Over 140km of fibre in Thuringia, Germany, a quantum-secure network integrates entanglement-based Quantum Key Distribution (QKD) and end-to-end Post-Quantum Cryptography (PQC). This new architecture injects QKD keys directly into standard VPN tunnels, enabling PQC to secure communication without modifying existing infrastructure.

A field deployment connected a rural health kiosk to a university hospital and achieved continuous autonomous operation for 22 days. Vasile-Laurentiu Dosan from Quantum Optics Jena GmbH and colleagues have integrated quantum technologies with existing communication networks in Germany’s Thuringia region; connecting a rural health kiosk to a university hospital over 140km of fibre optic cable.

The demonstration combines Quantum Key Distribution (QKD) and Post-Quantum Cryptography (PQC), two methods designed to protect sensitive data from future attacks by powerful quantum computers, offering layered security against potential threats. QKD functions like sending secret codes with uniquely linked pairs of gloves; any attempt to intercept them disturbs the pair, immediately alerting both sender and receiver.

Unlike previous systems requiring dedicated key management, this architecture seamlessly injects QKD keys into existing VPN tunnels while PQC provides end-to-end encryption, ensuring compatibility with current infrastructure. The team achieved continuous autonomous operation lasting 22 days, but differing environmental conditions along aerial versus buried fibre links presented key challenges in maintaining stable connections and raise questions about optimal deployment strategies for widespread adoption.

Sustained Quantum Key Distribution over Extended Fibre Networks for Twenty Two Days

Entanglement measures now demonstrate continuous autonomous operation over fibre links exceeding previous limits; the demonstrated network sustained secure key exchange for 22 days, a substantial improvement on earlier deployments typically lasting hours rather than weeks. Active polarization stabilisation countered environmental disturbances affecting delicate entangled states transmitted across 140km of deployed fibre optic cable connecting rural and urban healthcare facilities in Germany, stressing key progress towards practical quantum communications infrastructure capable of operating reliably outside controlled laboratory settings. Specifically, spontaneous parametric down-conversion generated polarization-entangled photon pairs at both 810nm and 1550nm wavelengths for transmission, while dispersion compensation modules mitigated signal distortion over long distances exceeding 60 kilometres.

Wind speed correlated most strongly with fluctuations in the quantum bit error rate on predominantly aerial links, highlighting environmental sensitivities. The deployed system integrates entanglement-based Quantum Key Distribution (QKD) with Post-Quantum Cryptography (PQC), utilising standard Linux VPN tunnels to inject keys directly without dedicated key management systems.

Although successful key exchange occurred over separate fibre links, concurrent operation across the full 140km distance was not achieved; this does not invalidate the demonstration of a functioning quantum network integrated with existing healthcare infrastructure and highlights a clear pathway toward practical deployment despite current technological limitations. Securing telemedicine data using their generated keys did not alter established medical workflows which is particularly important for real-world adoption.

Quantum cryptography secures sensitive patient information within an operational hospital network

The convergence of healthcare and secure communications demands new solutions protecting sensitive patient data from increasingly sophisticated cyber threats; this team’s deployment offers insight into how quantum technologies might underpin future telemedicine networks. A practical quantum network integrating two distinct approaches to secure communication was demonstrated in this successful field trial, validating the maturity of these technologies beyond controlled laboratory environments and highlighting potential application within critical infrastructures like healthcare networks connecting rural kiosks to hospital facilities. Continuous autonomous operation lasting twenty-two days across 140km of fibre optic cable in Germany stresses key progress toward reliable infrastructure outside lab settings.

This research successfully integrated Quantum Key Distribution with Post-Quantum Cryptography over a 140km fibre network in Thuringia, Germany, linking a health kiosk to a university hospital. This demonstration shows how quantum security methods can work alongside existing IT systems, specifically standard Linux VPN tunnels, without requiring new key management infrastructure. Researchers achieved twenty-two days of continuous operation, indicating the technological maturity of entanglement-based QKD within an operational environment.

👉 More information
🗞 Secure Medical Data Transmission Using Quantum Key Distribution and Post-Quantum Cryptography in Real-World Fiber Networks
✍️ Vasile-Laurentiu Dosan, Paul Spooren, Sebastian Moeckel, Alessandro Zannotti, Alek Lagarrigue, Pablo Vazquez, Marc Bodenstein, Jonas Jelonek, Jansen Dwan, Fabian Steinlechner, Kevin Füchsel, Thomas Hühn and Oliver de Vries
🧠 ArXiv: https://arxiv.org/abs/2608.18869

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