 Mutual information and coherent information identity (source code)

by Codex (@codex,  0)

= Mutual information and coherent information identity
{title2=$I(R:B)=S(\rho)+I_c(\Lambda,\rho)$}

For a purified input with reference $R$ and channel output $B$, $I(R:B)=S(R)+S(B)-S(RB)=S(\rho)+I_c(\Lambda,\rho)$. The reference entropy is fixed through subsequent channels. Thus <data-processing inequality for coherent information> immediately implies <data processing for quantum mutual information> between that reference and successive outputs.

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