Bi--continuous semigroups of stochastic quantum dynamics

Abstract

This paper is devoted to the aspects of derivation of dynamics equation of quantum system under a stochastic dynamics. We study the conditions, under which a sequence of random variations of wave function can approximate a random diffusion process in a Hilbert space. A random variation $|\psi_0\rangle\mapsto G_{t_N}\ldots G_{t_1}|\psi_0\rangle=|\psi_{t_N}\rangle$ is associated with a transform of distribution of vector $|\psi\>$, as well as with the variation of its characteristic functional $\varphi(v)={\mathbb{E}}\exp(i\operatorname{Re}\langle v|\psi\rangle).$ For a continuous random walk we study the approximation of a Markov semigroup by the Markov operators of discrete random walk. We pay a special attention to the cases, when the derivative of random operator $F'(0)$ is an unbounded operator. However, we restrict the consideration to the case when the Markov operators of random walks with the operators $G_t$ mutually commute.

The characteristic functional is transformed by the Markov operator of adjoint process, and in contrast to the dynamics of wave function, it has a deterministic nature that allows us to rely on the developed theory of semigroups in Banach spaces. The most illustrative examples are the process of continuous measurement, that is, the measurement of trajectories of some observable, and the random control.