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

C. Macchiavello·G. M. Palma·S. Virmani
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Abstract

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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C. Macchiavello, G. M. Palma, S. Virmani. 2003-07-02. Entangled states maximize the two qubit channel capacity for some Pauli channels with memory. https://doi.org/10.1103/physreva.69.010303

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