Pair-Partition Constructions for CPM-Based Quantum LDPC Codes

We construct binary Calderbank--Shor--Steane (CSS) quantum low-density parity-check (LDPC) codes from circulant permutation matrices (CPMs). The construction is parameterized by column weight J, row weight L, and prime lift size P. A J x J array of pair partitions imposes linear paired-difference equations on the CPM exponents. These equations give CSS orthogonality. The main finite examples reported here are the (J,L)=(4,12)-regular girth-six code [[372,130,16]] with rate 0.349, and the (J,L)=(4,14)-regular girth-six code [[518,228,16]] with rate 0.440. We also record (J,L)=(3,8)-regular girth-six instances [[472,122,14]] and [[488,126,14]], with lift sizes P=59 and P=61, respectively. The stated distances are established for the fixed matrices by exhaustive low-weight exclusion together with explicit non-stabilizer witnesses.