Spin waves in a spin-1 Bose gas

TL;DR

This paper develops a comprehensive theory of spin waves in a non-condensed spin-1 Bose gas, combining analytic and numerical methods to reveal how spin-dependent interactions influence the dynamics and stability of the system.

Contribution

It introduces a detailed analytic and numerical framework for understanding spin wave behavior and instabilities in a thermal spin-1 Bose gas, highlighting the effects of spin-dependent interactions.

Findings

Polar state of Rb-87 is unstable to collisional mixing.

Long wavelength spin waves are set by small spin-dependent interactions.

Strong anti-ferromagnetic interactions cause instability in the polar gas.

Abstract

We present a theory of spin waves in a non-condensed gas of spin-1 bosons: providing both analytic calculations of the linear theory, and full numerical simulations of the nonlinear response. We highlight the role of spin-dependent contact interactions in the dynamics of a thermal gas. Although these interactions are small compared to the thermal energy, they set the scale for low energy long wavelength spin waves. In particular, we find that the polar state of Rb-87 is unstable to collisional mixing of magnetic sublevels even in the normal state. We augment our analytic calculations by providing full numerical simulations of a trapped gas, explicitly demonstrating this instability. Further we show that for strong enough anti-ferromagnetic interactions, the polar gas is unstable. Finally we explore coherent population dynamics in a collisionless transversely polarized gas.