Gaussian Decoherence from Random Spin Environments

We examine an exactly solvable model of decoherence - a spin-system interacting with a collection of environment spins. We show that in this model (introduced some time ago to illustrate environment-induced superselection) generic assumptions about the coupling strengths lead to a universal (Gaussian) suppression of coherence between pointer states. We explore the regimes of validity of these results and discuss their relation to the spectral features of the environment and to the Loschmidt echo (or fidelity). Finally, we comment on the observation of such time dependence in spin echo experiments.