The performance of quantum key distribution (QKD) is heavily dependent on the physical properties of the channel over which it is executed. Propagation losses and perturbations in the encoded photons’ degrees of freedom, such as polarisation or phase, limit both the QKD range and key rate. The maintenance of phase coherence over optical fibres has lately received considerable attention as it enables QKD over long distances, e.g., through phase-based protocols like Twin-Field (TF) QKD. While optical single mode fibres (SMFs) are the current standard type of fibre, recent hollow core fibres (HCFs) could become a superior alternative in the future. Whereas the co-existence of quantum and classical signals in HCF has already been demonstrated, the phase noise resilience required for phase-based QKD protocols is yet to be established. This work explores the behaviour of HCF with respect to phase noise for the purpose of TF-QKD-like protocols. To achieve this, two experiments are performed. The first, is a set of concurrent measurements on 2 km of HCF and SMF in a double asymmetric Mach-Zehnder interferometer configuration. The second, uses a TF-QKD interferometer consisting of HCF and SMF channels. These initial results indicate that HCF is suitable for use in TF-QKD and other phase-based QKD protocols.
Twin-field (TF) quantum key distribution (QKD) fundamentally alters the rate-distance relationship of QKD, offering the scaling of a single-node quantum repeater. Although recent experiments have demonstrated the new opportunities for secure long-distance communications allowed by TF-QKD, formidable challenges remain to unlock its true potential. Here, we introduce a novel wavelength-multiplexed stabilisation scheme that overcomes past limitations and can be adapted to other phase-sensitive single-photon applications. In our work, we develop a setup that provides key rates over a record fibre distance of 605 km and increases the secure key rate at long distances by two orders of magnitude to values of practical significance.
Quantum key distribution (QKD) allows users to generate shared encryption keys that are guaranteed to be theoretically secure by the laws of quantum mechanics. Most implementations use light pulses that are attenuated by the propagation medium. This leads to a fundamental rate-distance limit in QKD that was thought to be impossible to overcome with current technology. The recent proposal of "Twin-Field QKD", however, changed this belief and showed how to overcome this limit and perform long-distance QKD with present-day technology.
In my talk I will review the most significant theoretical and experimental results in this emerging and rapidly growing research area.
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