Abstract

The decay of coherence when a quantum system interacts with a much larger environment is usually described by a master equation for the system reduced density matrix, and emphasises the evolution of an entire ensemble. A number of methods have been developed recently to simulate the evolution of single realizations. Quantum state diffusion involves both diffusion, where the individual quantum trajectory fluctuates through a Wiener process deriving from the environment, and localization to a coherent state, an eigenstate of the relevant Lindblad operator describing the coupling of the system to the environment.¹ Wiseman and Milburn² connect quantum state diffusion method to a heterodyne measurement of oscillation amplitudes. They show that conventional quantum mechanics produces a conditioned state vector, which diffuses according to the nonlinear stochastic differential equation:^1,3 where dξ, is a random complex Wiener variable, or Gaussian noise term.

© 1994 IEEE