Around Shannon's interpretation for entropy-preserving stochastic averages
Abstract
Let Φ be a positive unital Tr-preserving map on Mn(ℂ). We give various characterizations for Φ to preserve the von Neumann entropy of a state ρ on Mn(ℂ). Among others, it is given by that Φ behaves to ρ as a *-automorphism. This is also equivalent to that the entropy of the stochastic matrix arising from {ρ, Φ} is zero.