FL-QKD based on optical-THz biphotons generated by spontaneous parametric downconversion in inter-satellite wireless communication

Floodlight quantum key distribution (FL-QKD) is a new QKD protocol that can achieve a 2 Gbps secret key rate (SKR) in a 50 km fiber link without multiplexing technology [Q. Zhuang et al., Phys. Rev. A94, 012322 (2016)PLRAAN1050-294710.1103/PhysRevA.94.012322]. In this paper, we propose a wireless FL-QKD at terahertz bands (THz-FL-QKD) in inter-satellite links. THz-FL-QKD is the two-way protocol that sends quantum signals in the forward channel, modulates and amplifies the received signals at the receiver, and then returns to the transmitter through the backward channel for homodyne detection and decoding. We analyze the security of THz-FL-QKD against individual attacks and optimum collective attacks. Numerical simulations show that THz-FL-QKD is capable of a 50 Mbps SKR at 10 THz frequency in a 200 km inter-satellite wireless link. We expect this work will provide an efficient path to build a high-speed global quantum communication network.