Multi-field quantum conferencing overcomes the network capacity limit

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.