Rate-2/3 Girth-8 (3,18)-Regular Quantum LDPC Codes from Two-Branch Finite-Field Bases and CPM Lifts

• URL: http://arxiv.org/abs/2606.27130v1
• Date: Thu, 25 Jun 2026 15:08:16 GMT
• Title: Rate-2/3 Girth-8 (3,18)-Regular Quantum LDPC Codes from Two-Branch Finite-Field Bases and CPM Lifts
• Abstract summary: The code is a Calderbank-Shor-Steane (CSS) code with parameters $[34542,23032,dle 310]]$.<n>We do not regard this upper bound as an estimate of the true minimum distance; rather, $dle310$ is the tightest upper bound currently obtained from structural lifts and decoder-produced logical errors.
• Score: 0.0
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: We construct a rate-$2/3$ quantum low-density parity-check (LDPC) code from a $(3,18)$-regular two-branch finite-field base and a circulant-permutation-matrix (CPM) lift of degree $P=101$. The resulting code is a Calderbank-Shor-Steane (CSS) code with parameters $[[34542,23032,d\le 310]]$. We do not regard this upper bound as an estimate of the true minimum distance; rather, $d\le310$ is the tightest upper bound currently obtained from structural lifts and decoder-produced logical errors. The construction has row weight 18 and column weight 3, and the Tanner graphs of $H_X$ and $H_Z$ separately have girth 8. Decoder experiments with log-likelihood-ratio (LLR) joint belief propagation (BP) and deterministic post-processing show no failures in $10^8$ trials at $p=0.01$, and a finite-length frame error rate (FER) sweep estimates the transition near $p=0.029$.

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