ABSTRACT:

The talk is an attempt to convince the audience that there is merit in regarding the reduced density matrix of an open quantum system as a physical property that evolves in a pseudorandom fashion, analogous to a classical Brownian motion. Such a point of view is illustrated by developing a model of the quantum Zeno effect, where the repeated or continuous act of measurement slows down the evolution of a system. The main motive for adopting this position is to introduce an entropy that quantifies subjective uncertainty in the density matrix and which differs from von Neumann entropy. An entropy production associated with the manipulation of an open quantum system can then be computed which satisfies the second law. As an example, we compute the cost in entropy production of performing a quantum measurement.