Aspects of Open Quantum Dynamics

Keith H. Hughes

Walter T. Strunz

The interaction of a quantum system with a many degree of freedom environment entails damping and the loss of quantum coherence. In these two lectures we focus on two aspects of open quantum system dynamics. First, we present decoherence as a dynamical phenomenon and determine the corresponding time scales, discuss an experiment and the nature of robust states, and mention universal properties of short-time decoherence of macroscopic superpositions. Secondly, in analogy to the classical description of open systems in terms of Langevin equations, we present a stochastic approach to open quantum system dynamics in terms of a stochastic Schrödinger equation. We give a microscopic derivation that allows us to generalize the stochastic approach to non-Markovian situations. We discuss a convolutionless formulation of our theory and finally, we focus on the quantised version of Brownian motion as an often-employed example.

Juan P. Garrahan

Jacek Okołowicz, Marek Płoszajczak, I. Rotter

Ángel S. Sanz, Salvador Miret-Artés

Roberto Floreanini B

The dynamics of an open quantum system is usually assumed to be generated by time-evolution equations of Lindblad form. It follows that the time evolutors are completely positive. Far from being just a useful technicality, complete positivity is one of the many aspects of quantum entanglement and is necessary to avoid physical inconsistencies. This issue is addressed by examining the open dynamics of two level systems in situations typical of chemical physics and quantum optics.