摘要
Ground-based free-space optical (FSO) quantum networks (QNs) have been regarded as a viable alternative to overcome the scalability and service availability limitations of fiber- or satellite-based QNs. However, FSO channels require line-of-sight connections between quantum access nodes (QANs) and user devices (UDs), making them highly susceptible to blockage by obstacles. Reconfigurable intelligent surfaces (RISs) have emerged as a promising solution by dynamically redirecting optical links to maintain connectivity. Despite their potential, RIS-assisted quantum transmissions pose challenges, including limited QAN capacity, fidelity degradation, UD demand requirements, and RIS assignments. To address these challenges, we formulate an optimization problem and propose a 2-approximation algorithm that jointly determines UD-RIS assignment and entanglement distribution while incorporating entanglement purification. Finally, simulation results demonstrate that our proposed algorithm outperforms existing baselines by at least 16% - 38%.