Coherent output, stimulated quantum evaporation, and pair breaking in a trapped atomic bose gas

We investigate the spectrum and coherence of an atomic beam slowly coupled out of an atomic trap which contains a partially condensed Bose gas at a finite temperature. The spectrum contains a coherent fraction emerging from the condensate and a thermal fraction emerging from the thermal excitations in the trap. We show the existence of a remarkable process involving the simultaneous creation of an output atom and an elementary excitation (quasiparticle) inside the trap. This process, which can serve as a probe to pair correlations in the condensate, can become dominant for a suitable choice of the coupling parameters.