Spin Rotations in a Bose-Einstein Condensate Driven by Counterflow and Spin-independent Interactions

TL;DR

This paper demonstrates that atomic collisions in a non-equilibrium Bose-Einstein condensate of rubidium induce spin rotations, revealing a novel form of spin dynamics driven by counterflow and spin-independent interactions, previously thought exclusive to nondegenerate gases.

Contribution

It provides the first experimental observation and theoretical explanation of spin rotations caused by collisions in a Bose-Einstein condensate with spin-independent interactions.

Findings

Spin rotations observed in a BEC due to collisions.

A local magnetodynamic model explains the spin textures.

Clarification that such phenomena are not limited to nondegenerate gases.

Abstract

We observe spin rotations caused by atomic collisions in a non-equilibrium Bose-condensed gas of $^{87}$Rb. Reflection from a pseudomagnetic barrier creates counterflow in which forward- and backward-propagating matter waves have partly transverse spin directions. Even though inter-atomic interaction strengths are state-independent, the indistinguishability of parallel spins leads to spin dynamics. A local magnetodynamic model, which captures the salient features of the observed spin textures, highlights an essential connection between four-wave mixing and collisional spin rotation. The observed phenomenon has previously been thought to exist only in nondegenerate gases; our observations and model clarify the nature of these effective-magnetic spin rotations.