Twin-field Quantum Key Distribution without Phase Post-Selection

TL;DR

This paper demonstrates a twin-field quantum key distribution protocol that surpasses the rate-loss limit without requiring phase post-selection, simplifying implementation and maintaining security against advanced attacks.

Contribution

The authors propose a new TF-QKD protocol that removes phase randomization and post-selection, achieving a higher key rate and practical feasibility while ensuring security.

Findings

Achieves secure key rate of O(√η) without phase post-selection.

Removes the need for active phase randomization in TF-QKD.

Security proof counters collective and coherent attacks asymptotically.

Abstract

Twin-field quantum key distribution (TF-QKD) protocol and its variants, e.g. phase-matching (PM) QKD and TF-QKD based on sending or not sending, are highly attractive since they are able to overcome the well-known rate-loss limit for QKD protocols without repeater: $R=O(\eta)$ with $\eta$ standing for the channel transmittance. However, all these protocols require active phase randomization and post-selection that play an essential role together in their security proof. Counterintuitively, we find that in TF-QKD, beating the rate-loss limit is still possible even if phase randomization and post-selection in the coding mode are both removed, which means our final secure key rate $R=O(\sqrt{\eta})$. Furthermore, our protocol is more feasible in practice and more promising according to its higher final key rate in the valid distance. Our security proof counters collective attack and can also counter coherent attack in asymptotical case