Twin-field quantum key distribution with partial phase postselection

TL;DR

This paper introduces a new twin-field quantum key distribution protocol with partial phase postselection, enhancing key rate and distance by combining features of existing variants and providing security proof under realistic conditions.

Contribution

It proposes a novel TF-QKD protocol with partial phase postselection, balancing high key rate and extended distance, with a security proof for finite-key scenarios under coherent attacks.

Findings

The protocol achieves higher key rates than no-phase-postselection variants.

Numerical simulations show increased achievable distance.

Security is proven under finite-key conditions with coherent attacks.

Abstract

Quantum key distribution (QKD) allows two remote parties to share information-theoretically secure keys. In recent years, a revolutionary breakthrough called twin-field (TF) QKD has been developed to overcome the linear key-rate constraint and greatly increases the achievable distance. Phase-randomization and subsequent postselection play important roles in its security proof. Later, no-phase-postselection TF-QKD was proposed and became a popular variant, since the removal of phase postselection leads to a higher key rate. However, the achievable distance is decreased compared to the original one. Here, we propose a TF-QKD protocol with partial phase postselection. Namely, its code mode is still free from global phase randomization and postselection to make sure the advantage of the high key rate remains. On other hand, phase postselection is introduced in the decoy mode to improve the performance. Applying an operator dominance condition, we prove universal security of the proposed protocol in the finite-key case under coherent attacks, and numerical simulations confirm its potential advantages in terms of key rate and achievable distance.