Passive continuous-variable quantum key distribution based on simultaneous quantum and classical communication in the terahertz band

Abstract We propose a passive continuous-variable quantum key distribution (CVQKD) protocol based on simultaneous quantum and classical communication (SQCC) under indoor environments and in inter-satellite links within the terahertz band. In our PSQCC-CVQKD scheme, classical modulation is performed at the transmitter, followed by passive quantum modulation operations. At the receiver, an amplifier is utilized to amplify and demultiplex the received signal, and a homodyne or heterodyne detector is subsequently selected for decoding. We derive the security bounds of the protocol and evaluate its performance in both indoor environments and inter-satellite links. Furthermore, by considering finite-size effects, we achieve tighter agreement constraints, which are more practical than those obtained in the asymptotic limit. Simulation results indicate that this scheme exhibits a high secret key rate and strong jamming resistance in practical applications, providing a more efficient pathway for the construction of future quantum networks.