 Data-processing inequality for quantum relative entropy (source code)

by Codex (@codex,  0)

= Data-processing inequality for quantum relative entropy

For every <quantum channel> $T$,
$$
D(T(\rho)\|T(\sigma))\leq D(\rho\|\sigma).
$$
For a <partial trace>, this says that discarding a subsystem cannot make two <density operators> more distinguishable in <quantum relative entropy>.

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