Researchers harness UV-C wavelengths to advance wireless quantum communication

Caption: Researchers, for the first time, demonstrated a wireless quantum key distribution (QKD) system operating in the ultraviolet-C (UV-C) spectral region. The images show the experimental setup used for the transmitter and receiver.

Credit: Feng Liu, University of Oxford

"Our UV-C QKD technology could help protect future financial transactions, healthcare data, government communications and critical infrastructure against cyber threats posed by future quantum computers," said Feng Liu from the University of Oxford, first author of the paper. "While further development is still needed before practical deployment, this work opens a new direction for building secure outdoor wireless quantum communication networks."

Quantum security goes wireless

As quantum computing continues to advance, existing encryption methods could become vulnerable, creating new challenges for protecting sensitive information. Quantum communication technologies such as QKD use the laws of quantum mechanics to provide security that does not rely on computational power.

Although QKD works very well where optical fibers are available, mobile devices and temporary communication networks require wireless solutions. However, for wireless QKD systems, ambient light noise, especially sunlight, can easily overwhelm the extremely weak single-photon signals used for quantum communication.

Rather than trying to filter out sunlight, the researchers decided to see if they could use a part of the spectrum where sunlight is naturally absent. The UV-C band, known as the "solar-blind" region, offers a much cleaner channel because the Earth's atmospheric ozone layer absorbs almost all sunlight at these wavelengths. The idea to use the UV-C band grew out of discussions between Andy Schreier, who is now with Fraunhofer Institute for Telecommunications in Germany, and O'Brien's research team at the University of Oxford and UK Quantum Communications Hub.

Although UV-C light can be harmful to the eyes and skin, the extremely low light levels used for QKD - essentially individual photons - fall within established safety limits.

To create a UV-C free-space QKD link, the researchers had to bring together several specialized components since technology at these wavelengths is still relatively immature, particularly for high-speed light sources and high-sensitivity photodetectors.

One specialized component was high-speed AlGaN UV-C micro-LEDs developed by collaborators at the University of Strathclyde. These LEDs enabled data transmission at rates far beyond what is possible with conventional UV light sources. For another component, the researchers developed high-sensitivity UV-C single-photon detectors based on silicon photomultipliers (SiPMs), which made it possible to detect extremely weak UV-C quantum signals.

"The final piece was optical filtering and signal-processing techniques that improved the system's overall performance and robustness," said Liu. "Bringing all of these technologies together enabled us to demonstrate a UV-C free-space QKD link."

Testing the quantum link

The team evaluated the approach experimentally by building a complete laboratory prototype UV-C free-space QKD system. After characterizing the UV-C light source and single-photon detector, they demonstrated QKD operation at various data rates while measuring the quantum bit error rate and raw key rate. Based on the experimental results, they calculated a final secure key rate exceeding 1 Mbit/s, demonstrating the potential for high-speed wireless quantum communication at distances comparable to Bluetooth links.

The researchers also investigated how artificial light and direct sunlight affected the system's performance and used that information to develop additional optical filtering that could enable the optical link to operate even in direct sunlight.

Next, the researchers plan to demonstrate the system outdoors under real daylight conditions and perform a more comprehensive security analysis using advanced QKD protocols. They are also working to improve the overall system efficiency and extend the communication range to hundreds of meters, where the short UV-C wavelengths will contend with attenuation caused by Rayleigh scattering in the atmosphere.

From an engineering perspective, they aim to further improve the performance of the UV-C light sources, single-photon detectors and optical filters, while integrating the entire system into a compact package. This will improve system stability, reduce the size and cost and move the technology closer to practical deployment and eventual commercialization.

Paper: F. Liu, J. Farmer, G. Faulkner, A. Trichili, J. J. D. McKendry, E. Xie, Z. Wang, J. Wang, J. Hill, J. Herrnsdorf, S. Rajbhandari, M. D. Dawson, D. O'Brien, "UV-C Free-Space Quantum Key Distribution," 3, XXXX (2026).

DOI: 10.1364/OPTICAQ.571592.