Quantum conference key agreement using photonic graph states

Future quantum networks will provide multi-node entanglement enabling secure quantum communication on a global scale. Traditional two-party quantum key distribution (2QKD) consumes pairwise entanglement which is costly in constrained networks. Quantum conference key agreement (QCKA) leverages multipartite entanglement within networks to directly produce identical keys among N users, providing up to N-1 rate advantage over 2QKD. Here, we present a four-user QCKA protocol using photonic GHZ states distributed over fibre with combined lengths up to 50 km. Furthermore, we investigate a constrained network consisting of a 6-qubit photonic graph state which we apply network coding routines to distil suitable resource states.