Observation of superradiant Raman scattering in a Bose-Einstein condensate

We observed superradiant Raman scattering from a Bose-Einstein condensate irradiated by a single off-resonant light beam. Spontaneous mode selection of the scattered radiation turns probabilistic optical pumping into a stimulated Raman process, whereby the atoms are coherently transferred into a different hyperfine state. The population in the pumped state grew exponentially in time, demonstrating the emergence of bosonic stimulation in the optical pumping process.