Discrete-modulation continuous-variable quantum key distribution with high key rate

TL;DR

This paper proposes a two-ring constellation structure for discrete-modulation continuous-variable quantum key distribution, significantly increasing the key rate and approaching Gaussian modulation performance for secure quantum communication.

Contribution

The paper introduces a novel two-ring constellation structure that enhances the key rate of discrete-modulation CV-QKD protocols, making them more competitive with Gaussian modulation schemes.

Findings

8-PSK increases key rate by 60% over 4-PSK.

Two-ring constellation achieves 2.4 times the 4-PSK key rate.

Key rate reaches 70% of Gaussian modulation at long distances.

Abstract

Discrete-modulation continuous-variable quantum key distribution has the potential for large-scale deployment in the secure quantum communication networks due to low implementation complexity and compatibility with the current telecom systems. The security proof for four coherent states phase-shift keying (4-PSK) protocol has recently been established by applying numerical methods. However, the achievable key rate is relatively low compared with the optimal Gaussian modulation scheme. To enhance the key rate of discrete-modulation protocol, we first show that 8-PSK increases the key rate by about 60\% in comparison to 4-PSK, whereas the key rate has no significant improvement from 8-PSK to 12-PSK. We then expand the 12-PSK to two-ring constellation structure with four states in the inner ring and eight states in the outer ring, which significantly improves the key rate to be 2.4 times of that of 4-PSK. The key rate of the two-ring constellation structure can reach 70\% of the key rate achieved by Gaussian modulation in long distance transmissions, making this protocol an attractive alternative for high-rate and low-cost application in secure quantum communication networks.