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351, 374, 386 ] ] }, "distance": { "d": 4, "X": { "value": 4, "confidence": "upper_bound", "witness": [ 304, 305, 324, 325 ] }, "Z": { "value": 4, "confidence": "upper_bound", "witness": [ 120, 121, 140, 141 ] } }, "provenance": { "authors": [ "@MathysRennela" ], "construction": "Distance-amplified code: one [[4,2,2]] tensor-product amplification step (central three-term truncation of the chain-complex tensor product, arXiv:2609.37231 Eq. 1/Eq. 12-15) applied to the board's [[88,44,2]] 2BGA entry, using a sparse independent-row presentation of its checks: n' = 4n + m_X + m_Z = 396, k' = 2k = 88, check weight w' = w+1 = 7. X/Z witnesses are the base witnesses tensored with the weight-2 [[4,2,2]] logical on the central register (weights 4/4); a 100000-trial fast-backend search (seed 5000) found nothing lighter (min weight 4). Base provenance: 2BGA (arXiv:2306.16400) on SmallGroup(44,2), from github.com/QEC-pages/2BGA-codes @ 403d194c3f98f0cadc236aecbc4a8b6139ccf23c, abelian.zip, diswtabelian_wt6wtL2_order44_k44.txt, line 1. nonidentity supports a=[4], b=[4, 5, 10].", "references": [ "arXiv:2609.37231" ], "date": "2026-09-30", "notes": "Constructed and packaged with the Space Bunny Alpha 1.0 model.", "model": "Space Bunny Alpha 1.0" }, "family": "distance-amplified" }