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

Spin dynamics in cold atomic gases exhibit rich phenomena due to the interplay of particle interactions, quantum coherence, and particle statistics. In a Bose-Einstein condensate (BEC) with only contact interactions, spin dynamics can be induced by the spin dependence of the interaction strengths between particles. If interspin and intraspin interaction strengths are the same, on the other hand, there is only one scattering length, a.

Publication Date: April 23, 2024

Authors: David C. Spierings, Joseph H. Thywissen, and Aephraim M. Steinberg

Abstract: We observe spin rotations caused by atomic collisions in a nonequilibrium Bose-condensed gas of ⁸⁷Rb. 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 is commonly thought not to occur in Bose condensates; our observations and model clarify the nature of these effective-magnetic spin rotations.

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