Critical Rotation of an Annular Superfluid Bose Gas

TL;DR

This paper investigates the excitation spectrum of a rotating superfluid Bose-Einstein condensate in a ring trap, revealing edge modes that cause superfluid instability and a maximum circulation limit for superflow stability.

Contribution

It identifies two key edge mode branches responsible for superfluid instability and introduces the concept of a maximum circulation threshold beyond which superflow decays.

Findings

Outer and inner edge modes lead to superfluid instability

Existence of a maximum circulation for stable superflow

Superfluid decay cannot be explained by average sound speed

Abstract

We analyze the excitation spectrum of a superfluid Bose-Einstein condensate rotating in a ring trap. We identify two important branches of the spectrum related to outer and inner edge surface modes that lead to the instability of the superfluid. Depending on the initial circulation of the annular condensate, either the outer or the inner modes become first unstable. This instability is crucially related to the superfluid nature of the rotating gas. In particular we point out the existence of a maximal circulation above which the superflow decays spontaneously, which cannot be explained by invoking the average speed of sound.