Nonlinear dynamics of coupled superfluids

TL;DR

This paper investigates the complex nonlinear dynamics of two coupled superfluids in a trap, revealing new excitation mechanisms and threshold velocities for dissipation through analytical and numerical methods.

Contribution

It introduces a combined analytical and numerical study of coupled superfluids, identifying new decay mechanisms influenced by inhomogeneities and non-uniform motion.

Findings

Identification of two excitation mechanisms leading to dissipation

Discovery of a Landau-like decay process in inhomogeneous systems

Determination of threshold velocities for excitation onset

Abstract

Following recent experiments on ultracold dual superflows, we model in this work the dynamics of two harmonically trapped counterflowing superfluids. Using complementary analytical and numerical approaches, we study the shedding of elementary excitations triggered by the relative motion of the two species. We exhibit two different excitation mechanisms leading to distinct threshold velocities for the onset of dissipation: in addition to the parametric pair production present in homogeneous , galilean-invariant systems, we show that non-uniform motion and density inhomogeneities allow for a Landau-like decay mechanism where single excitations are produced.