Breaking the Fluctuation-Dissipation Relation by Universal Transport Processes

TL;DR

This paper demonstrates how nonequilibrium transport processes in ultracold Bose gases lead to the breakdown of the fluctuation-dissipation relation, revealing independent scaling behaviors and a transport peak in correlations.

Contribution

It introduces a universal scaling regime for nonequilibrium transport in Bose gases and shows how it causes the fluctuation-dissipation relation to break down.

Findings

Spectral functions and statistical correlations scale independently with distinct exponents.

A transport peak appears in the statistical correlator but not in the spectral function.

The fluctuation-dissipation relation is violated in the studied nonequilibrium regime.

Abstract

Universal phenomena far from equilibrium exhibit additional independent scaling exponents and functions as compared to thermal universal behavior. For the example of an ultracold Bose gas we simulate nonequilibrium transport processes in a universal scaling regime and show how they lead to the breaking of the fluctuation-dissipation relation. As a consequence, the scaling of spectral functions (commutators) and statistical correlations (anticommutators) between different points in time and space become linearly independent with distinct dynamic scaling exponents. As a macroscopic signature of this phenomenon we identify a transport peak in the statistical two-point correlator, which is absent in the spectral function showing the quasiparticle peaks of the Bose gas.