Lower Estimates for Distances from a Given Quantum Channel to Certain Classes of Quantum Channels

详细

By using estimates for the variation of quantum mutual information and the relative entropy of entanglement, we obtain ε-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 ε-exact lower estimates for the distance from a given two-particle state to the set of all separable states.