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Jun 30, 2018
06/18

Jun 30, 2018
by
H. Wilming; M. Goihl; C. Krumnow; J. Eisert

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One of the main questions of research on quantum many-body systems following unitary out of equilibrium dynamics is to find out how local expectation values equilibrate in time. For non-interacting models, this question is rather well understood. However, the best known bounds for general quantum systems are vastly crude, scaling unfavorable with the system size. Nevertheless, empirical and numerical evidence suggests that for generic interacting many-body systems, generic local observables,...

Topics: Statistical Mechanics, Quantum Physics, Condensed Matter

Source: http://arxiv.org/abs/1704.06291

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0.0

Jun 30, 2018
06/18

Jun 30, 2018
by
M. Perarnau-Llobet; H. Wilming; A. Riera; R. Gallego; J. Eisert

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We derive general limitations concerning efficiency and power of heat engines strongly coupled to thermal baths. We build this framework on the insight that quantum systems strongly coupled to many-body systems will equilibrate to the reduced state of a global thermal state, deviating from the local thermal state of the system as it occurs in the weak-coupling limit. Taking this observation as the starting point of our analysis, we first provide strong-coupling corrections to the second law in...

Topics: Condensed Matter, Quantum Physics, Other Condensed Matter

Source: http://arxiv.org/abs/1704.05864

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0.0

Jun 30, 2018
06/18

Jun 30, 2018
by
A. Nietner; C. Krumnow; E. J. Bergholtz; J. Eisert

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Strongly correlated quantum many-body systems at low dimension exhibit a wealth of phenomena, ranging from features of geometric frustration to signatures of symmetry-protected topological order. In suitable descriptions of such systems, it can be helpful to resort to effective models which focus on the essential degrees of freedom of the given model. In this work, we analyze how to determine the validity of an effective model by demanding it to be in the same phase as the original model. We...

Topics: Strongly Correlated Electrons, Condensed Matter, Quantum Physics

Source: http://arxiv.org/abs/1704.02992

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0.0

Jun 30, 2018
06/18

Jun 30, 2018
by
M. Gluza; M. Kliesch; J. Eisert; L. Aolita

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The experimental interest in realizing quantum spin-1/2-chains has increased uninterruptedly over the last decade. In many instances, the target quantum simulation belongs to the broader class of non-interacting fermionic models, constituting an important benchmark. In spite of this class being analytically efficiently tractable, no direct certification tool has yet been reported for it. In fact, in experiments, certification has almost exclusively relied on notions of quantum state tomography...

Topics: Condensed Matter, Quantum Physics, Other Condensed Matter

Source: http://arxiv.org/abs/1703.03152

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1.0

Jun 30, 2018
06/18

Jun 30, 2018
by
M. Friesdorf; A. H. Werner; M. Goihl; J. Eisert; W. Brown

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Interacting quantum many-body systems are usually expected to thermalise, in the sense that the evolution of local expectation values approach a stationary value resembling a thermal ensemble. This intuition is notably contradicted in systems exhibiting many-body localisation, a phenomenon receiving significant recent attention. One of its most intriguing features is that, in stark contrast to the non-interacting case, entanglement of states grows without limit over time, albeit slowly. In this...

Topics: Quantum Physics, Mathematics, Mathematical Physics, Disordered Systems and Neural Networks,...

Source: http://arxiv.org/abs/1412.5605

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0.0

Jun 30, 2018
06/18

Jun 30, 2018
by
A. H. Werner; D. Jaschke; P. Silvi; M. Kliesch; T. Calarco; J. Eisert; S. Montangero

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Open many-body quantum systems play an important role in quantum optics and condensed-matter physics, and capture phenomena like transport, 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...

Topics: Quantum Physics, Strongly Correlated Electrons, Statistical Mechanics, Condensed Matter

Source: http://arxiv.org/abs/1412.5746

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1.0

Jun 30, 2018
06/18

Jun 30, 2018
by
H. Wilming; R. Gallego; J. Eisert

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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...

Topics: Quantum Physics, Statistical Mechanics, Condensed Matter

Source: http://arxiv.org/abs/1411.3754

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2.0

Jun 30, 2018
06/18

Jun 30, 2018
by
M. Friesdorf; A. H. Werner; W. Brown; V. B. Scholz; J. Eisert

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The phenomenon of many-body localisation received a lot of attention recently, both for its implications in condensed-matter physics of allowing systems to be an insulator even at non-zero temperature as well as in the context of the foundations of quantum statistical mechanics, providing examples of systems showing the absence of thermalisation following out-of-equilibrium dynamics. In this work, we establish a novel link between dynamical properties - the absence of a group velocity and...

Topics: Quantum Physics, Mathematics, Mathematical Physics, Disordered Systems and Neural Networks,...

Source: http://arxiv.org/abs/1409.1252

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2.0

Jun 30, 2018
06/18

Jun 30, 2018
by
J. Eisert; M. Friesdorf; C. Gogolin

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Closed quantum many-body systems out of equilibrium pose several long-standing problems in physics. Recent years have seen a tremendous progress in approaching these questions, not least due to experiments with cold atoms and trapped ions in instances of quantum simulations. This article provides an overview on the progress in understanding dynamical equilibration and thermalisation of closed quantum many-body systems out of equilibrium due to quenches, ramps and periodic driving. It also...

Topics: Quantum Physics, Quantum Gases, Statistical Mechanics, Condensed Matter

Source: http://arxiv.org/abs/1408.5148

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1.0

Jun 30, 2018
06/18

Jun 30, 2018
by
L. Aolita; C. Gogolin; M. Kliesch; J. Eisert

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A major roadblock for large-scale photonic quantum technologies is the lack of practical reliable certification tools. We introduce an experimentally friendly - yet mathematically rigorous - certification test for experimental preparations of arbitrary m-mode pure Gaussian states, pure non-Gaussian states generated by linear-optical circuits with n-boson Fock-basis states as inputs, and states of these two classes subsequently post-selected with local measurements on ancillary modes. The...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1407.4817

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0.0

Jun 30, 2018
06/18

Jun 30, 2018
by
A. Steffens; M. Friesdorf; T. Langen; B. Rauer; T. Schweigler; R. Hübener; J. Schmiedmayer; C. A. Riofrío; J. Eisert

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The experimental realisation of large scale many-body systems has seen immense progress in recent years, rendering full tomography tools for state identification inefficient, especially for continuous systems. In order to work with these emerging physical platforms, new technologies for state identification are required. In this work, we present first steps towards efficient experimental quantum field tomography. We employ our procedure to capture ultracold atomic systems using atom chips, a...

Topics: Quantum Physics, Quantum Gases, High Energy Physics - Theory, Condensed Matter

Source: http://arxiv.org/abs/1406.3632

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3.0

Jun 30, 2018
06/18

Jun 30, 2018
by
A. Steffens; C. A. Riofrío; R. Hübener; J. Eisert

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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, a complete set of variational states grasping states in 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,...

Topics: Quantum Physics, Quantum Gases, Condensed Matter

Source: http://arxiv.org/abs/1406.3631

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0.0

Jun 30, 2018
06/18

Jun 30, 2018
by
J. C. Budich; J. Eisert; E. J. Bergholtz; S. Diehl; P. Zoller

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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., PNAS 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...

Topics: Quantum Physics, Mesoscale and Nanoscale Physics, Condensed Matter

Source: http://arxiv.org/abs/1405.6641

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0.0

Jun 30, 2018
06/18

Jun 30, 2018
by
M. Kliesch; D. Gross; J. Eisert

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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...

Topics: Quantum Physics, Mathematics, Strongly Correlated Electrons, Mathematical Physics, Condensed Matter

Source: http://arxiv.org/abs/1404.4466

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1.0

Jun 30, 2018
06/18

Jun 30, 2018
by
S. Braun; M. Friesdorf; S. S. Hodgman; M. Schreiber; J. P. Ronzheimer; A. Riera; M. del Rey; I. Bloch; J. Eisert; U. Schneider

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The dynamics of quantum phase transitions poses 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 one-dimensional Bose-Hubbard model, we find perfect agreement between experimental observations and numerical simulations for the resulting coherence length. We thereby...

Topics: Quantum Gases, Quantum Physics, Strongly Correlated Electrons, Statistical Mechanics, Condensed...

Source: http://arxiv.org/abs/1403.7199

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0.0

Jun 30, 2018
06/18

Jun 30, 2018
by
R. Hübener; Y. Sekino; J. Eisert

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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 low-dimensional bosonic matrix models. In this equivalent model significant local structure becomes apparent and it can serve as a simple toy model for analytical and precise numerical study. We derive a substantial part of the low energy...

Topics: Quantum Physics, High Energy Physics - Theory, Nonlinear Sciences, Chaotic Dynamics

Source: http://arxiv.org/abs/1403.1392

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2.0

Jun 29, 2018
06/18

Jun 29, 2018
by
J. Lekscha; H. Wilming; J. Eisert; R. Gallego

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We investigate the limitations that emerge in thermodynamic tasks as a result of having local control only over the components of a thermal machine. These limitations are particularly relevant for devices composed of interacting many-body systems. Specifically, we study protocols of work extraction that employ a many-body system as a working medium whose evolution can be driven by tuning the on-site Hamiltonian terms. This provides a restricted set of thermodynamic operations, giving rise to...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1612.00029

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0.0

Jun 29, 2018
06/18

Jun 29, 2018
by
J. Eisert; V. Eisler; Z. Zimborás

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The entanglement negativity is a versatile measure of entanglement that has numerous applications in quantum information and in condensed matter theory. It can not only efficiently be computed in the Hilbert space dimension, but for non-interacting bosonic systems, one can compute the negativity efficiently in the number of modes. However, such an efficient computation does not carry over to the fermionic realm, the ultimate reason for this being that the partial transpose of a fermionic...

Topics: Quantum Physics, Condensed Matter, Other Condensed Matter

Source: http://arxiv.org/abs/1611.08007

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0.0

Jun 29, 2018
06/18

Jun 29, 2018
by
A. Steffens; P. Rebentrost; I. Marvian; J. Eisert; S. Lloyd

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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...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1609.08170

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2.0

Jun 29, 2018
06/18

Jun 29, 2018
by
V. Abrol; O. Absil; P. -A. Absil; S. Anthoine; P. Antoine; T. Arildsen; N. Bertin; F. Bleichrodt; J. Bobin; A. Bol; A. Bonnefoy; F. Caltagirone; V. Cambareri; C. Chenot; V. Crnojević; M. Daňková; K. Degraux; J. Eisert; J. M. Fadili; M. Gabrié; N. Gac; D. Giacobello; A. Gonzalez; C. A. Gomez Gonzalez; A. González; P. -Y. Gousenbourger; M. Græsbøll Christensen; R. Gribonval; S. Guérit; S. Huang; P. Irofti; L. Jacques; U. S. Kamilov; S. Kiticć; M. Kliesch; F. Krzakala; J. A. Lee; W. Liao; T. Lindstrøm Jensen; A. Manoel; H. Mansour; A. Mohammad-Djafari; A. Moshtaghpour; F. Ngolè; B. Pairet; M. Panić; G. Peyré; A. Pižurica; P. Rajmic; M. Roblin; I. Roth; A. K. Sao; P. Sharma; J. -L. Starck; E. W. Tramel; T. van Waterschoot; D. Vukobratovic; L. Wang; B. Wirth; G. Wunder; H. Zhang

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The third edition of the "international - Traveling Workshop on Interactions between Sparse models and Technology" (iTWIST) took place in Aalborg, the 4th largest city in Denmark situated beautifully in the northern part of the country, from the 24th to 26th of August 2016. The workshop venue was at the Aalborg University campus. One implicit objective of this biennial workshop is to foster collaboration between international scientific teams by disseminating ideas through both...

Topics: Computer Vision and Pattern Recognition, Numerical Analysis, Mathematics, Optimization and Control,...

Source: http://arxiv.org/abs/1609.04167

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0.0

Jun 29, 2018
06/18

Jun 29, 2018
by
J. Gertis; M. Friesdorf; C. A. Riofrio; J. Eisert

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Ultra-cold atoms in optical lattices provide one of the most promising platforms for analog quantum simulations of complex quantum many-body systems. Large-size systems can now routinely be reached and are already used to probe a large variety of different physical situations, ranging from quantum phase transitions to artificial gauge theories. At the same time, measurement techniques are still limited and full tomography for these systems seems out of reach. Motivated by this observation, we...

Topics: Quantum Physics, Condensed Matter, Quantum Gases

Source: http://arxiv.org/abs/1606.01913

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1.0

Jun 29, 2018
06/18

Jun 29, 2018
by
H. Wilming; M. J. Kastoryano; A. H. Werner; J. Eisert

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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...

Topics: Quantum Physics, Other Condensed Matter, Statistical Mechanics, Condensed Matter, Mathematics,...

Source: http://arxiv.org/abs/1602.01108

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0.0

Jun 29, 2018
06/18

Jun 29, 2018
by
D. Hangleiter; M. Kliesch; M. Schwarz; J. Eisert

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One of the main challenges in the field of quantum simulation and computation is to identify ways to certify the correct functioning of a device when a classical efficient simulation is not available. Important cases are situations in which one cannot classically calculate local expectation values of state preparations efficiently. In this work, we develop weak-membership formulations of the certification of ground state preparations. We provide a non-interactive protocol for certifying ground...

Topics: Quantum Physics, Condensed Matter, Quantum Gases

Source: http://arxiv.org/abs/1602.00703

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1.0

Jun 29, 2018
06/18

Jun 29, 2018
by
M. Goihl; M. Friesdorf; A. H. Werner; W. Brown; J. Eisert

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The phenomenon of many-body localised (MBL) systems has attracted significant interest in recent years, for its intriguing implications from a perspective of both condensed-matter and statistical physics: they are insulators even at non-zero temperature and fail to thermalise, violating expectations from quantum statistical mechanics. What is more, recent seminal experimental developments with ultra-cold atoms in optical lattices constituting analog quantum simulators have pushed many-body...

Topics: Statistical Mechanics, Condensed Matter, Quantum Gases, Quantum Physics

Source: http://arxiv.org/abs/1601.02666

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1.0

Jun 29, 2018
06/18

Jun 29, 2018
by
M. Gluza; C. Krumnow; M. Friesdorf; C. Gogolin; J. Eisert

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In this work, we present a result on the non-equilibrium dynamics causing equilibration and Gaussification of quadratic non-interacting 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...

Topics: Statistical Mechanics, Condensed Matter, Quantum Gases, Quantum Physics

Source: http://arxiv.org/abs/1601.00671

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0.0

Jun 28, 2018
06/18

Jun 28, 2018
by
M. Perarnau-Llobet; A. Riera; R. Gallego; H. Wilming; J. Eisert

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Recent years have seen an enormously revived interest in the study of thermodynamic notions in the quantum regime. This applies both to the study of notions of work extraction in thermal machines in the quantum regime, as well as to questions of equilibration and thermalisation of interacting quantum many-body systems as such. In this work we bring together these two lines of research by studying work extraction in a closed system that undergoes a sequence of quenches and equilibration steps...

Topics: Quantum Physics, Statistical Mechanics, Quantum Gases, Condensed Matter

Source: http://arxiv.org/abs/1512.03823

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4.0

Jun 27, 2018
06/18

Jun 27, 2018
by
J. Goold; C. Gogolin; S. R. Clark; J. Eisert; A. Scardicchio; A. Silva

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The intriguing phenomenon of many-body localization (MBL) has attracted significant interest recently, but a complete characterization is still lacking. In this work, we introduce the total correlations, a concept from quantum information theory capturing multi-partite correlations, to the study of this phenomenon. We demonstrate that the total correlations of the diagonal ensemble provides a meaningful diagnostic tool to pin-down, probe, and better understand the MBL transition and ergodicity...

Topics: Condensed Matter, Quantum Physics, Disordered Systems and Neural Networks

Source: http://arxiv.org/abs/1504.06872

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5.0

Jun 27, 2018
06/18

Jun 27, 2018
by
R. Gallego; J. Eisert; H. Wilming

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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 of several attempts to resolve this issue by putting forward specific models, these are far from capturing realistically...

Topics: Condensed Matter, Quantum Physics, Statistical Mechanics, Mathematics, Mathematical Physics

Source: http://arxiv.org/abs/1504.05056

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4.0

Jun 27, 2018
06/18

Jun 27, 2018
by
G. Haack; A. Steffens; J. Eisert; R. Hübener

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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 in quantum field theory has been established. So far, however, this connection has not been extended to the condensed-matter context. In this work, we substantially develop further and apply a machinery of continuous matrix product states (cMPS) to perform tomography of transport experiments. We first present an extension of the...

Topics: Condensed Matter, Quantum Physics, Mesoscale and Nanoscale Physics

Source: http://arxiv.org/abs/1504.04194

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Jun 27, 2018
06/18

Jun 27, 2018
by
C. Krumnow; L. Veis; Ö. Legeza; J. Eisert

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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 non-local fermionic systems is the choice of orbitals, it being far from clear what choice of fermionic orbitals to make. In this work, we propose a way to overcome this challenge. We...

Topics: Condensed Matter, Quantum Physics, Strongly Correlated Electrons, Chemical Physics, Physics

Source: http://arxiv.org/abs/1504.00042

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Jun 27, 2018
06/18

Jun 27, 2018
by
C. Gogolin; J. Eisert

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We review selected advances in the theoretical understanding of complex quantum many-body systems with regard to emergent notions of quantum statistical mechanics. We cover topics such as equilibration and thermalisation in pure state statistical mechanics, the eigenstate thermalisation hypothesis, the equivalence of ensembles, non-equilibration dynamics following global and local quenches as well as ramps. We also address initial state independence, absence of thermalisation, and many-body...

Topics: Condensed Matter, Quantum Physics, Statistical Mechanics, Mathematics, Mathematical Physics,...

Source: http://arxiv.org/abs/1503.07538

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Sep 24, 2013
09/13

Sep 24, 2013
by
M. M. Wolf; J. Eisert

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We consider the additivity of the minimal output entropy and the classical information capacity of a class of quantum channels. For this class of channels the norm of the output is maximized for the output being a normalized projection. We prove the additivity of the minimal output Renyi entropies with entropic parameters contained in [0, 2], generalizing an argument by Alicki and Fannes, and present a number of examples in detail. In order to relate these results to the classical information...

Source: http://arxiv.org/abs/quant-ph/0412133v3

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Sep 24, 2013
09/13

Sep 24, 2013
by
K. Audenaert; J. Eisert; E. Jane; M. B. Plenio; S. Virmani; B. De Moor

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We present an analytical formula for the asymptotic relative entropy of entanglement for Werner states of arbitrary dimension. We then demonstrate its validity using methods from convex optimization. To our knowledge, this is the first case in which the value of a subadditive entanglement measure has been obtained in the asymptotic limit.

Source: http://arxiv.org/abs/quant-ph/0103096v2

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Sep 23, 2013
09/13

Sep 23, 2013
by
P. Hyllus; J. Eisert

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This paper is concerned with all tests for continuous-variable entanglement that arise from linear combinations of second moments or variances of canonical coordinates, as they are commonly used in experiments to detect entanglement. All such tests for bi-partite and multi-partite entanglement correspond to hyperplanes in the set of second moments. It is shown that all optimal tests, those that are most robust against imperfections with respect to some figure of merit for a given state, can be...

Source: http://arxiv.org/abs/quant-ph/0510077v3

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34

Sep 23, 2013
09/13

Sep 23, 2013
by
D. Gross; J. Eisert

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We present a simple way to quantize the well-known Margulis expander map. The result is a quantum expander which acts on discrete Wigner functions in the same way the classical Margulis expander acts on probability distributions. The quantum version shares all essential properties of the classical counterpart, e.g., it has the same degree and spectrum. Unlike previous constructions of quantum expanders, our method does not rely on non-Abelian harmonic analysis. Analogues for continuous variable...

Source: http://arxiv.org/abs/0710.0651v2

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Sep 23, 2013
09/13

Sep 23, 2013
by
M. Kliesch; T. Barthel; C. Gogolin; M. Kastoryano; J. Eisert

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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...

Source: http://arxiv.org/abs/1105.3986v4

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Sep 23, 2013
09/13

Sep 23, 2013
by
D. Gross; S. Flammia; J. Eisert

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It is often argued that entanglement is at the root of the speedup for quantum compared to classical computation, and that one needs a sufficient amount of entanglement for this speedup to be manifest. In measurement-based quantum computing (MBQC), the need for a highly entangled initial state is particularly obvious. Defying this intuition, we show that quantum states can be too entangled to be useful for the purpose of computation. We prove that this phenomenon occurs for a dramatic majority...

Source: http://arxiv.org/abs/0810.4331v3

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Sep 23, 2013
09/13

Sep 23, 2013
by
D. Gross; J. Eisert

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We introduce the notion of quantum computational webs: These are quantum states universal for measurement-based computation which can be built up from a collection of simple primitives. The primitive elements - reminiscent of building blocks in a construction kit - are (i) states on a one-dimensional chain of systems ("computational quantum wires") with the power to process one logical qubit and (ii) suitable couplings which connect the wires to a computationally universal...

Source: http://arxiv.org/abs/0810.2542v2

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Sep 23, 2013
09/13

Sep 23, 2013
by
J. DiGuglielmo; A. Samblowski; B. Hage; C. Pineda; J. Eisert; R. Schnabel

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Among the possibly most intriguing aspects of quantum entanglement is that it comes in "free" and "bound" instances. Bound entangled states require entangled states in preparation but, once realized, no free entanglement and therefore no pure maximally entangled pairs can be regained. Their existence hence certifies an intrinsic irreversibility of entanglement in nature and suggests a connection with thermodynamics. In this work, we present a first experimental unconditional...

Source: http://arxiv.org/abs/1006.4651v3

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Sep 23, 2013
09/13

Sep 23, 2013
by
A. Mari; J. Eisert

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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 [Phys. Rev. Lett. 103, 213603 (2009)]. It is demonstrated that with suitable driving, the maximum degree of entanglement can be significantly enhanced, in...

Source: http://arxiv.org/abs/1111.2415v1

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Sep 23, 2013
09/13

Sep 23, 2013
by
J. Eisert; M. P. Mueller; C. Gogolin

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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...

Source: http://arxiv.org/abs/1111.3965v3

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Sep 23, 2013
09/13

Sep 23, 2013
by
J. Eisert; M. Wilkens; M. Lewenstein

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We investigate the quantization of non-zero sum games. For the particular case of the Prisoners' Dilemma we show that this game ceases to pose a dilemma if quantum strategies are allowed for. We also construct a particular quantum strategy which always gives reward if played against any classical strategy.

Source: http://arxiv.org/abs/quant-ph/9806088v3

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Sep 23, 2013
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Sep 23, 2013
by
J. Eisert; T. Prosen

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We discuss a notion of quantum critical exponents in open quantum many-body systems driven by quantum noise. We show that in translationally invariant quantum lattice models undergoing quasi-local Markovian dissipative processes, mixed states emerge as stationary points that show scaling laws for the divergence of correlation lengths giving rise to well-defined critical exponents. The main new technical tool developed here is a complete description of steady states of free bosonic or fermionic...

Source: http://arxiv.org/abs/1012.5013v1

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Sep 23, 2013
09/13

Sep 23, 2013
by
J. Eisert; M. B. Plenio

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We present a general necessary and sufficient criterion for the possibility of a state transformation from one mixed Gaussian state to another of a bi-partite continuous-variable system with two modes. The class of operations that will be considered is the set of local Gaussian completely positive trace-preserving maps.

Source: http://arxiv.org/abs/quant-ph/0109126v2

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Sep 23, 2013
09/13

Sep 23, 2013
by
J. Eisert; M. B. Plenio

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We outline the basic questions that are being studied in the theory of entanglement. Following a brief review of some of the main achievements of entanglement theory for finite-dimensional quantum systems such as qubits, we will consider entanglement in infinite-dimensional systems. Asking for a theory of entanglement in such systems under experimentally feasible operations leads to the development of the theory of entanglement of Gaussian states. Results of this theory are presented and the...

Source: http://arxiv.org/abs/quant-ph/0312071v2

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Sep 22, 2013
09/13

Sep 22, 2013
by
J. Eisert

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In this paper, the problem of finding optimal success probabilities of static linear optics quantum gates is linked to the theory of convex optimization. It is shown that by exploiting this link, upper bounds for the success probability of networks realizing single-mode gates can be derived, which hold in generality for linear optical networks followed by postselection, i.e., for networks of arbitrary size, any number of auxiliary modes, and arbitrary photon numbers. As a corollary, the...

Source: http://arxiv.org/abs/quant-ph/0409156v4

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Sep 22, 2013
09/13

Sep 22, 2013
by
M. Ohliger; K. Kieling; J. Eisert

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We discuss the potential and limitations of Gaussian cluster states for measurement-based quantum computing. Using a framework of Gaussian projected entangled pair states (GPEPS), we show that no matter what Gaussian local measurements are performed on systems distributed on a general graph, transport and processing of quantum information is not possible beyond a certain influence region, except for exponentially suppressed corrections. We also demonstrate that even under arbitrary non-Gaussian...

Source: http://arxiv.org/abs/1004.0081v2

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Sep 22, 2013
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Sep 22, 2013
by
J. Eisert; D. E. Browne; S. Scheel; M. B. Plenio

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We present an event-ready procedure that is capable of distilling Gaussian two-mode entangled states from a supply of weakly entangled states that have become mixed in a decoherence process. This procedure relies on passive optical elements and photon detectors distinguishing the presence and the absence of photons, but does not make use of photon counters. We identify fixed points of the iteration map, and discuss in detail its convergence properties. Necessary and sufficient criteria for the...

Source: http://arxiv.org/abs/quant-ph/0307106v3

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Sep 22, 2013
09/13

Sep 22, 2013
by
M. Hein; J. Eisert; H. J. Briegel

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Graph states are multi-particle entangled states that correspond to mathematical graphs, where the vertices of the graph take the role of quantum spin systems and edges represent Ising interactions. They are many-body spin states of distributed quantum systems that play a significant role in quantum error correction, multi-party quantum communication, and quantum computation within the framework of the one-way quantum computer. We characterize and quantify the genuine multi-particle...

Source: http://arxiv.org/abs/quant-ph/0307130v7

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Sep 22, 2013
09/13

Sep 22, 2013
by
J. Eisert; M. Wilkens

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In these lecture notes we investigate the implications of the identification of strategies with quantum operations in game theory beyond the results presented in [J. Eisert, M. Wilkens, and M. Lewenstein, Phys. Rev. Lett. 83, 3077 (1999)]. After introducing a general framework, we study quantum games with a classical analogue in order to flesh out the peculiarities of game theoretical settings in the quantum domain. Special emphasis is given to a detailed investigation of different sets of...

Source: http://arxiv.org/abs/quant-ph/0004076v1