Title: Exploiting Spatial Diversity in Earth-to-Satellite Quantum-Classical Communications Show Chinese title

Title: 利用星地量子-经典通信中的空间多样性

Abstract: Despite being an integral part of the vision of quantum Internet, Earth-to-satellite (uplink) quantum communications have been considered more challenging than their satellite-to-Earth (downlink) counterparts due to the severe channel-loss fluctuations (fading) induced by atmospheric turbulence. The question of how to address the negative impact of fading on Earth-to-satellite quantum communications remains largely an open issue. In this work, we explore the feasibility of exploiting spatial diversity as a means of fading mitigation in Earth-to-satellite Continuous-Variable (CV) quantum-classical optical communications. We demonstrate, via both our theoretical analyses of quantum-state evolution and our detailed numerical simulations of uplink optical channels, that the use of spatial diversity can improve the effectiveness of entanglement distribution through the use of multiple transmitting ground stations and a single satellite with multiple receiving apertures. We further show that the transfer of both large (classically-encoded) and small (quantum-modulated) coherent states can benefit from the use of diversity over fading channels. Our work represents the first quantitative investigation into the use of spatial diversity for satellite-based quantum communications in the uplink direction, showing under what circumstances this fading-mitigation paradigm, which has been widely adopted in classical communications, can be helpful within the context of Earth-to-satellite CV quantum communications. Show Chinese abstract

Abstract: 尽管是量子互联网愿景的重要组成部分，由于大气湍流引起的信道损耗波动（衰减），地对星（上行链路）量子通信被认为比星对地（下行链路）通信更具挑战性。如何应对衰减对地对星量子通信的负面影响仍然是一个开放问题。在本工作中，我们探讨了利用空间分集作为地对星连续变量（CV）量子经典光通信中衰减缓解手段的可行性。我们通过量子态演化的理论分析以及上行链路光信道的详细数值模拟，证明了使用空间分集可以通过多个发射地面站和一个具有多个接收孔径的卫星来提高纠缠分发的有效性。我们进一步表明，大（经典编码的）和小（量子调制的）相干态的传输都可以从衰减信道上的分集使用中受益。我们的工作是对上行链路方向基于卫星的量子通信中空间分集使用的首次定量研究，展示了在什么情况下这种在经典通信中广泛采用的衰减缓解范式可以在地对星CV量子通信的背景下有所帮助。