Critical Velocity and Arrest of a Superfluid in a Point-Like Disordered Potential

TL;DR

This paper investigates how superfluid flow is affected by disordered point-like barriers, identifying critical velocities, vortex nucleation, and vortex pinning effects, with implications for quantum turbulence and superfluid breakdown.

Contribution

It introduces a mapping between the critical velocities of systems with two obstacles and many obstacles, and explores vortex dynamics in disordered potentials.

Findings

Critical velocity depends on barrier arrangement.

Vortex pinning increases with barrier width.

Superflow breakdown involves vortex nucleation and turbulence.

Abstract

Superfluid flow past a potential barrier is a well studied problem in ultracold Bose gases, however, fewer studies have considered the case of flow through a disordered potential. Here we consider the case of a superfluid flowing through a channel containing multiple point-like barriers, randomly placed to form a disordered potential. We begin by identifying the relationship between the relative position of two point-like barriers and the critical velocity of such an arrangement. We then show that there is a mapping between the critical velocity of a system with two obstacles, and a system with a large number of obstacles. By establishing an initial superflow through a point-like disordered potential, moving faster than the critical velocity, we study how the superflow is arrested through the nucleation of vortices and the breakdown of superfluidity, a problem with interesting connections to quantum turbulence and coarsening. We calculate the vortex decay rate as the width of the barriers is increased, and show that vortex pinning becomes a more important effect for these larger barriers.