Experimental anonymous quantum conferencing

Anonymous quantum conference key agreement (AQCKA) allows a group of users within a network to establish a shared cryptographic key without revealing their participation. Although this can be achieved using bipartite primitives alone, it is costly in the number of network rounds required. By allowing the use of multi-partite entanglement, there is a substantial efficiency improvement. We experimentally implement the AQCKA task in a six-user quantum network using Greenberger–Horne–Zeilinger (GHZ)-state entanglement and obtain a significant resource cost reduction in line with theory when compared to a bipartite-only approach. We also demonstrate that the protocol retains an advantage in a four-user scenario with finite key effects taken into account.