Integrating Quantum and HPC: A Prototype Hybrid Implementation and Benchmark of Quantum-Selected Configuration Interaction

We present a prototype implementation of the Quantum-Selected Configuration Interaction (QSCI) method on a heterogeneous platform that integrates quantum simulation with high-performance computing (HPC). In this workflow, a GPU-based simulator emulates a quantum processor to prepare and sample reference states via the variational quantum eigensolver (VQE), while CPU nodes perform optimization and large-scale subspace diagonalization using EigenExa. This design enables seamless coordination between quantum state preparation and numerical linear algebra within HPC environments. The framework efficiently handles subspace dimensions up to 100,000 and exhibits favorable scaling with system size. Benchmark experiments on hydrogen chains demonstrate that relatively large systems can be processed within practical runtimes, highlighting the potential of hybrid HPC-QC integration for scalable quantum chemistry.