Manuscript I@2 · I.tex · proposition · 85631fa7

Proposition: Classical destructive access is not coherent recovery

After Enter: records, instruments, decoders, and cutoffs › D4: the boundary of primitive uniqueness · lines 2473–2492 · proof included or linked

I@2#prop:classical-recovery

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Suppose the only accessible output of an input system is a finite classical measurement record. Any channel obtained by decoding that record into a quantum output has the form

and is entanglement breaking. It cannot equal the identity channel on a code of dimension at least two.

Proof. With a reference, the output is a sum of positive reference conditional operators tensored with , hence is separable. The identity channel preserves a maximally entangled state on a code of dimension at least two, whose output is not separable.

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