Entropy of a Turbulent Bose-Einstein Condensate

TL;DR

This paper investigates the entropy dynamics of trapped Bose-Einstein condensates across different regimes, revealing how entropy changes can characterize the onset and development of quantum turbulence.

Contribution

It derives an entropy expression for BECs that aligns with experimental data and links entropy features to turbulence stages, advancing understanding of quantum turbulence.

Findings

Entropy increases sharply during particle cascade formation

Distinct entropy features correspond to different turbulence stages

Proposed entropy as a tool to characterize quantum turbulence

Abstract

Quantum turbulence deals with the phenomenon of turbulence in quantum fluids, such as superfluid helium and trapped Bose-Einstein condensates (BECs). Although much progress has been made in understanding quantum turbulence, several fundamental questions remain to be answered. In this work, we investigated the entropy of a trapped BEC in several regimes, including equilibrium, small excitations, the onset of turbulence, and a turbulent state. We considered the time evolution when the system is perturbed and let to evolve after the external excitation is turned off. We derived an expression for the entropy consistent with the accessible experimental data, that is, using the assumption that the momentum distribution is well-known. We related the excitation amplitude to different stages of the perturbed system, and we found distinct features of the entropy in each of them. In particular, we observed a sudden increase in the entropy following the establishment of a particle cascade. We argue that entropy and related quantities can be used to investigate and characterize quantum turbulence.