Abstract

We construct a complete finite instrument for a two-zone qubit–antiqubit toy model. The antiqubit designation means a declared inverse response to one specified unitary generator; it does not introduce antimatter, an antiunitary operation, or backward physical time. Both data qubits are read destructively in the computational basis. The resulting channel returns a classical word, consumes the corresponding quantum names, and agrees exactly with its projective recorded-channel specification on all operators, including arbitrary untouched references.

For an independently supplied one-parameter source family, a separate classical inference map estimates the normalized source weight. Its finite-shot confidence radius, sensitivity denominator, Fisher-information ledger, and implementation-error allowance are explicit. A concrete instance has entirely rational outcome probabilities and estimator values. We also prove a record-only quantum-recovery obstruction and non-identifiability of parameters omitted from the frozen model.

The philosophical contribution is an application of Enter's interface discipline: a record is not a quantum return; an inference map is not the record; an inaccessible complement is not destroyed information; a channel is not a thermal machine; and a finite analog is not an astrophysical identification. No Galactic quantum state, 511\,keV morphology, absolute Galactic rate, continuum transport law, or spacetime geometry is reconstructed.