Equitable Multiparty Quantum Communication without a Trusted Third Party

Multiparty quantum communication provides delightful applications, including quantum cryptographic communication and quantum secret sharing. Quantum communication based on the Greenberg-Horne-Zeilinger (GHZ) state measurement provides a practical way to implement multiparty quantum communication. With the standard spatially localized GHZ state measurement, however, information can be imbalanced among the communication parties that can cause significant problems in some applications of multiparty cryptographic communication, e.g., secret sharing. Here, we propose an equitable multiparty quantum communication where information balance among the communication parties is achieved without a trusted third party. Our scheme is based on the GHZ state measurement that is not spatially localized but implemented in a way that all the distant communication parties symmetrically participate. We also verify the feasibility of our scheme by presenting the proof-of-principle experimental demonstration of informationally balanced three-party quantum communication using weak coherent pulses.