Wen Xuan, Li Qiong, Mao Haokun, Wen Xiaojun, Chen Nan
Department of Computer Science and Technology, Harbin Institute of Technology, Harbin 150000, China.
School of Electronics and Information Engineering, Shenzhen Polytechnic, Shenzhen 518000, China.
Entropy (Basel). 2021 Oct 9;23(10):1317. doi: 10.3390/e23101317.
Reconciliation is an essential procedure for continuous-variable quantum key distribution (CV-QKD). As the most commonly used reconciliation protocol in short-distance CV-QKD, the slice error correction (SEC) allows a system to distill more than 1 bit from each pulse. However, the quantization efficiency is greatly affected by the noisy channel with a low signal-to-noise ratio (SNR), which usually limits the secure distance to about 30 km. In this paper, an improved SEC protocol, named Rotated-SEC (RSEC), is proposed through performing a random orthogonal rotation on the raw data before quantization, and deducing a new estimator for the quantized sequences. Moreover, the RSEC protocol is implemented with polar codes. The experimental results show that the proposed protocol can reach up to a quantization efficiency of about 99%, and maintain at around 96% even at the relatively low SNRs (0.5,1), which theoretically extends the secure distance to about 45 km. When implemented with the polar codes with a block length of 16 Mb, the RSEC achieved a reconciliation efficiency of above 95%, which outperforms all previous SEC schemes. In terms of finite-size effects, we achieved a secret key rate of 7.83×10-3 bits/pulse at a distance of 33.93 km (the corresponding SNR value is 1). These results indicate that the proposed protocol significantly improves the performance of SEC and is a competitive reconciliation scheme for the CV-QKD system.
协调是连续变量量子密钥分发（CV-QKD）的一个基本过程。作为短距离CV-QKD中最常用的协调协议，切片误差校正（SEC）允许系统从每个脉冲中提取超过1比特的信息。然而，量化效率会受到低信噪比（SNR）噪声信道的极大影响，这通常将安全距离限制在约30公里。本文提出了一种改进的SEC协议，称为旋转SEC（RSEC），通过在量化前对原始数据进行随机正交旋转，并为量化序列推导一种新的估计器。此外，RSEC协议采用极化码实现。实验结果表明，所提出的协议可以达到约99%的量化效率，即使在相对较低的信噪比（0.5,1）下也能保持在96%左右，从理论上将安全距离扩展到约45公里。当采用块长为16 Mb的极化码实现时，RSEC实现了超过95%的协调效率，优于所有先前的SEC方案。在有限尺寸效应方面，我们在33.93公里的距离（相应的SNR值为1）处实现了7.83×10-3比特/脉冲的密钥率。这些结果表明，所提出的协议显著提高了SEC的性能，是CV-QKD系统中一种有竞争力的协调方案。
