  We show that the phase difference of two overlapping ground state
Bose-Einstein condensates can effect 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.
