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arXiv:1802.06610 · Physical Review A

Nonperturbative method to compute thermal correlations in one-dimensional systems

Stefan Beck, I. E. Mazets, Thomas Schweigler

Published Aug 13, 2018• 16 citations
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Abstract

We develop a highly efficient method to numerically simulate thermal fluctuations and correlations in nonrelativistic continuous bosonic one-dimensional systems. The method is suitable for arbitrary local interactions as long as the system remains dynamically stable. We start by proving the equivalence of describing the systems through the transfer matrix formalism and a Fokker-Planck equation for a distribution evolving in space. The Fokker-Planck equation is known to be equivalent to a stochastic differential (It\ifmmode \bar{o}\else \={o}\fi{}) equation. The latter is very suitable for computer simulations, allowing the calculation of any desired correlation function. As an illustration, we apply our method to the case of two tunnel-coupled quasicondensates of bosonic atoms. The results are compared to the predictions of the sine-Gordon model for which we develop analytic expression directly from the transfer matrix formalism.

DOI
10.1103/physreva.98.023613

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We develop a highly efficient method to numerically simulate thermal fluctuations and correlations in nonrelativistic continuous bosonic one-dimensional systems. The method is suitable for arbitrary local interactions as long as the system remains dynamically stable. We start by proving the equivalence of describing the systems through the transfer matrix formalism and a Fokker-Planck equation for a distribution evolving in space. The Fokker-Planck equation is known to be equivalent to a stochastic differential (It\ifmmode \bar{o}\else ={o}\fi{}) equation. The latter is very suitable for computer simulations, allowing the calculation of any desired correlation function. As an illustration, we apply our method to the case of two tunnel-coupled quasicondensates of bosonic atoms. The results are compared to the predictions of the sine-Gordon model for which we develop analytic expression directly from the transfer matrix formalism.
We develop a highly efficient method to numerically simulate thermal fluctuations and correlations in non-relativistic continuous bosonic one-dimensional systems. We start by noticing the equivalence of their description through the transfer matrix formalism and a Fokker-Planck equation for a distribution evolving in space. The corresponding stochastic differential (Itō) equation is very suitable for computer simulations, allowing the calculation of arbitrary correlation functions. As an illustration, we apply our method to the case of two tunnel-coupled quasicondensates of bosonic atoms.
We present a numerically exact method to compute the full counting statistics of heat transfer in non-Markovian open quantum systems, which is based on the time-evolving matrix product operator algorithm.This approach is applied to the paradigmatic spin-boson model in order to calculate the mean and fluctuations of the heat transferred to the environment during thermal equilibration.We show that system-reservoir correlations make a significant contribution to the heat statistics at low temperature and present a variational theory that quantitatively explains our numerical results.We also demonstrate a fluctuation-dissipation relation connecting the mean and variance of the heat distribution at high temperature.Our results reveal that system-bath interactions make a significant contribution to heat transfer even when the dynamics of the open system is effectively Markovian.The method presented here provides a flexible and general tool to predict the fluctuations of heat transfer in open quantum systems in nonperturbative regimes.
We study the fluctuation properties of a one-dimensional many-body quantum system composed of interacting bosons and investigate the regimes where quantum noise or, respectively, thermal excitations are dominant. For the latter, we develop a semiclassical description of the fluctuation properties based on the Ornstein-Uhlenbeck stochastic process. As an illustration, we analyze the phase correlation functions and the full statistical distributions of the interference between two one-dimensional systems, either independent or tunnel-coupled, and compare with the Luttinger-liquid theory.
We present a numerically exact method to compute the full counting statistics of heat transfer in non-Markovian open quantum systems, which is based on the time-evolving matrix product operator (TEMPO) algorithm. This approach is applied to the paradigmatic spin-boson model in order to calculate the mean and fluctuations of the heat transferred to the environment during thermal equilibration. We show that system-reservoir correlations make a significant contribution to the heat statistics at low temperature and present a variational theory that quantitatively explains our numerical results. We also demonstrate a fluctuation-dissipation relation connecting the mean and variance of the heat distribution at high temperature. Our results reveal that system-bath interactions make a significant contribution to heat dissipation even when the dynamics of the open system is effectively Markovian. The method presented here provides a flexible and general tool to predict the fluctuations of heat transfer in open quantum systems in non-perturbative regimes.
The Schrodinger equation with Gaussian dynamic fluctuating potentials is considered. This model gives a convenient example of an open quantum system coupled to a given external environment. The evolution equations for averaged correlators are derived and it is shown that a system coupled to a thermoequilibrium environment tends asymptotically with time to a thermodynamic density matrix. At high temperatures the quantum evolution equation for the density matrix can be approximated by the quasiclassical Fokker-Planck equation. The generalisation for multiparticle systems is also given. The results are illustrated by the particular examples of coupling with phonons and of two-level systems. Finally, it is shown how the problem can be reformulated in terms of continuous stochastic evolution in the space of psi functions and a corresponding functional formalism based on the continuous Fokker-Planck equation in the space of psi functions.
We develop a dynamical tensor-train method for the Wigner--Fokker--Planck equation arising in continuous-variable open quantum systems. The Wigner function is evolved directly in tensor-train form using a projector-splitting integrator, while the nonlocal Wigner pseudo-differential operator is treated through low-rank representations of the potential difference and matrix-free exponential actions. The resulting method avoids full tensor-product computations in high-dimensional phase space. Numerical experiments in one, two, and three spatial dimensions demonstrate the accuracy and scalability of the method, including simulations in a six-dimensional phase space.