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arXiv:2406.15853 · Reports on Progress in Physics

Repeater-like asynchronous measurement-device-independent quantum conference key agreement

Yu-Shuo Lu, Hua-Lei Yin, Yuan-Mei Xie, Yao Fu, Zeng‐Bing Chen

Published May 30, 2025• 31 citations
arXivHTMLPDF

Abstract

Quantum conference key agreement (QCKA) enables secure communication among multiple parties by leveraging multipartite entanglement, which is expected to play a crucial role in future quantum networks. However, its practical implementation has been severely limited by the experimental complexity and low efficiency associated with the requirement for synchronous detection of multipartite entangled states. In this work, we propose a measurement-device-independent QCKA protocol that employs asynchronous Greenberger-Horne-Zeilinger state measurement. Our protocol enables a linear scaling of the conference key rate among multiple parties, demonstrating performance comparable to that of the single-repeater scheme in quantum networks. Additionally, we achieve intercity transmission distances with composable security under finite-key conditions. By adopting the generalized asynchronous pairing strategy, our approach eliminates the need for complex global phase locking techniques. Furthermore, by integrating asynchronous pairing with ring-interference network structure, our method provides insights for various quantum tasks beyond quantum communication, including multiparty computing and quantum repeaters.

DOI
10.1088/1361-6633/addeec

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Quantum conference key agreement (QCKA) enables secure communication among multiple parties by leveraging multipartite entanglement, which is expected to play a crucial role in future quantum networks. However, its practical implementation has been severely limited by the experimental complexity and low efficiency associated with the requirement for synchronous detection of multipartite entangled states. In this work, we propose a measurement-device-independent QCKA protocol that employs asynchronous Greenberger-Horne-Zeilinger state measurement. Our protocol enables a linear scaling of the conference key rate among multiple parties, demonstrating performance comparable to that of the single-repeater scheme in quantum networks. Additionally, we achieve intercity transmission distances with composable security under finite-key conditions. By adopting the generalized asynchronous pairing strategy, our approach eliminates the need for complex global phase locking techniques. Furthermore, by integrating asynchronous pairing with ring-interference network structure, our method provides insights for various quantum tasks beyond quantum communication, including multiparty computing and quantum repeaters.
Quantum networks aim to enable quantum information tasks among multiple parties. Quantum conference key agreement (QCKA) is a typical task in quantum networks, which distributes information-theoretically secure keys among multiple users. However, QCKA relying on directly distributing Greenberger-Horne-Zeilinger (GHZ) states over long distances faces significant challenges due to the fragility of these states. Measurement-device-independent QCKA (MDI-QCKA) based on distributing the postselected GHZ entanglement can address this issue and eliminate all loopholes in detection side channels. Here, by developing three-photon GHZ interference technology with high visibility among three independent coherent sources, we realized the first MDI-QCKA experiment over a 60 km fiber link, achieving a secret key rate of 45.5 bits/s. Our result represents a significant step towards practical long-distance QCKA using realistic devices. Moreover, the technology we developed opens the way to future multiparty quantum communications in quantum networks.
Multipartite entanglement enables secure group key distribution among multiple users while providing immunity against hacking attacks targeting source devices, thereby realizing source-independent quantum conference key agreement (SI-QCKA). However, previous experimental demonstrations of SI-QCKA have encountered substantial technical challenges, primarily due to the low efficiency and scalability limitations inherent in the generation and distribution of multipartite entanglement. Here, we experimentally demonstrate a scalable and efficient SI-QCKA protocol using polarization-entangled photon pairs in a three-user star network, where Greenberger-Horne-Zeilinger correlations are realized via a post-matching method. We achieve a secure group key rate of 2.11×1042.11 \times 10^{4}2.11×104 bits/s under the single-user channel transmission of 1.64 ×\times× 10−110^{-1}10−1 in a symmetric channel loss network. Additionally, we conduct six sets of experiments to investigate the impact of varying channel transmission and random basis selection probabilities on secure key rates. Our work establishes an efficient pathway for SI-QCKA and demonstrates potential scalability for future large-scale multi-user quantum networks.
Abstract Multi-party quantum key sharing is the foundation for constructing quantum communication networks. The source-independent quantum conference key agreement (QCKA) distributes multiple Bell state pairs, which are post-processed to construct equivalent Greenberger-Horne-Zeilinger (GHZ) states and achieve multi-party key sharing. This helps maintain key rates at reasonable levels as the number of users increases, improving practicality and scalability. However, in the original source-independent QCKA protocol, the users receiving Bell states are assumed to be symmetrically distributed, which actually contradicts the distinct functional roles of the protocol participants (Alice and Bobs), and also limits the conference key rate of the protocol. To address this, we propose a source-independent QCKA protocol under an asymmetric architecture and perform simulations using parameters from existing commercial products, increasing the conference key rate and reducing deployment costs in practical applications.
Abstract Measurement-device-independent Quantum conference key agreement (MDI-QCKA) shares secure keys among multiple users by distributing postselected Greenberger-Horne-Zeilinger (GHZ) entanglement, improving practicality and security. Currently, the proposed QCKA protocols can achieve a communication distance of hundreds of kilometers over fiber link. However, such performance is only applicable to quantum communication within an inter-city range. To enable multi-user communication to cover a broader area, quantum satellites offer a solution. Here, one of the communication parties of MDI-QCKA is set as a satellite, and its performance is analyzed in combination with the characteristics of satellite-based link. Simulation results demonstrate the impact of the asymmetry of satellite-based and fiber link on system performance. In addition, considering the fluctuation of satellite-based link, the limitations on system performance caused by atmospheric turbulence, scattering particles, and pointing error are also simulated. These results provide a detailed analysis of the performance of satellite-based MDI-QCKA from the perspectives of satellite operation and the atmospheric environment, contributing to the expansion of MDI-QCKA to future global quantum communication networks.
Quantum conference key agreement (QCKA) enables the unconditional secure distribution of conference keys among multiple participants. Due to challenges in high-fidelity preparation and long-distance distribution of multi-photon entanglement, entanglement-based QCKA is facing severe limitations in both key rate and scalability. Here, we propose a source-independent QCKA scheme utilizing the post-matching method, feasible within the entangled photon pair distribution network. We introduce an equivalent distributing virtual multi-photon entanglement protocol for providing unconditional security proof even in the case of coherent attacks. For the symmetry star network, compared with the previous n -photon entanglement protocol, the conference key rate is improved from O ( η n ) to O ( η 2 ), where η is the transmittance from the entanglement source to one participant. Simulation results show that the performance of our protocol has multiple orders of magnitude advantages in the intercity distance. We anticipate that our approach will demonstrate its potential in the implementation of quantum networks.
Quantum conference key agreement is a cryptographic task in which more than two parties aim to generate a common secret key. Leveraging properties of multipartite quantum correlations, quantum conference key agreement can be implemented more efficiently in large-scale quantum networks. Inspired by the all-photonic quantum repeater, we propose an open-destination measurement-device-independent quantum conference key agreement network based on all-photonic architectures. The scheme enables flexible generation of common secret keys among users without the need for quantum memories, and it can even work if some users do not actively send signals. As an illustration, we show in detail a four-party network, in which secure communications are established among two or three participants. We present further simulation results that incorporate detector imperfections to evaluate the performance and feasibility in real-life situations.