Three-qubit phase readout in Theory Φ and standard quantum mechanics

A three-qubit GHZ decoder proposed in the earlier Q1 spin-star preprint transfers a global phase sign to one central qubit. This follow-up traces its implementation on Rigetti Cepheus-1-108Q (centre q107, neighbours q106 and q98) and asks whether its readout can distinguish Theory Φ from standard quantum mechanics. It connects the theoretical preprint, the book The Language of Φ and the programme’s methodological evidence review to the original measurement records. Five completed acquisition stages account for 101,860 physical shots: a 10-shot native timing witness, a 10,240-shot Ramsey measurement of individual and concurrent couplers, 28,082 intermediate calibration and decoding controls, 42,024 shots in the primary GHZ cycle (including 33,792 primary shots in 12 trajectory blocks), and a 21,504-shot frequency pilot. The original Ramsey report figure, full phase-and-contrast scan, intermediate control figures and Part I hardware figures are reproduced. With full-amplitude joint drive the first scan could not identify either phase rate. Reducing the drive to 75% restored measurable responses. In the primary experiment the serial/joint sign-error rates were 12.66%/16.20% for transverse disturbances and 19.59%/21.64% for commuting disturbances. None of the three prespecified criteria for the predicted hardware advantage was met. Carrier retuning improved the worst-case joint inversion from 97/384 to 199/384; the development threshold was 346/384. The published ideal Q1 mapping and a separate standard quantum calculation predict the same 3.522800135 percentage-point transverse advantage at mean jump count π/20. Their difference for this observable is exactly zero. The broader equations reviewed supply no independently specified correction on this register. The release provides original shot records, numerical estimates, program-timing evidence, uncertainty analyses, editable figures and manuscripts, and offline reproduction tools.