Guillermo Curras Lorenzo

Twin-field (TF) quantum key distribution (QKD) can overcome fundamental secret-key-rate bounds on point-to-point QKD links, allowing us to reach longer distances than ever before. Since its introduction, several practical TF-QKD variants have been proposed, and some of them have already been implemented experimentally. All of them assume that the users can emit weak coherent pulses with a continuous random phase, either to generate the key, or to prove its security. In practice, this assumption is often not satisfied, which could open up security loopholes in their implementations. Here, we propose and prove the security of a TF-QKD variant that relies exclusively on discrete phase randomisation, which is easier to achieve in practice. Remarkably, our results show that it can also provide higher secret-key rates than other variants.