Anomalous hydrodynamics and "normal" fluids in rapidly rotating BECs

TL;DR

This paper explores anomalous hydrodynamics in rapidly rotating Bose-Einstein condensates, revealing a regime with no normal fluid and unconventional superfluid behavior, including vortex-surface wave interactions and long-lived vortex patches.

Contribution

It introduces the concept of anomalous hydrodynamics in rotating BECs and describes non-conventional fluid dynamics, vortex-surface wave relations, and long-lived vortex structures.

Findings

Existence of anomalous hydrodynamics in the quantum Hall regime

Surface waves can form a 'normal fluid' absorbing vortex energy

Long-lived vortex patches observed, possibly related to experiments

Abstract

In rapidly rotating bose systems we show that there is a region of anomalous hydrodynamics whilst the system is still condensed, which coincides with the mean field quantum Hall regime. An immediate consequence is the absence of a normal fluid in any conventional sense. However, even the superfluid hydrodynamics is not described by conventional Bernoulli and continuity equations. We show there are kinematic constraints which connect spatial variations of density and phase, that the positions of vortices are not the simplest description of the dynamics of such a fluid (despite their utility in describing the instantaneous state of the condensate) and that the most compact description allows solution of some illuminating examples of motion. We demonstrate, inter alia, a very simple relation between vortices and surface waves. We show the surface waves can form a "normal fluid" which absorbs energy and angular momentum from vortex motion in the trap. The time scale of this process is sensitive to the initial configuration of the vortices, which can lead to long-lived vortex patches - perhaps related to those observed at JILA.