Quantum Dynamical Entropy from Relative entropy

In this exposition we prove an existence theorem for a quantum mechanical dynamical entropy based on von-Neumann’s measurement theory. To that end we introduced a Shannon type of information associated with a quantum channel or measurement based on Araki’s relative entropy. This is an invariance for the dynamics which generalizes Kolmogorov-Sinai ’s notion of dynamical entropy of a measure preserving transformation. In this context we also introduce a natural notion of channel capacity as a generalization of Shannon’s capacity of a channel and finds its relation with A.S. Holevo’s notion of capacity. 2 A measurement in classical dynamics gives rise to a measurable partition ζ = (ζi) of the configuration space ( measure space) (M, B, µ). For a par-µ(E∩ζi) tition ζ, we can associate a family of measure µζi(E) =