Decoherence from spontaneous emission

Starting from a generalization of the Weisskopf-Wigner model for the case of a two-level atom with a largely spread center-of-mass wave function, we show that spatial correlations are destroyed to some extent by a spontaneously emitted photon. We derive a particularly simple form of the corresponding decoherence function and determine the dependence of the decoherence on orientation and size of a detector registering the outgoing photon.