Non-thermal fixed points: universality, topology, & turbulence in Bose gases

TL;DR

This paper reviews recent advances in understanding non-thermal fixed points in Bose gases, highlighting their universal properties, topological features, and turbulent behaviors during non-equilibrium dynamics.

Contribution

It provides a comprehensive overview connecting universal scaling, topological configurations, and turbulence in Bose gases far from equilibrium.

Findings

Identification of non-thermal fixed points with metastable states

Universal scaling laws in correlation functions

Connection between defects, domain formation, and turbulence

Abstract

In these notes we discuss recent developments in the field of non-equilibrium quantum dynamics. Specifically, we consider nearly coherent Bose gases brought far out of equilibrium and study their behaviour in view of connections between universal properties, (quasi-)topological field configurations and turbulent dynamics. We demonstrate that the isolated Bose gas, on its way back to thermal equilibrium, can approach metastable non-equilibrium configurations and spend a long time in their vicinity. In such configurations, which have been termed non-thermal fixed points, the system shows universal long-range properties manifest through scaling, i.e., self-similar correlations. The spatial field pattern, at the same time, is characterized by the appearance of defects and domain formation whose geometry gives rise to the particular scaling laws seen in the correlation functions. We obtain an overall picture which connects well-known concepts for describing universal dynamics such as wave-turbulence, superfluid turbulence, and (quasi-)topological excitations. This allows to bring together a wide range of concepts and methods with a large spectrum of applications.