3,774 research outputs found
From quantum chaos and eigenstate thermalization to statistical mechanics and thermodynamics
This review gives a pedagogical introduction to the eigenstate thermalization hypothesis (ETH), its basis, and its implications to statistical mechanics and thermodynamics. In the first part, ETH is introduced as a natural extension of ideas from quantum chaos and random matrix theory (RMT). To this end, we present a brief overview of classical and quantum chaos, as well as RMT and some of its most important predictions. The latter include the statistics of energy levels, eigenstate components, and matrix elements of observables. Building on these, we introduce the ETH and show that it allows one to describe thermalization in isolated chaotic systems without invoking the notion of an external bath. We examine numerical evidence of eigenstate thermalization from studies of many-body lattice systems. We also introduce the concept of a quench as a means of taking isolated systems out of equilibrium, and discuss results of numerical experiments on quantum quenches. The second part of the review explores the implications of quantum chaos and ETH to thermodynamics. Basic thermodynamic relations are derived, including the second law of thermodynamics, the fundamental thermodynamic relation, fluctuation theorems, the fluctuation–dissipation relation, and the Einstein and Onsager relations. In particular, it is shown that quantum chaos allows one to prove these relations for individual Hamiltonian eigenstates and thus extend them to arbitrary stationary statistical ensembles. In some cases, it is possible to extend their regimes of applicability beyond the standard thermal equilibrium domain. We then show how one can use these relations to obtain nontrivial universal energy distributions in continuously driven systems. At the end of the review, we briefly discuss the relaxation dynamics and description after relaxation of integrable quantum systems, for which ETH is violated. We present results from numerical experiments and analytical studies of quantum quenches at integrability. We introduce the concept of the generalized Gibbs ensemble and discuss its connection with ideas of prethermalization in weakly interacting systems.This work was supported by the Army Research Office [grant number W911NF1410540] (L.D., A.P, and M.R.), the U.S.-Israel Binational Science Foundation [grant number 2010318] (Y.K. and A.P.), the Israel Science Foundation [grant number 1156/13] (Y.K.), the National Science Foundation [grant numbers DMR-1506340 (A.P.)and PHY-1318303 (M.R.)], the Air Force Office of Scientific Research [grant number FA9550-13-1-0039] (A.P.), and the Office of Naval Research [grant number N000141410540] (M.R.). The computations were performed in the Institute for CyberScience at Penn State. (W911NF1410540 - Army Research Office; 2010318 - U.S.-Israel Binational Science Foundation; 1156/13 - Israel Science Foundation; DMR-1506340 - National Science Foundation; PHY-1318303 - National Science Foundation; FA9550-13-1-0039 - Air Force Office of Scientific Research; N000141410540 - Office of Naval Research)Accepted manuscrip
The one-dimensional contact process: duality and renormalisation
We study the one-dimensional contact process in its quantum version using a
recently proposed real space renormalisation technique for stochastic
many-particle systems. Exploiting the duality and other properties of the
model, we can apply the method for cells with up to 37 sites. After suitable
extrapolation, we obtain exponent estimates which are comparable in accuracy
with the best known in the literature.Comment: 15 page
Two spin liquid phases in the spatially anisotropic triangular Heisenberg model
The quantum spin-1/2 antiferromagnetic Heisenberg model on a two dimensional
triangular lattice geometry with spatial anisotropy is relevant to describe
materials like and organic compounds like
{-(ET)Cu(CN)}. The strength of the spatial anisotropy can
increase quantum fluctuations and can destabilize the magnetically ordered
state leading to non conventional spin liquid phases. In order to understand
these intriguing phenomena, quantum Monte Carlo methods are used to study this
model system as a function of the anisotropic strength, represented by the
ratio between the intra-chain nearest neighbor coupling and the
inter-chain one . We have found evidence of two spin liquid regions. The
first one is stable for small values of the coupling J'/J \alt 0.65, and
appears gapless and fractionalized, whereas the second one is a more
conventional spin liquid with a small spin gap and is energetically favored in
the region 0.65\alt J'/J \alt 0.8. We have also shown that in both spin
liquid phases there is no evidence of broken translation symmetry with dimer or
spin-Peirls order or any broken spatial reflection symmetry of the lattice. The
various phases are in good agreement with the experimental findings, thus
supporting the existence of spin liquid phases in two dimensional quantum
spin-1/2 systems.Comment: 35 pages, 24 figures, 3 table
Dynamics and hysteresis in square lattice artificial spin-ice
Dynamical effects under geometrical frustration are considered in a model for
artificial spin ice on a square lattice in two dimensions. Each island of the
spin ice has a three-component Heisenberg-like dipole moment subject to shape
anisotropies that influence its direction. The model has real dynamics,
including rotation of the magnetic degrees of freedom, going beyond the
Ising-type models of spin ice. The dynamics is studied using a Langevin
equation solved via a second order Heun algorithm. Thermodynamic properties
such as the specific heat are presented for different couplings. A peak in
specific heat is related to a type of melting-like phase transition present in
the model. Hysteresis in an applied magnetic field is calculated for model
parameters where the system is able to reach thermodynamic equilibrium.Comment: Revised versio
Random words, quantum statistics, central limits, random matrices
Recently Tracy and Widom conjectured [math.CO/9904042] and Johansson proved
[math.CO/9906120] that the expected shape \lambda of the semi-standard tableau
produced by a random word in k letters is asymptotically the spectrum of a
random traceless k by k GUE matrix. In this article we give two arguments for
this fact. In the first argument, we realize the random matrix itself as a
quantum random variable on the space of random words, if this space is viewed
as a quantum state space. In the second argument, we show that the distribution
of \lambda is asymptotically given by the usual local limit theorem, but the
resulting Gaussian is disguised by an extra polynomial weight and by reflecting
walls. Both arguments more generally apply to an arbitrary finite-dimensional
representation V of an arbitrary simple Lie algebra g. In the original
question, V is the defining representation of g = su(k).Comment: 11 pages. Minor changes suggested by the refere
Stochastic lattice models for the dynamics of linear polymers
Linear polymers are represented as chains of hopping reptons and their motion
is described as a stochastic process on a lattice. This admittedly crude
approximation still catches essential physics of polymer motion, i.e. the
universal properties as function of polymer length. More than the static
properties, the dynamics depends on the rules of motion. Small changes in the
hopping probabilities can result in different universal behavior. In particular
the cross-over between Rouse dynamics and reptation is controlled by the types
and strength of the hoppings that are allowed. The properties are analyzed
using a calculational scheme based on an analogy with one-dimensional spin
systems. It leads to accurate data for intermediately long polymers. These are
extrapolated to arbitrarily long polymers, by means of finite-size-scaling
analysis. Exponents and cross-over functions for the renewal time and the
diffusion coefficient are discussed for various types of motion.Comment: 60 pages, 19 figure
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