Pre-registration: a calibrated test of the independence premise of fault tolerance on public QEC syndrome data (premise meter, frozen protocol)

Version 2: pre-registration addendum for Phase D Outcome of the registered gate (G0) The G0 gate failed for every dataset, window family and null. No twin built from independent error mechanisms with circuit-local supports reproduces the bulk of the window-count distributions in the public data from Google Willow, Google Sycamore or Rigetti. For larger codes the twin cannot even be simulated. As the protocol requires, hypotheses H1–H3 are therefore not tested. This version adds pre-registration addendum 1. It fixes the analyses run instead, before either touches the test halves: • Model-free certificate (T3), on the test halves. It covers every registered configuration that has a circuit (the Google archives and Rigetti D6e). Windows are whole-patch windows of 1 and of 5 rounds, separated by one unused round, and the disjointness of their fault-location sets is checked from each circuit. Each stratum (archive, code family, code distance, window family) gets a premise curve ε_lo(k) on the grid k = c·j, j = 1–16, with Bonferroni correction at family-wise α = 0.05.• Threshold values for the certificate. ε* = 7.4 × 10⁻⁴ (Fowler, PRL 109, 180502, 2012) is the primary value; 2.73 × 10⁻⁵ (Aliferis, Gottesman and Preskill, QIC 6, 97, 2006) is a sensitivity check. Certificates against ε* are computed for surface-code strata only. Repetition-code, colour-code and stability strata get premise curves only.• Bursts. The primary analysis uses all windows; a secondary one excludes the windows flagged by the frozen burst classifier. B1/B2 event rates are reported descriptively.• Cat-qubit case study (exploratory). The model-based premise meter is applied to the AWS cat-qubit (D4) distance-3 configurations whose twin was simulable in G0. It reports R(k) intervals and k_cert, with the H1 reading (consistent if R_hi ≤ 3 for all k ≤ k_cert). It is labelled exploratory because D4's own G0 verdict is a fail. Status of the data when version 2 was created G0, which uses only the bulk bins, has run on the test halves. Its stored histograms include tail bins, but no tail statistic has been computed or examined. Both new analyses were dry-run on fit halves as pipeline checks. One choice was made after that dry run, and it is recorded in the addendum: ε* certificates were limited to surface-code strata, and strata were split by code family. The dry run had shown repetition-code and stability strata crossing ε* at k = c, i.e. at their base error rate, where Fowler's surface-code theorem does not apply. The model-based certification horizon is not computed, because it needs a twin tail. Files added in version 2 • phaseD_addendum.json: the machine-readable addendum. SHA-256: a458bcb40aa474d94a882a563a38a1a152d7bfb4404df9299f99fb020ab78834• ADDENDUM.md: the readable version of the addendum.• qpremise_code_phaseD_ade59b0.zip: the code that will run. The addendum's code_sha256 (794122ae1557c009664127e1c2e6b109781d5a71efcc566bc637b991c0403ab6) can be recomputed from it as the SHA-256 over the files matching qpremise/**/*.py, phaseD/scripts/*.py and phaseC/scripts/run_g0.py, taken in path order: each file's relative path, then its bytes with LF line endings.• SHA256SUMS_addendum.txt: checksums of the three files above. The version 1 files are unchanged. The original registration text follows. ──────────────────────────── Version 1 registration (2026-10-01) What this registers The analysis protocol of the premise meter. It tests whether public quantum-error-correction syndrome data agree with an independent-noise "twin" fitted to the same data. It also measures how far each dataset can certify the local-stochastic premise of the threshold theorem. Every analysis choice is fixed in frozen_protocol.json:• configuration eligibility, and the pre-registered subset in g0_selection.json;• the interleaved fit/test split;• the window families;• twin construction: candidate mechanisms from each circuit, an exact parity-moment fit, and a signed quasi-probability simulation with local weights;• the G0 gate decision rule;• the burst classifiers B1 and B2 with their validation targets;• the excess-tail-ratio interval and the certification-horizon conditions;• the model-free certificate's window rule. qpremise_code_at_freeze_79dbf14.zip holds the analysis code at the freeze. The protocol's code_sha256 can be recomputed from it: the SHA-256 over every qpremise/**/*.py file in path order, each file's relative path followed by its bytes with LF line endings. Hypotheses analysed after this registration (on test halves only) H1. After removing windows flagged by the frozen burst classifier, the excess tail ratio R(k) = P_obs(K ≥ k) / P_twin(K ≥ k) has an upper 95% confidence bound ≤ 3 for all k ≤ k_cert. Failure: a lower bound > 3 that replicates on the held-out half. H2. Including burst windows, R(k) > 10 for k ≥ k_b in at least one dataset, and a burst-mixture model fitted to the flagged windows predicts the published repetition-code error floor within a factor of 10. H3. The empirical horizon (power ≥ 0.8 at α = 0.05 against a factor-5 excess) agrees with the exact binomial computation within ±1. At least one dataset certifies k ≥ 10 in whole-patch windows. These are evaluated only on (dataset, window family) pairs that pass the G0 gate under both the stationary (N1) and drift-aware (N5) twins. The model-free certificate (T3) does not depend on the twin. Its threshold ε* is fixed before any certificate is computed. Timing and what had been seen Frozen 2026-10-01 17:31 IST (git commit 79dbf14). Before the freeze, only fit halves had been analysed. The G0 gate (bulk of the window-count distributions only; decision rule frozen) began on the test halves minutes after the freeze. When this record was created, no tail statistic (R(k), H1–H3, burst rates, certificates) had been computed from the test halves, and their tail bins had not been examined. The planned cloud-hardware contrast experiment (H4, H5) is not part of this registration and will be registered separately before any hardware run. Full details are in PREREGISTRATION.md. Protocol SHA-256: 5f7458cfdbe0e203fd9e2bf5d579703509c8374bae53096c37f8f1530540707a