3rd: WAN Link

The third Q-net-Q test field comprises a long-distance QKD link between Berlin and Frankfurt. This is implemented by a chain of QKD point-to-point connections in a so-called trusted relay configuration. The QKD keys generated by each individual connection are cryptographically combined by a key management system layer to establish a final secret key between the remote endpoints in Berlin and Frankfurt. The QKD nodes are installed in secure locations along the fiber optic route, which are approximately 80 km apart. This test field serves as an exemplary test for future wide-area QKD networks within the EuroQCI and enables the experimental characterization and validation of the scalability of QKD technology over long distances. New use cases are also being explored, such as the architecture of open interfaces between QKD and mobile network operators for 4G/5G and 6G, and the implementation of information-theoretically secure distributed storage of highly sensitive data based on Shamir secret sharing.