molecular switches, with possible applications to molecular spintronics. In this paper, we consider current-induced switching in single-molecule junctions containing an anisotropic magnetic molecule. We assume that the carriers interact with the magnetic molecule through the exchange interaction and focus on the regime of high currents in which the molecular spin dynamics is slow compared to the time which the electrons spend on the molecule. In this limit, the molecular spin obeys a nonequilibrium Langevin equation which takes the form of a generalized Landau-Lifshitz-Gilbert equation and which we derive microscopically by means of a nonequilibrium Born-Oppenheimer approximation. We exploit this Langevin equation to identify the relevant switching mechanisms and to derive the current-induced switching rates. As a by-product, we also derive S-matrix expressions for the various torques entering into the Landau-Lifshitz-Gilbert equation which generalize previous expressions in the literature to nonequilibrium situations. BibTeX:  @article{Bode2012a, author = Niels Bode, Liliana Arrachea, Gustavo S. Lozano, Tamara S. Nunner and Felix von Oppen, title = Current-induced switching in transport through anisotropic magnetic molecules, journal = Phys. Rev. B, year = 2012, volume = 85, number = 11, pages = 115440, url = http://link.aps.org/doi/10.1103/PhysRevB.85.115440, doi = http://dx.doi.org/10.1103/PhysRevB.85.115440 }  Jochen Brüggemann, Guillaume Weick, Fabio Pistolesi and Felix von Oppen Large current noise in nanoelectromechanical systems close to continuous mechanical instabilities Phys. Rev. B 85(12), 125441 (2012). Abstract: We investigate the current noise of nanoelectromechanical systems close to a continuous mechanical instability. In the vicinity of the latter, the vibrational frequency of the nanomechanical system vanishes, rendering the system very sensitive to charge fluctuations and, hence, resulting in very large (super-Poissonian) current noise. Specifically, we consider a suspended single-electron transistor close to the Euler buckling instability. We show that such a system exhibits an exponential enhancement of the current noise when approaching the Euler instability which we explain in terms of telegraph noise. BibTeX:  @article{Bruggemann2012, author = Jochen Brüggemann, Guillaume Weick, Fabio Pistolesi and Felix von Oppen, title = Large current noise in nanoelectromechanical systems close to continuous mechanical instabilities, journal = Phys. Rev. B, year = 2012, volume = 85, number = 12, pages = 125441, url = http://link.aps.org/doi/10.1103/PhysRevB.85.125441, doi = http://dx.doi.org/10.1103/PhysRevB.85.125441 }  Toby S. Cubitt, Jens Eisert and Michael M. Wolf Extracting Dynamical Equations from Experimental Data is NP Hard Phys. Rev. Lett. 108(12), 120503 (2012). Abstract: The behavior of any physical system is governed by its underlying dynamical equations. Much of physics is concerned with discovering these dynamical equations and understanding their consequences. In this Letter, we show that, remarkably, identifying the underlying dynamical equation from any amount of experimental data, however precise, is a provably computationally hard problem (it is NP hard), both for classical and quantum mechanical systems. As a by-product of this work, we give complexity-theoretic answers to both the quantum and classical embedding problems, two long-standing open problems in mathematics (the classical problem, in particular, dating back over 70 years). BibTeX:  @article{Cubitt2012a, author = Toby S. Cubitt, Jens Eisert and Michael M. Wolf, title = Extracting Dynamical Equations from Experimental Data is NP Hard, journal = Phys. Rev. Lett., year = 2012, volume = 108, number = 12, pages = 120503, url = http://link.aps.org/doi/10.1103/PhysRevLett.108.120503, doi = http://dx.doi.org/10.1103/PhysRevLett.108.120503 }  A. Mari and J. Eisert Cooling by Heating: Very Hot Thermal Light Can Significantly Cool Quantum Systems Phys. Rev. Lett. 108(12), 120602 (2012). Abstract: We introduce the idea of actually cooling quantum systems by means of incoherent thermal light, hence giving rise to a counterintuitive mechanism of âcooling by heating.â In this effect, the mere incoherent occupation of a quantum mechanical mode serves as a trigger to enhance the coupling between other modes. This notion of effectively rendering states more coherent by driving with incoherent thermal quantum noise is applied here to the optomechanical setting, where this effect occurs most naturally. We discuss two ways of describing this situation, one of them making use of stochastic sampling of Gaussian quantum states with respect to stationary classical stochastic processes. The potential of experimentally demonstrating this counterintuitive effect in optomechanical systems with present technology is sketched. BibTeX:  @article{Mari2012, author = A. Mari and J. Eisert, title = Cooling by Heating: Very Hot Thermal Light Can Significantly Cool Quantum Systems, journal = Phys. Rev. Lett., year = 2012, volume = 108, number = 12, pages = 120602, url = http://link.aps.org/doi/10.1103/PhysRevLett.108.120602, doi = http://dx.doi.org/10.1103/PhysRevLett.108.120602 }  Emma Wikberg, Jonas Larson, Emil J. Bergholtz and Anders Karlhede Fractional domain walls from on-site softening in dipolar bosons Phys. Rev. A 85(3), 033607 (2012). Abstract: We study dipolar bosons in a 1D optical lattice and identify a region in parameter space—strong coupling but relatively weak on-site repulsion—hosting a series of stable charge-density-wave (CDW) states whose low-energy excitations, built from “fractional domain walls,” have remarkable similarities to those of non-Abelian fractional quantum Hall states. Here, a conventional domain wall between translated CDW's may be split by inserting strings of degenerate, but inequivalent, CDW states. Outside these insulating regions, we find numerous supersolids as well as a superfluid regime. The mentioned phases should be accessible experimentally and, in particular, the fractional domain walls can be created in the ground state using single-site addressing, i.e., by locally changing the chemical potential. BibTeX:  @article{Wikberg2012, author = Emma Wikberg, Jonas Larson, Emil J. Bergholtz and Anders Karlhede, title = Fractional domain walls from on-site softening in dipolar bosons, journal = Phys. Rev. A, year = 2012, volume = 85, number = 3, pages = 033607, url = http://link.aps.org/doi/10.1103/PhysRevA.85.033607, doi = http://dx.doi.org/10.1103/PhysRevA.85.033607 }  Niels Bode, Silvia Viola Kusminskiy, Reinhold Egger and Felix von Oppen Current-induced forces in mesoscopic systems: A scattering-matrix approach Beilstein Journal of Nanotechnology 3(), 144-162 (2012). Abstract: Nanoelectromechanical systems are characterized by an intimate connection between electronic and mechanical degrees of freedom. Due to the nanoscopic scale, current flowing through the system noticeably impacts upons the vibrational dynamics of the device, complementing the effect of the vibrational modes on the electronic dynamics. We employ the scattering-matrix approach to quantum transport in order to develop a unified theory of nanoelectromechanical systems out of equilibrium. For a slow mechanical mode the current can be obtained from the Landauer–Büttiker formula in the strictly adiabatic limit. The leading correction to the adiabatic limit reduces to Brouwer’s formula for the current of a quantum pump in the absence of a bias voltage. The principal results of the present paper are the scattering-matrix expressions for the current-induced forces acting on the mechanical degrees of freedom. These forces control the Langevin dynamics of the mechanical modes. Specifically, we derive expressions for the (typically nonconservative) mean force, for the (possibly negative) damping force, an effective “Lorentz” force that exists even for time-reversal-invariant systems, and the fluctuating Langevin force originating from Nyquist and shot noise of the current flow. We apply our general formalism to several simple models that illustrate the peculiar nature of the current-induced forces. Specifically, we find that in out-of-equilibrium situations the current-induced forces can destabilize the mechanical vibrations and cause limit-cycle dynamics. BibTeX:  @article{Bode2012, author = Niels Bode, Silvia Viola Kusminskiy, Reinhold Egger and Felix von Oppen, title = Current-induced forces in mesoscopic systems: A scattering-matrix approach, journal = Beilstein Journal of Nanotechnology, year = 2012, volume = 3, number = , pages = 144-162, url = http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3304326/, doi = http://dx.doi.org/10.3762/bjnano.3.15 }  Francois Crépin, Gergely Zaránd and Pascal Simon Mixtures of ultracold atoms in one-dimensional disordered potentials Phys. Rev. A 85(2), 023625 (2012). Abstract: We study interacting one-dimensional two-component mixtures of cold atoms in a random potential, and extend the results reported earlier [ Phys. Rev. Lett. 105 115301 (2010)]. We construct the phase diagram of a disordered Bose-Fermi mixture as a function of the strength of the Bose-Bose and Bose-Fermi interactions, and the ratio of the bosonic sound velocity and the Fermi velocity. Performing renormalization group and variational calculations, three phases are identified: (i) a fully delocalized two-component Luttinger liquid with superfluid bosons and fermions, (ii) a fully localized phase with both components pinned by disorder, and (iii) an intermediate phase where fermions are localized but bosons are superfluid. Within the variational approach, each phase corresponds to a different level of replica symmetry breaking. In the fully localized phase we find that the bosonic and fermionic localization lengths can largely differ. We also compute the long-wavelength asymptotic behavior of the momentum distribution as well as that of the structure factor of the atoms (both experimentally accessible), and discuss how the three phases can be experimentally distinguished. BibTeX:  @article{PhysRevA.85.023625, author = Francois Crépin, Gergely Zaránd and Pascal Simon, title = Mixtures of ultracold atoms in one-dimensional disordered potentials, journal = Phys. Rev. A, year = 2012, volume = 85, number = 2, pages = 023625, url = http://link.aps.org/doi/10.1103/PhysRevA.85.023625, doi = http://dx.doi.org/10.1103/PhysRevA.85.023625 }  G. Kells, D. Meidan and P. W. Brouwer Low-energy subgap states in multichannel $p$-wave superconducting wires Phys. Rev. B 85(6), 060507 (2012). Abstract: One-dimensional p-wave superconductors are known to harbor Majorana bound states at their ends. Superconducting wires with a finite width W may have fermionic subgap states in addition to possible Majorana end states. While they do not necessarily inhibit the use of Majorana end states for topological computation, these subgap states can obscure the identification of a topological phase through a density-of-states measurement. We present two simple models to describe low-energy fermionic subgap states. If the wire's width W is much smaller than the superconductor coherence length ξ, the relevant subgap states are localized near the ends of the wire and cluster near zero energy, whereas the lowest-energy subgap states are delocalized if W\geq \xi. Notably, the energy of the lowest-lying fermionic subgap state (if present at all) has a maximum for W~\xi. BibTeX:  @article{PhysRevB.85.060507, author = G. Kells, D. Meidan and P. W. Brouwer, title = Low-energy subgap states in multichannel $p$-wave superconducting wires, journal = Phys. Rev. B, year = 2012, volume = 85, number = 6, pages = 060507, url = http://link.aps.org/doi/10.1103/PhysRevB.85.060507, doi = http://dx.doi.org/10.1103/PhysRevB.85.060507 }  Arnau Riera, Christian Gogolin and Jens Eisert Thermalization in Nature and on a Quantum Computer Phys. Rev. Lett. 108(8), 080402 (2012). Abstract: In this work, we show how Gibbs or thermal states appear dynamically in closed quantum many-body systems, building on the program of dynamical typicality. We introduce a novel perturbation theorem for physically relevant weak system-bath couplings that is applicable even in the thermodynamic limit. We identify conditions under which thermalization happens and discuss the underlying physics. Based on these results, we also present a fully general quantum algorithm for preparing Gibbs states on a quantum computer with a certified runtime and error bound. This complements quantum Metropolis algorithms, which are expected to be efficient but have no known runtime estimates and only work for local Hamiltonians. BibTeX:  @article{Riera2012, author = Arnau Riera, Christian Gogolin and Jens Eisert, title = Thermalization in Nature and on a Quantum Computer, journal = Phys. Rev. Lett., year = 2012, volume = 108, number = 8, pages = 080402, url = http://link.aps.org/doi/10.1103/PhysRevLett.108.080402, doi = http://dx.doi.org/10.1103/PhysRevLett.108.080402 }  S. Trotzky, Y-A. Chen, A. Flesch, I. P. McCulloch, U. Schollwock, J. Eisert and I. Bloch Probing the relaxation towards equilibrium in an isolated strongly correlated one-dimensional Bose gas Nat Phys advance online publication(4), -- (2012). Abstract: The problem of how complex quantum systems eventually come to rest lies at the heart of statistical mechanics. The maximum-entropy principle describes which quantum states can be expected in equilibrium, but not how closed quantum many-body systems dynamically equilibrate. Here, we report the experimental observation of the non-equilibrium dynamics of a density wave of ultracold bosonic atoms in an optical lattice in the regime of strong correlations. Using an optical superlattice, we follow its dynamics in terms of quasi-local densities, currents and coherences—all showing a fast relaxation towards equilibrium values. Numerical calculations based on matrix-product states are in an excellent quantitative agreement with the experimental data. The system fulfills the promise of being a dynamical quantum simulator, in that the controlled dynamics runs for longer times than present classical algorithms can keep track of. BibTeX:  @article{Trotzky2012, author = S. Trotzky, Y-A. Chen, A. Flesch, I. P. McCulloch, U. Schollwock, J. Eisert and I. Bloch, title = Probing the relaxation towards equilibrium in an isolated strongly correlated one-dimensional Bose gas, journal = Nat Phys, year = 2012, volume = advance online publication, number = 4, pages = --, url = http://dx.doi.org/10.1038/nphys2232, doi = http://dx.doi.org/10.1038/nphys2232 }  J. Basset, A. Yu. Kasumov, C. P. Moca, G. Zaránd, P. Simon, H. Bouchiat and R. Deblock Measurement of Quantum Noise in a Carbon Nanotube Quantum Dot in the Kondo Regime Phys. Rev. Lett. 108(4), 046802 (2012). Abstract: The current emission noise of a carbon nanotube quantum dot in the Kondo regime is measured at frequencies ν of the order or higher than the frequency associated with the Kondo effect kBTK/h, with TK the Kondo temperature. The carbon nanotube is coupled via an on-chip resonant circuit to a quantum noise detector, a superconductor-insulator-superconductor junction. We find for hν≈kBTK a Kondo effect related singularity at a voltage bias eV≈hν, and a strong reduction of this singularity for hν≈3kBTK, in good agreement with theory. Our experiment constitutes a new original tool for the investigation of the nonequilibrium dynamics of many-body phenomena in nanoscale devices. BibTeX:  @article{PhysRevLett.108.046802, author = J. Basset, A. Yu. Kasumov, C. P. Moca, G. Zaránd, P. Simon, H. Bouchiat and R. Deblock, title = Measurement of Quantum Noise in a Carbon Nanotube Quantum Dot in the Kondo Regime, journal = Phys. Rev. Lett., year = 2012, volume = 108, number = 4, pages = 046802, url = http://link.aps.org/doi/10.1103/PhysRevLett.108.046802, doi = http://dx.doi.org/10.1103/PhysRevLett.108.046802 }  Earl T. Campbell and Jens Eisert Gaussification and Entanglement Distillation of Continuous-Variable Systems: A Unifying Picture Phys. Rev. Lett. 108(2), 020501 (2012). Abstract: Distillation of entanglement using only Gaussian operations is an important primitive in quantum communication, quantum repeater architectures, and distributed quantum computing. Existing distillation protocols for continuous degrees of freedom are only known to converge to a Gaussian state when measurements yield precisely the vacuum outcome. In sharp contrast, non-Gaussian states can be deterministically converted into Gaussian states while preserving their second moments, albeit by usually reducing their degree of entanglement. In this workâbased on a novel instance of a noncommutative central limit theoremâwe introduce a picture general enough to encompass the known protocols leading to Gaussian states, and new classes of protocols including multipartite distillation. This gives the experimental option of balancing the merits of success probability against entanglement produced. BibTeX:  @article{Campbell2012, author = Earl T. Campbell and Jens Eisert, title = Gaussification and Entanglement Distillation of Continuous-Variable Systems: A Unifying Picture, journal = Phys. Rev. Lett., year = 2012, volume = 108, number = 2, pages = 020501, url = http://link.aps.org/doi/10.1103/PhysRevLett.108.020501, doi = http://dx.doi.org/10.1103/PhysRevLett.108.020501 }  Zhao Liu, Emil J. Bergholtz, Heng Fan and Andreas M. Läuchli Edge-mode combinations in the entanglement spectra of non-Abelian fractional quantum Hall states on the torus Phys. Rev. B 85(4), 045119 (2012). Abstract: We present a detailed analysis of bi-partite entanglement in the non-Abelian Moore-Read fractional quantum Hall state of bosons and fermions on the torus. In particular, we show that the entanglement spectra can be decomposed into intricate combinations of different sectors of the conformal field theory describing the edge physics, and that the edge level counting and tower structure can be microscopically understood by considering the vicinity of the thin- torus limit. We also find that the boundary entropy density of the Moore-Read state is markedly higher than in the Laughlin states investigated so far. Despite the torus geometry being somewhat more involved than in the sphere geometry, our analysis and insights may prove useful when adopting entanglement probes to other systems that are more easily studied with periodic boundary conditions, such as fractional Chern insulators and lattice problems in general. BibTeX:  @article{PhysRevB.85.045119, author = Zhao Liu, Emil J. Bergholtz, Heng Fan and Andreas M. Läuchli, title = Edge-mode combinations in the entanglement spectra of non-Abelian fractional quantum Hall states on the torus, journal = Phys. Rev. B, year = 2012, volume = 85, number = 4, pages = 045119, url = http://link.aps.org/doi/10.1103/PhysRevB.85.045119, doi = http://dx.doi.org/10.1103/PhysRevB.85.045119 }  Alessandro Romito, Jason Alicea, Gil Refael and Felix von Oppen Manipulating Majorana fermions using supercurrents Phys. Rev. B 85(2), 020502 (2012). Abstract: Topological insulator edges and spin-orbit-coupled quantum wires in proximity to s-wave superconductors can be tuned through a topological quantum phase transition by a Zeeman field. Here we show that a supercurrent flowing in the s-wave superconductor also drives such a transition. We propose to use this mechanism to generate and manipulate Majorana fermions that localize at domain walls between topological and nontopological regions of an edge or wire. In quantum wires, this method carries the added benefit that a supercurrent reduces the critical Zeeman field at which the topological phase appears. BibTeX:  @article{PhysRevB.85.020502, author = Alessandro Romito, Jason Alicea, Gil Refael and Felix von Oppen, title = Manipulating Majorana fermions using supercurrents, journal = Phys. Rev. B, year = 2012, volume = 85, number = 2, pages = 020502, url = http://link.aps.org/doi/10.1103/PhysRevB.85.020502, doi = http://dx.doi.org/10.1103/PhysRevB.85.020502 }  2011 BibTeX:  @unpublished{20112012,, title = {Preprints}, year = 2011 }  J. Danon and P. W. Brouwer Dephasing in ferromagnetic nanowires: Role of spin waves Phys. Rev. B 84(22), 224433 (2011). Abstract: We present a calculation of the dephasing time of electrons in a ferromagnet relevant for the conductance fluctuations. We focus on the contribution from the interaction with spin waves. Explicit results are presented for quasi-one-dimensional systems. Going beyond previous calculations, we do not restrict ourselves to the limit of a small exchange splitting compared to the electronic elastic scattering time, nor does our calculation rely on the diffusion approximation to describe electronic transport. BibTeX:  @article{PhysRevB.84.224433, author = J. Danon and P. W. Brouwer, title = Dephasing in ferromagnetic nanowires: Role of spin waves, journal = Phys. Rev. B, year = 2011, volume = 84, number = 22, pages = 224433, url = http://link.aps.org/doi/10.1103/PhysRevB.84.224433, doi = http://dx.doi.org/10.1103/PhysRevB.84.224433 }  J. DiGuglielmo, A. Samblowski, B. Hage, C. Pineda, J. Eisert and R. Schnabel Experimental Unconditional Preparation and Detection of a Continuous Bound Entangled State of Light Phys. Rev. Lett. 107(24), 240503 (2011). Abstract: Among the possibly most intriguing aspects of quantum entanglement is that it comes in free and bound instances. The existence of bound entangled states certifies an intrinsic irreversibility of entanglement in nature and suggests a connection with thermodynamics. In this Letter, we present a first unconditional, continuous-variable preparation and detection of a bound entangled state of light. We use convex optimization to identify regimes rendering its bound character well certifiable, and continuously produce a distributed bound entangled state with an extraordinary and unprecedented significance of more than 10 standard deviations away from both separability and distillability. Our results show that the approach chosen allows for the efficient and precise preparation of multimode entangled states of light with various applications in quantum information, quantum state engineering, and high precision metrology. BibTeX:  @article{DiGuglielmo2011, author = J. DiGuglielmo, A. Samblowski, B. Hage, C. Pineda, J. Eisert and R. Schnabel, title = Experimental Unconditional Preparation and Detection of a Continuous Bound Entangled State of Light, journal = Phys. Rev. Lett., year = 2011, volume = 107, number = 24, pages = 240503, url = http://link.aps.org/doi/10.1103/PhysRevLett.107.240503, doi = http://dx.doi.org/10.1103/PhysRevLett.107.240503 }  C. P. Moca, I. Weymann and G. Zarand Theory of ac spin current noise and spin conductance through a quantum dot in the Kondo regime: Equilibrium case Phys. Rev. B 84(23), 235441 (2011). Abstract: We analyze the equilibrium frequency-dependent spin current noise and spin conductance through a quantum dot in the local moment regime. Spin current correlations behave markedly differently from charge correlations. Equilibrium spin correlations are characterized by two universal scaling functions in the absence of an external field: one of them is related to charge correlations, while the other one describes cross-spin correlations. We characterize these functions using a combination of perturbative and nonperturbative methods. We find that at low-temperatures spin cross correlations are suppressed at frequencies below the Kondo scale, TK, and a dynamical spin accumulation resonance is found at the Kondo energy, ω∼TK. At higher temperatures, T>TK, surprising low-frequency anomalies related to overall spin conservation appear in the spin noise and spin conductance, and the Korringa rate is shown to play a distinguished role. The transient spin current response also displays universal and singular properties. BibTeX:  @article{PhysRevB.84.235441, author = C. P. Moca, I. Weymann and G. Zarand, title = Theory of ac spin current noise and spin conductance through a quantum dot in the Kondo regime: Equilibrium case, journal = Phys. Rev. B, year = 2011, volume = 84, number = 23, pages = 235441, url = http://link.aps.org/doi/10.1103/PhysRevB.84.235441, doi = http://dx.doi.org/10.1103/PhysRevB.84.235441 }  Piet W. Brouwer, Mathias Duckheim, Alessandro Romito and Felix von Oppen Probability Distribution of Majorana End-State Energies in Disordered Wires Phys. Rev. Lett. 107(19), 196804 (2011). Abstract: One-dimensional topological superconductors harbor Majorana bound states at their ends. For superconducting wires of finite length L, these Majorana states combine into fermionic excitations with an energy ε0 that is exponentially small in L. Weak disorder leaves the energy splitting exponentially small, but affects its typical value and causes large sample-to-sample fluctuations. We show that the probability distribution of ε0 is log normal in the limit of large L, whereas the distribution of the lowest-lying bulk energy level ε1 has an algebraic tail at small ε1. Our findings have implications for the speed at which a topological quantum computer can be operated. BibTeX:  @article{Brouwer2011b, author = Piet W. Brouwer, Mathias Duckheim, Alessandro Romito and Felix von Oppen, title = Probability Distribution of Majorana End-State Energies in Disordered Wires, journal = Phys. Rev. Lett., year = 2011, volume = 107, number = 19, pages = 196804, url = http://prl.aps.org/abstract/PRL/v107/i19/e196804, doi = http://dx.doi.org/10.1103/PhysRevLett.107.196804 }  B. Horváth, B. Lazarovits and G. Zarand Fluctuation-exchange approximation theory of the nonequilibrium singlet-triplet transition Phys. Rev. B 84(20), 205117 (2011). Abstract: As a continuation of a previous work [ B. Horváth et al. Phys. Rev. B 82 165129 (2010)], here we extend the so-called fluctuation exchange approximation (FLEX) to study the nonequilibrium singlet-triplet transition. We show that, while being relatively fast and a conserving approximation, FLEX is able to recover all important features of the transition, including the evolution of the linear conductance throughout the transition, the two-stage Kondo effect on the triplet side, and the gradual opening of the singlet-triplet gap on the triplet side of the transition. A comparison with numerical renormalization-group calculations also shows that FLEX captures rather well the width of the Kondo resonance. FLEX thus offers a viable route to describe correlated multilevel systems under nonequilibrium conditions, and in its rather general form, as formulated here, it could find a broad application in molecular electronics calculations. BibTeX:  @article{PhysRevB.84.205117, author = B. Horváth, B. Lazarovits and G. Zarand, title = Fluctuation-exchange approximation theory of the nonequilibrium singlet-triplet transition, journal = Phys. Rev. B, year = 2011, volume = 84, number = 20, pages = 205117, url = http://link.aps.org/doi/10.1103/PhysRevB.84.205117, doi = http://dx.doi.org/10.1103/PhysRevB.84.205117 }  Liang Jiang, David Pekker, Jason Alicea, Gil Refael, Yuval Oreg and Felix von Oppen Unconventional Josephson Signatures of Majorana Bound States Phys. Rev. Lett. 107(23), 236401 (2011). Abstract: A junction between two topological superconductors containing a pair of Majorana fermions exhibits a “fractional” Josephson effect, 4π periodic in the superconductors’ phase difference. An additional fractional Josephson effect, however, arises when the Majorana fermions are spatially separated by a superconducting barrier. This new term gives rise to a set of Shapiro steps which are essentially absent without Majorana modes and therefore provides a unique signature for these exotic states. BibTeX:  @article{PhysRevLett.107.236401, author = Liang Jiang, David Pekker, Jason Alicea, Gil Refael, Yuval Oreg and Felix von Oppen, title = Unconventional Josephson Signatures of Majorana Bound States, journal = Phys. Rev. Lett., year = 2011, volume = 107, number = 23, pages = 236401, url = http://link.aps.org/doi/10.1103/PhysRevLett.107.236401, doi = http://dx.doi.org/10.1103/PhysRevLett.107.236401 }  Dganit Meidan, Tobias Micklitz and Piet W. Brouwer Topological classification of adiabatic processes Phys. Rev. B. 84(19), 195410 (2011). Abstract: Certain band insulators allow for the adiabatic pumping of quantized charge or spin for special time dependences of the Hamiltonian. These “topological pumps” are closely related to two-dimensional topological insulating phases of matter upon rolling the insulator up to a cylinder and threading it with a time-dependent flux. In this paper we extend the classification of topological pumps to the Wigner-Dyson and chiral classes, coupled to multichannel leads. The topological index distinguishing different topological classes is formulated in terms of the scattering matrix of the system. We argue that similar to topologically nontrivial insulators, topological pumps are characterized by the appearance of protected gapless end states during the course of a pumping cycle. We show that this property allows for the pumping of quantized charge or spin in the weak-coupling limit. Our results may also be applied to two-dimensional topological insulators, where they give a physically transparent interpretation of the topologically nontrivial phases in terms of scattering matrices. BibTeX:  @article{PhysRevB.84.195410, author = Dganit Meidan, Tobias Micklitz and Piet W. Brouwer, title = Topological classification of adiabatic processes, journal = Phys. Rev. B., year = 2011, volume = 84, number = 19, pages = 195410, url = http://prb.aps.org/abstract/PRB/v84/i19/e195410, doi = http://dx.doi.org/10.1103/PhysRevB.84.195410 }  Dganit Meidan, Bernd Rosenow, Yuval Oreg and Gil Refael Gapless Excitations in Strongly Fluctuating Superconducting Wires Phys. Rev. Lett. 107(22), 227004 (2011). Abstract: We study the low-temperature tunneling density of states of thin wires where superconductivity is destroyed through quantum phase-slip proliferation. Although this regime is believed to behave as an insulator, we show that for a large temperature range this phase is characterized by a conductivity falling off at most linearly with temperature, and has a gapless excitation spectrum. This novel conducting phase results from electron-electron interaction induced pair breaking. Also, it may help clarify the low-temperature metallic features found in films and wires whose bulk realization is superconducting. BibTeX:  @article{PhysRevLett.107.227004, author = Dganit Meidan, Bernd Rosenow, Yuval Oreg and Gil Refael, title = Gapless Excitations in Strongly Fluctuating Superconducting Wires, journal = Phys. Rev. Lett., year = 2011, volume = 107, number = 22, pages = 227004, url = http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.107.227004, doi = http://dx.doi.org/10.1103/PhysRevLett.107.227004 }  and L. R. Schreiber AND F. R. Braakman AND T. Meunier AND V. Calado AND J. Danon AND J. M. Taylor AND W. Wegscheider AND L. M. K. Vandersypen Coupling artificial molecular spin states by photon-assisted tunnelling Nat. Comm. 2(), 556 (2011). Abstract: Artificial molecules containing just one or two electrons provide a powerful platform for studies of orbital and spin quantum dynamics in nanoscale devices. A well-known example of these dynamics is tunnelling of electrons between two coupled quantum dots triggered by microwave irradiation. So far, these tunnelling processes have been treated as electric-dipole-allowed spin-conserving events. Here we report that microwaves can also excite tunnelling transitions between states with different spin. We show that the dominant mechanism responsible for violation of spin conservation is the spin–orbit interaction. These transitions make it possible to perform detailed microwave spectroscopy of the molecular spin states of an artificial hydrogen molecule and open up the possibility of realizing full quantum control of a two-spin system through microwave excitation. BibTeX:  @article{Schreiber2011, author = and L. R. Schreiber AND F. R. Braakman AND T. Meunier AND V. Calado AND J. Danon AND J. M. Taylor AND W. Wegscheider AND L. M. K. Vandersypen, title = Coupling artificial molecular spin states by photon-assisted tunnelling, journal = Nat. Comm., year = 2011, volume = 2, number = , pages = 556, url = http://www.nature.com/ncomms/journal/v2/n11/full/ncomms1561.html, doi = http://dx.doi.org/10.1038/ncomms1561 }  Piet W. Brouwer, Mathias Duckheim, Alessandro Romito and Felix von Oppen Topological superconducting phases in disordered quantum wires with strong spin-orbit coupling Phys. Rev. B 84(14), 144526 (2011). Abstract: Zeeman fields can drive semiconductor quantum wires with strong spin-orbit coupling and in proximity to s-wave superconductors into a topological phase which supports end Majorana fermions and offers an attractive platform for realizing topological quantum information processing. Here, we investigate how potential disorder affects the topological phase by a combination of analytical and numerical approaches. Most prominently, we find that the robustness of the topological phase against disorder depends sensitively and nonmonotonously on the Zeeman field applied to the wire. BibTeX:  @article{PhysRevB.84.144526, author = Piet W. Brouwer, Mathias Duckheim, Alessandro Romito and Felix von Oppen, title = Topological superconducting phases in disordered quantum wires with strong spin-orbit coupling, journal = Phys. Rev. B, year = 2011, volume = 84, number = 14, pages = 144526, url = http://link.aps.org/doi/10.1103/PhysRevB.84.144526, doi = http://dx.doi.org/10.1103/PhysRevB.84.144526 }  Torsten Karzig, Gil Refael, Leonid I. Glazman and Felix von Oppen Energy Partitioning of Tunneling Currents into Luttinger Liquids Phys. Rev. Lett. 107(17), 176403 (2011). Abstract: Tunneling of electrons of definite chirality into a quantum wire creates counterpropagating excitations, carrying both charge and energy. We find that the partitioning of energy is qualitatively different from that of charge. The partition ratio of energy depends on the excess energy of the tunneling electrons (controlled by the applied bias) and on the interaction strength within the wire (characterized by the Luttinger-liquid parameter κ), while the partitioning of charge is fully determined by κ. Moreover, unlike for charge currents, the partitioning of energy current should manifest itself in dc experiments on wires contacted by conventional (Fermi-liquid) leads. BibTeX:  @article{Karzig2011, author = Torsten Karzig, Gil Refael, Leonid I. Glazman and Felix von Oppen, title = Energy Partitioning of Tunneling Currents into Luttinger Liquids, journal = Phys. Rev. Lett., year = 2011, volume = 107, number = 17, pages = 176403, url = http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.107.176403, doi = http://dx.doi.org/10.1103/PhysRevLett.107.176403 }  Graham Kells, J. Kailasvuori, J. K. Slingerland and J. Vala Kaleidoscope of topological phases with multiple Majorana species New J. Phys. 13(9), 095014 (2011). Abstract: Exactly solvable lattice models for spins and non-interacting fermions provide fascinating examples of topological phases, some of them exhibiting the localized Majorana fermions that feature in proposals for topological quantum computing. The Chern invariant ν is an important characterization of such phases. Here we look at the square–octagon variant of Kitaev's honeycomb model. It maps to spinful paired fermions and enjoys a rich phase diagram featuring distinct Abelian and non-Abelian phases with ν = 0,±1,±2,±3 and ±4. The ν = ±1 and ν = ±3 phases all support localized Majorana modes and are examples of Ising and SU(2)2 anyon theories, respectively. BibTeX:  @article{NewJPhys13.095014, author = Graham Kells, J. Kailasvuori, J. K. Slingerland and J. Vala, title = Kaleidoscope of topological phases with multiple Majorana species, journal = New J. Phys., year = 2011, volume = 13, number = 9, pages = 095014, url = http://iopscience.iop.org/1367-2630/13/9/095014/, doi = http://dx.doi.org/10.1088/1367-2630/13/9/095014 }  M. Kliesch, T. Barthel, C. Gogolin, M. Kastoryano and J. Eisert Dissipative Quantum Church-Turing Theorem Phys. Rev. Lett. 107(12), 120501 (2011). Abstract: We show that the time evolution of an open quantum system, described by a possibly time dependent Liouvillian, can be simulated by a unitary quantum circuit of a size scaling polynomially in the simulation time and the size of the system. An immediate consequence is that dissipative quantum computing is no more powerful than the unitary circuit model. Our result can be seen as a dissipative Church-Turing theorem, since it implies that under natural assumptions, such as weak coupling to an environment, the dynamics of an open quantum system can be simulated efficiently on a quantum computer. Formally, we introduce a Trotter decomposition for Liouvillian dynamics and give explicit error bounds. This constitutes a practical tool for numerical simulations, e.g., using matrix-product operators. We also demonstrate that most quantum states cannot be prepared efficiently. BibTeX:  @article{Kliesch2011, author = M. Kliesch, T. Barthel, C. Gogolin, M. Kastoryano and J. Eisert, title = Dissipative Quantum Church-Turing Theorem, journal = Phys. Rev. Lett., year = 2011, volume = 107, number = 12, pages = 120501, url = http://link.aps.org/doi/10.1103/PhysRevLett.107.120501, doi = http://dx.doi.org/10.1103/PhysRevLett.107.120501 }  Alex Levchenko, Tobias Micklitz, Zoran Ristivojevic and K. A. Matveev Interaction effects on thermal transport in quantum wires Phys. Rev. B 84(11), 115447 (2011). Abstract: We develop a theory of thermal transport of weakly interacting electrons in quantum wires. Unlike higher dimensional systems, energy relaxation of one-dimensional electron gas requires three-particle collisions. The fastest relaxation is provided by the intra-branch scattering of co-moving electrons which establishes a partially-equilibrated form of the distribution function. Thermal conductance is governed by the slower inter-branch processes which enable energy exchange between counter-propagating particles. We derive an analytic expression for the thermal conductance of interacting electrons valid at arbitrary relation between the wire length and electron thermalization length. We find that in sufficiently long wires interaction-induced correction to thermal conductance saturates to an interaction-independent value. BibTeX:  @article{Levchenko2011, author = Alex Levchenko, Tobias Micklitz, Zoran Ristivojevic and K. A. Matveev, title = Interaction effects on thermal transport in quantum wires, journal = Phys. Rev. B, year = 2011, volume = 84, number = 11, pages = 115447, url = http://link.aps.org/doi/10.1103/PhysRevB.84.115447, doi = http://dx.doi.org/10.1103/PhysRevB.84.115447 }  Martin Schneider and Piet W. Brouwer Resonant scattering in graphene with a gate-defined chaotic quantum dot Phys. Rev. B 84(11), 115440 (2011). Abstract: We investigate the conductance of an undoped graphene sheet with two metallic contacts and an electrostatically gated island (quantum dot) between the contacts. Our analysis is based on the matrix Green function formalism, which was recently adapted to graphene by Titov et al. [Phys. Rev. Lett. 104 076802 (2010)]. We find pronounced differences between the case of a stadium-shaped dot (which has chaotic classical dynamics) and a disk-shaped dot (which has integrable classical dynamics) in the limit that the dot size is small in comparison to the distance between the contacts. In particular, for the stadium-shaped dot the two-terminal conductance shows Fano resonances as a function of the gate voltage, which cross over to Breit-Wigner resonances only in the limit of completely separated resonances, whereas for a disk-shaped dot sharp Breit-Wigner resonances resulting from higher angular momentum remain present throughout. BibTeX:  @article{Schneider2011a, author = Martin Schneider and Piet W. Brouwer, title = Resonant scattering in graphene with a gate-defined chaotic quantum dot, journal = Phys. Rev. B, year = 2011, volume = 84, number = 11, pages = 115440, url = http://journals.aps.org/prb/abstract/10.1103/PhysRevB.84.115440, doi = http://dx.doi.org/10.1103/PhysRevB.84.115440 }  M. Gradhand, D. V. Fedorov, F. Pientka, P. Zahn, I. Mertig and B. L. Györffy Calculating the Berry curvature of Bloch electrons using the KKR method Phys. Rev. B 84(7), 075113 (2011). Abstract: We propose and implement a particularly effective method for calculating the Berry curvature arising from adiabatic evolution of Bloch states in {\bf k} space. The method exploits a unique feature of the Korringa-Kohn-Rostoker (KKR) approach to solve the Schr\"odinger or Dirac equations. Namely, it is based on the observation that in the KKR theory the wave vector {\bf k} enters the calculation only via the structure constants which reflect the geometry of the lattice but not the crystal potential. For both the Abelian and non-Abelian Berry curvature we derive an analytic formula whose evaluation does not require any numerical differentiation with respect to {\bf k}. We present explicit calculations for Al, Cu, Au, and Pt bulk crystals. BibTeX:  @article{PhysRevB.84.075113, author = M. Gradhand, D. V. Fedorov, F. Pientka, P. Zahn, I. Mertig and B. L. Györffy, title = Calculating the Berry curvature of Bloch electrons using the KKR method, journal = Phys. Rev. B, year = 2011, volume = 84, number = 7, pages = 075113, url = http://link.aps.org/doi/10.1103/PhysRevB.84.075113, doi = http://dx.doi.org/10.1103/PhysRevB.84.075113 }  B. Horovitz, P. Le Doussal and G. Zarand Zero-temperature geometric spin dephasing on a ring in the presence of an Ohmic environment EPL (Europhysics Letters) 95(5), 57004 (2011). Abstract: We study zero-temperature spin dynamics of a particle confined to a ring in the presence of spin-orbit coupling and Ohmic electromagnetic fluctuations. We show that the dynamics of the angular position Î¸( t ) are decoupled from the spin dynamics and that the latter is mapped to certain correlations of a spinless particle. We find that the spin correlations in the z -direction (perpendicular to the ring) are finite at long times, i.e. do not dephase. The parallel (in-plane) components for spin #"IMG"# [http://ej.iop.org/images/0295-5075/95/5/57004/epl13758ieqn1.gif] {\mbox{\small$\frac{1}{2}$}} do not dephase at weak dissipation but they probably decay as a power law with time at strong dissipation. BibTeX:  @article{0295-5075-95-5-57004, author = B. Horovitz, P. Le Doussal and G. Zarand, title = Zero-temperature geometric spin dephasing on a ring in the presence of an Ohmic environment, journal = EPL (Europhysics Letters), year = 2011, volume = 95, number = 5, pages = 57004, url = http://stacks.iop.org/0295-5075/95/i=5/a=57004, doi = http://dx.doi.org/10.1209/0295-5075/95/57004 }  Matthias C. Lüffe, Janik Kailasvuori and Tamara S. Nunner Relaxation mechanisms of the persistent spin helix Phys. Rev. B 84(7), 075326 (2011). Abstract: We study the lifetime of the persistent spin helix in semiconductor quantum wells with equal Rashba and linear Dresselhaus spin-orbit coupling strengths. In order to address the temperature dependence of the relevant spin relaxation mechanisms we derive and solve a semiclassical spin diffusion equation taking into account the effects of spin-dependent impurity scattering, cubic Dresselhaus spin-orbit coupling and electron-electron interactions. For the experimentally relevant regime we find that the lifetime of the persistent spin helix is mainly determined by the interplay of cubic Dresselhaus spin-orbit interaction and electron-electron interactions. We propose that even longer lifetimes can be achieved by generating a spatially damped spin profile instead of the persistent spin helix state. BibTeX:  @article{PhysRevB.84.075326, author = Matthias C. Lüffe, Janik Kailasvuori and Tamara S. Nunner, title = Relaxation mechanisms of the persistent spin helix, journal = Phys. Rev. B, year = 2011, volume = 84, number = 7, pages = 075326, url = http://link.aps.org/doi/10.1103/PhysRevB.84.075326, doi = http://dx.doi.org/10.1103/PhysRevB.84.075326 }  Dganit Meidan, Tobias Micklitz and Piet W. Brouwer Topological classification of interaction-driven spin pumps Phys. Rev. B 84(7), 075325 (2011). Abstract: When adiabatically varied in time, certain one-dimensional band insulators allow for the quantized noiseless pumping of spin even in the presence of strong spin-orbit scattering. These spin pumps are closely related to the quantum spin Hall system, and their properties are protected by a time-reversal restriction on the pumping cycle. In this paper we study pumps formed of one-dimensional insulators with a time-reversal restriction on the pumping cycle and a bulk energy gap which arises due to interactions. We find that the correlated gapped phase can lead to novel pumping properties. In particular, systems with d different ground states can give rise to d+1 different classes of spin pumps, including a trivial class which does not pump quantized spin and d nontrivial classes allowing for the pumping of quantized spin $\hbar/n$ on average per cycle, where $1\leq n \leq d$ . We discuss an example of a spin pump that transfers an average of spin $\hbar /2$ without transferring charge. BibTeX:  @article{PhysRevB.84.075325, author = Dganit Meidan, Tobias Micklitz and Piet W. Brouwer, title = Topological classification of interaction-driven spin pumps, journal = Phys. Rev. B, year = 2011, volume = 84, number = 7, pages = 075325, url = http://journals.aps.org/prb/abstract/10.1103/PhysRevB.84.075325, doi = http://dx.doi.org/10.1103/PhysRevB.84.075325 }  Martin Schneider, Dmitry A. Bagrets and Alexander D. Mirlin Theory of the nonequilibrium electronic Mach-Zehnder interferometer Phys. Rev. B 84(7), 075401 (2011). Abstract: We develop a theoretical description of interaction-induced phenomena in an electronic Mach-Zehnder interferometer formed by integer quantum Hall edge states (with ν=1 and 2 channels) out of equilibrium. Using the nonequilibrium functional bosonization framework, we derive an effective action which contains all the relevant physics of the problem. We apply the theory to the model of a short-range interaction and to a more realistic case of long-range Coulomb interaction. The theory takes into account interaction-induced effects of dispersion of plasmons, charging, and decoherence. In the case of long-range interaction we find a good agreement between our theoretical results for the visibility of Aharonov-Bohm oscillations and experimental data. BibTeX:  @article{Schneider2011, author = Martin Schneider, Dmitry A. Bagrets and Alexander D. Mirlin, title = Theory of the nonequilibrium electronic Mach-Zehnder interferometer, journal = Phys. Rev. B, year = 2011, volume = 84, number = 7, pages = 075401, url = http://journals.aps.org/prb/abstract/10.1103/PhysRevB.84.075401, doi = http://dx.doi.org/10.1103/PhysRevB.84.075401 }  Niels Bode, Silvia Viola Kusminskiy, Reinhold Egger and Felix von Oppen Scattering Theory of Current-Induced Forces in Mesoscopic Systems Phys. Rev. Lett. 107(3), 036804 (2011). Abstract: We develop a scattering theory of current-induced forces exerted by the conduction electrons of a general mesoscopic conductor on slow “mechanical” degrees of freedom. Our theory describes the current-induced forces both in and out of equilibrium in terms of the scattering matrix of the phase-coherent conductor. Under general nonequilibrium conditions, the resulting mechanical Langevin dynamics is subject to both nonconservative and velocity-dependent Lorentz-like forces, in addition to (possibly negative) friction. We illustrate our results with a two-mode model inspired by hydrogen molecules in a break junction which exhibits limit-cycle dynamics of the mechanical modes. BibTeX:  @article{PhysRevLett.107.036804, author = Niels Bode, Silvia Viola Kusminskiy, Reinhold Egger and Felix von Oppen, title = Scattering Theory of Current-Induced Forces in Mesoscopic Systems, journal = Phys. Rev. Lett., year = 2011, volume = 107, number = 3, pages = 036804, url = http://link.aps.org/doi/10.1103/PhysRevLett.107.036804, doi = http://dx.doi.org/10.1103/PhysRevLett.107.036804 }  Tamara S. Nunner and Felix von Oppen Quasilinear spin-voltage profiles in spin thermoelectrics Phys. Rev. B 84(2), 020405 (2011). Abstract: Recent experiments show that spin thermoelectrics is a promising approach to generate spin voltages. While spin chemical potentials are often limited to a surface layer of the order of the spin-diffusion length, we show that thermoelectrically induced spin chemical potentials can extend much further in itinerant ferromagnets with paramagnetic impurities. In some cases, conservation laws, e.g., for a combination of spin and heat currents, give rise to a linear spin-voltage profile. More generally, we find quasilinear profiles involving a spin thermoelectric length scale which far exceeds the spin-diffusion length. BibTeX:  @article{PhysRevB.84.020405, author = Tamara S. Nunner and Felix von Oppen, title = Quasilinear spin-voltage profiles in spin thermoelectrics, journal = Phys. Rev. B, year = 2011, volume = 84, number = 2, pages = 020405, url = http://link.aps.org/doi/10.1103/PhysRevB.84.020405, doi = http://dx.doi.org/10.1103/PhysRevB.84.020405 }  F. G. S. L. Brandão, J. Eisert, M. Horodecki and D. Yang Entangled Inputs Cannot Make Imperfect Quantum Channels Perfect Phys. Rev. Lett. 106(23), 230502 (2011). Abstract: Entangled inputs can enhance the capacity of quantum channels, this being one of the consequences of the celebrated result showing the nonadditivity of several quantities relevant for quantum information science. In this work, we answer the converse question (whether entangled inputs can ever render noisy quantum channels to have maximum capacity) to the negative: No sophisticated entangled input of any quantum channel can ever enhance the capacity to the maximum possible value, a result that holds true for all channels both for the classical as well as the quantum capacity. This result can hence be seen as a bound as to how ânonadditive quantum information can be.â As a main result, we find first practical and remarkably simple computable single-shot bounds to capacities, related to entanglement measures. As examples, we discuss the qubit amplitude damping and identify the first meaningful bound for its classical capacity. BibTeX:  @article{Brand2011, author = F. G. S. L. Brandão, J. Eisert, M. Horodecki and D. Yang, title = Entangled Inputs Cannot Make Imperfect Quantum Channels Perfect, journal = Phys. Rev. Lett., year = 2011, volume = 106, number = 23, pages = 230502, url = http://link.aps.org/doi/10.1103/PhysRevLett.106.230502, doi = http://dx.doi.org/10.1103/PhysRevLett.106.230502 }  J. Danon and Yu. V. Nazarov Nuclear spin pumping and electron spin susceptibilities Phys. Rev. B 83(24), 245306 (2011). Abstract: In this work we present a new formalism to evaluate the nuclear spin dynamics driven by hyperfine interaction with nonequilibrium electron spins. To describe the dynamics up to second order in the hyperfine coupling it suffices to evaluate the susceptibility and fluctuations of the electron spin. Our approach does not rely on a separation of electronic energy scales or the specific choice of electronic basis states, thereby overcoming practical problems which may arise in certain limits when using a more traditional formalism based on rate equations. BibTeX:  @article{PhysRevB.83.245306, author = J. Danon and Yu. V. Nazarov, title = Nuclear spin pumping and electron spin susceptibilities, journal = Phys. Rev. B, year = 2011, volume = 83, number = 24, pages = 245306, url = http://link.aps.org/doi/10.1103/PhysRevB.83.245306, doi = http://dx.doi.org/10.1103/PhysRevB.83.245306 }  Tobias Micklitz and Alex Levchenko Thermalization of Nonequilibrium Electrons in Quantum Wires Phys. Rev. Lett. 106(19), 196402 (2011). Abstract: We study the problem of energy relaxation in a one-dimensional electron system. The leading thermalization mechanism is due to three-particle collisions. We show that for the case of spinless electrons in a single channel quantum wire the corresponding collision integral can be transformed into an exactly solvable problem. The latter is known as the Schr\"odinger equation for a quantum particle moving in a P\"oschl-Teller potential. The spectrum for the resulting eigenvalue problem allows for bound state solutions, which can be identified with the zero-modes of the collision integral, and a continuum of propagating modes, which are separated by a gap from the bound states. The inverse gap gives the time scale at which counter-propagating electrons thermalize. BibTeX:  @article{Micklitz2011, author = Tobias Micklitz and Alex Levchenko, title = Thermalization of Nonequilibrium Electrons in Quantum Wires, journal = Phys. Rev. Lett., year = 2011, volume = 106, number = 19, pages = 196402, url = http://link.aps.org/doi/10.1103/PhysRevLett.106.196402, doi = http://dx.doi.org/10.1103/PhysRevLett.106.196402 }  Mathias Duckheim and Piet W. Brouwer Andreev reflection from noncentrosymmetric superconductors and Majorana bound-state generation in half-metallic ferromagnets Phys. Rev. B 83(5), 054513 (2011). Abstract: We study Andreev reflection at an interface between a half metal and a superconductor with spin-orbit interaction. While the absence of minority carriers in the half metal makes singlet Andreev reflection impossible, the spin-orbit interaction gives rise to triplet Andreev reflection (i.e., the reflection of a majority electron into a majority hole or vice versa). As an application of our calculation, we consider a thin half-metal film or wire laterally attached to a superconducting contact. If the half metal is disorder free, an excitation gap is opened that is proportional to the spin-orbit interaction strength in the superconductor. For electrons with energy below this gap a lateral half-metal-superconductor contact becomes a perfect triplet Andreev reflector. We show that the system supports localized Majorana end states in this limit. BibTeX:  @article{Duckheim2011, author = Mathias Duckheim and Piet W. Brouwer, title = Andreev reflection from noncentrosymmetric superconductors and Majorana bound-state generation in half-metallic ferromagnets, journal = Phys. Rev. B, year = 2011, volume = 83, number = 5, pages = 054513, url = http://journals.aps.org/prb/abstract/10.1103/PhysRevB.83.054513, doi = http://dx.doi.org/10.1103/PhysRevB.83.054513 }  Oded Zilberberg, Alessandro Romito and Yuval Gefen Charge Sensing Amplification via Weak Values Measurement Phys. Rev. Lett. 106(8), 080405 (2011). Abstract: A protocol employing weak values (WVs) to obtain ultrasensitive amplification of weak signals in the context of a solid-state setup is proposed. We consider an Aharonov-Bohm interferometer where both the orbital and the spin degrees of freedom are weakly affected by the presence of an external charge to be detected. The interplay between the spin and the orbital WVs leads to a significant amplification even in the presence of finite temperature, voltage, and external noise. BibTeX:  @article{PhysRevLett.106.080405, author = Oded Zilberberg, Alessandro Romito and Yuval Gefen, title = Charge Sensing Amplification via Weak Values Measurement, journal = Phys. Rev. Lett., year = 2011, volume = 106, number = 8, pages = 080405, url = http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.106.080405, doi = http://dx.doi.org/10.1103/PhysRevLett.106.080405 }  Jason Alicea, Yuval Oreg, Gil Refael, Felix von Oppen and Matthew P. A. Fisher Non-Abelian statistics and topological quantum information processing in 1D wire networks Nature Physics 7(5), 412 (2011). Abstract: The synthesis of a quantum computer remains an ongoing challenge in modern physics. Whereas decoherence stymies most approaches, topological quantum computation schemes evade decoherence at the hardware level by storing quantum information non-locally. Here we establish that a key operation--braiding of non-Abelian anyons--can be implemented using one-dimensional semiconducting wires. Such wires can be driven into a topological phase supporting long-sought particles known as Majorana fermions that can encode topological qubits. We show that in wire networks, Majorana fermions can be meaningfully braided by simply adjusting gate voltages, and that they exhibit non-Abelian statistics like vortices in a p+ip superconductor.We propose experimental set-ups that enable probing of the Majorana fusion rules and the efficient exchange of arbitrary numbers of Majorana fermions. This work should open a new direction in topological quantum computation that benefits from physical transparency and experimental feasibility. BibTeX:  @article{Alicea2011, author = Jason Alicea, Yuval Oreg, Gil Refael, Felix von Oppen and Matthew P. A. Fisher, title = Non-Abelian statistics and topological quantum information processing in 1D wire networks, journal = Nature Physics, year = 2011, volume = 7, number = 5, pages = 412, url = http://www.nature.com/nphys/journal/v7/n5/full/nphys1915.html, doi = http://dx.doi.org/10.1038/nphys1915 }  Joern N. Kupferschmidt and Piet W. Brouwer Andreev reflection at half-metal/superconductor interfaces with nonuniform magnetization Phys. Rev. B 83(1), 014512 (2011). Abstract: Andreev reflection at the interface between a half-metallic ferromagnet and a spin-singlet superconductor is possible only if it is accompanied by a spin flip. Here we calculate the Andreev reflection amplitudes for the case where the spin flip originates from a spatially nonuniform magnetization direction in the half-metal. We calculate both the microscopic Andreev reflection amplitude for a single reflection event and an effective Andreev reflection amplitude describing the effect of multiple Andreev reflections in a ballistic thin film geometry. It is shown that the angle and energy dependence of the Andreev reflection amplitude strongly depends on the orientation of the gradient of the magnetization with respect to the interface. We calculate the resulting effects on the subgap conductance as well as Josephson current for a few exemplary cases. Establishing a connection between the scattering approach employed here and earlier work that employs the quasiclassical formalism, we connect the symmetry properties of the Andreev reflection amplitudes to the symmetry properties of the anomalous Green function in the half-metal. BibTeX:  @article{PhysRevB.83.014512, author = Joern N. Kupferschmidt and Piet W. Brouwer, title = Andreev reflection at half-metal/superconductor interfaces with nonuniform magnetization, journal = Phys. Rev. B, year = 2011, volume = 83, number = 1, pages = 014512, url = http://journals.aps.org/prb/abstract/10.1103/PhysRevB.83.014512, doi = http://dx.doi.org/10.1103/PhysRevB.83.014512 }  A. Levchenko, Z. Ristivojevic and T. Micklitz Interaction-induced corrections to conductance and thermopower in quantum wires Phys. Rev. B 83(4), 041303 (2011). Abstract: We develop transport theory of spin-polarized electrons in one-dimensional quantum wires. Effects of interaction manifest at the level of three-particle collisions due to the severe constraints imposed by the conservation laws on the two-body processes. Interaction induced correction to conductance and thermopower relies on the scattering processes that change number of right- and left-moving electrons. The latter requires transition at the bottom of the band which is exponentially suppressed at low temperatures. Conversely, correction to thermal conductance is governed by the processes where all particles lie near the Fermi points and thus exhibits only power-law dependence on temperature. Our theory is based on the scattering approach that is beyond the Luttinger-liquid limit. We also emphasize the crucial role of the exchange terms in the three-particle scattering amplitude. BibTeX:  @article{Levchenko2011a, author = A. Levchenko, Z. Ristivojevic and T. Micklitz, title = Interaction-induced corrections to conductance and thermopower in quantum wires, journal = Phys. Rev. B, year = 2011, volume = 83, number = 4, pages = 041303, url = http://journals.aps.org/prb/abstract/10.1103/PhysRevB.83.041303, doi = http://dx.doi.org/10.1103/PhysRevB.83.041303 }  Guillaume Weick, Felix von Oppen and Fabio Pistolesi Euler buckling instability and enhanced current blockade in suspended single-electron transistors Phys. Rev. B 83(3), 035420 (2011). Abstract: Single-electron transistors embedded in a suspended nanobeam or carbon nanotube may exhibit effects originating from the coupling of the electronic degrees of freedom to the mechanical oscillations of the suspended structure. Here, we investigate theoretically the consequences of a capacitive electromechanical interaction when the supporting beam is brought close to the Euler buckling instability by a lateral compressive strain. Our central result is that the low-bias current blockade, originating from the electromechanical coupling for the classical resonator, is strongly enhanced near the Euler instability. We predict that the bias voltage below which transport is blocked increases by orders of magnitude for typical parameters. This mechanism may make the otherwise elusive classical current blockade experimentally observable. BibTeX:  @article{PhysRevB.83.035420, author = Guillaume Weick, Felix von Oppen and Fabio Pistolesi, title = Euler buckling instability and enhanced current blockade in suspended single-electron transistors, journal = Phys. Rev. B, year = 2011, volume = 83, number = 3, pages = 035420, url = http://link.aps.org/doi/10.1103/PhysRevB.83.035420, doi = http://dx.doi.org/10.1103/PhysRevB.83.035420 }  2010 BibTeX:  @unpublished{20102011,, title = {Preprints}, year = 2010 }  I. Adagideli, Ph. Jacquod, M. Scheid, M. Duckheim, D. Loss and K. Richter Geometric Correlations and Breakdown of Mesoscopic Universality in Spin Transport Phys. Rev. Lett. 105(24), 246807 (2010). Abstract: We construct a unified semiclassical theory of charge and spin transport in chaotic ballistic and disordered diffusive mesoscopic systems with spin-orbit interaction. Neglecting dynamic effects of spin-orbit interaction, we reproduce the random matrix theory results that the spin conductance fluctuates universally around zero average. Incorporating these effects in the theory, we show that geometric correlations generate finite average spin conductances, but that they do not affect the charge conductance to leading order. The theory, which is confirmed by numerical transport calculations, allows us to investigate the entire range from the weak to the previously unexplored strong spin-orbit regime, where the spin rotation time is shorter than the momentum relaxation time. BibTeX:  @article{Adagideli2010, author = I. Adagideli, Ph. Jacquod, M. Scheid, M. Duckheim, D. Loss and K. Richter, title = Geometric Correlations and Breakdown of Mesoscopic Universality in Spin Transport, journal = Phys. Rev. Lett., year = 2010, volume = 105, number = 24, pages = 246807, url = http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.105.246807, doi = http://dx.doi.org/10.1103/PhysRevLett.105.246807 }  Georg Schwiete and Yuval Oreg Fluctuation persistent current in small superconducting rings Phys. Rev. B 82(21), 214514 (2010). Abstract: We extend previous theoretical studies of the contribution of fluctuating Cooper pairs to the persistent current in superconducting rings subjected to a magnetic field. For sufficiently small rings, in which the coherence length \xi exceeds the radius R, mean-field theory predicts the emergence of a flux-tuned quantum-critical point separating metallic and superconducting phases near half-integer flux through the ring. For larger rings with R =>\xi, the transition temperature is periodically reduced but superconductivity prevails at very low temperatures. We calculate the fluctuation persistent current in different regions of the metallic phase for both types of rings. Particular attention is devoted to the interplay of the angular momentum modes of the fluctuating order parameter field. We discuss the possibility of using a combination of different pair-breaking mechanisms to simplify the observation of the flux-tuned transition in rings with \xi>R. BibTeX:  @article{Schwiete2010, author = Georg Schwiete and Yuval Oreg, title = Fluctuation persistent current in small superconducting rings, journal = Phys. Rev. B, year = 2010, volume = 82, number = 21, pages = 214514, url = http://journals.aps.org/prb/abstract/10.1103/PhysRevB.82.214514, doi = http://dx.doi.org/10.1103/PhysRevB.82.214514 }  Torsten Karzig, Leonid I. Glazman and Felix von Oppen Energy Relaxation and Thermalization of Hot Electrons in Quantum Wires Phys. Rev. Lett. 105(22), 226407 (2010). Abstract: We develop a theory of energy relaxation and thermalization of hot carriers in clean quantum wires. Our theory is based on a controlled perturbative approach for large excitation energies and emphasizes the important roles of the electron spin and finite temperature. Unlike in higher dimensions, relaxation in one-dimensional electron liquids requires three-body collisions and is much faster for particles than holes which relax at nonzero temperatures only. Moreover, comoving carriers thermalize more rapidly than counterpropagating carriers. Our results are quantitatively consistent with a recent experiment. BibTeX:  @article{Karzig2010a, author = Torsten Karzig, Leonid I. Glazman and Felix von Oppen, title = Energy Relaxation and Thermalization of Hot Electrons in Quantum Wires, journal = Phys. Rev. Lett., year = 2010, volume = 105, number = 22, pages = 226407, url = http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.105.226407, doi = http://dx.doi.org/10.1103/PhysRevLett.105.226407 }  Eros Mariani and Felix von Oppen Temperature-dependent resistivity of suspended graphene Phys. Rev. B 82(19), 195403 (2010). Abstract: In this paper we investigate the electron-phonon contribution to the resistivity of suspended single-layer graphene. In-plane as well as flexural phonons are addressed in different temperature regimes. We focus on the intrinsic electron-phonon coupling due to the interaction of electrons with elastic deformations in the graphene membrane. The competition between screened deformation potential vs fictitious gauge-field coupling is discussed together with the role of tension in the suspended flake. In the absence of tension, flexural phonons dominate the phonon contribution to the resistivity at any temperature T with a T5/2 and T2 dependence at low and high temperatures, respectively. Sample-specific tension suppresses the contribution due to flexural phonons, yielding a linear temperature dependence due to in-plane modes. We compare our results with recent experiments. BibTeX:  @article{PhysRevB.82.195403, author = Eros Mariani and Felix von Oppen, title = Temperature-dependent resistivity of suspended graphene, journal = Phys. Rev. B, year = 2010, volume = 82, number = 19, pages = 195403, url = http://link.aps.org/doi/10.1103/PhysRevB.82.195403, doi = http://dx.doi.org/10.1103/PhysRevB.82.195403 }  J. H. Bardarson, P. W. Brouwer and J. E. Moore Aharonov-Bohm Oscillations in Disordered Topological Insulator Nanowires Phys. Rev. Lett. 105(15), 156803 (2010). Abstract: A direct signature of electron transport at the metallic surface of a topological insulator is the Aharonov-Bohm oscillation observed in a recent study of Bi2Se3 nanowires [Peng et al., Nature Mater. 9, 225 (2010)] where conductance was found to oscillate as a function of magnetic flux ϕ through the wire, with a period of one flux quantum ϕ0=h/e and maximum conductance at zero flux. This seemingly agrees neither with diffusive theory, which would predict a period of half a flux quantum, nor with ballistic theory, which in the simplest form predicts a period of ϕ0 but a minimum at zero flux due to a nontrivial Berry phase in topological insulators. We show how h/e and h/2e flux oscillations of the conductance depend on doping and disorder strength, provide a possible explanation for the experiments, and discuss further experiments that could verify the theory. BibTeX:  @article{PhysRevLett.105.156803, author = J. H. Bardarson, P. W. Brouwer and J. E. Moore, title = Aharonov-Bohm Oscillations in Disordered Topological Insulator Nanowires, journal = Phys. Rev. Lett., year = 2010, volume = 105, number = 15, pages = 156803, url = http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.105.156803, doi = http://dx.doi.org/10.1103/PhysRevLett.105.156803 }  Dganit Meidan, Tobias Micklitz and Piet W. Brouwer Optimal topological spin pump Phys. Rev. B 82(16), 161303 (2010). Abstract: We study the recently introduced Z2 pump consisting of a family of one-dimensional bulk insulators with time-reversal restriction on the pumping cycle. We find that the scattering matrices of these pumps are dichotomized by a topological index. We show that the class of pumps characterized by a nontrivial topological index allows, in contrast to its topologically trivial counterpart, for the noiseless pumping of quantized spin, even in the absence of spin conservation. This distinction sheds light on the Z2 classification of two-dimensional time-reversal invariant insulators. BibTeX:  @article{PhysRevB.82.161303, author = Dganit Meidan, Tobias Micklitz and Piet W. Brouwer, title = Optimal topological spin pump, journal = Phys. Rev. B, year = 2010, volume = 82, number = 16, pages = 161303, url = http://journals.aps.org/prb/abstract/10.1103/PhysRevB.82.161303, doi = http://dx.doi.org/10.1103/PhysRevB.82.161303 }  Yuval Oreg, Gil Refael and Felix von Oppen Helical Liquids and Majorana Bound States in Quantum Wires Phys. Rev. Lett. 105(17), 177002 (2010). Abstract: We show that the combination of spin-orbit coupling with a Zeeman field or strong interactions may lead to the formation of a helical electron liquid in single-channel quantum wires, with spin and velocity perfectly correlated. We argue that zero-energy Majorana bound states are formed in various situations when such wires are situated in proximity to a conventional s-wave superconductor. This occurs when the external magnetic field, the superconducting gap, or, most simply, the chemical potential vary along the wire. These Majorana states do not require the presence of a vortex in the system. Experimental consequences of the helical liquid and the Majorana states are also discussed. BibTeX:  @article{Oreg2010, author = Yuval Oreg, Gil Refael and Felix von Oppen, title = Helical Liquids and Majorana Bound States in Quantum Wires, journal = Phys. Rev. Lett., year = 2010, volume = 105, number = 17, pages = 177002, url = http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.105.177002, doi = http://dx.doi.org/10.1103/PhysRevLett.105.177002 }  J. Danon and P. W. Brouwer Non-Gaussian Fluctuations of Mesoscopic Persistent Currents Phys. Rev. Lett. 105(13), 136803 (2010). Abstract: The persistent current in an ensemble of normal-metal rings shows Gaussian distributed sample-to-sample fluctuations with non-Gaussian corrections, which are precursors of the transition into the Anderson localized regime. We here report a calculation of the leading non-Gaussian correction to the current autocorrelation function, which is of third-order in the current. Although the third-order correlation function is small, inversely proportional to the dimensionless conductance g of the ring, the mere fact that it is nonzero is remarkable, since it is an odd moment of the current distribution. BibTeX:  @article{PhysRevLett.105.136803, author = J. Danon and P. W. Brouwer, title = Non-Gaussian Fluctuations of Mesoscopic Persistent Currents, journal = Phys. Rev. Lett., year = 2010, volume = 105, number = 13, pages = 136803, url = http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.105.136803, doi = http://dx.doi.org/10.1103/PhysRevLett.105.136803 }  Alex Levchenko, Tobias Micklitz, Jér\^ome Rech and K. A. Matveev Transport in partially equilibrated inhomogeneous quantum wires Phys. Rev. B 82(11), 115413 (2010). Abstract: We study transport properties of weakly interacting one-dimensional electron systems including on an equal footing thermal equilibration due to three-particle collisions and the effects of large-scale inhomogeneities. We show that equilibration in an inhomogeneous quantum wire is characterized by the competition of interaction processes which reduce the electrons total momentum and such which change the number of right- and left-moving electrons. We find that the combined effect of interactions and inhomogeneities can dramatically increase the resistance of the wire. In addition, we find that the interactions strongly affect the thermoelectric properties of inhomogeneous wires and calculate their thermal conductance, thermopower, and Peltier coefficient. BibTeX:  @article{Levchenko2010, author = Alex Levchenko, Tobias Micklitz, Jér\^ome Rech and K. A. Matveev, title = Transport in partially equilibrated inhomogeneous quantum wires, journal = Phys. Rev. B, year = 2010, volume = 82, number = 11, pages = 115413, url = http://link.aps.org/doi/10.1103/PhysRevB.82.115413, doi = http://dx.doi.org/10.1103/PhysRevB.82.115413 }  A. Levchenko, T. Micklitz, M. R. Norman and I. Paul Transport implications of Fermi arcs in the pseudogap phase of the cuprates Phys. Rev. B 82(6), 060502 (2010). Abstract: We develop transport theory of spin-polarized electrons in one-dimensional quantum wires. Effects of interaction manifest at the level of three-particle collisions due to the severe constraints imposed by the conservation laws on the two-body processes. Interaction induced correction to conductance and thermopower relies on the scattering processes that change number of right- and left-moving electrons. The latter requires transition at the bottom of the band which is exponentially suppressed at low temperatures. Conversely, correction to thermal conductance is governed by the processes where all particles lie near the Fermi points and thus exhibits only power-law dependence on temperature. Our theory is based on the scattering approach that is beyond the Luttinger-liquid limit. We also emphasize the crucial role of the exchange terms in the three-particle scattering amplitude. BibTeX:  @article{Levchenko2010a, author = A. Levchenko, T. Micklitz, M. R. Norman and I. Paul, title = Transport implications of Fermi arcs in the pseudogap phase of the cuprates, journal = Phys. Rev. B, year = 2010, volume = 82, number = 6, pages = 060502, url = http://link.aps.org/doi/10.1103/PhysRevB.82.060502, doi = http://dx.doi.org/10.1103/PhysRevB.82.060502 }  J. Kailasvuori and M. C. Lüffe Quantum corrections in the Boltzmann conductivity of graphene and their sensitivity to the choice of formalism J. Stat. Mech.: Theory and Experiment 2010(06), P06024 (2010). Abstract: Semiclassical spin-coherent kinetic equations can be derived from quantum theory with many different approaches (Liouville equation based approaches, nonequilibrium Green's functions techniques, etc.). The collision integrals turn out to be formally different, but coincide in textbook examples as well as for systems where the spin-orbit coupling is only a small part of the kinetic energy like in related studies on the spin Hall effect. In Dirac cone physics (graphene, surface states of topological insulators like Bi_ {1-x}Sb_x, Bi_2Te_3 etc.), where this coupling constitutes the entire kinetic energy, the difference manifests itself in the precise value of the electron-hole coherence originated quantum correction to the Drude conductivity $\sim e^2/h * \ell k_F$. The leading correction is derived analytically for single and multilayer graphene with general scalar impurities. The often neglected principal value terms in the collision integral are important. Neglecting them yields a leading correction of order $(\ell k_F)^{-1}$, whereas including them can give a correction of order $(\ell k_F)^0$. The latter opens up a counterintuitive scenario with finite electron-hole coherent effects at Fermi energies arbitrarily far above the neutrality point regime, for example in the form of a shift $\sim e^2/h$ that only depends on the dielectric constant. This residual conductivity, possibly related to the one observed in recent experiments, depends crucially on the approach and could offer a setting for experimentally singling out one of the candidates. Concerning the different formalisms we notice that the discrepancy between a density matrix approach and a Green's function approach is removed if the Generalized Kadanoff-Baym Ansatz in the latter is replaced by an anti-ordered version. BibTeX:  @article{Kailasvuori2010, author = J. Kailasvuori and M. C. Lüffe, title = Quantum corrections in the Boltzmann conductivity of graphene and their sensitivity to the choice of formalism, journal = J. Stat. Mech.: Theory and Experiment, year = 2010, volume = 2010, number = 06, pages = P06024, url = http://iopscience.iop.org/1742-5468/2010/06/P06024/, doi = http://dx.doi.org/10.1088/1742-5468/2010/06/P06024 }  T. Micklitz and M. R. Norman Spin Hamiltonian of hyper-kagome ${\text{Na}}_{4}{\text{Ir}}_{3}{\text{O}}_{8}$ Phys. Rev. B 81(17), 174417 (2010). Abstract: We derive the spin Hamiltonian for the quantum spin liquid Na$_4$Ir$_3$O$_8$, and then estimate the direct and superexchange contributions between near neighbor iridium ions using a tight binding parametrization of the electronic structure. We find a magnitude of the exchange interaction comparable to experiment for a reasonable value of the on-site Coulomb repulsion. For one of the two tight binding parametrizations we have studied, the direct exchange term, which is isotropic, dominates the total exchange. This provides support for those theories proposed to describe this novel quantum spin liquid that assume an isotropic Heisenberg model. BibTeX:  @article{Micklitz2010, author = T. Micklitz and M. R. Norman, title = Spin Hamiltonian of hyper-kagome ${\text{Na}}_{4}{\text{Ir}}_{3}{\text{O}}_{8}$, journal = Phys. Rev. B, year = 2010, volume = 81, number = 17, pages = 174417, url = http://link.aps.org/doi/10.1103/PhysRevB.81.174417, doi = http://dx.doi.org/10.1103/PhysRevB.81.174417 }  S. Nadj-Perge, S. M. Frolov, J. W. W. van Tilburg, J. Danon, Yu. V. Nazarov, R. Algra, E. P. A. M. Bakkers and L. P. Kouwenhoven Disentangling the effects of spin-orbit and hyperfine interactions on spin blockade Phys. Rev. B 81(20), 201305 (2010). Abstract: We have achieved the few-electron regime in InAs nanowire double quantum dots. Spin blockade is observed for the first two half-filled orbitals, where the transport cycle is interrupted by forbidden transitions between triplet and singlet states. Partial lifting of spin blockade is explained by spin-orbit and hyperfine mechanisms that enable triplet to singlet transitions. The measurements over a wide range of interdot coupling and tunneling rates to the leads are well reproduced by a simple transport model. This allows us to separate and quantify the contributions of the spin-orbit and hyperfine interactions. BibTeX:  @article{Nadj-Perge2010, author = S. Nadj-Perge, S. M. Frolov, J. W. W. van Tilburg, J. Danon, Yu. V. Nazarov, R. Algra, E. P. A. M. Bakkers and L. P. Kouwenhoven, title = Disentangling the effects of spin-orbit and hyperfine interactions on spin blockade, journal = Phys. Rev. B, year = 2010, volume = 81, number = 20, pages = 201305, url = http://prb.aps.org/abstract/PRB/v81/i20/e201305, doi = http://dx.doi.org/10.1103/PhysRevB.81.201305 }  Eran Ginossar, Leonid I. Glazman, Teemu Ojanen, Felix von Oppen, William E. Shanks, Ania C. Bleszynski-Jayich and J. G. E. Harris Mesoscopic persistent currents in a strong magnetic field Phys. Rev. B 81(15), 155448 (2010). Abstract: Recent precision measurements of mesoscopic persistent currents in normal-metal rings rely on the interaction between the magnetic moment generated by the current and a large applied magnetic field. Motivated by this technique, we extend the theory of mesoscopic persistent currents to include the effect of the finite thickness of the ring and the resulting penetration of the large magnetic field. We discuss both the sample-specific typical current and the ensemble-averaged current which is dominated by the effects of electron-electron interactions. We find that the magnetic field strongly suppresses the interaction-induced persistent current and so provides direct access to the independent-electron contribution. Moreover, the technique allows for measurements of the entire distribution function of the persistent current. We also discuss the consequences of the Zeeman splitting and spin-orbit scattering, and include a detailed and quantitative comparison of our theoretical results to experimental data. BibTeX:  @article{Ginossar2010, author = Eran Ginossar, Leonid I. Glazman, Teemu Ojanen, Felix von Oppen, William E. Shanks, Ania C. Bleszynski-Jayich and J. G. E. Harris, title = Mesoscopic persistent currents in a strong magnetic field, journal = Phys. Rev. B, year = 2010, volume = 81, number = 15, pages = 155448, url = http://journals.aps.org/prb/abstract/10.1103/PhysRevB.81.155448, doi = http://dx.doi.org/10.1103/PhysRevB.81.155448 }  E. Rossi, J. H. Bardarson, P. W. Brouwer and S. Das Sarma Signatures of Klein tunneling in disordered graphene $p-n-p$ junctions Phys. Rev. B 81(12), 121408 (2010). Abstract: We present a method for obtaining quantum transport properties in graphene that uniquely combines three crucial features: microscopic treatment of charge disorder, fully quantum-mechanical analysis of transport, and the ability to model experimentally relevant system sizes. As a pertinent application we study the disorder dependence of Klein tunneling dominated transport in p-n-p junctions. Both the resistance and the Fano factor show broad resonance peaks due to the presence of quasi-bound-states. This feature is washed out by the disorder when the mean free path becomes of the order of the distance between the two p-n interfaces. BibTeX:  @article{Rossi2010, author = E. Rossi, J. H. Bardarson, P. W. Brouwer and S. Das Sarma, title = Signatures of Klein tunneling in disordered graphene $p-n-p$ junctions, journal = Phys. Rev. B, year = 2010, volume = 81, number = 12, pages = 121408, url = http://journals.aps.org/prb/abstract/10.1103/PhysRevB.81.121408, doi = http://dx.doi.org/10.1103/PhysRevB.81.121408 }  Guillaume Weick, Fabio Pistolesi, Eros Mariani and Felix von Oppen Discontinuous Euler instability in nanoelectromechanical systems Phys. Rev. B 81(12), 121409 (2010). Abstract: We investigate nanoelectromechanical systems near mechanical instabilities. We show that, quite generally, the interaction between the electronic and the vibronic degrees of freedom can be accounted for essentially exactly when the instability is continuous. We apply our general framework to the Euler buckling instability and find that the interaction between electronic and vibronic degrees of freedom qualitatively affects the mechanical instability, turning it into a discontinuous one in close analogy with tricritical points in the Landau theory of phase transitions. BibTeX:  @article{Weick2010, author = Guillaume Weick, Fabio Pistolesi, Eros Mariani and Felix von Oppen, title = Discontinuous Euler instability in nanoelectromechanical systems, journal = Phys. Rev. B, year = 2010, volume = 81, number = 12, pages = 121409, url = http://journals.aps.org/prb/abstract/10.1103/PhysRevB.81.121409, doi = http://dx.doi.org/10.1103/PhysRevB.81.121409 }  C. D. Graf, G. Weick and E. Mariani Parametric resonance and spin-charge separation in 1D fermionic systems EPL (Europhys. Lett.) 89(4), 40005 (2010). Abstract: We show that the periodic modulation of the Hamiltonian parameters for 1D correlated fermionic systems can be used to parametrically amplify their bosonic collective modes. Treating the problem within the Luttinger-liquid picture, we show how charge and spin density waves with different momenta are simultaneously amplified. We discuss the implementation of our predictions for cold atoms in 1D modulated optical lattices, showing that the fermionic momentum distribution directly provides a clear signature of spin-charge separation. BibTeX:  @article{Graf2010, author = C. D. Graf, G. Weick and E. Mariani, title = Parametric resonance and spin-charge separation in 1D fermionic systems, journal = EPL (Europhys. Lett.), year = 2010, volume = 89, number = 4, pages = 40005, url = http://stacks.iop.org/0295-5075/89/i=4/a=40005, doi = http://dx.doi.org/10.1209/0295-5075/89/40005 }  Gilad Barak, Hadar Steinberg, Loren N. Pfeiffer, Ken W. West, Leonid Glazman, Felix von Oppen and Amir Yacoby Interacting electrons in one dimension beyond the Luttinger-liquid limit Nature Physics 6(7), 489 (2010). Abstract: Over the past several decades, Luttinger-liquid theory has a framework for interacting electrons in one dimension. However, the validity of the theory is strictly limited to low-energy excitations where the electron dispersion is linear. Interacting electrons in one-dimension beyond the Luttinger-liquid limit, where the underlying dispersion of electrons is no longer linear, exhibit intriguing manifestations of the interactions, which have direct implications on many experimental systems. For example, consider the energy relaxation of particles or holes, the unoccupied states in a Fermi sea. Whereas in Luttinger-liquid theory such energy relaxation is strictly forbidden, in a nonlinearly dispersing one-dimensional electron system energy relaxation is allowed but very different for particles and holes. Here, we use momentum-resolved tunnelling to selectively inject energetic particles and holes into a quantum wire and study their relaxation processes. Our measurements confirm that energetic particles undergo fast relaxation to a thermalized distribution and holes retain their original injection energy, thereby providing a clear demonstration of electron dynamics beyond the Luttinger limit. A model of thermalization derived in the limit of weak interactions shows quantitative agreement with the experimental findings. BibTeX:  @article{Barak2010, author = Gilad Barak, Hadar Steinberg, Loren N. Pfeiffer, Ken W. West, Leonid Glazman, Felix von Oppen and Amir Yacoby, title = Interacting electrons in one dimension beyond the Luttinger-liquid limit, journal = Nature Physics, year = 2010, volume = 6, number = 7, pages = 489, url = http://www.nature.com/nphys/journal/v6/n7/full/nphys1678.html, doi = http://dx.doi.org/10.1038/nphys1678 }  Torsten Karzig and Felix von Oppen Signatures of critical full counting statistics in a quantum-dot chain Phys. Rev. B 81(4), 045317 (2010). Abstract: We consider current shot noise and the full counting statistics in a chain of quantum dots which exhibits a continuous nonequilibrium phase transition as a function of the tunnel couplings of the chain with the electrodes. Using a combination of analytical and numerical methods, we establish that the full counting statistics is conventional away from the phase transition, but becomes, in a well-defined sense, essentially non-Gaussian on the critical line, where the current fluctuations are controlled by the dynamic critical exponent z. We find that signatures of the critical full counting statistics persist in quantum-dot chains of finite length. BibTeX:  @article{Karzig2010, author = Torsten Karzig and Felix von Oppen, title = Signatures of critical full counting statistics in a quantum-dot chain, journal = Phys. Rev. B, year = 2010, volume = 81, number = 4, pages = 045317, url = http://journals.aps.org/prb/abstract/10.1103/PhysRevB.81.045317, doi = http://dx.doi.org/10.1103/PhysRevB.81.045317 }  2009 BibTeX:  @unpublished{20092010,, title = {Preprints}, year = 2009 }  and Teemu Ojanen Selection-rule blockade and rectification in quantum heat transport Phys. Rev. B 80(18), 180301 (2009). Abstract: We present a thermal transport phenomenon, a unidirectional selection-rule blockade, and show how it produces unprecedented rectification of bosonic heat flow through molecular or mesoscopic quantum systems. Rectification arises from the quantization of energy levels of the conduction element and selection rules of reservoir coupling operators. The simplest system exhibiting the selection-rule blockade is an appropriately coupled three-level system, providing a candidate for a high-performance heat diode. We present an analytical treatment of the transport problem and discuss how the phenomenon generalizes to multilevel systems. BibTeX:  @article{Ojanen2009a, author = and Teemu Ojanen, title = Selection-rule blockade and rectification in quantum heat transport, journal = Phys. Rev. B, year = 2009, volume = 80, number = 18, pages = 180301, url = http://journals.aps.org/prb/abstract/10.1103/PhysRevB.80.180301, doi = http://dx.doi.org/10.1103/PhysRevB.80.180301 }  Teemu Ojanen, Friedrich C. Gethmann and Felix von Oppen Electromechanical instability in vibrating quantum dots with effectively negative charging energy Phys. Rev. B 80(19), 195103 (2009). Abstract: In quantum dots or molecules with vibrational degrees of freedom the electron-vibron coupling renormalizes the electronic charging energy. For sufficiently strong coupling, the renormalized charging energy can become negative. Here, we discuss an instability toward adding or removing an arbitrary number of electrons when the magnitude of the renormalized charging energy exceeds the single-particle level spacing. We show that the instability is regularized by the anharmonic contribution to the vibron energy. The resulting effective charging energy as a function of the electron number has a double-well structure causing a variety of novel features in the Coulomb-blockade properties. BibTeX:  @article{Ojanen2009, author = Teemu Ojanen, Friedrich C. Gethmann and Felix von Oppen, title = Electromechanical instability in vibrating quantum dots with effectively negative charging energy, journal = Phys. Rev. B, year = 2009, volume = 80, number = 19, pages = 195103, url = http://journals.aps.org/prb/abstract/10.1103/PhysRevB.80.195103, doi = http://dx.doi.org/10.1103/PhysRevB.80.195103 }