Production of Multiple Rb Condensates and Atom Lasers by Rf Coupling

One of the major goals in the study of Bose–Einstein condensation (BEC) in dilute atomic gases has been the realization and development of atom lasers. An atom laser may be understood as a source of coherent matter waves. One can extract coherent matter waves from a magnetically trapped Bose condensate. Schemes to couple the atomic beam out of the magnetic trap have been demonstrated [1, 2, 3, 4]. In the experiments of [1, 2] the output coupling is performed by the application of a radio–frequency (rf) field that induces atomic transitions to untrapped Zeeman states. The atom laser described in [3] is based on the Josephson tunnelling of an optically trapped condensate and in [4] a two–photon Raman process is described that allows directional output coupling from a trapped condensate. Characterizing the output coupler is necessary to understand the atom laser itself. The literature dealing with theoretical descriptions of output couplers for Bose–Einstein condensates has focused both on the use of rf transitions [5, 6, 7, 8] and Raman processes [9]. Rf output coupling is based on single– or multi– step transitions between trapped and untrapped atomic states. As a consequence, a rich phenomenology arises that include the observation of ”multiple” condensates corresponding to atoms in different atomic states. These may display varied dynamical behaviour while in the trap. Also, both pulsed and continuous output–coupled coherent matter beams have been observed. The phenomenology is made even more varied by the possibility of out–coupling solely under gravity and also of magnetically pushed out beams. The apparatus operated by the Florence group [10] offers the