Spontaneous photon emission stimulated by two Bose-Einstein condensates

We show that the phase difference of two overlapping ground-state Bose-Einstein condensates can affect the optical spontaneous emission rate of excited atoms. Depending on the phase difference the atom-stimulated spontaneous emission rate can vary between zero and the rate corresponding to all the ground-state atoms in a single condensate. Besides giving control over spontaneous emission this provides an optical method for detecting the condensate phase difference. It differs from previous methods in that no light fields are applied. Instead the light is spontaneously emitted when excited atoms make a transition into either condensate.