Manuscript En01-A@1 · En01-A.tex · proposition · 558b972b

Proposition: Flagged adaptive access

Sequential agreement and accessible adaptive sectors · lines 2456–2496 · proof included or linked

En01-A@1#prop:adaptive

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Let be orthogonal sector projectors commuting with , and define

for . Suppose the interface supplies an accessible orthogonal sector flag:

where is CPTP on the -sector. Then

Sector-wise Helstrom effects attain this value. After forgetting the flag, only the upper bound by this sum is guaranteed, and signed sector contributions may cancel.

Proof. Commutation gives

Off-diagonal sectors are removed by the flagged interface. Trace norm is additive on orthogonal direct sums, and the resulting blocks are traceless. Assemble the positive-spectral projectors blockwise. Forgetting the flag is CPTP post-processing, so Corollary cor:dp gives the upper bound. Without the flag, the block effects need not be separately implementable.

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