Model-independent approach to nondissipative decoherence

We consider the case when decoherence is due to the fluctuations of some classical variable or parameter of a system and not to its entanglement with the environment. Under few and quite general assumptions, we derive a model-independent formalism for this nondissipative decoherence, and we apply it to explain the decoherence observed in some recent experiments in cavity QED and on trapped ions.