Entangled states maximize the two qubit channel capacity for some Pauli channels with memory

Macchiavello, C.; Palma, G. M.; Virmani, S.

Entangled states maximize the two qubit channel capacity for some Pauli channels with memory

Authors

Macchiavello, C.

Palma, G. M.

Virmani, S.

Description

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. It is noteworthy that the resulting channel capacity is a non-differentiable function of the memory parameter.
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