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Rigetti Cepheus-1-108Q: neighbour effects
Runs. AWS Braket, Rigetti Cepheus-1-108Q, 28 September and 4 October 2026 (task IDs in the data file).
What holds
- With a directly coupled neighbour (q0) prepared in |2⟩, Ramsey qubit q9’s precession rate shifts by −54.93 ± 1.28 °/µs on 28 September and −38.64 ± 1.62 °/µs on 4 October (windows 0.5–2 µs; shot noise only; the dates differ by 16.3 ± 2.1 °/µs). The pair is the same on both dates; between them the pulse amplitude was retuned, the number of simultaneous Ramsey qubits changed from 1 to 106 and the processor was recalibrated, so the difference is not assigned to the coupling.
- Over 22 other pairs of a qubit in |2⟩ and a coupled neighbour (4 October, 1 µs window; seven emitters and their 22 neighbours) the shift spans −72.8 to +30.9 °/µs (median −6.4): on this processor sign and size are properties of the pair. There is no readout-against-idle design on this processor.
Run it
Download the script and the files in data/ into one folder (data in data/), then python3 verify_rigetti_extra.py. Standard library only; it prints each figure beside the recomputed value. The compact data were cut from the raw results; the raw files and the reduction scripts are available on request.
Files: verify_rigetti_extra.py · data/rigetti_extra.json