PennyLane-Lightning MPI: A massively scalable quantum circuit simulator based on distributed computing in CPU clusters
Quantum circuit simulation faces severe computational bottlenecks due to the exponential growth of Hilbert space dimension with qubit count. To address this, we propose an index-dependent, gate-specific parallelization strategy that exploits the locality of single-qubit gates and the block structure of the state vector, enabling efficient distributed-memory quantum state evolution on CPU clusters. Our approach employs MPI for inter-node parallelism, integrates with the PennyLane plugin interface, and leverages fine-grained vector partitioning to maximize scalability. Experiments on standard multi-core CPU clusters successfully simulate 41-qubit circuits using over 100,000 concurrent processes, outperforming generic unitary-matrix-based methods in both speed and memory efficiency. The implementation achieves strong scaling and has been deployed as the high-performance simulation backend of a national cloud-based quantum computing platform in Korea.