On approximation of quantum channels
arXiv:0711.2245
Abstract
We develop an approximation approach to infinite dimensional quantum channels based on detailed investigation of the continuity properties of entropic characteristics of quantum channels and operations (trace-nonincreasing completely positive maps) as functions of a pair ``channel, input state''. The obtained results are then applied to the following problems: continuity of the -capacity as function of a channel; strong additivity of the -capacity for infinite dimensional channels; the analytical expression for the convex closure of the output entropy of arbitrary quantum channel.
26 pages