Entanglement-based quantum key distribution using frequency-bin encoding in a flexible frequency-multiplexed network

Large-scale quantum networks require dynamic and resource-efficient solutions to reduce system complexity while maintaining security and performance over large distances. We demonstrate the first implementation of frequency-bin-encoded entanglement-based quantum key distribution and show reconfigurable transmission of frequency-entangled states. Our scalable frequency-bin basis analyzer module enables passive random basis selection and reduces the number of required detectors per user from four in conventional schemes to only one. This minimizes resource overhead, dark count contribution, vulnerability to detector side-channel attacks, and detector imbalance, hence an improved security. Our approach allows for an adaptive frequency-multiplexing capability to increase the number of channels without additional hardware, improving the secret key rate and enabling reconfigurable multi-user operations. In perspective, our scheme supports dynamic, resource-efficient quantum key distribution among multiple users across diverse network topologies, facilitating scalability to large-scale quantum networks.