# Improving the performance of Twin-Field Quantum Key Distribution

## TL;DR

This paper enhances twin-field quantum key distribution by introducing an additional decoy mode, which tightens information leakage estimates and significantly improves key rate and distance without complicating experimental implementation.

## Contribution

It proposes a novel method using an extra decoy mode to improve TF-QKD performance, addressing distance limitations and practical implementation issues.

## Key findings

- Key rate and distance are significantly improved.
- The method works with finite decoy states, suitable for practical use.
- The additional decoy mode does not complicate experimental setup.

## Abstract

Among the various versions of the twin-field quantum key distribution (TF-QKD) protocol [M.Lucamarini, Z. Yuan, J. Dynes, and A. Shields, Nature (London) 557, 400 (2018)] that can overcome the rate-distance limit, the TF-QKD without phase postselection proposed by Cui et al. [Phys. Rev. Appl. 11, 034053 (2019)] is an elegant TF-QKD that can provide high key rates since the postselection of global phases has been removed. However, the achievable distance of this variant is shorter than that of the original phase-matching QKD [X. Ma, P. Zeng, and H. Zhou, Phys. Rev. X 8, 031043 (2018)]. In this paper, we propose a method for improving its performance by introducing an additional decoy mode. The upper bound of the information leakage can be more tightly estimated; hence, both the key rate and the achievable distance are significantly improved. Interestingly, the operation of the proposed additional decoy mode is the same as that of the code mode; hence, it does not introduce difficulties into the experimental system. In addition, the improvement is substantial with finite decoy states, which is meaningful in practice.