Satellite-based multi-user quantum conference key agreement

Federico Grasselli

Guoqi Huang, Lu Wang, Wei Cui +2 more

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.

Sheng‐Kai Liao, Wenqi Cai, Wei-Yue Liu +31 more

Fisher, Benjamin J

Quantum Conference Key Agreement (QCKA) enables a group of users to generate a shared secret key, which reduces the latency and equipment overhead of establishing multiple Quantum Key Distribution (QKD) links. Conventional QCKA protocols send a multi-photon entangled state from one user to others and a key is generated only when all photons are detected, which is inefficient at high loss and opens side-channels at the receiver side. Here, we overcome this barrier through a multi-field QCKA protocol enabled by designing, fabricating, and testing an integrated photonic Green Machine that implements an eight-mode Hadamard unitary transformation through a beam-splitter network. With this integrated photonic circuit as a central untrusted relay, up to eight users can generate the same secure key upon measuring a single arriving photon. In addition to the first-ever realization and packaging of this integrated photonic Green Machine chip, we characterize the Green Machine and create a digital twin simulator which predicts that this chip enables multi-field QCKA among five users up to a range of 154 km between each party and a central relay.

Wei Cui, Ziang Song, Guoqi Huang +1 more

Jonathan Webb, Joseph Ho, Federico Grasselli +4 more

Quantum conference key agreement (QCKA) generalises the traditional two-party quantum key distribution (QKD) paradigm to multiple users, enabling them to share a common quantum-safe key. Deriving quantum conference keys from multi-partite entanglement can have significant resource advantages over two-party schemes [1]. Anonymous quantum key agreement (AQCKA) is a related protocol which has been theoretically shown to obtain an even more substantial reduction in network resources when multi-partite entanglement is available and incorporated into the protocol. The addition of anonymity can be useful in circumstances where users require guaranteed secrecy, e.g. for electronic voting, or for whistle blowers.