Castaing's instability in a trapped ultra-cold gas

TL;DR

This paper investigates the stability of spin polarization in a trapped ultra-cold bosonic gas, revealing Castaing's instability that can generate spontaneous transverse spin waves, with implications for quantum gas experiments.

Contribution

It provides a numerical analysis of Castaing's instability in a trapped ultra-cold gas, linking theoretical predictions to experimental conditions.

Findings

Identification of Castaing's instability at long wavelengths

Numerical solution of kinetic equations matching experimental setups

Potential to generate spontaneous transverse spin waves

Abstract

We consider a trapped ultra-cold gas of (non-condensed) bosons with two internal states (described by a pseudo spin) and study the stability of a longitudinal pseudo spin polarization gradient. For this purpose, we numerically solve a kinetic equation corresponding to a situation close to an experiment at JILA. It shows the presence of Castaing's instability of transverse spin polarization fluctuations at long wavelengths. This phenomenon could be used to create spontaneous transverse spin waves.