Decoherence by spontaneous emission: a single-atom analog of superradiance

We show that the stationary decoherence rate of an open quantum system can be decomposed as a sum of local and nonlocal contributions, respectively related to the strength of the coupling between system and environment, and to the quality of the information about the system leaking into the environment. Both terms arise naturally in the framework of the influence functional, with the nonlocal term arising from the coupling between the backward and forward histories describing the open quantum system time evolution. While the local contribution always yields a positive decoherence rate, the nonlocal one may lead to recoherence when only partial information about the system is obtained from the disturbed environment. We illustrate these concepts in the framework of interferometry with trapped atoms, by analyzing the effect of spontaneous emission on the coherence of the center-of-mass.