# Coherent-State-Based Twin-Field Quantum Key Distribution

## TL;DR

This paper introduces a new coherent-state-based twin-field quantum key distribution protocol that enhances secure communication distance by leveraging entanglement swapping and improved security proof techniques.

## Contribution

It presents a novel coherent-state-based TF-QKD protocol with optimal secret key rate and a unified security proof applicable to recent protocols.

## Key findings

- Achieves longer transmission distances with entanglement purification.
- Provides a security proof that unifies recent coherent-state TF-QKD protocols.
- Demonstrates the protocol's optimal secret key rate under various channel conditions.

## Abstract

Large-scale quantum communication networks are still a huge challenge due to the rate-distance limit of quantum key distribution (QKD). Recently, twin-field (TF) QKD has been proposed to overcome this limit. Here, we prove that coherent-state-based TF-QKD is a time-reversed entanglement protocol, where the entanglement generation is realized with entanglement swapping operation via an entangled coherent state measurement. We propose a coherent-state-based TF-QKD with optimal secret key rate under symmetric and asymmetric channels by using coherent state and cat state coding. Furthermore, we show that our protocol can be converted to all recent coherent-state-based TF-QKD protocols by using our security proof. By using the entanglement purification with two-way classical communication, we improve the transmission distance of all coherent-state-based TF-QKD protocols.