Quantum secret sharing (QSS) has been previously demonstrated with conceivability in optical-fiber channels. However, extending this framework to the microwave frequency band presents challenges in achieving secure quantum communications over turbulent channels, as intricate turbulence can induce amplitude and phase jitter in quantum signals, leading to decoherence or even interruptions in the communication link. In this work, we propose a microwave-enabled continuous-variable quantum secret sharing (CVQSS) scheme operating over turbulent free-space channels. The protocol explicitly addresses the extreme sensitivity of microwave quantum states to environmental turbulence, which manifests as severe amplitude and phase fluctuations. It incorporates the Shamir threshold scheme to facilitate multi-user secret sharing. We suggest a flexible approach to solving problems of adaptive phase compensation and multi-aperture reception techniques when characterizing an equivalent noise channel based on the Kolmogorov turbulence model. The proposed measurement-device-independent (MDI) architecture renders the protocol immune to all detector-side attacks, provided that the state preparation at the users' side is trusted. Numerical simulations ascertain the performance of the microwave continuous-variable measurement-device-independent quantum secret sharing (CV-MDI-QSS) system and demonstrate the feasibility of practical deployment in complicated turbulent channels. This approach offers a turbulence-resistant solution for dynamic quantum networks through harsh free-space channels implemented in microwave-propagated environments.
Quantum secret sharing (QSS) has been previously demonstrated with conceivability in optical-fiber channels. However, extending this framework to the microwave frequency band presents challenges in achieving secure quantum communications over turbulent channels, as intricate turbulence can induce amplitude and phase jitter in quantum signals, leading to decoherence or even interruptions in the communication link. In this work, we propose a microwave-enabled continuous-variable quantum secret sharing (CVQSS) scheme operating over turbulent free-space channels. The protocol explicitly addresses the extreme sensitivity of microwave quantum states to environmental turbulence, which manifests as severe amplitude and phase fluctuations. It incorporates the Shamir threshold scheme to facilitate multi-user secret sharing. We suggest a flexible approach to solving problems of adaptive phase compensation and multi-aperture reception techniques when characterizing an equivalent noise channel based on the Kolmogorov turbulence model. The proposed measurement-device-independent (MDI) architecture renders the protocol immune to all detector-side attacks, provided that the state preparation at the users' side is trusted. Numerical simulations ascertain the performance of the microwave continuous-variable measurement-device-independent quantum secret sharing (CV-MDI-QSS) system and demonstrate the feasibility of practical deployment in complicated turbulent channels. This approach offers a turbulence-resistant solution for dynamic quantum networks through harsh free-space channels implemented in microwave-propagated environments.
Free-space quantum cryptography holds significant potential for enabling global quantum communication networks. This paper proposes a free-space continuous-variable quantum secret sharing (CV-QSS) protocol employing a local local oscillator (LLO). The proposed protocol simplifies the system architecture by requiring only two heterodyne detections at the dealer’s side, thereby eliminating the additional noise and complexity associated with coherent measurements at each participant’s side in conventional schemes. Theoretically, we establish a channel transmittance model that comprehensively incorporates the effects of rain extinction and atmospheric turbulence, and derive the bound of the secret key rate. Experimentally, we systematically evaluate the impact of weather conditions and atmospheric turbulence on protocol performance and conduct comparative evaluations against existing schemes. The results demonstrate that the proposed protocol outperforms the previously proposed free-space LLO-based CV-QSS protocol in terms of key rate, transmission distance, noise tolerance, and participant capacity. Furthermore, this protocol supports secret sharing among 5 participants over 75 km or up to 37 participants within 10 km, outperforming the LLO-based CV-QSS system in a fiber channel. This study validates the potential of free-space CV-QSS as a viable solution for medium-to-long-distance and multi-user quantum secret sharing.
Abstract The developing tendency of continuous-variable (CV) measurement-device-independent (MDI) quantum cryptography is to cope with the practical issue of implementing scalable quantum networks. Up to now, most theoretical and experimental researches on CV-MDI QKD are focused on two-party protocols. However, we suggest a CV-MDI multipartite quantum secret sharing (QSS) protocol use the EPR states coupled with optical amplifiers. More remarkable, QSS is the real application in multipartite CV-MDI QKD, in other words, is the concrete implementation method of multipartite CV-MDI QKD. It can implement a practical quantum network scheme, under which the legal participants create the secret correlations by using EPR states connecting to an untrusted relay via insecure links and applying the multi-entangled Greenberger–Horne–Zeilinger (GHZ) state analysis at relay station. Even if there is a possibility that the relay may be completely tampered, the legal participants are still able to extract a secret key from network communication. The numerical simulation indicates that the quantum network communication can be achieved in an asymmetric scenario, fulfilling the demands of a practical quantum network. Additionally, we illustrate that the use of optical amplifiers can compensate the partial inherent imperfections of detectors and increase the transmission distance of the CV-MDI quantum system .
Abstract Although continuous‐variable quantum secret sharing (CVQSS) is theoretically proven to be secure, it may still be subject to various practical attacks due to the imperfections of devices. In this study, measurement‐device‐independent CVQSS (MDI‐CVQSS) is proposed in which measurement is no longer the duty for the dealer but is performed by an untrusted party Charlie, so that all detector side‐channel attacks can be eliminated, greatly enhancing the practical security of CVQSS system. The security bound is derived for the proposed MDI‐CVQSS, and its numerical simulation shows that MDI‐CVQSS outperforms conventional CVQSS in terms of both secret key rate and maximal number of users. It is found that MDI‐CVQSS possesses several unique properties, such as local stability of the secret key rate, low total excess noise and high utilization rate of raw data, which indicate that MDI‐CVQSS has the potential for efficiently building a large‐scale quantum communication network. Moreover, it is also suggested three variations of MDI‐CVQSS to satisfy the requirements of different multi‐point quantum communication scenarios.
Quantum secret sharing (QSS) faces inherent limitations in scaling to multi-user networks due to excess noise introduced by highly asymmetric beam splitters (HABSs) in chain-structured topologies. To overcome this challenge, we propose an optical frequency comb-based continuous-variable QSS (OFC CV-QSS) scheme that establishes parallel frequency channels between users and the dealer via OFC-generated multi-wavelength carriers. By replacing the chain-structured links with dedicated frequency channels and integrating the Chinese remainder theorem (CRT) with a decentralized architecture, our design eliminates excess noise from all users using HABS while providing mathematical- and physical-layer security. Simulation results demonstrate that the scheme achieves a more than 50% improvement in maximum transmission distance compared to chain-based QSS, with significantly slower performance degradation as users scale to 20. Numerical simulations confirm the feasibility of this theoretical framework for multi-user quantum networks, offering dual-layer confidentiality without compromising key rates.
This study investigates the implementation of measurement-device-independent multiparty quantum communication using continuous-variable Greenberger-Horne-Zeilinger (CV GHZ) states under the fast fading channel. The communication parties are connected through free space, and factors such as atmospheric turbulence cause beam drift, resulting in variations in channel transmittance according to specific probability distributions. We assume a worst-case scenario in which an eavesdropper has complete control over the channel, forcing the communicators to estimate the channel based on this probability distribution. The protocol employs CV GHZ states to achieve secure communication through quantum cryptographic conference and quantum secret sharing. For the aspect of security, independent entangling cloner attack and coherent attack are analyzed. Simulation results demonstrate that the protocol can withstand advantageous attacks from eavesdroppers.
Abstract Building scalable and secure quantum networks requires advanced quantum key distribution (QKD) protocols that support multi-user connectivity. Continuous-variable (CV) measurement-device-independent (MDI) QKD, which eliminates all detector side-channel attacks, is a promising candidate for creating various quantum network topologies-such as quantum access networks and star-type topologies-using standard technology and providing high secure key rates. However, its security has so far only been experimentally demonstrated in asymptotic regimes with limited secret key rates and complex experimental setups, limiting its practical applications. Here, we report an experimental validation of a CV MDI-QKD system, achieving a secure key rate of 2.6 Mbit s −1 against collective attacks in the finite-size regime over a 10 km fiber link. This is achieved using a new system design, incorporating a locally generated local oscillator, a new relay structure, a real-time phase locking system, and a well-designed digital-signal-processing pipeline for quantum state preparation and CV Bell measurements at a symbol rate of 20 MBaud. Our results set a new benchmark for secure key exchange and open the possibility of establishing high-performance CV MDI-QKD networks, paving the way toward a scalable quantum network.