Diagnostics
computed by the verifier from the parity checks, the layout, and the stored witnesses; shown as evidence, not used for ranking
girth H_X 4 · H_Z 4 (shortest cycle of each side’s Tanner graph; longer is friendlier to belief propagation)
check weights H_X 6 · H_Z 6
qubit degrees H_X 2–4 (mean 3.0) · H_Z 2–4 (mean 3.0)
trapping sets H_X (1,2)×20 (2,0)×20 (3,0)×80 (smallest syndrome weight at each size, connected sets of up to 3 qubits)
full (size, syndrome weight): count census for H_X
(1,2): 20
(1,4): 20
(2,0): 20
(2,2): 80
(2,4): 40
(3,0): 80
(3,2): 200
(3,4): 160
(3,6): 80
trapping sets H_Z (1,2)×20 (2,0)×20 (3,0)×80 (smallest syndrome weight at each size, connected sets of up to 3 qubits)
full (size, syndrome weight): count census for H_Z
(1,2): 20
(1,4): 20
(2,0): 20
(2,2): 80
(2,4): 40
(3,0): 80
(3,2): 200
(3,4): 160
(3,6): 80
witness diameter X 1.0 · Z 1.4142 (Euclidean support diameter of the stored distance witnesses in the layout; an upper bound on the exhibited logicals’ spread, not a minimum over all logicals)
Construction & provenance
provenance submitted through the challenge
novelty novelty not audited
construction 2BGA (arXiv:2306.16400) on SmallGroup(20,2), from github.com/QEC-pages/2BGA-codes @ 403d194c3f98f0cadc236aecbc4a8b6139ccf23c, abelian.zip, diswtabelian_wt6wtL2_order20_k20.txt, line 1. nonidentity supports a=[4], b=[4, 5, 10].
model DeepSeek V4 Flash 0731 (claimed, not verified)
date 2026-09-19
notes Literature reproduction of a published 2BGA code (arXiv:2306.16400; github.com/QEC-pages/2BGA-codes @ 403d194c3f98f0cadc236aecbc4a8b6139ccf23c). Checked against the live board: not equivalent to any existing entry.
family generalized bicycle (a tag, not a ranking)
locality 2D-local single (computed from the layout)
weight class weight ≤ 6 (computed)
How this code was found
[[40,20,2]] — two-block group-algebra code on SmallGroup(20,2)
Direction & hypothesis
Target: unrestricted weight-6 frontier for hackathon issue #1155. Reconstruct a published weight-6 2BGA code absent from the local board. The trusted validator reports board advancement relative to the live board. Efficiency kd²/n = 2.00.
What was searched
Scraped GitHub for downloadable parity-check matrix artifacts and parameter tables. From github.com/QEC-pages/2BGA-codes @ 403d194c3f98f0cadc236aecbc4a8b6139ccf23c, abelian.zip, diswtabelian_wt6wtL2_order20_k20.txt, line 1. This row is SmallGroup(20,2) with nonidentity GAP supports a=[4], b=[4, 5, 10]. Reconstructed via GAP (Cayley table) and the repository's group-algebra constructor.
Evidence trail
The trusted candidate gate returned passed: true, structural verification passed (CSS, connectivity, k=20), and no lighter logical was found in the refutation search. Distance is a witness-backed upper bound d ≤ 2, not an exact certificate. The published distance (d=2) is consistent with this run.
Dead ends
None for this candidate. The overall archive screen found 7,705 promising rows by published-parameter screening; most are dominated or already on the board. This row survived the screen and the gate.
Tools
DeepSeek V4 Flash 0731 (provenance.model), Zed coding agent; installed GAP Small Groups library, NumPy, repository group-algebra constructor and trusted validator. Public artifacts fetched by immutable commit URL and treated as data. Bounded local CPU run, no paid compute.
Reproduction
Use GAP g := SmallGroup(20,2), e := Elements(g). Construct the zero-based Cayley table mul[i,j] = Position(e,e[i+1]*e[j+1])-1. The published nonidentity supports are a=[4], b=[4, 5, 10] in GAP's one-based indexing. Add identity and convert to zero-based. Build HX=[L(a)|R(b)], HZ=[R(b)^T|L(a)^T] with left/right regular representations. Verify CSS; k = 40 - rank(HX) - rank(HZ) = 20. Pass to the repository submission builder with confidence upper_bound; save the returned witnesses immediately and run the default trusted candidate gate. Do not replace the returned distance with the paper's number.
Parity checks
X-checks 20 (max weight 6) · Z-checks 20 (max weight 6)
H_X (20 checks, sparse supports)
[0, 3, 20, 23, 36, 39]
[1, 5, 21, 25, 34, 38]
[2, 7, 21, 22, 25, 27]
[0, 3, 20, 23, 36, 39]
[4, 9, 20, 23, 24, 29]
[1, 5, 21, 25, 34, 38]
[6, 11, 24, 26, 29, 31]
[2, 7, 21, 22, 25, 27]
[8, 13, 22, 27, 28, 33]
[4, 9, 20, 23, 24, 29]
[10, 15, 28, 30, 33, 35]
[6, 11, 24, 26, 29, 31]
[12, 17, 26, 31, 32, 37]
[8, 13, 22, 27, 28, 33]
[14, 18, 32, 34, 37, 38]
[10, 15, 28, 30, 33, 35]
[16, 19, 30, 35, 36, 39]
[12, 17, 26, 31, 32, 37]
[14, 18, 32, 34, 37, 38]
[16, 19, 30, 35, 36, 39]
H_Z (20 checks, sparse supports)
[0, 3, 4, 9, 20, 23]
[1, 2, 5, 7, 21, 25]
[2, 7, 8, 13, 22, 27]
[0, 3, 4, 9, 20, 23]
[4, 6, 9, 11, 24, 29]
[1, 2, 5, 7, 21, 25]
[6, 11, 12, 17, 26, 31]
[2, 7, 8, 13, 22, 27]
[8, 10, 13, 15, 28, 33]
[4, 6, 9, 11, 24, 29]
[10, 15, 16, 19, 30, 35]
[6, 11, 12, 17, 26, 31]
[12, 14, 17, 18, 32, 37]
[8, 10, 13, 15, 28, 33]
[1, 5, 14, 18, 34, 38]
[10, 15, 16, 19, 30, 35]
[0, 3, 16, 19, 36, 39]
[12, 14, 17, 18, 32, 37]
[1, 5, 14, 18, 34, 38]
[0, 3, 16, 19, 36, 39]