Finite-key analysis of an experimentally realized practical COW-QKD protocol

An experimental implementation of the coherent one-way quantum key distribution (COW-QKD) protocol is reported under realistic conditions, and a clean and easy-to-use framework for performing finite-key analysis of the COW-QKD protocol is provided by extending a set of existing results. The framework provided here is used to perform finite-key rate analysis of the COW-QKD protocol with respect to the actual parameters used in the experimental realization reported here. The system is kept running for several hours with different experimental parameters, and stable secure key rates between 1.2 and 1.6 kbps are observed. Using the proposed finite-key framework, the secure transmission distance is numerically estimated for the experimentally characterized system, indicating secure operation up to approximately 156 km (171 km) for detector efficiencies of 10% (20%), assuming standard telecom fiber with attenuation of 0.2 dB/km and all other system parameters identical to those measured experimentally. These distance estimates represent finite-key security projections based on experimentally calibrated parameters rather than direct experimental demonstrations.