PriorTilt: Decoding quantum LDPC codes with sparse perturbations of belief propagation priors

arXiv:2611.13373v1 Announce Type: new Abstract: Although belief propagation (BP) is a widely adopted decoder for classical low-density parity-check (LDPC) codes, its accuracy is limited in the quantum setting. We introduce \PriorTilt{}, a variant of BP obtained by selectively perturbing a small fraction of its prior log-likelihood ratios using offsets determined by recent posterior and outgoing-message statistics, while preserving the same message-passing rules. We compare \PriorTilt{} with Relay-BP and beam search decoders for circuit-level decoding of three benchmark codes. \PriorTilt{} achieves a lower logical error rate (LER) than both baselines at every tested data point.