Rotation Based Slice Error Correction Protocol for Continuous-variable Quantum Key Distribution and its Implementation with Polar Codes

Abstract

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, its 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 Rotation-based SEC (RSEC), is proposed through performing a random orthogonal rotation on the raw data before quantization, and deducing a new estimator for quantized sequences. Moreover, the RSEC protocol is implemented with polar codes. Experimental results show that the proposed protocol can reach up to a quantization efficiency of about 99%, and maintains 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 block length of 16 Mb, the RSEC can achieve a reconciliation efficiency of above 95%, which outperforms all previous SEC schemes. In terms of finite-size effects, we achieve 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.

Continuous-variable quantum key distribution: security analysis with trusted hardware noise against general attacks

“…To evaluate the channel, states are disclosed for which insignificant bits have not been discarded. After that, errors are corrected using multi-level encoding and multi-stage decoding [53][54][55]. During error correction, three of the four bits are revealed, thereby reducing the bit sequence to a length of 5.4 • 10 8 bits.…”

Continuous-variable quantum key distribution: security analysis with trusted hardware noise against general attacks

“…To evaluate the channel, states are disclosed for which insignificant bits have not been discarded. After that, errors are corrected using multi-level encoding and multi-stage decoding [50][51][52]. During error correction, three of the four bits are revealed, thereby reducing the bit sequence to a length of 5.4 • 10 8 bits.…”

The Road to Near-Capacity CV-QKD Reconciliation: An FEC-Agnostic Design

“…For instance, a simple Hamming code was utilized in the reconciliation step to correct the bit errors in the raw key string shared by the satellite and the ground station for the experimental satellite-to-ground QKD system used in the Micius experiment [62]. Inspired by this development, some more advanced forward error correction (FEC) codes have also been investigated, such as low-density paritycheck (LDPC) codes [13], [63]- [68], polar codes [55], [69]- [71], rateless codes [72], [73], and their diverse variants. As a further advance, instead of using a fixed FEC code rate, adaptive-rate reconciliation schemes were proposed in [74]- [76], where the secret key rate (SKR) and the secure transmission distance were optimized for different signal-tonoise ratios (SNRs).…”