A novel error correction protocol for continuous variable quantum key distribution

Kadir Gümüş,Tobias A Eriksson,Mikio Fujiwara,Masahide Sasaki,Laurent Schmalen,Alex Alvarado,Masahiro Takeoka

doi:10.1038/s41598-021-90055-3

Abstract

Reconciliation is a key element of continuous-variable quantum key distribution (CV-QKD) protocols, affecting both the complexity and performance of the entire system. During the reconciliation protocol, error correction is typically performed using low-density parity-check (LDPC) codes with a single decoding attempt. In this paper, we propose a modification to a conventional reconciliation protocol used in four-state protocol CV-QKD systems called the multiple decoding attempts (MDA) protocol. MDA uses multiple decoding attempts with LDPC codes, each attempt having fewer decoding iteration than the conventional protocol. Between each decoding attempt we propose to reveal information bits, which effectively lowers the code rate. MDA is shown to outperform the conventional protocol in regards to the secret key rate (SKR). A 10% decrease in frame error rate and an 8.5% increase in SKR are reported in this paper. A simple early termination for the LDPC decoder is also proposed and implemented. With early termination, MDA has decoding complexity similar to the conventional protocol while having an improved SKR.

Highlights

Because of the potential advantages CV-QKD, it has been gaining a lot of attention recently
We propose a new reconciliation protocol, called the multiple decoding attempts (MDA) protocol, which is a modification of the one-dimensional reconciliation protocol as described in Ref.[14] which we will refer to as the conventional protocol throughout the rest of this paper
This gap exists a trade-off between β and frame error rate (FER), which affects the secret key rates (SKR) in Ref.[1]: the higher β becomes, the higher the FER

Summary

Introduction

Because of the potential advantages CV-QKD, it has been gaining a lot of attention recently. Because of the very low signal-to-noise ratio (SNR) operating range of the system, error correcting codes with large block sizes and low rates, which require computationally complex decoding algorithms , are necessary for the error correction[13]. Due to these requirements, reconciliation is a major bottleneck of the entire CV-QKD system in regards to both speed and hardware complexity[14]. In order to maximize the SKR during reconciliation, it is preferred that the rates of the codes operate as closely as possible to the capacity, and that the FER is as low as possible. Numerical results show that MDA offers gains of up to 8.5% in terms of SKR for a typical CV-QKD link

Methods

Results

Conclusion