A Village Health Kiosk, 70 Kilometers of Fiber, and 12.7 Bits a Second
Two links, two very different sets of numbers
In a health kiosk in the Thuringian village of Sundhausen, a participant sat down for a fifteen-minute simulated consultation with a physician at the university hospital in Jena, and audio and video ran without interruption. The keys protecting that traffic came from polarization-entangled photon pairs sent down installed telecommunications fiber. A German research team has now published its field report, pairing entanglement-based quantum key distribution on the BBM92 protocol with end-to-end post-quantum cryptography running sntrup761 and ML-KEM-768. The network spans about 140 kilometers in total, arranged as two links through a trusted node at Erfurt: 70 kilometers from Sundhausen with 51 of them aerial, and 69 kilometers from Jena that are almost entirely buried.
The fiber construction shows up in the measurements
On the aerial-heavy village link the secure key rate averaged 12.7 bits per second with a standard deviation of 10.3, at a quantum bit error rate of 13.3 percent. On the mostly buried Jena link the same system produced 22.2 bits per second with a deviation of 4.7, at an error rate of 6.1 percent. Nearly twice the key rate on the buried link, less than half the error rate, and an error-rate spread of 0.8 points against 9.6. The authors report that error-rate variation on the aerial link correlated most strongly with wind speed. The two links were operated separately, for 22 days and 2 days respectively, so the 22-day endurance figure belongs to the village link alone, and the final hop into the hospital used previously generated keys from a local keystore.
What a hospital would actually be buying
The quantum keys were pushed straight into standard Linux VPN tunnels between adjacent nodes, with no dedicated key management system and no modification to the existing medical systems, which is the commercially load-bearing choice for buyers who cannot re-platform. Trusted nodes remain the structural caveat: four European cybersecurity agencies hold that end-to-end security cannot be achieved over long distances using fibre-based quantum key distribution, and place the clear priority on post-quantum cryptography. Set against a breach record in which vulnerability exploitation accounts for 20 percent of healthcare intrusions, a hardened regional link answers one threat model and leaves the other untouched.
Quantum entropy without the fiber
The debate usually settles into quantum key distribution versus post-quantum cryptography, and both depend on the randomness the keys are made from. Chip-scale quantum random number generators, such as Quantum eMotion's electron-tunneling design reported at 1.8 gigabits per second and already running with Becton Dickinson and GreyBox Solutions in remote patient monitoring, deliver that entropy at the endpoint itself, with no dedicated fiber, no weather exposure and no intermediate node to trust. Quantum-grade keys and quantum key distribution are separable purchases, and for most clinical endpoints the chip fits the installed base.