Heisenberg picture operators in the quantum state diffusion model
  A stochastic simulation algorithm for the computation of multitime correlation functions which is based on the quantum state diffusion model of open systems is developed. The crucial point of the proposed scheme is a suitable extension of the quantum master equation to a doubled Hilbert space which is then unraveled by a stochastic differential equation. 
Heinz-Peter Breuer, Bernd Kappler, and Francesco Petruccione