Transition behavior in the channel capacity of two-quibit channels with memory
Chiara Macchiavello, G. Massimo Palma, S. Virmani · Physical Review A · 2004
We prove that a general upper bound on the maximal mutual information of quantum channels is saturated in the case of Pauli channels with an arbitrary degree of memory. For a subset of such channels we explicitly identify the optimal signal states. We show analytically that for such a class of channels entangled states are indeed optimal above a given memory threshold.