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An output coupler for Bose condensed atoms

The observations of BEC have stimulated interest in atom lasers, coherent sources of atomic matter waves. The build-up of atoms in the ground state of a magnetic trap is analogous to stimulated emission into a single mode of an optical laser. An important element of a laser is an output coupler, which provides a controlled way of generating a coherent propagating beam. We demonstrated a scheme for doing this with Bose condensed atoms [1]. A variable fraction of atoms was extracted coherently from the condensate by applying rf radiation to the cloud, thereby coupling atoms to untrapped hyperfine states (see figure).