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Sep 22, 2013
09/13

by
J. Eisert; M. B. Plenio

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We compare the entanglement of formation with a measure defined as the modulus of the negative eigenvalue of the partial transpose. In particular, we investigate whether both measures give the same ordering of density operators with respect to the amount of entanglement.

Source: http://arxiv.org/abs/quant-ph/9807034v2

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24

Sep 23, 2013
09/13

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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0.0

Jun 30, 2018
06/18

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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45

Sep 21, 2013
09/13

by
H. B. Coldenstrodt-Ronge; J. S. Lundeen; A. Feito; B. J. Smith; W. Mauerer; Ch. Silberhorn; J. Eisert; M. B. Plenio; I. A. Walmsley

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Measurement is the only part of a general quantum system that has yet to be characterized experimentally in a complete manner. Detector tomography provides a procedure for doing just this; an arbitrary measurement device can be fully characterized, and thus calibrated, in a systematic way without access to its components or its design. The result is a reconstructed POVM containing the measurement operators associated with each measurement outcome. We consider two detectors, a single-photon...

Source: http://arxiv.org/abs/0902.4384v1

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0.0

Jun 29, 2018
06/18

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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37

Sep 18, 2013
09/13

by
M. Cramer; J. Eisert; M. B. Plenio; J. Dreissig

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We demonstrate that the entropy of entanglement and the distillable entanglement of regions with respect to the rest of a general harmonic lattice system in the ground or a thermal state scale at most as the boundary area of the region. This area law is rigorously proven to hold true in non-critical harmonic lattice system of arbitrary spatial dimension, for general finite-ranged harmonic interactions, regions of arbitrary shape and states of nonzero temperature. For nearest-neighbor...

Source: http://arxiv.org/abs/quant-ph/0505092v3

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81

Sep 21, 2013
09/13

by
J. Eisert; M. Cramer; M. B. Plenio

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Physical interactions in quantum many-body systems are typically local: Individual constituents interact mainly with their few nearest neighbors. This locality of interactions is inherited by a decay of correlation functions, but also reflected by scaling laws of a quite profound quantity: The entanglement entropy of ground states. This entropy of the reduced state of a subregion often merely grows like the boundary area of the subregion, and not like its volume, in sharp contrast with an...

Source: http://arxiv.org/abs/0808.3773v4

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35

Sep 21, 2013
09/13

by
H. Bernigau; M. J. Kastoryano; J. Eisert

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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 framework for 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...

Source: http://arxiv.org/abs/1301.5646v1

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66

Sep 17, 2013
09/13

by
M. M. Wolf; J. Eisert; T. S. Cubitt; J. I. Cirac

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We investigate what a snapshot of a quantum evolution - a quantum channel reflecting open system dynamics - reveals about the underlying continuous time evolution. Remarkably, from such a snapshot, and without imposing additional assumptions, it can be decided whether or not a channel is consistent with a time (in)dependent Markovian evolution, for which we provide computable necessary and sufficient criteria. Based on these, a computable measure of `Markovianity' is introduced. We discuss how...

Source: http://arxiv.org/abs/0711.3172v2

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42

Sep 19, 2013
09/13

by
J. Eisert; M. Wilkens

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We consider entanglement-assisted remote quantum state manipulation of bi-partite mixed states. Several aspects are addressed: we present a class of mixed states of rank two that can be transformed into another class of mixed states under entanglement-assisted local operations with classical communication, but for which such a transformation is impossible without assistance. Furthermore, we demonstrate enhancement of the efficiency of purification protocols with the help of...

Source: http://arxiv.org/abs/quant-ph/9912080v3

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47

Sep 21, 2013
09/13

by
J. Eisert; T. Felbinger; P. Papadopoulos; M. B. Plenio; M. Wilkens

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We establish a quantitative connection between the amount of lost classical information about a quantum state and the concomitant loss of entanglement. Using methods that have been developed for the optimal purification of mixed states we find a class of mixed states with known distillable entanglement. These results can be used to determine the quantum capacity of a quantum channel which randomizes the order of transmitted signals.

Source: http://arxiv.org/abs/quant-ph/9907021v2

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33

Sep 24, 2013
09/13

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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30

Sep 19, 2013
09/13

by
K. Kieling; D. Gross; J. Eisert

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Several physical architectures allow for measurement-based quantum computing using sequential preparation of cluster states by means of probabilistic quantum gates. In such an approach, the order in which partial resources are combined to form the final cluster state turns out to be crucially important. We determine the influence of this classical decision process on the expected size of the final cluster. Extending earlier work, we consider different quantum gates operating at various...

Source: http://arxiv.org/abs/quant-ph/0703045v2

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33

Sep 21, 2013
09/13

by
J. Eisert; P. Hyllus; O. Guehne; M. Curty

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We investigate several problems in entanglement theory from the perspective of convex optimization. This list of problems comprises (A) the decision whether a state is multi-party entangled, (B) the minimization of expectation values of entanglement witnesses with respect to pure product states, (C) the closely related evaluation of the geometric measure of entanglement to quantify pure multi-party entanglement, (D) the test whether states are multi-party entangled on the basis of witnesses...

Source: http://arxiv.org/abs/quant-ph/0407135v3

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0.0

Jun 30, 2018
06/18

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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83

Jul 20, 2013
07/13

by
J. Eisert

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The density matrix renormalization group (DMRG) approach is arguably the most successful method to numerically find ground states of quantum spin chains. It amounts to iteratively locally optimizing matrix-product states, aiming at better and better approximating the true ground state. To date, both a proof of convergence to the globally best approximation and an assessment of its complexity are lacking. Here we establish a result on the computational complexity of an approximation with...

Source: http://arxiv.org/abs/quant-ph/0609051v3

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34

Sep 23, 2013
09/13

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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4.0

Jun 27, 2018
06/18

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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31

Sep 21, 2013
09/13

by
A. Mari; J. Eisert

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We introduce the idea of actually cooling quantum systems by means of incoherent thermal light, hence giving rise to a counter-intuitive mechanism of "cooling by heating". 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 opto-mechanical setting, where this effect...

Source: http://arxiv.org/abs/1104.0260v1

39
39

Sep 18, 2013
09/13

by
M. Cramer; J. Eisert

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We investigate the relationship between the gap between the energy of the ground state and the first excited state and the decay of correlation functions in harmonic lattice systems. We prove that in gapped systems, the exponential decay of correlations follows for both the ground state and thermal states. Considering the converse direction, we show that an energy gap can follow from algebraic decay and always does for exponential decay. The underlying lattices are described as general graphs...

Source: http://arxiv.org/abs/quant-ph/0509167v3

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59

Sep 18, 2013
09/13

by
O. Gühne; P. Hyllus; O. Gittsovich; J. Eisert

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We propose a unifying approach to the separability problem using covariance matrices of locally measurable observables. From a practical point of view, our approach leads to strong entanglement criteria that allow to detect the entanglement of many bound entangled states in higher dimensions and which are at the same time necessary and sufficient for two qubits. From a fundamental perspective, our approach leads to insights into the relations between several known entanglement criteria -- such...

Source: http://arxiv.org/abs/quant-ph/0611282v3

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79

Jul 20, 2013
07/13

by
M. Paternostro; D. Vitali; S. Gigan; M. S. Kim; C. Brukner; J. Eisert; M. Aspelmeyer

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We describe a scheme showing signatures of macroscopic optomechanical entanglement generated by radiation pressure in a cavity system with a massive movable mirror. The system we consider reveals genuine multipartite entanglement. We highlight the way the entanglement involving the inaccessible massive object is unravelled, in our scheme, by means of field-field quantum correlations.

Source: http://arxiv.org/abs/quant-ph/0609210v1

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0.0

Jun 29, 2018
06/18

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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38

Jul 19, 2013
07/13

by
A. Mari; K. Kieling; B. Melholt Nielsen; E. S. Polzik; J. Eisert

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We establish a method of directly measuring and estimating non-classicality - operationally defined in terms of the distinguishability of a given state from one with a positive Wigner function. It allows to certify non-classicality, based on possibly much fewer measurement settings than necessary for obtaining complete tomographic knowledge, and is at the same time equipped with a full certificate. We find that even from measuring two conjugate variables alone, one may infer the...

Source: http://arxiv.org/abs/1005.1665v2

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34

Sep 22, 2013
09/13

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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26

Sep 18, 2013
09/13

by
M. Cramer; S. Ospelkaus; C. Ospelkaus; K. Bongs; K. Sengstock; J. Eisert

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Mixtures of bosonic and fermionic atoms in optical lattices provide a promising arena to study strongly correlated systems. In experiments realizing such mixtures in the quantum degenerate regime the temperature is a key parameter. In this work, we investigate the intrinsic heating and cooling effects due to an entropy-preserving raising of the optical lattice potential. We analyze this process, identify the generic behavior valid for a wide range of parameters, and discuss it quantitatively...

Source: http://arxiv.org/abs/0707.3633v1

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29

Sep 20, 2013
09/13

by
D. E. Browne; J. Eisert; S. Scheel; M. B. Plenio

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We introduce a protocol that maps finite-dimensional pure input states onto approximately Gaussian states in an iterative procedure. This protocol can be used to distill highly entangled bi-partite Gaussian states from a supply of weakly entangled pure Gaussian states. The entire procedure requires only the use of passive optical elements and photon detectors that solely distinguish between the presence and absence of photons.

Source: http://arxiv.org/abs/quant-ph/0211173v5

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31

Sep 21, 2013
09/13

by
M. B. Plenio; J. Hartley; J. Eisert

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We study the entanglement dynamics of a system consisting of a large number of coupled harmonic oscillators in various configurations and for different types of nearest neighbour interactions. For a one-dimensional chain we provide compact analytical solutions and approximations to the dynamical evolution of the entanglement between spatially separated oscillators. Key properties such as the speed of entanglement propagation, the maximum amount of transferred entanglement and the efficiency for...

Source: http://arxiv.org/abs/quant-ph/0402004v2

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36

Sep 21, 2013
09/13

by
M. Ohliger; V. Nesme; J. Eisert

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We present a novel method to perform quantum state tomography for many-particle systems which are particularly suitable for estimating states in lattice systems such as of ultra-cold atoms in optical lattices. We show that the need for measuring a tomographically complete set of observables can be overcome by letting the state evolve under some suitably chosen random circuits followed by the measurement of a single observable. We generalize known results about the approximation of unitary...

Source: http://arxiv.org/abs/1204.5735v2

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1.0

Jun 30, 2018
06/18

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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1.0

Jun 29, 2018
06/18

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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119

Sep 21, 2013
09/13

by
M. Hein; W. Dür; J. Eisert; R. Raussendorf; M. Van den Nest; H. -J. Briegel

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Graph states form a rich class of entangled states that exhibit important aspects of multi-partite entanglement. At the same time, they can be described by a number of parameters that grows only moderately with the system size. They have a variety of applications in quantum information theory, most prominently as algorithmic resources in the context of the one-way quantum computer, but also in other fields such as quantum error correction and multi-partite quantum communication, as well as in...

Source: http://arxiv.org/abs/quant-ph/0602096v1

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163

Sep 19, 2013
09/13

by
J. Eisert

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This thesis covers several aspects of entanglement in the context of quantum information theory.

Source: http://arxiv.org/abs/quant-ph/0610253v1

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0.0

Jun 29, 2018
06/18

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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85

Sep 22, 2013
09/13

by
K. Audenaert; J. Eisert; M. B. Plenio; R. F. Werner

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We study the entanglement properties of a closed chain of harmonic oscillators that are coupled via a translationally invariant Hamiltonian, where the coupling acts only on the position operators. We consider the ground state and thermal states of this system, which are Gaussian states. The entanglement properties of these states can be completely characterized analytically when one uses the logarithmic negativity as a measure of entanglement.

Source: http://arxiv.org/abs/quant-ph/0205025v2

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29

Sep 20, 2013
09/13

by
G. Giedke; J. Eisert; J. I. Cirac; M. B. Plenio

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We present a theory of entanglement transformations of Gaussian pure states with local Gaussian operations and classical communication. This is the experimentally accessible set of operations that can be realized with optical elements such as beam splitters, phase shifts and squeezers, together with homodyne measurements. We provide a simple necessary and sufficient condition for the possibility to transform a pure bipartite Gaussian state into another one. We contrast our criterion with what...

Source: http://arxiv.org/abs/quant-ph/0301038v1

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46

Sep 20, 2013
09/13

by
M. B. Plenio; J. Eisert; J. Dreissig; M. Cramer

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We revisit the question of the relation between entanglement, entropy, and area for harmonic lattice Hamiltonians corresponding to discrete versions of real free Klein-Gordon fields. For the ground state of the d-dimensional cubic harmonic lattice we establish a strict relationship between the surface area of a distinguished hypercube and the degree of entanglement between the hypercube and the rest of the lattice analytically, without resorting to numerical means. We outline extensions of...

Source: http://arxiv.org/abs/quant-ph/0405142v3

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0.0

Jun 30, 2018
06/18

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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1.0

Jun 29, 2018
06/18

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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6.0

Jun 27, 2018
06/18

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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0.0

Jun 29, 2018
06/18

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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Sep 18, 2013
09/13

by
D. Gross; K. Audenaert; J. Eisert

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We clarify the mathematical structure underlying unitary $t$-designs. These are sets of unitary matrices, evenly distributed in the sense that the average of any $t$-th order polynomial over the design equals the average over the entire unitary group. We present a simple necessary and sufficient criterion for deciding if a set of matrices constitutes a design. Lower bounds for the number of elements of 2-designs are derived. We show how to turn mutually unbiased bases into approximate 2-designs...

Source: http://arxiv.org/abs/quant-ph/0611002v2

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37

Sep 21, 2013
09/13

by
J. Eisert

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In this paper it is shown that exact decoherence to minimal uncertainty Gaussian pointer states is generic for free quantum particles coupled to a heat bath. More specifically, the paper is concerned with damped free particles linearly coupled under product initial conditions to a heat bath at arbitrary temperature, with arbitrary coupling strength and spectral densities covering the Ohmic, subohmic, and supraohmic regime. Then it is true that there exists a time t_c such that for times...

Source: http://arxiv.org/abs/quant-ph/0311022v3

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Sep 19, 2013
09/13

by
M. Cramer; C. M. Dawson; J. Eisert; T. J. Osborne

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A reasonable physical intuition in the study of interacting quantum systems says that, independent of the initial state, the system will tend to equilibrate. In this work we study a setting where relaxation to a steady state is exact, namely for the Bose-Hubbard model where the system is quenched from a Mott quantum phase to the strong superfluid regime. We find that the evolving state locally relaxes to a steady state with maximum entropy constrained by second moments, maximizing the...

Source: http://arxiv.org/abs/cond-mat/0703314v2

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1.0

Jun 29, 2018
06/18

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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Sep 22, 2013
09/13

by
M. Cramer; A. Flesch; I. P. McCulloch; U. Schollwoeck; J. Eisert

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We establish a setting - atoms in optical superlattices with period 2 - in which one can experimentally probe signatures of the process of local relaxation and apparent thermalization in non-equilibrium dynamics without the need of addressing single sites. This opens up a way to explore the convergence of subsystems to maximum entropy states in quenched quantum many-body systems with present technology. Remarkably, the emergence of thermal states does not follow from a coupling to an...

Source: http://arxiv.org/abs/0805.0798v2

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Sep 18, 2013
09/13

by
S. Scheel; W. J. Munro; J. Eisert; K. Nemoto; P. Kok

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Nonlinear optical quantum gates can be created probabilistically using only single photon sources, linear optical elements and photon-number resolving detectors. These gates are heralded but operate with probabilities much less than one. There is currently a large gap between the performance of the known circuits and the established upper bounds on their success probabilities. One possibility for increasing the probability of success of such gates is feed-forward, where one attempts to correct...

Source: http://arxiv.org/abs/quant-ph/0509075v3

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Jun 27, 2018
06/18

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 30, 2018
06/18

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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Jun 30, 2018
06/18

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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