# Asymmetric sending or not-sending twin-field quantum key distribution in practice

## TL;DR

This paper extends the sending or not-sending twin-field quantum key distribution protocol to asymmetric channels, significantly improving key rates and transmission distances, advancing practical quantum communication.

## Contribution

It introduces a general model for SNS QKD with asymmetric channels, enhancing performance over the original symmetric protocol.

## Key findings

- Increased key generation rate with asymmetric channels.
- Extended transmission distance compared to symmetric protocols.
- Demonstrated practical advantages for real-world QKD implementations.

## Abstract

Quantum key distribution (QKD) offers a secret way to share keys between legitimate users which is guaranteed by the law of quantum mechanics. Most recently, the limitation of transmission distance without quantum repeaters was broken through by twin-field QKD [Nature (London) 557, 400 (2018)]. Based on its main idea, sending or not-sending (SNS) QKD protocol was proposed [Phys. Rev. A 98, 062323 (2018)], which filled the remaining security loopholes and can tolerate large misalignment errors. In this paper, we give a more general model for SNS QKD, where the two legitimate users, Alice and Bob, can possess asymmetric quantum channels. By applying the method present in the work, the legitimate users can achieve dramatically increased key generation rate and transmission distance compared with utilizing the original symmetric protocol. Therefore, our present work represents a further step along the progress of practical QKD.