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 "provenance": {
  "authors": [
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  "origin": "baseline",
  "construction": "Rotated surface code, distance 9.",
  "date": "1997-07-09",
  "references": [
   "arXiv:quant-ph/9707021"
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  "notes": "Distance is exact by construction. 2D layout added 2026-07-23: qubit q at (q//9, q%9) on the 9x9 planar grid; single layer, measured interaction radius sqrt(2)."
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}