Fraunhofer IOF presents: Quantum keys for technological sovereignty

From the perspective of SpectroNet, the recent achievements of our member Fraunhofer Institute for Applied Optics and Precision Engineering IOF represent a major milestone for the future of secure communication in Germany and Europe. Within the framework of the QuNET project, researchers have now demonstrated that quantum key distribution (QKD) can operate reliably not only via optical fiber, but also through hybrid and mobile channels. These results have been published in the renowned journal New Journal of Physics, underlining their international scientific relevance.

Quantum communication is widely regarded as a key technology for long-term data security and technological sovereignty. At its core lies the distribution of cryptographic keys based on quantum physical processes, making eavesdropping fundamentally detectable. QKD will be essential not only for highly secure communication in government agencies, the military, and industry, but also for protecting sensitive data in everyday digital life. With the QuNET project, Germany is taking decisive steps toward building sovereign quantum-secured communication infrastructures.

Funded by the German Federal Ministry of Research, Technology and Space with 125 million euros, QuNET brings together leading research institutions, including Fraunhofer IOF and Fraunhofer HHI, the Max Planck Institute for the Science of Light, Friedrich Alexander University Erlangen-Nuremberg, and the DLR Institute of Communication and Navigation. This strong interdisciplinary collaboration reflects the complexity of quantum communication, which requires expertise spanning photonics, information technology, aerospace, and network integration.

Over the past years, the project partners have demonstrated a series of important breakthroughs: from the first quantum-secured video conference between two federal authorities in 2021, to ad hoc point-to-point connections in 2023, secure data transmission within Berlin’s metropolitan fiber network in 2024, and most recently, the exchange of quantum information using a research aircraft in 2025. Building on these experiments, the newly published scientific article shows how a wide range of different technologies can be combined into a functioning, heterogeneous quantum-secured network – a world first in this level of integration.

A particular highlight from Fraunhofer IOF’s perspective is the successful testing of hybrid and mobile quantum channels. Quantum signals, often consisting of only a few photons, are extremely fragile. While transmission via optical fiber is well established, free-space transmission through turbulent air presents significant challenges. The team in Jena demonstrated systems that enable stable quantum key transmission even under such conditions, paving the way for mobile, ad hoc connections that can bridge gaps in fiber networks. According to Dr. Matthias Goy from Fraunhofer IOF, the integration of different QKD protocols and link types into one overall network represents a level of heterogeneity that has not yet been published anywhere in the world.

Fraunhofer IOF has also contributed crucial hardware innovations, such as a special container module with an integrated telescope for sending and receiving quantum keys. This development makes it possible to establish highly secure and mobile quantum networks. In parallel, the researchers focused on methods to stabilize free-space quantum channels under atmospheric turbulence and to seamlessly integrate these links into existing fiber infrastructures. The result is a future-proof urban quantum network that strengthens Germany’s technological sovereignty in the field of cybersecurity.

Looking ahead, the next step within QuNET is ambitious: the demonstration of a Germany-wide hybrid quantum network connecting nodes in Berlin, Jena, Erlangen, and Oberpfaffenhofen. This distributed network will combine fiber-based and free-space links and prepare the ground for future satellite-based quantum communication. As Dr. Goy emphasizes, this transition from local testbeds to scalable networks is essential for establishing a sovereign quantum network that ensures secure communication for the state, industry, and critical infrastructures.

At SpectroNet, we see Fraunhofer IOF’s work in the QuNET project as a powerful example of how photonics and quantum technologies can translate cutting-edge research into strategic technological capabilities. These achievements not only advance quantum communication, but also reinforce Germany’s and Europe’s position in a security-critical field of the future.

The scientific results of this work have been published in the peer-reviewed article “Ad-hoc hybrid-heterogeneous metropolitan-range quantum key distribution network” by Matthias Goy et al. in New Journal of Physics (2025). The publication provides detailed insights into the architecture and experimental validation of the hybrid quantum network and is available online at: https://iopscience.iop.org/article/10.1088/1367-2630/ae1864

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