Denis Boiron

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 when the source clouds are not cylindrically symmetric around the collision axis. There are two competing anisotropic processes: classical trajectory deflections due to the mean-field potential, and Bose enhanced scattering. The bosonic enhancement process bears similarity to superradiance, although a consideration of the differences explains why it is more difficult to achieve strongly dominant end-fire modes with atom optics.

Ionization in a Bose-Einstein condensate of metastable Helium: a quantitative monitoring tool

Residual ionization in a BEC of 2 S1 metastable Helium (He*), can be used to monitor in real time the evolution of a single sample of condensate. We use this method, combined to Time Of Flight measurements, to study the decay of the condensate. It has also allowed us to measure 2-body and 3-body ionizing collisions rate constants. This method should allow for the study of the growth of a condensate, in particular in the hydrodynamic regime. We point out the importance of quantum depletion in He* BEC’s.