The sound-ring radiation of expanding vortex clusters

TL;DR

This paper studies wave-vortex interactions in expanding vortex clusters within 2D Bose-Einstein condensates, revealing analogies to gravitational phenomena and providing analytical and numerical insights into their spectral properties.

Contribution

It introduces a novel analytical approach to characterize wave-vortex interactions in expanding vortex clusters, drawing parallels to gravitational light-rings and validating results with numerical simulations.

Findings

Existence of orbits or sound-rings analogous to gravitational light-rings.

Analytical spectrum predictions match numerical simulations.

Relevance to 2D quantum turbulence and rotating fluid systems.

Abstract

We investigate wave-vortex interaction emerging from an expanding compact vortex cluster in a two-dimensional Bose-Einstein condensate. We adapt techniques developed for compact gravitational objects to derive the characteristic modes of the wave-vortex interaction perturbatively around an effective vortex flow field. We demonstrate the existence of orbits or sound-rings, in analogy to gravitational light-rings, and compute the characteristic spectrum for the out-of-equilibrium vortex cluster. The spectrum obtained from numerical simulations of a stochastic Gross-Pitaevskii equation exhibiting an expanding vortex cluster is in excellent agreement with analytical predictions. Our findings are relevant for 2d-quantum turbulence, the semi-classical limit around fluid flows, and rotating compact objects exhibiting discrete circulation.