Short-time decoherence for general system-environment interactions

A short-time approximation is developed for system-environmental bath mode interactions involving a general non-Hermitian system operator Lambda and its conjugate Lambda(dagger) in order to evaluate the onset of decoherence at low temperatures in quantum systems interacting with the environment. The developed approach is complementary to Markovian approximations and appropriate for the evaluation of quantum computing schemes. An example of a spin system coupled to a bosonic heat bath via Lambdaproportional tosigma(-) is worked out in detail.