LOSS OF SPATIAL COHERENCE BY A SINGLE SPONTANEOUS EMISSION

We have demonstrated the loss of transverse spatial coherence of an at omic wave function after a single spontaneous emission. He atoms were both diffracted and excited by a standing light wave with a variable period. After the interaction, the excited atoms decay by a single spo ntaneously emitted photon. By changing the period of the standing ligh t wave, we have mapped the loss of spatial coherence as a function of the transverse coordinate. By detecting the emitted photon one could ' 'erase'' the position information available and recover the transverse coherence in a correlation experiment, or realize a Heisenberg micros cope.