Squeezed excitations in trapped Bose-Einstein condensates

Summary form only given. The microscopic theory of interacting Bose gases developed more than 50 years ago by Bogoliubov plays an essential role in the description of these systems. However, processes such as Beliaev damping are not predicted by the mean field approximation. Recently, the observation of Beliaev damping for a scissors mode of a BEC of rubidium atoms has been reported allowing the consideration of theory beyond the mean field. The Beliaev damping process is, in a sense, analogous to parametric down conversion of light, where one photon incident on a nonlinear crystal with second order susceptibility is split into two new photons of lower frequencies. Parametric down conversion has long been considered as an important source of squeezed states. In this paper we point out that similar processes can be observed in BEC.