Quantum Receivers for Future Space-Terrestrial Integrated Networks: Functions, Challenges, and Prospects

Future global connectivity demands necessitate space-terrestrial integrated networks (STINs), where high-speed laser communication forms the backbone of inter-satellite and satellite-ground links as well as the ground backbone network. Concurrently, the inherent openness of STINs requires physical layer security, which can be addressed by continuous-variable quantum key distribution (CV-QKD) based on laser coherent states for its high key rates and compatibility to existing laser communication infrastructures. Both classical laser communication performance and CV-QKD security are fundamentally limited by the standard quantum limit (SQL) of homodyne detection. This paper mainly focuses the vital roles and functions of quantum receivers in overcoming the SQL to enhance network capacity of future STINs. We first outline the development history of quantum receivers, highlighting displacement receivers as a promising solution. Then displacement receivers for both coherent communications and incoherent communications are introduced. At last, we identify the major challenges and potential breakthrough directions for implementing quantum receivers in future STINs.