Passive continuous-variable quantum key distribution based on orthogonal frequency-division multiplexing in the terahertz band

Abstract

We propose a passive continuous-variable quantum key distribution protocol based on multicarrier multiplexing technology in the terahertz band. In this paper, we realize the superposition of multipath coherent states by inverse Fourier transform and passive modulation. At the receiving end, the coherent states of the subcarriers are separated by quantum Fourier transform, and the keys are obtained in parallel by a homodyne (heterodyne) detector and post-processing. In addition, we derive the security bounds of the protocol and evaluate the performance in indoor environments and intersatellite links. Furthermore, we consider finite-size effects and propose tighter agreement constraints, which are more practical than those obtained in the asymptotic limit. This work will provide an effective way to build efficient wireless quantum communication networks.