Anisotropy in s-wave Bose-Einstein condensate collisions and its   relationship to superradiance
  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. 
Piotr Deuar, Jean-Christophe Jaskula, Marie Bonneau, Valentina   Krachmalnicoff, Denis Boiron, Christoph I. Westbrook, Karen...
cond-mat.quant-gas