Obada Alia

We demonstrated for the first time a coexistence between a quantum QKD channel and 4×100 Gbps pm-qpsk carrier-grade classical optical channels in a 2 km Nested Antiresonant Nodeless Hollow Core fibre. Our results show a drop of less than 10% in the Secret Key Rate (SKR) when using a HCF compared to a significant drop of 97% in the SKR when quantum and classical signals coexist on a single core of a Multicore fibre (MCF) with equal losses, indicating that NANF type HCF significantly outperforms single-mode fibres (SMF) performance for quantum/classical coexistence. This significant difference in the SKR drop is due to the ultra-low nonlinear effects in HCF comparing to glass core fibres such as SMF and MCF.

Client authentication (CA) is a cryptographic protocol where a server tries to validate the identity of a client. Fehr et. al. proposed a CA protocol with pre-shared basis information between the client and server which has a nice key recycling property, where secrets including the pre-shared basis can be securely reused after each successful round. We extend the protocol to a practical setting by including decoy state and error correction, but the leakage of pre-shared basis information via multi-photon events limits the performance of such a protocol. As such, we propose the use of a pseudorandom number generator (PRNG), assumed to be secure only during each run of the protocol, to perform basis selection to reduce information leakage. A formal proof of the protocol security is provided by modifying the entropic uncertainty relation to account for basis generated by a PRNG, which could be of independent interest as it may be applicable to other protocols such as quantum key distribution. An experimental implementation of the protocol, with appropriate post-selection, was performed to demonstrate its feasibility. We also designed a CA protocol secure in the practical setting with only two rounds of communication: a challenge by the server and a response by the client.