Characterizations of symmetric monotone metrics on the state space of quantum systems

The quantum Fisher information is a Riemannian metric, defined on the state space of a quantum system, which is symmetric and decreasing under stochastic mappings. Contrary to the classical case such a metric is not unique. We complete the characterization, initiated by Morozova, Chentsov and Petz, of these metrics by providing a closed and tractable formula for the set of Morozova-Chentsov functions. In addition, we provide a continuously increasing bridge between the smallest and largest symmetric monotone metrics.

Contraction of Generalized Relative Entropy Under Stochastic Mappings on Matrices

The contraction coefficient of stochastic mappings between full matrix algebras is introduced with respect to a generalized relative entropy labeled by an operator convex function g. It is proved that the coefficient is actually independent of g, in particular, it can be most conveniently computed by means of the square function.