Cold matter and short laser pulses: creating cold molecules and probing pair correlations in condensates.

We have analyzed the formation of Rb$_2$ molecules with short photoassociation pulses applied to a cold $^{85}$Rb sample. The laser field couples a continuum level of the ground electronic state X$^1\Sigma_{\textrm{g}}^+$ with bound levels in the 0$_{\textrm{u}}^+$(5S+5P$_{1/2}$) and 0$_{\textrm{u}}^+$(5S+5P$_{3/2}$) vibrational series. The non-adiabatic coupling between the two excited channels induces time-dependent beatings in their populations [1]. We propose to take advantage of these oscillations either to probe the photoassociation process via a photoionization pulse, or to optimize the stabilization step into deep levels of the ground state [1]. Presently, in collaboration with the experimental group of Chris Westbrook in Orsay, we are extending our dynamical calculations to study the time-dependent correlations that the photoassociation laser triggers in an atomic condensate [2], and how they can be experimentally measured, {\em e.\ g.} in cold samples of metastable helium [3]. \newline {\bf References:} \noindent[1] J.\ Mur-Petit, E.Luc-Koenig, and F.\ Masnou-Seeuws, arXiv:physics/0612143. \noindent [2] P. Naidon and F. Masnou-Seeuws,{\em Phys. Rev. A} {\bf 73}, 043611 (2006).\noindent [3] M. Schellekens {\em et al.},{\em Science} {\bf 310}, 648 (2005).