Overcoming the private capacity of optical point-to-point quantum key distribution

The private capacity of a lossy bosonic channel shows that there remains not much room to improve known point-to-point quantum key distribution (QKD) protocols further, in terms of the key rate versus distance. The current question in our field is how to overcome this fundamental limit with the help of a single station in the middle between communicators. In this talk, we explore recent trials to achieve this goal, such as adaptive measurement-device-independent QKD and twin-field QKD. These trials are good milestones towards the realization of quantum repeater networks.