Orthogonal Frequency-Division Multiplexing Continuous-Variable Terahertz QKD for Large-Scale Wireless Quantum Communication

Abstract

In this article, we introduce a continuous-variable quantum key distribution (CVQKD) protocol that combines orthogonal frequency-division multiplexing with terahertz (THz) carriers to deliver high-throughput and hardware-compatible quantum communication. By distributing quantum states across multiple subcarriers, our approach achieves a noticeable increase in spectral efficiency while mitigating dispersion and atmospheric losses that limit the performance of existing optical and microwave CVQKD systems. A full security analysis under collective Gaussian attacks is presented, incorporating realistic noise models for both terrestrial and intersatellite channels. In terrestrial free-space links, our simulations show secret key rates approaching 72 bits per channel use, with secure distances up to 4.5 m under strong humidity-induced absorption. For intersatellite links, where propagation losses are minimal, secure transmission is sustained over 100 km. A distinctive feature of our work is its direct link to practical hardware. We evaluate implementation using emerging on-chip coherent THz sources based on superconducting Josephson junctions. These compact voltage-tunable emitters provide wideband coherent radiation ideally matched to our protocol, enabling scalable chip-integrated quantum networks. By incorporating their measured characteristics into our models, we demonstrate secure communication up to 3 m in ambient conditions and ∼26 km under cryogenic or vacuum conditions. By uniting advanced protocol design, rigorous security modeling, and hardware-driven performance analysis, this work establishes THz CVQKD as a viable and scalable route to next-generation terrestrial and space-based quantum communication.