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Measurement-device-independent quantum conference key agreement network based on an all-photonic repeater

Shuming Hu, Jun-Hao Wei, Xin-Yu Xu, Qing Fa Zhou, Li Li, N.-L. Liu, Kai Chen

Published Oct 27, 2025• 0 citations
Publisher

Abstract

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.

DOI
10.1364/oe.575352

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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.
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.
Quantum key distribution (QKD) networks hold promise for sharing secure randomness over multi-partities. Most existing QKD network schemes and demonstrations are based on trusted relays or limited to point-to-point scenario. Here, we propose a flexible and extensible scheme named as open-destination measurement-device-independent QKD network. The scheme enjoys security against untrusted relays and all detector side-channel attacks. Particularly, any users can accomplish key distribution under assistance of others in the network. As an illustration, we show in detail a four-user network where two users establish secure communication and present realistic simulations by taking into account imperfections of both sources and detectors.
Abstract Quantum conference key agreement is an important cryptographic primitive for future quantum network. Realizing this primitive requires high-brightness and robust multiphoton entanglement sources, which is challenging in experiment and unpractical in application because of limited transmission distance caused by channel loss. Here we report a measurement-device-independent quantum conference key agreement protocol with enhanced transmission efficiency over lossy channel. With spatial multiplexing nature and adaptive operation, our protocol can break key rate bounds on quantum communication over quantum network without quantum memory. Compared with previous work, our protocol shows superiority in key rate and transmission distance within the state-of-the-art technology. Furthermore, we analyse the security of our protocol in the composable framework and evaluate its performance in the finite-size regime to show practicality. Based on our results, we anticipate that our protocol will play an important role in constructing multipartite quantum network.
Quantum conferencing enables multiple nodes within a quantum network to share a secure conference key for private message broadcasting. The key rate, however, is limited by the repeaterless capacity to distribute multipartite entangled states across the network. Currently, in the finite-size regime, no feasible schemes utilizing existing experimental techniques can overcome the fundamental rate-distance limit of quantum conferencing in quantum networks without repeaters. Here, we propose a practical, multi-field scheme that breaks this limit, involving virtually establishing Greenberger-Horne-Zeilinger states through post-measurement coincidence matching. This proposal features a measurement-device-independent characteristic and can directly scale to support any number of users. Simulations show that the fundamental limitation on the conference key rate can be overcome in a reasonable running time of sending 1014 pulses. We predict that it offers an efficient design for long-distance broadcast communication in future quantum networks. Quantum networks require secure conference keys for users to communicate and decrypt broadcasts. The authors propose a quantum conferencing protocol that overcomes key rate limits in networks without repeaters by using post-measurement coincidence matching, enabling secure, efficient, and flexible communication resistant to detector side channel attacks.
Sharing multi-partite quantum entanglement between parties allows for diverse secure communication tasks to be performed. Among them, conference key agreement (CKA), an extension of key distribution to multiple parties, has received much attention recently. Interestingly, CKA can also be performed in a way that protects the identities of the participating parties, therefore providing anonymity. In this work, we propose an anonymous CKA protocol for three parties that is implemented in a highly practical network setting. Specifically, a line of quantum repeater nodes is used to build a linear cluster state among all nodes, which is then used to anonymously establish a secret key between any three of them. The nodes need only share maximally entangled pairs with their neighbours, therefore avoiding the necessity of a central server sharing entangled states. This repeater setup makes our protocol an excellent candidate for implementation in future quantum networks. We explicitly prove that our protocol protects the identities of the participants from one another and perform an analysis of the key rate in the finite regime, contributing to the quest of identifying feasible quantum communication tasks for network architectures beyond point-to-point.