# Continuous-Variable Quantum Key Distribution with Rateless Reconciliation Protocol

## TL;DR

This paper introduces a rateless reconciliation protocol for continuous-variable quantum key distribution that maintains high efficiency across various SNRs, simplifies optimization, and extends secure transmission distances.

## Contribution

It proposes a novel rateless reconciliation protocol using Raptor codes for CV-QKD, enhancing robustness and efficiency over a wide SNR range with a single degree distribution.

## Key findings

- Achieves over 95% reconciliation efficiency from -20 dB to 0 dB SNR.
- Enables high secret key rates at various distances, up to 132 km.
- Outperforms previous methods in secret key rate at maximum distance.

## Abstract

Information reconciliation is crucial for continuous-variable quantum key distribution (CV-QKD) because its performance affects the secret key rate and maximal secure transmission distance. Fixed-rate error correction codes limit the potential applications of the CV-QKD because of the difficulty of optimizing such codes for different low SNRs. In this paper, we propose a rateless reconciliation protocol combined multidimensional scheme with Raptor codes that not only maintains the rateless property but also achieves high efficiency in different SNRs using just one degree distribution. It significantly decreases the complexity of optimization and increases the robustness of the system. Using this protocol, the CV-QKD system can operate with the optimal modulation variance which maximizes the secret key rate. Simulation results show that the proposed protocol can achieve reconciliation efficiency of more than 95% within the range of SNR from -20 dB to 0 dB. It also shows that we can obtain a high secret key rate at arbitrary distances in a certain range and achieve a secret key rate of about 5*10^(-4) bits/pulse at a maximum distance of 132 km (corresponding SNR is -20dB) that is higher than previous works. The proposed protocol can maintain high efficient key extraction under the wide range of SNRs and paves the way toward the practical application of CV-QKD systems in flexible scenarios.