Stochastic Schr\"odinger equation from an interaction with the   environment
  We consider a class of models describing a quantum oscillator in interaction with an environment. We show that models of continuous spontaneous localization based on a stochastic Schr\"odinger equation can be derived as an approximation to purely deterministic Hamiltonian systems. We show an exponential decay of off-diagonal matrix elements in the energy representation. 
Z. Haba