Emergence of order from turbulence in an isolated planar superfluid

TL;DR

This paper investigates how a superfluid Bose-Einstein condensate with randomly distributed vortices relaxes and self-organizes into stable vortex clusters through a novel evaporative heating mechanism, revealing a negative temperature phase transition.

Contribution

It uncovers a new physical mechanism for vortex self-organization and demonstrates the formation of stable Onsager vortex clusters in an isolated superfluid system.

Findings

Vortices self-organize into stable Onsager clusters after annihilation.

Evaporative heating leads to a negative temperature phase transition.

The system remains in a non-thermal state at the end of the simulation.

Abstract

We study the relaxation dynamics of an isolated zero temperature quasi-two-dimensional superfluid Bose-Einstein condensate (BEC) that is imprinted with a spatially random distribution of quantum vortices. Following a period of vortex annihilation, we find that the remaining vortices self-organise into two macroscopic coherent `Onsager vortex' clusters that are stable indefinitely. We demonstrate that this occurs due to a novel physical mechanism --- the evaporative heating of the vortices --- that results in a negative temperature phase transition in the vortex degrees of freedom. At the end of our simulations the system is trapped in a non-thermal state. Our computational results provide a pathway to observing Onsager vortex states in a superfluid Bose gas.