Anisotropy in s-wave Bose-Einstein condensate collisions and its relationship to superradiance

TL;DR

This paper experimentally observes anisotropic scattering in s-wave BEC collisions, explained by anisotropic gain mechanisms, including mean-field effects and superradiance-like processes, revealing complex anisotropic dynamics.

Contribution

It demonstrates anisotropic scattering in s-wave BEC collisions and analyzes the roles of mean-field deflections and superradiance-like amplification in this phenomenon.

Findings

Scattered atom pairs exhibit non-isotropic angular distribution.

Anisotropic gain is influenced by mean-field effects and superradiance.

Comparison with optical super-radiance highlights similar amplification mechanisms.

Abstract

We report the experimental realization of a single-species atomic four-wave mixing process with BEC collisions for which the angular distribution of scattered atom pairs is not isotropic, despite the collisions being in the $s$-wave regime. Theoretical analysis indicates that this anomalous behavior can be explained by the anisotropic nature of the gain in the medium. There are two competing anisotropic processes: classical trajectory deflections due to the mean-field potential, and Bose enhanced scattering which bears similarity to super-radiance. We analyse the relative importance of these processes in the dynamical buildup of the anisotropic density distribution of scattered atoms, and compare to optically pumped super-radiance.