Conference key agreement is a multiparty communication scheme where n users try to obtain a common random bit string (e.g., the key) that is guaranteed to be secure from an eavesdropper. One approach is to iterate two-party quantum key distribution protocols among all users followed by classical co-ordination of a shared key (2QKD). However, by using multipartite entanglement the shared key can be distributed to n-users directly (NQKD). Here we implement a proof-of-principle experiment demonstrating salient features of a discrete-variable NQKD protocol in the presence of loss and environmental effects inherent in the use of optical fibre links.

Our approach leverages the design of high-brightness single photon sources in the telecom regime (1550 nm), using spontaneous parametric down-conversion (SPDC) mediated by a nonlinear crystal (ppKTP). We can generate Bell states directly from the source by embedding the ppKTP crystal into a compact Sagnac interferometer. We use two such sources to deliver high generation rates of the four-photon GHZ state, based non-deterministic linear optics approaches, used in the NQKD scheme.

Bio

Joseph Ho is currently a postdoctoral research associate at Heriot-Watt University (UK) in the group of Prof. Alessandro Fedrizzi. His research focus is on the realisation of quantum information protocols using high-brightness sources for the generation of multiqubit photonic cluster states compatible for a network setting. His PhD was carried out in the research group of Prof. Geoff Pryde at Griffith University (Australia) on the topic of multiqubit linear optics gates and their applications, notably the quantum Fredkin gate.