We introduce a continuous-variable quantum key distribution (CVQKD) protocol that combines orthogonal frequency-division multiplexing (OFDM) 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 inter-satellite 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 inter satellite 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 modelling, 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.
We introduce a continuous-variable quantum key distribution (CVQKD) protocol that combines orthogonal frequency-division multiplexing (OFDM) 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 inter-satellite 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 inter satellite 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 modelling, 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.
We propose a novel continuous-variable quantum key distribution (CVQKD) protocol that employs orthogonal frequency-division multiplexing (OFDM) in the terahertz (THz) band to enable high-throughput and secure quantum communication. By encoding quantum information across multiple subcarriers, the protocol enhances spectral efficiency and mitigates channel dispersion and atmospheric attenuation. We present a comprehensive security analysis under collective Gaussian attacks, considering both terrestrial free-space channels, accounting for humidity-induced absorption, and inter-satellite links, incorporating realistic intermodulation noise. Simulations show secret key rates (SKR) reaching ~72 bits per channel use in open-air conditions. While intermodulation noise imposes trade-offs, optimised modulation variance enables resilience and secure communication range. The maximum terrestrial quantum link extends up to 4.5 m due to atmospheric THz absorption, whereas inter-satellite links can support secure communication over distances exceeding 100 km, owing to minimal propagation channel losses in space. We evaluate the practical implementation of our protocol using recently developed on-chip coherent THz sources based on superconducting Josephson junctions. These compact, voltage-tunable emitters produce wideband coherent radiation, making them ideal candidates for integration in scalable quantum networks. By incorporating their characteristics into our simulations, we assess secure key generation under various environmental conditions. Our results show secure communication over distances up to 3 m in open air, and up to 26 km in cryogenic or vacuum environments. This work advances the prospect of compact, high-capacity CVQKD systems for both terrestrial and space-based THz quantum communication.
We propose a continuous-variable quantum key distribution (CVQKD) scheme at terahertz (THz) bands based on multicarrier multiplexing (MCM) technology. In this scheme, multiple Gaussian modulated subcarriers are coupled to transmit multipath superposed thermal Gaussian states. At the receiver, optical discrete Fourier transform (ODFT) is used to demultiplex the received subcarriers, and the keys can be generated in parallel by homodyne detection and post processing. We analyze the security of the scheme against the optimal collective Gaussian attack under indoor environment and in inter-satellite links respectively. Results indicate that by using MCM technology, each subchannel may be affected by crosstalk, resulting in slight shortening of the maximal transmission distance while the total secret key rate can be greatly increased. We also verify the feasibility of higher key rate and longer distance THz-QKD by using MCM technology in inter-satellite links communication. We expect this work will provide an efficient path to build a global quantum communication network.
With the exponentially increased demands for large bandwidth, it is important to think about the best network platform as well as the security and privacy of the information in communication networks. Millimetre (mm)-waves and terahertz (THz) with high carrier frequency are proposed as the enabling technologies to overcome Shannon's channel capacity limit of existing communication systems by providing ultrawide bandwidth signals. Mm-waves and THz are also able to build wireless links compatible with optical communication systems. However, most solid-state components that can operate reasonably efficiently at these frequency ranges (100GHz-10THz), especially sources and detectors, require cryogenic cooling, as is a requirement for most quantum systems. Here, we show that secure mm-waves and THz QKD can be achieved when the sources and detectors operate at cryogenic temperatures down toT= 4K. We compare single-input single-output (SISO) and multiple-input multiple-output (MIMO) Continuous Variable THz Quantum Key Distribution (CVQKD) schemes and find the positive secret key rate in the frequency ranges betweenf=100 GHz and 1 THz. Moreover, we find that the maximum transmission distance could be extended, the secret key rate could be improved in lower temperatures, and achieve a maximum secrete communication distance of more than 5km atf=100GHz andT=4K by using 1024×1024 antennas. Our results for the first time show the possibility of mm-waves and THz MIMO CVQKD with the system operating at temperatures belowT= 50K, which may contribute to the efforts to develop next-generation secure wireless communication systems and quantum internet for applications from inter-satellite and deep space to indoor and short-distance communications.
We experimentally demonstrated a high-performance multi-protocol continuous-variable quantum key distribution (CV-QKD) using one transceiver. The demonstrated multi-protocol CV-QKD system can simultaneously distribute 5 subcarriers with Gaussian, 4QAM, 16QAM, 64QAM, and 1024QAM modulation protocols based on orthogonal-frequency-division-multiplexing (OFDM) technology. Moreover, the modulation variance and probability distribution factor of 5 subcarriers are carefully optimized to maximize their respective SKRs. Besides, we innovatively design an effective OFDM-based DSP scheme and a precise dual-stage phase noise compensation scheme to realize a low excess noise for each subcarrier operating at a 2 GHz symbol rate. Thus, the multi-protocol CV-QKD achieves multiple SKRs of 48.79, 7.58, 23.67, 32.93, and 36.78 Mbps over a typical transmission distance of 50 km within a single transmission. Therefore, our work provides a practical solution to achieve highly efficient, interoperable, flexible, and secure QKDs for high-speed quantum secure communication.
Although multiple-input multiple-output (MIMO) terahertz (THz) continuous-variable quantum key distribution (CVQKD) is theoretically secure, practical vulnerabilities may arise due to detector imperfections. This paper explores a CV measurement-device-independent (MDI) QKD system operating at THz frequencies within a MIMO framework. In this system, measurement is delegated to an untrusted third party, Charlie, rather than the receiver, eliminating all detector attacks and significantly enhancing the system's practical security. Using transmit-receive beamforming techniques, the system transforms MIMO channels into multiple parallel lossy quantum channels, enabling robust key distribution between Alice and Bob. This study examines entanglement-based and prepare-and-measure protocols, deriving secret key rates for both asymptotic and finite code scenarios. Simulations reveal the critical role of multiple antenna configurations and efficient homodyne detection in mitigating free-space path loss and maximizing key rates. Results indicate that system performance is optimized at lower THz frequencies for long-range transmissions and higher frequencies for short-range applications. The proposed protocol offers a scalable solution for secure quantum communications in next-generation wireless networks, demonstrating potential for deployment in both indoor and outdoor environments.
With the exponentially increased demands for large bandwidth, it is important to think about the best network platform as well as the security and privacy of the information in communication networks. Millimetre (mm)-waves and terahertz (THz) with high carrier frequency are proposed as the enabling technologies to overcome Shannons channel capacity limit of existing communication systems by providing ultrawide bandwidth signals. Mm-waves and THz are also able to build wireless links compatible with optical communication systems. However, most solid-state components that can operate reasonably efficiently at these frequency ranges (100GHz-10THz), especially sources and detectors, require cryogenic cooling, as is a requirement for most quantum systems. Here, we show that secure mm-waves and THz QKD can be achieved when the sources and detectors operate at cryogenic temperatures down to T= 4K. We compare single-input single-output (SISO) and multiple-input multiple-output (MIMO) Continuous Variable THz Quantum Key Distribution (CVQKD) schemes and find the positive secret key rate in the frequency ranges between f=100 GHz and 1 THz. Moreover, we find that the maximum transmission distance could be extended, the secret key rate could be improved in lower temperatures, and achieve a maximum secrete communication distance of more than 5 km at f=100GHz and T=4K by using 1024*1024 antennas. Our results may contribute to the efforts to develop next-generation secure wireless communication systems and quantum internet for applications from inter-satellite and deep space, to indoor and short-distance communications.