  We suggest a novel proposal to express decoherence in open quantum systems by
jointly employing spectral and stochastic methods. This proposal, which
basically perturbs the unitary evolution operator in a random fashion, allows
us to embrace both markovian and nonmarkovian situations with little extra
effort. We argue that it can be very suitable to deal with models where an
approximation neglecting some degrees of freedom is undertaken. Mathematical
simplicity is also obtained both to solve some master equations and to arrive
at experimentally measured decoherence functions.
