Experimental Implementation of Enhanced Security Coherent One-Way Quantum Key Distribution

Coherent One-Way (COW) is a simple and widely utilized quantum key distribution (QKD) protocol, favored in both experimental and commercial applications. In this paper, we compare the information that an eavesdropper, Eve, can acquire in both the 2-decoy and 1-decoy COW protocols. Our findings demonstrate that the 2-decoy protocol offers enhanced security compared to the original 1-decoy COW, all while preserving the simplicity of implementation. Furthermore, we have experimentally implemented the improved security COW-QKD (2-decoy protocol), achieving a secure key rate exceeding 0.5 kbps over a distance of 110 km (22 dB loss) in optical fiber, with an interference visibility greater than 80%. We also emphasize that monitoring the click rates of the data line detector for each state individually serves as a powerful method for detecting zero-error attacks.