Performance assessment of fiber-optic railway infrastructure QKD testbed by upper bounded deviation method

In this paper, we present an inter-city Quantum Key Distribution network testbed spanning tens of kilometers within the Central Bohemian Region. The testbed operates under harsh conditions, leveraging a robust fiber-optic infrastructure. Specifically, the quantum key distribution devices using two different key generating protocols underwent rigorous testing during winter months. The experiment assesses the performance and stability of quantum key distribution devices in a communication channel under real-world conditions. A quantum channel utilized for this experiment was established along the railway tracks provided by the Czech Railway Administration. Our findings contribute to advancing secure quantum communication networks by addressing key rate stability challenges. An upper bound for relative secret key rate deviation is introduced to support link design. Moreover, it has been experimentally verified that the measured key rate demonstrated robust stability despite its quantum nature and strong influence from outside conditions.