Urban Ad-hoc QKD Network successfully demonstrated:
With the increasing interconnectedness of our world, the exchange of vast amounts of data, and the growing threat to critical infrastructures, the security of digital systems is becoming ever more important. In the era of powerful Quantum Computers, however, traditional encryption methods based on computational complexity are reaching their limits. This is where Quantum Communication comes into play: Quantum Key Distribution (QKD) is considered a key technology for the future of digital security. It enables the generation and distribution of a shared secret cryptographic key between two parties without relying solely on computational assumptions. Instead, its security is grounded in the fundamental laws of Quantum Physics. Since every measurement necessarily alters Quantum States, eavesdropping attempts can be detected immediately.
In recent years, experimental demonstrations of QKD have gained significant momentum worldwide. Key areas of focus include, for example, the integration of QKD into existing communication networks and new approaches to scaling QKD systems to more complex network topologies. Against this background, researchers at the Fraunhofer-Instituts für Nachrichtentechnik, Heinrich-Hertz-Institut (HHI), together with partners from the Fraunhofer-Institut für Angewandte Optik und Feinmechanik (IOF), the Max-Planck-Institut für die Physik des Lichts (MPL), and the Deutsche Zentrum für Luft- und Raumfahrt (DLR), published a new article in mid-November 2025. The paper describes the development and successful implementation of a versatile ad-hoc network for Quantum Key Distribution in an urban environment.
The approach presented in the paper integrates multiple physical channels and QKD protocols, as well as a combination of trusted nodes and intermodal coupling. Unlike conventional QKD networks, which mostly rely solely on fiber-optic or free-space optical (FSO) links, the developed testbed combines both types of transmission, thereby overcoming key limitations of previous systems. For network expansion, various strategies were explored – ranging from permanent infrastructure to flexible ad-hoc connections – with the aim of closing existing coverage gaps. Using portable FSO terminals, the researchers were able to rapidly establish a functional QKD network, test different connection topologies, and set up a quantum-secure link to a cloud server. Click here for more information about the paper.
Source reference: https://iopscience.iop.org/article/10.1088/1367–2630/ae1864