Giant Vortex Clusters in a Two-Dimensional Quantum Fluid

TL;DR

This paper experimentally demonstrates persistent vortex clusters in a two-dimensional superfluid, revealing high-energy, long-lived ordered states that challenge typical expectations of disorder from energy input.

Contribution

It provides the first experimental realization of vortex clusters in a 2D quantum fluid, exploring negative temperature regimes and long-term stability.

Findings

Vortex clusters persist for long times in a superfluid.

Clusters form at high energy states far from equilibrium.

Relevance to various physical systems like helium films and quark-gluon plasmas.

Abstract

Adding energy to a system through transient stirring usually leads to more disorder. In contrast, point-like vortices in a bounded two-dimensional fluid are predicted to reorder above a certain energy, forming persistent vortex clusters. Here we realize experimentally these vortex clusters in a planar superfluid: a $^{87}$Rb Bose-Einstein condensate confined to an elliptical geometry. We demonstrate that the clusters persist for long times, maintaining the superfluid system in a high energy state far from global equilibrium. Our experiments explore a regime of vortex matter at negative absolute temperatures, and have relevance to the dynamics of topological defects, two-dimensional turbulence, and systems such as helium films, nonlinear optical materials, fermion superfluids, and quark-gluon plasmas.