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   "witness_provenance": {
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    "date": "2026-10-30",
    "found_at_samples": 300000000,
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    "tool": "verify/ris_gpu.py (Perlmutter A100)",
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 "provenance": {
  "authors": [
   "@vprusso"
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  "construction": "Bivariate bicycle on Z_6 x Z_11 (n = 2lm = 132) with A = y^5 + xy^6 + xy + x^4y^5 and B = x^2y^3 + y + xy^10 + x, H_X = [A | B], H_Z = [B^T | A^T]; built by research/kit/bb.build_bb(l=6, m=11, A_terms=[[0, 5], [1, 6], [1, 1], [4, 5]], B_terms=[[2, 3], [0, 1], [1, 10], [1, 0]]).",
  "references": [
   "S. Bravyi, A. W. Cross, J. M. Gambetta, D. Maslov, P. Rall, and T. J. Yoder, High-threshold and low-overhead fault-tolerant quantum memory, Nature 627, 778 (2024), arXiv:2308.07915"
  ],
  "date": "2026-10-25",
  "notes": "Unattended loop run on Perlmutter, iteration 862, direction bb-w4-mid, seed 20261879. The deeper rungs recorded in notes/ agree with the gate's reading of d = 17.",
  "model": "Claude Fable 5.1 (Claude Code) working for @vprusso",
  "origin": "submission",
  "search_budget": {
   "candidates_screened": 106817,
   "tool": "research/kit/search.screen_adaptive; verify/heuristic_distance.estimate; verify/ris_gpu.py",
   "notes": "candidates_screened counts direction bb-w4-mid of the loop through 29 October; the loop's 390.6 CPU hours cover all five directions",
   "gpu_hours": 0.34,
   "ris_trials_per_side": 300000000
  }
 },
 "family": "bivariate-bicycle",
 "circuit": {
  "d_circ": {
   "Z": {
    "value": 17,
    "confidence": "upper_bound",
    "witness": [
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     128520,
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     128531,
     128534,
     128552
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   },
   "X": {
    "value": 17,
    "confidence": "upper_bound",
    "witness": [
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  "rounds": 17,
  "stim_version": "1.16.0",
  "notes": "Interleaved two-block extraction (Bravyi et al. arXiv:2308.07915 Table 5 style): joint reset and measurement layers, 9 CX layers per round; X-check term slots [2, 7, 6, 1, 3, 5, 8, 4], Z-check term slots [6, 1, 2, 7, 4, 3, 0, 5] over terms A_0..A_3, B_0..B_3; terms recovered from H alone by a commuting permutation decomposition; generated by qldpc submit (research/circuit_autogen.py, seed 0), the first of up to 6 candidates whose RIS screen at 2 rounds found nothing below d; witnesses from RIS on ker(H_dem) at twice the gate's trial budget, validated in GF(2)",
  "contributed_by": {
   "by": [
    "@vprusso"
   ],
   "date": "2026-11-06",
   "method": "circuit_autogen schedule search (two-block interleaved, then layout, then generic), verified by verify/circuit_verify.py before writing"
  }
 }
}