Hm. Wiseman et L. Diosi, Complete parameterization, and invariance, of diffusive quantum trajectories for Markovian open systems, CHEM PHYS, 268(1-3), 2001, pp. 91-104
The state matrix rho for an open quantum system with Markovian evolution ob
eys a master equation. The master equation evolution can be unraveled into
stochastic nonlinear trajectories for a pure state P, such that on average
P reproduces rho. Here we give for the first time a complete parameterizati
on of all diffusive unravelings (in which P evolves continuously but non-di
fferentiably in time). We give an explicit measurement theory interpretatio
n for these quantum trajectories, in terms of monitoring the system's envir
onment. We also introduce new classes of diffusive unravelings that are inv
ariant under the linear operator transformations under which the master equ
ation is invariant. We illustrate these invariant unravelings by numerical
simulations. Finally, we discuss generalized gauge transformations as a met
hod of connecting apparently disparate descriptions of the same trajectorie
s by stochastic Schrodinger equations, and their invariance properties. (C)
2001 Elsevier Science B.V. All rights reserved.