Observation of Relaxation Stages in a Nonequilibrium Closed Quantum System: Decaying Turbulence in a Trapped Superfluid

TL;DR

This paper observes and characterizes the relaxation stages of decaying turbulence in trapped Bose-Einstein condensates, revealing universal scaling laws and cascade processes that deepen understanding of non-equilibrium quantum dynamics.

Contribution

It provides the first experimental observation of distinct relaxation stages and cascades in a nonequilibrium quantum system, supported by wave turbulence theory.

Findings

Identification of a direct particle cascade with universal scaling

Observation of an inverse particle cascade restoring condensate

Validation of wave turbulence theory in quantum turbulence

Abstract

The dynamics of non-equilibrium closed quantum systems and their route to thermalization are of fundamental interest to several fields, from cosmology to particle physics. However, a comprehensive description of non-equilibrium phenomena still presents a significant challenge. In this work, we report the observation of distinct stages during the relaxation of the decaying turbulence in trapped Bose-Einstein condensates. Our findings show a direct particle cascade from low to high momenta, a consequence of the energy injection in the system, exhibiting a characteristic universal scaling. This stage is followed by an inverse particle cascade responsible for repopulating the previously depleted condensate. Both cascades can be explained through self-similar solutions provided by wave turbulence theory. These findings provide important insights into the relaxation stages of out-of-equilibrium quantum many-body systems.