PERTURBATIVE EXPANSION FOR COHERENCE LOSS

We construct a generally applicable short-time perturbative expansion for coherence loss. Successive terms of this expansion yield character istic times for decorrelation processes involving successive powers of the Hamiltonian. The second order results are sufficient to precisely reproduce expressions for ''decoherence times'' obtained in the liter ature by much more involved and indirect methods. Examples illustratin g the influence of initial conditions and the need to evaluate higher order terms are given in the context of the Jaynes-Cummings model. It is shown that, in this case, the short-time decoherence behavior can p robe the importance of antiresonant contributions.