LOWER ESTIMATES FOR DISTANCES FROM A GIVEN QUANTUM CHANNEL TO CERTAIN CLASSES OF QUANTUM CHANNELS

摘要

By using estimates for the variation of quantum mutual information and the relative entropy of entanglement, we obtain e-exact lower estimates for distances from a given quantum channels to sets of degradable, antidegradable, and entanglement-breaking channels. As an auxiliary result, we obtain e-exact lower estimates for the distance from a given two-particle state to the set of all separable states.