Universal Behavior on the Relaxation Dynamics of Far-From-Equilibrium Quantum Fluids

TL;DR

This study explores the relaxation dynamics of turbulent Bose-Einstein condensates under different energy injections, revealing universal features in their thermalization process despite differing final states.

Contribution

It demonstrates that turbulence evolution exhibits universal behavior during relaxation, regardless of initial conditions or final states, in far-from-equilibrium quantum fluids.

Findings

Identified two regimes of excitation leading to distinct final states.

Observed universal scaling and key relaxation features in both regimes.

Visualized coherence length dynamics during relaxation processes.

Abstract

Investigating the initial conditions that lead many-body quantum systems to an out-of-equilibrium state is fundamental for understanding their thermalization dynamics. In this work we observe the relaxation for two regimes of excitation that can drive the turbulent Bose-Einstein condensate into two distinct final states, and are defined by the amount of energy injected into the system. The subcritical regime is characterized by a lower injection of energy, which can lead to an inverse particle cascade and, consequently, to the BEC mode repopulation during the relaxation process. The supercritical regime is marked by a higher energy injection, that may lead to the BEC dissolution and a final thermal state. In both cases we observe relaxation stages that exhibit the same key features: a direct cascade, a non-thermal fixed point with the same exponents, a prethermalization region and, finally, the thermalization of the system. In the final thermalization stage, universal scaling is observed for both regimes, even though their final states are completely different. By analyzing the coherence length of our turbulent cloud, we clearly visualize the recovery and the loss of the coherence for the subcritical and supercritical regimes after relaxation. These results indicate that the evolution of turbulence occurs independent of its initial conditions and of the final state achieved.