Part 2: GPU-accelerated BP-OSD decoding for High-rate Quantum LDPC Codes

High-rate quantum LDPC codes promise low overhead for fault-tolerant quantum computing, but their utility hinges on fast, accurate decoding in practice. We present CUDA-Q QEC's GPU accelerated belief propagation (BP) decoder with ordered statistics decoding (OSD) post-processing for quantum LDPC codes and highlight GPUs as a natural fit for its parallel structure within hybrid quantum–classical computing workflows. We emphasize the importance of QPU+GPU system integration—including batching, data movement, and codesign—to deliver practical throughput without sacrificing decoding quality. CUDA-Q QEC's GPU-accelerated BP+OSD implementation achieves substantial speedups over CPU baselines while maintaining strong decoding performance across representative noise models. We illustrate the approach on the [[30,8,3]] Bring's hyperbolic surface code for quantum memory and fault-tolerant logical circuits, demonstrating efficient decoding consistent with its high-rate structure. Together with the high-rate code architecture and logical gate constructions presented in part 1, these results chart a coherent path toward low overhead, fault-tolerant quantum computation enabled by GPU-accelerated decoding.