Publications of Thomas Barthel    :chronological  by type listing:

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@article{fds302498,
   Author = {Cai, Z and Barthel, T},
   Title = {Algebraic versus exponential decoherence in dissipative
             many-particle systems},
   Journal = {Physical Review Letters},
   Volume = {111},
   Number = {15},
   Pages = {150403},
   Year = {2013},
   Month = {October},
   ISSN = {0031-9007},
   url = {http://dx.doi.org/10.1103/PhysRevLett.111.150403},
   Abstract = {The interplay between dissipation and internal interactions
             in quantum many-body systems gives rise to a wealth of novel
             phenomena. Here we investigate spin-1/2 chains with uniform
             local couplings to a Markovian environment using the
             time-dependent density matrix renormalization group. For the
             open XXZ model, we discover that the decoherence time
             diverges in the thermodynamic limit. The coherence decay is
             then algebraic instead of exponential. This is due to a
             vanishing gap in the spectrum of the corresponding Liouville
             superoperator and can be explained on the basis of a
             perturbative treatment. In contrast, decoherence in the open
             transverse-field Ising model is found to be always
             exponential. In this case, the internal interactions can
             both facilitate and impede the environment-induced
             decoherence. © 2013 American Physical Society.},
   Doi = {10.1103/PhysRevLett.111.150403},
   Key = {fds302498}
}

@article{fds318404,
   Author = {Alba, V},
   Title = {Bound states and entanglement in the excited states of
             quantum spin chains},
   Journal = {Journal of Statistical Mechanics: Theory and
             Experiment},
   Volume = {2014},
   Number = {10},
   Pages = {P10029-P10029},
   Publisher = {IOP Publishing},
   Year = {2014},
   Month = {October},
   url = {http://dx.doi.org/10.1088/1742-5468/2014/10/P10029},
   Abstract = {© 2014 IOP Publishing Ltd and SISSA Medialab srl. We
             investigate the entanglement properties of the excited
             states of the spin-1/2 Heisenberg (XXX) chain with isotropic
             antiferromagnetic interactions, by exploiting the Bethe
             ansatz solution of the model. We consider eigenstates
             obtained from both real and complex solutions ('strings') of
             the Bethe equations. Physically, the former are states of
             interacting magnons, whereas the latter contain bound states
             of groups of particles. We first focus on the situation with
             few particles in the chain. Using exact results and
             semiclassical arguments, we derive an upper bound SMAX for
             the entanglement entropy. This exhibits an intermediate
             behaviour between logarithmic and extensive, and it is
             saturated for highly-entangled states. As a function of the
             eigenstate energy, the entanglement entropy is organized in
             bands. Their number depends on the number of blocks of
             contiguous Bethe.Takahashi quantum numbers. In the presence
             of bound states a significant reduction in the entanglement
             entropy occurs, reflecting that a group of bound particles
             behaves effectively as a single particle. Interestingly, the
             associated entanglement spectrum shows edge-related levels.
             At a finite particle density, the semiclassical bound
             SMAXbecomes inaccurate. For highly-entangled states SA∝
             Lc, with Lcthe chord length, signalling the crossover to
             extensive entanglement. Finally, we consider eigenstates
             containing a single pair of bound particles. No significant
             entanglement reduction occurs, in contrast with the
             fewparticle case.},
   Doi = {10.1088/1742-5468/2014/10/P10029},
   Key = {fds318404}
}

@article{fds302487,
   Author = {Barthel, T and Pineda, C and Eisert, J},
   Title = {Contraction of fermionic operator circuits and the
             simulation of strongly correlated fermions},
   Journal = {Physical Review A},
   Volume = {80},
   Number = {4},
   Publisher = {American Physical Society (APS)},
   Year = {2009},
   Month = {October},
   ISSN = {1050-2947},
   url = {http://dx.doi.org/10.1103/PhysRevA.80.042333},
   Abstract = {A fermionic operator circuit is a product of fermionic
             operators of usually different and partially overlapping
             support. Further elements of fermionic operator circuits
             (FOCs) are partial traces and partial projections. The
             presented framework allows for the introduction of fermionic
             versions of known qudit operator circuits (QUOC), important
             for the simulation of strongly correlated d -dimensional
             systems: the multiscale entanglement renormalization
             ansätze (MERA), tree tensor networks (TTN), projected
             entangled pair states (PEPS), or their infinite-size
             versions (iPEPS etc.). After the definition of a FOC, we
             present a method to contract it with the same computation
             and memory requirements as a corresponding QUOC, for which
             all fermionic operators are replaced by qudit operators of
             identical dimension. A given scheme for contracting the QUOC
             relates to an analogous scheme for the corresponding
             fermionic circuit, where additional marginal computational
             costs arise only from reordering of modes for operators
             occurring in intermediate stages of the contraction. Our
             result hence generalizes efficient schemes for the
             simulation of d -dimensional spin systems, as MERA, TTN, or
             PEPS to the fermionic case. © 2009 The American Physical
             Society.},
   Doi = {10.1103/PhysRevA.80.042333},
   Key = {fds302487}
}

@article{fds302492,
   Author = {Barthel, T and Schollwöck, U},
   Title = {Dephasing and the steady state in quantum many-particle
             systems},
   Journal = {Physical Review Letters},
   Volume = {100},
   Number = {10},
   Pages = {100601},
   Year = {2008},
   Month = {March},
   ISSN = {0031-9007},
   url = {http://dx.doi.org/10.1103/PhysRevLett.100.100601},
   Abstract = {We discuss relaxation in bosonic and fermionic many-particle
             systems. For integrable systems, time evolution can cause a
             dephasing effect, leading for finite subsystems to steady
             states. We explicitly derive those steady subsystem states
             and devise sufficient prerequisites for the dephasing to
             occur. We also find simple scenarios, in which dephasing is
             ineffective and discuss the dependence on dimensionality and
             criticality. It follows further that, after a quench of
             system parameters, entanglement entropy will become
             extensive. This provides a way of creating strong
             entanglement in a controlled fashion. © 2008 The American
             Physical Society.},
   Doi = {10.1103/PhysRevLett.100.100601},
   Key = {fds302492}
}

@article{fds302493,
   Author = {Kliesch, M and Barthel, T and Gogolin, C and Kastoryano, M and Eisert,
             J},
   Title = {Dissipative quantum Church-Turing theorem},
   Journal = {Physical Review Letters},
   Volume = {107},
   Number = {12},
   Pages = {120501},
   Year = {2011},
   Month = {September},
   ISSN = {0031-9007},
   url = {http://dx.doi.org/10.1103/PhysRevLett.107.120501},
   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. © 2011 American Physical
             Society.},
   Doi = {10.1103/PhysRevLett.107.120501},
   Key = {fds302493}
}

@article{fds302499,
   Author = {Halimeh, JC and Wöllert, A and McCulloch, I and Schollwöck, U and Barthel, T},
   Title = {Domain-wall melting in ultracold-boson systems with hole and
             spin-flip defects},
   Journal = {Physical Review A},
   Volume = {89},
   Number = {6},
   Publisher = {American Physical Society (APS)},
   Year = {2014},
   Month = {June},
   ISSN = {1050-2947},
   url = {http://dx.doi.org/10.1103/PhysRevA.89.063603},
   Abstract = {Quantum magnetism is a fundamental phenomenon of nature. As
             of late, it has garnered a lot of interest because
             experiments with ultracold atomic gases in optical lattices
             could be used as a simulator for phenomena of magnetic
             systems. A paradigmatic example is the time evolution of a
             domain-wall state of a spin-1/2 Heisenberg chain, the
             so-called domain-wall melting. The model can be implemented
             by having two species of bosonic atoms with unity filling
             and strong on-site repulsion U in an optical lattice. In
             this paper, we study the domain-wall melting in such a setup
             on the basis of the time-dependent density matrix
             renormalization group (tDMRG). We are particularly
             interested in the effects of defects that originate from an
             imperfect preparation of the initial state. Typical defects
             are holes (empty sites) and flipped spins. We show that the
             dominating effects of holes on observables like the
             spatially resolved magnetization can be taken account of by
             a linear combination of spatially shifted observables from
             the clean case. For sufficiently large U, further effects
             due to holes become negligible. In contrast, the effects of
             spin flips are more severe as their dynamics occur on the
             same time scale as that of the domain-wall melting itself.
             It is hence advisable to avoid preparation schemes that are
             based on spin flips. © 2014 American Physical
             Society.},
   Doi = {10.1103/PhysRevA.89.063603},
   Key = {fds302499}
}

@article{fds302485,
   Author = {Zhou, HQ and Barthel, T and Fjærestad, JO and Schollwöck,
             U},
   Title = {Entanglement and boundary critical phenomena},
   Journal = {Physical Review A},
   Volume = {74},
   Number = {5},
   Publisher = {American Physical Society (APS)},
   Year = {2006},
   Month = {November},
   ISSN = {1050-2947},
   url = {http://dx.doi.org/10.1103/PhysRevA.74.050305},
   Abstract = {We investigate boundary critical phenomena from a
             quantum-information perspective. Bipartite entanglement in
             the ground state of one-dimensional quantum systems is
             quantified using the Rényi entropy Sα, which includes the
             von Neumann entropy (α→1) and the single-copy
             entanglement (α→) as special cases. We identify the
             contribution of the boundaries to the Rényi entropy, and
             show that there is an entanglement loss along boundary
             renormalization group (RG) flows. This property, which is
             intimately related to the Affleck-Ludwig g theorem, is a
             consequence of majorization relations between the spectra of
             the reduced density matrix along the boundary RG flows. We
             also point out that the bulk contribution to the single-copy
             entanglement is half of that to the von Neumann entropy,
             whereas the boundary contribution is the same. © 2006 The
             American Physical Society.},
   Doi = {10.1103/PhysRevA.74.050305},
   Key = {fds302485}
}

@article{fds302491,
   Author = {Barthel, T and Dusuel, S and Vidal, J},
   Title = {Entanglement entropy beyond the free case},
   Journal = {Physical Review Letters},
   Volume = {97},
   Number = {22},
   Pages = {220402},
   Year = {2006},
   Month = {January},
   ISSN = {0031-9007},
   url = {http://dx.doi.org/10.1103/PhysRevLett.97.220402},
   Abstract = {We present a perturbative method to compute the ground state
             entanglement entropy for interacting systems. We apply it to
             a collective model of mutually interacting spins in a
             magnetic field. At the quantum critical point, the
             entanglement entropy scales logarithmically with the
             subsystem size, the system size, and the anisotropy
             parameter. We determine the corresponding scaling prefactors
             and evaluate the leading finite-size correction to the
             entropy. Our analytical predictions are in perfect agreement
             with numerical results. © 2006 The American Physical
             Society.},
   Doi = {10.1103/PhysRevLett.97.220402},
   Key = {fds302491}
}

@article{fds302484,
   Author = {Vidal, J and Dusuel, S and Barthel, T},
   Title = {Entanglement entropy in collective models},
   Journal = {Journal of Statistical Mechanics: Theory and
             Experiment},
   Volume = {2007},
   Number = {1},
   Pages = {P01015-P01015},
   Publisher = {IOP Publishing},
   Year = {2007},
   Month = {January},
   url = {http://dx.doi.org/10.1088/1742-5468/2007/01/P01015},
   Abstract = {We discuss the behaviour of the entanglement entropy of the
             ground state in various collective systems. Results for
             general quadratic two-mode boson models are given, yielding
             the relation between quantum phase transitions of the system
             (signalled by a divergence of the entanglement entropy) and
             the excitation energies. Such systems naturally arise when
             expanding collective spin Hamiltonians at leading order via
             the Holstein-Primakoff mapping. In a second step, we analyse
             several such models (the Dicke model, the two-level
             Bardeen-Cooper-Schrieffer model, the Lieb-Mattis model and
             the Lipkin-Meshkov-Glick model) and investigate the
             properties of the entanglement entropy over the whole
             parameter range. We show that when the system contains
             gapless excitations the entanglement entropy of the ground
             state diverges with increasing system size. We derive and
             classify the scaling behaviours that can be met. © IOP
             Publishing Ltd.},
   Doi = {10.1088/1742-5468/2007/01/P01015},
   Key = {fds302484}
}

@article{fds302486,
   Author = {Barthel, T and Chung, MC and Schollwöck, U},
   Title = {Entanglement scaling in critical two-dimensional fermionic
             and bosonic systems},
   Journal = {Physical Review A},
   Volume = {74},
   Number = {2},
   Publisher = {American Physical Society (APS)},
   Year = {2006},
   Month = {September},
   ISSN = {1050-2947},
   url = {http://dx.doi.org/10.1103/PhysRevA.74.022329},
   Abstract = {We relate the reduced density matrices of quadratic
             fermionic and bosonic models to their Green's function
             matrices in a unified way and calculate the scaling of the
             entanglement entropy of finite systems in an infinite
             universe exactly. For critical fermionic two-dimensional
             (2D) systems at T=0, two regimes of scaling are identified:
             generically, we find a logarithmic correction to the area
             law with a prefactor dependence on the chemical potential
             that confirms earlier predictions based on the Widom
             conjecture. If, however, the Fermi surface of the critical
             system is zero-dimensional, then we find an area law with a
             sublogarithmic correction. For a critical bosonic 2D array
             of coupled oscillators at T=0, our results show that the
             entanglement entropy follows the area law without
             corrections. © 2006 The American Physical
             Society.},
   Doi = {10.1103/PhysRevA.74.022329},
   Key = {fds302486}
}

@article{fds302483,
   Author = {Kliesch, M and Barthel, T and Gogolin, C and Kastoryano, M and Eisert,
             J},
   Title = {Erratum: Dissipative quantum church-turing theorem (Physical
             Review Letters (2011) 107 (120501))},
   Journal = {Physical Review Letters},
   Volume = {109},
   Number = {11},
   Publisher = {American Physical Society (APS)},
   Year = {2012},
   Month = {September},
   ISSN = {0031-9007},
   url = {http://dx.doi.org/10.1103/PhysRevLett.109.119904},
   Doi = {10.1103/PhysRevLett.109.119904},
   Key = {fds302483}
}

@article{fds318402,
   Author = {Modugno, G and Giamarchi, T and D'Errico, C and Roux,
             G},
   Title = {Finite-temperature effects on interacting bosonic
             one-dimensional systems in disordered lattices},
   Journal = {Physical Review A},
   Volume = {93},
   Number = {3},
   Publisher = {American Physical Society (APS)},
   Year = {2016},
   Month = {March},
   url = {http://dx.doi.org/10.1103/PhysRevA.93.033650},
   Abstract = {© 2016 American Physical Society. We analyze the
             finite-temperature effects on the phase diagram describing
             the insulating properties of interacting one-dimensional
             bosons in a quasiperiodic lattice. We examine thermal
             effects by comparing experimental results to exact
             diagonalization for small-sized systems and to
             density-matrix renormalization group (DMRG) computations. At
             weak interactions, we find short thermal correlation
             lengths, indicating a substantial impact of temperature on
             the system coherence. Conversely, at strong interactions,
             the obtained thermal correlation lengths are significantly
             larger than the localization length, and the quantum nature
             of the T=0 Bose-glass phase is preserved up to a crossover
             temperature that depends on the disorder strength.
             Furthermore, in the absence of disorder, we show how
             quasiexact finite-T DMRG computations, compared to
             experimental results, can be employed to estimate the
             temperature, which is not directly accessible in the
             experiment.},
   Doi = {10.1103/PhysRevA.93.033650},
   Key = {fds318402}
}

@article{fds338335,
   Author = {Barthel, T and Lu, J},
   Title = {Fundamental Limitations for Measurements in Quantum
             Many-Body Systems},
   Journal = {Physical Review Letters},
   Volume = {121},
   Number = {8},
   Pages = {080406},
   Year = {2018},
   Month = {August},
   url = {http://dx.doi.org/10.1103/PhysRevLett.121.080406},
   Abstract = {© 2018 American Physical Society. Dynamical measurement
             schemes are an important tool for the investigation of
             quantum many-body systems, especially in the age of quantum
             simulation. Here, we address the question whether generic
             measurements can be implemented efficiently if we have
             access to a certain set of experimentally realizable
             measurements and can extend it through time evolution. For
             the latter, two scenarios are considered: (a) evolution
             according to unitary circuits and (b) evolution due to
             Hamiltonians that we can control in a time-dependent
             fashion. We find that the time needed to realize a certain
             measurement to a predefined accuracy scales in general
             exponentially with the system size - posing a fundamental
             limitation. The argument is based on the construction of
             μ-packings for manifolds of observables with identical
             spectra and a comparison of their cardinalities to those of
             μ-coverings for quantum circuits and unitary time-evolution
             operators. The former is related to the study of Grassmann
             manifolds.},
   Doi = {10.1103/PhysRevLett.121.080406},
   Key = {fds338335}
}

@article{fds340902,
   Author = {Binder, M and Barthel, T},
   Title = {Infinite boundary conditions for response functions and
             limit cycles within the infinite-system density matrix
             renormalization group approach demonstrated for
             bilinear-biquadratic spin-1 chains},
   Journal = {Physical Review B},
   Volume = {98},
   Number = {23},
   Publisher = {American Physical Society (APS)},
   Year = {2018},
   Month = {December},
   url = {http://dx.doi.org/10.1103/physrevb.98.235114},
   Doi = {10.1103/physrevb.98.235114},
   Key = {fds340902}
}

@article{fds302496,
   Author = {Barthel, T and Kasztelan, C and McCulloch, IP and Schollwöck,
             U},
   Title = {Magnetism, coherent many-particle dynamics, and relaxation
             with ultracold bosons in optical superlattices},
   Journal = {Physical Review A},
   Volume = {79},
   Number = {5},
   Publisher = {American Physical Society (APS)},
   Year = {2009},
   Month = {May},
   ISSN = {1050-2947},
   url = {http://dx.doi.org/10.1103/PhysRevA.79.053627},
   Abstract = {We study how well magnetic models can be implemented with
             ultracold bosonic atoms of two different hyperfine states in
             an optical superlattice. The system is captured by a
             two-species Bose-Hubbard model, but realizes in a certain
             parameter regime actually the physics of a spin-1/2
             Heisenberg magnet, describing the second-order hopping
             processes. Tuning of the superlattice allows for controlling
             the effect of fast first-order processes versus the slower
             second-order ones. Using the density-matrix
             renormalization-group method, we provide the evolution of
             typical experimentally available observables. The validity
             of the description via the Heisenberg model, depending on
             the parameters of the Hubbard model, is studied numerically
             and analytically. The analysis is also motivated by recent
             experiments where coherent two-particle dynamics with
             ultracold bosonic atoms in isolated double wells were
             realized. We provide theoretical background for the next
             step, the observation of coherent many-particle dynamics
             after coupling the double wells. Contrary to the case of
             isolated double wells, relaxation of local observables can
             be observed. The tunability between the Bose-Hubbard model
             and the Heisenberg model in this setup could be used to
             study experimentally the differences in equilibration
             processes for nonintegrable and Bethe ansatz integrable
             models. We show that the relaxation in the Heisenberg model
             is connected to a phase averaging effect, which is in
             contrast to the typical scattering driven thermalization in
             nonintegrable models. We discuss the preparation of magnetic
             ground states by adiabatic tuning of the superlattice
             parameters. © 2009 The American Physical
             Society.},
   Doi = {10.1103/PhysRevA.79.053627},
   Key = {fds302496}
}

@article{fds332866,
   Author = {Barthel, T and De Bacco and C and Franz, S},
   Title = {Matrix product algorithm for stochastic dynamics on networks
             applied to nonequilibrium Glauber dynamics.},
   Journal = {Physical Review. E},
   Volume = {97},
   Number = {1-1},
   Pages = {010104},
   Year = {2018},
   Month = {January},
   url = {http://dx.doi.org/10.1103/physreve.97.010104},
   Abstract = {We introduce and apply an efficient method for the precise
             simulation of stochastic dynamical processes on locally
             treelike graphs. Networks with cycles are treated in the
             framework of the cavity method. Such models correspond, for
             example, to spin-glass systems, Boolean networks, neural
             networks, or other technological, biological, and social
             networks. Building upon ideas from quantum many-body theory,
             our approach is based on a matrix product approximation of
             the so-called edge messages-conditional probabilities of
             vertex variable trajectories. Computation costs and accuracy
             can be tuned by controlling the matrix dimensions of the
             matrix product edge messages (MPEM) in truncations. In
             contrast to Monte Carlo simulations, the algorithm has a
             better error scaling and works for both single instances as
             well as the thermodynamic limit. We employ it to examine
             prototypical nonequilibrium Glauber dynamics in the kinetic
             Ising model. Because of the absence of cancellation effects,
             observables with small expectation values can be evaluated
             accurately, allowing for the study of decay processes and
             temporal correlations.},
   Doi = {10.1103/physreve.97.010104},
   Key = {fds332866}
}

@article{fds322472,
   Author = {Barthel, T},
   Title = {Matrix product purifications for canonical ensembles and
             quantum number distributions},
   Journal = {Physical Review B},
   Volume = {94},
   Number = {11},
   Publisher = {American Physical Society (APS)},
   Year = {2016},
   Month = {September},
   url = {http://dx.doi.org/10.1103/PhysRevB.94.115157},
   Abstract = {© 2016 American Physical Society. Matrix product
             purifications (MPPs) are a very efficient tool for the
             simulation of strongly correlated quantum many-body systems
             at finite temperatures. When a system features symmetries,
             these can be used to reduce computation costs substantially.
             It is straightforward to compute an MPP of a grand-canonical
             ensemble, also when symmetries are exploited. This paper
             provides and demonstrates methods for the efficient
             computation of MPPs of canonical ensembles under utilization
             of symmetries. Furthermore, we present a scheme for the
             evaluation of global quantum number distributions using
             matrix product density operators (MPDOs). We provide exact
             matrix product representations for canonical
             infinite-temperature states, and discuss how they can be
             constructed alternatively by applying matrix product
             operators to vacuum-type states or by using entangler
             Hamiltonians. A demonstration of the techniques for
             Heisenberg spin-1/2 chains explains why the difference in
             the energy densities of canonical and grand-canonical
             ensembles decays as 1/L.},
   Doi = {10.1103/PhysRevB.94.115157},
   Key = {fds322472}
}

@article{fds302490,
   Author = {Binder, M and Barthel, T},
   Title = {Minimally entangled typical thermal states versus matrix
             product purifications for the simulation of equilibrium
             states and time evolution},
   Journal = {Physical Review B},
   Volume = {92},
   Number = {12},
   Publisher = {American Physical Society (APS)},
   Year = {2015},
   Month = {September},
   ISSN = {1098-0121},
   url = {http://dx.doi.org/10.1103/PhysRevB.92.125119},
   Abstract = {© 2015 American Physical Society. For the simulation of
             equilibrium states and finite-temperature response functions
             of strongly correlated quantum many-body systems, we compare
             the efficiencies of two different approaches in the
             framework of the density matrix renormalization group
             (DMRG). The first is based on matrix product purifications.
             The second, more recent one, is based on so-called minimally
             entangled typical thermal states (METTS). For the latter, we
             highlight the interplay of statistical and DMRG truncation
             errors, discuss the use of self-averaging effects, and
             describe schemes for the computation of response functions.
             For critical as well as gapped phases of the spin-1/2 XXZ
             chain and the one-dimensional Bose-Hubbard model, we assess
             the computation costs and accuracies of the two methods at
             different temperatures. For almost all considered cases, we
             find that, for the same computation cost, purifications
             yield more accurate results than METTS - often by orders of
             magnitude. The METTS algorithm becomes more efficient only
             for temperatures well below the system's energy gap. The
             exponential growth of the computation cost in the evaluation
             of response functions limits the attainable time scales in
             both methods and we find that in this regard, METTS do not
             outperform purifications.},
   Doi = {10.1103/PhysRevB.92.125119},
   Key = {fds302490}
}

@article{fds302497,
   Author = {Lake, B and Tennant, DA and Caux, JS and Barthel, T and Schollwöck, U and Nagler, SE and Frost, CD},
   Title = {Multispinon continua at zero and finite temperature in a
             near-ideal heisenberg Chain},
   Journal = {Physical Review Letters},
   Volume = {111},
   Number = {13},
   Pages = {137205},
   Year = {2013},
   Month = {September},
   ISSN = {0031-9007},
   url = {http://dx.doi.org/10.1103/PhysRevLett.111.137205},
   Abstract = {The space-and time-dependent response of many-body quantum
             systems is the most informative aspect of their emergent
             behavior. The dynamical structure factor, experimentally
             measurable using neutron scattering, can map this response
             in wave vector and energy with great detail, allowing
             theories to be quantitatively tested to high accuracy. Here,
             we present a comparison between neutron scattering
             measurements on the one-dimensional spin-1/2 Heisenberg
             antiferromagnet KCuF3, and recent state-of-the-art
             theoretical methods based on integrability and density
             matrix renormalization group simulations. The unprecedented
             quantitative agreement shows that precise descriptions of
             strongly correlated states at all distance, time, and
             temperature scales are now possible, and highlights the need
             to apply these novel techniques to other problems in
             low-dimensional magnetism. © 2013 American Physical
             Society.},
   Doi = {10.1103/PhysRevLett.111.137205},
   Key = {fds302497}
}

@article{fds318403,
   Author = {Schlittler, T and Barthel, T and Misguich, G and Vidal, J and Mosseri,
             R},
   Title = {Phase Diagram of an Extended Quantum Dimer Model on the
             Hexagonal Lattice.},
   Journal = {Physical Review Letters},
   Volume = {115},
   Number = {21},
   Pages = {217202},
   Year = {2015},
   Month = {November},
   url = {http://dx.doi.org/10.1103/physrevlett.115.217202},
   Abstract = {We introduce a quantum dimer model on the hexagonal lattice
             that, in addition to the standard three-dimer kinetic and
             potential terms, includes a competing potential part
             counting dimer-free hexagons. The zero-temperature phase
             diagram is studied by means of quantum Monte Carlo
             simulations, supplemented by variational arguments. It
             reveals some new crystalline phases and a cascade of
             transitions with rapidly changing flux (tilt in the height
             language). We analyze perturbatively the vicinity of the
             Rokhsar-Kivelson point, showing that this model has the
             microscopic ingredients needed for the "devil's staircase"
             scenario [Eduardo Fradkin et al. Phys. Rev. B 69, 224415
             (2004)], and is therefore expected to produce fractal
             variations of the ground-state flux.},
   Doi = {10.1103/physrevlett.115.217202},
   Key = {fds318403}
}

@article{fds329759,
   Author = {Schlittler, TM and Mosseri, R and Barthel, T},
   Title = {Phase diagram of the hexagonal lattice quantum dimer model:
             Order parameters, ground-state energy, and
             gaps},
   Journal = {Physical Review B},
   Volume = {96},
   Number = {19},
   Pages = {195142-195142},
   Publisher = {American Physical Society (APS)},
   Year = {2017},
   Month = {November},
   url = {http://dx.doi.org/10.1103/physrevb.96.195142},
   Abstract = {It is by now well-known that ground states of gapped
             one-dimensional (1d) quantum-many body systems with
             short-range interactions can be studied efficiently using
             classical computers and matrix product state techniques. A
             corresponding result for finite temperatures was missing.
             For 1d systems that can be described by a local 1+1d field
             theory, it is shown here that the cost for the classical
             simulation at finite temperatures grows in fact only
             polynomially with the inverse temperature and is system-size
             independent -- even for quantum critical systems. In
             particular, we show that the thermofield double state (TDS),
             a purification of the equilibrium density operator, can be
             obtained efficiently in matrix-product form. The argument is
             based on the scaling behavior of R\'{e}nyi entanglement
             entropies in the TDS. At finite temperatures, they obey the
             area law. For quantum critical systems, the entanglement is
             found to grow only logarithmically with inverse temperature,
             S~log(beta). The field-theoretical results are confirmed by
             quasi-exact numerical simulations of quantum magnets and
             interacting bosons.},
   Doi = {10.1103/physrevb.96.195142},
   Key = {fds329759}
}

@article{fds302500,
   Author = {Barthel, T},
   Title = {Precise evaluation of thermal response functions by
             optimized density matrix renormalization group
             schemes},
   Journal = {New Journal of Physics},
   Volume = {15},
   Number = {7},
   Pages = {073010-073010},
   Publisher = {IOP Publishing},
   Year = {2013},
   Month = {July},
   url = {http://dx.doi.org/10.1088/1367-2630/15/7/073010},
   Abstract = {This paper provides a study and discussion of earlier as
             well as novel more efficient schemes for the precise
             evaluation of finite-temperature response functions of
             strongly correlated quantum systems in the framework of the
             time-dependent density matrix renormalization group (tDMRG).
             The computational costs and bond dimensions as functions of
             time and temperature are examined for the example of the
             spin-1/2 XXZ Heisenberg chain in the critical XY phase and
             the gapped Néel phase. The matrix product state
             purifications occurring in the algorithms are in a
             one-to-one relation with the corresponding matrix product
             operators. This notational simplification elucidates
             implications of quasi-locality on the computational costs.
             Based on the observation that there is considerable freedom
             in designing efficient tDMRG schemes for the calculation of
             dynamical correlators at finite temperatures, a new class of
             optimizable schemes, as recently suggested in Barthel,
             Schollwöck and Sachdev (2012 arXiv:1212.3570), is explained
             and analyzed numerically. A specific novel near-optimal
             scheme that requires no additional optimization reaches
             maximum times that are typically increased by a factor of 2,
             when compared against earlier approaches. These increased
             reachable times make many more physical applications
             accessible. For each of the described tDMRG schemes, one can
             devise a corresponding transfer matrix renormalization group
             variant. © IOP Publishing and Deutsche Physikalische
             Gesellschaft.},
   Doi = {10.1088/1367-2630/15/7/073010},
   Key = {fds302500}
}

@article{fds302495,
   Author = {Barthel, T and Kliesch, M},
   Title = {Quasilocality and efficient simulation of Markovian quantum
             dynamics},
   Journal = {Physical Review Letters},
   Volume = {108},
   Number = {23},
   Pages = {230504},
   Year = {2012},
   Month = {June},
   ISSN = {0031-9007},
   url = {http://dx.doi.org/10.1103/PhysRevLett.108.230504},
   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. © 2012
             American Physical Society.},
   Doi = {10.1103/PhysRevLett.108.230504},
   Key = {fds302495}
}

@article{fds302489,
   Author = {Roux, G and Barthel, T and McCulloch, IP and Kollath, C and Schollwöck,
             U and Giamarchi, T},
   Title = {Quasiperiodic Bose-Hubbard model and localization in
             one-dimensional cold atomic gases},
   Journal = {Physical Review A},
   Volume = {78},
   Number = {2},
   Publisher = {American Physical Society (APS)},
   Year = {2008},
   Month = {August},
   ISSN = {1050-2947},
   url = {http://dx.doi.org/10.1103/PhysRevA.78.023628},
   Abstract = {We compute the phase diagram of the one-dimensional
             Bose-Hubbard model with a quasiperiodic potential by means
             of the density-matrix renormalization group technique. This
             model describes the physics of cold atoms loaded in an
             optical lattice in the presence of a superlattice potential
             whose wavelength is incommensurate with the main lattice
             wavelength. After discussing the conditions under which the
             model can be realized experimentally, the study of the
             density vs the chemical potential curves for a nontrapped
             system unveils the existence of gapped phases at
             incommensurate densities interpreted as incommensurate
             charge-density-wave phases. Furthermore, a localization
             transition is known to occur above a critical value of the
             potential depth V2 in the case of free and hard-core bosons.
             We extend these results to soft-core bosons for which the
             phase diagrams at fixed densities display new features
             compared with the phase diagrams known for random box
             distribution disorder. In particular, a direct transition
             from the superfluid phase to the Mott-insulating phase is
             found at finite V2. Evidence for reentrances of the
             superfluid phase upon increasing interactions is presented.
             We finally comment on different ways to probe the emergent
             quantum phases and most importantly, the existence of a
             critical value for the localization transition. The latter
             feature can be investigated by looking at the expansion of
             the cloud after releasing the trap. © 2008 The American
             Physical Society.},
   Doi = {10.1103/PhysRevA.78.023628},
   Key = {fds302489}
}

@article{fds302488,
   Author = {Barthel, T and Kliesch, M and Eisert, J},
   Title = {Real-space renormalization yields finite
             correlations},
   Journal = {Physical Review Letters},
   Volume = {105},
   Number = {1},
   Publisher = {American Physical Society (APS)},
   Year = {2010},
   Month = {July},
   ISSN = {0031-9007},
   url = {http://dx.doi.org/10.1103/PhysRevLett.105.010502},
   Abstract = {Real-space renormalization approaches for quantum lattice
             systems generate certain hierarchical classes of states that
             are subsumed by the multiscale entanglement renormalization
             Ansatz (MERA). It is shown that, with the exception of one
             spatial dimension, MERA states are actually states with
             finite correlations, i.e., projected entangled pair states
             (PEPS) with a bond dimension independent of the system size.
             Hence, real-space renormalization generates states which can
             be encoded with local effective degrees of freedom, and MERA
             states form an efficiently contractible class of PEPS that
             obey the area law for the entanglement entropy. It is
             further pointed out that there exist other efficiently
             contractible schemes violating the area law. © 2010 The
             American Physical Society.},
   Doi = {10.1103/PhysRevLett.105.010502},
   Key = {fds302488}
}

@article{fds302494,
   Author = {Barthel, T and Hübener, R},
   Title = {Solving condensed-matter ground-state problems by
             semidefinite relaxations},
   Journal = {Physical Review Letters},
   Volume = {108},
   Number = {20},
   Pages = {200404},
   Year = {2012},
   Month = {May},
   ISSN = {0031-9007},
   url = {http://dx.doi.org/10.1103/PhysRevLett.108.200404},
   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 Green'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 MonteCarlo
             calculations, and Anderson bounds, showing the
             competitiveness of the SDP method. © 2012 American Physical
             Society.},
   Doi = {10.1103/PhysRevLett.108.200404},
   Key = {fds302494}
}

@article{fds302501,
   Author = {Barthel, T and Schollwöck, U and White, SR},
   Title = {Spectral functions in one-dimensional quantum systems at
             finite temperature using the density matrix renormalization
             group},
   Journal = {Physical Review B},
   Volume = {79},
   Number = {24},
   Publisher = {American Physical Society (APS)},
   Year = {2009},
   Month = {June},
   ISSN = {1098-0121},
   url = {http://dx.doi.org/10.1103/PhysRevB.79.245101},
   Abstract = {We present time-dependent density matrix renormalization
             group simulations (t-DMRG) at finite temperatures. It is
             demonstrated how a combination of finite-temperature t-DMRG
             and time-series prediction allows for an easy and very
             accurate calculation of spectral functions in
             one-dimensional quantum systems, irrespective of their
             statistics for arbitrary temperatures. This is illustrated
             with spin structure factors of XX and XXX spin- 1 2 chains.
             For the XX model we can compare against an exact solution,
             and for the XXX model (Heisenberg antiferromagnet) against a
             Bethe ansatz solution and quantum Monte Carlo data. © 2009
             The American Physical Society.},
   Doi = {10.1103/PhysRevB.79.245101},
   Key = {fds302501}
}

@article{fds326914,
   Author = {Binder, M and Barthel, T},
   Title = {Symmetric minimally entangled typical thermal states for
             canonical and grand-canonical ensembles},
   Journal = {Physical Review B},
   Volume = {95},
   Number = {19},
   Publisher = {American Physical Society (APS)},
   Year = {2017},
   Month = {May},
   url = {http://dx.doi.org/10.1103/PhysRevB.95.195148},
   Abstract = {© 2017 American Physical Society. Based on the density
             matrix renormalization group (DMRG), strongly correlated
             quantum many-body systems at finite temperatures can be
             simulated by sampling over a certain class of pure matrix
             product states (MPS) called minimally entangled typical
             thermal states (METTS). When a system features symmetries,
             these can be utilized to substantially reduce MPS
             computation costs. It is conceptually straightforward to
             simulate canonical ensembles using symmetric METTS. In
             practice, it is important to alternate between different
             symmetric collapse bases to decrease autocorrelations in the
             Markov chain of METTS. To this purpose, we introduce
             symmetric Fourier and Haar-random block bases that are
             efficiently mixing. We also show how grand-canonical
             ensembles can be simulated efficiently with symmetric METTS.
             We demonstrate these approaches for spin-1/2 XXZ chains and
             discuss how the choice of the collapse bases influences
             autocorrelations as well as the distribution of measurement
             values and, hence, convergence speeds.},
   Doi = {10.1103/PhysRevB.95.195148},
   Key = {fds326914}
}

@article{fds302482,
   Author = {Pineda, C and Barthel, T and Eisert, J},
   Title = {Unitary circuits for strongly correlated
             fermions},
   Journal = {Physical Review A},
   Volume = {81},
   Number = {5},
   Publisher = {American Physical Society (APS)},
   Year = {2010},
   Month = {May},
   ISSN = {1050-2947},
   url = {http://dx.doi.org/10.1103/PhysRevA.81.050303},
   Abstract = {We introduce a scheme for efficiently describing pure states
             of strongly correlated fermions in higher dimensions using
             unitary circuits featuring a causal cone. A local way of
             computing local expectation values is presented. We
             formulate a dynamical reordering scheme, corresponding to
             time-adaptive Jordan-Wigner transformation, that avoids
             nonlocal string operators. Primitives of such a reordering
             scheme are highlighted. Fermionic unitary circuits can be
             contracted with the same complexity as in the spin case. The
             scheme gives rise to a variational description of fermionic
             models not suffering from a sign problem. We present
             numerical examples in a 9×9 and 6×6 fermionic lattice
             model to show the functioning of the approach. © 2010 The
             American Physical Society.},
   Doi = {10.1103/PhysRevA.81.050303},
   Key = {fds302482}
}