Quantum Keys Travel 18 Kilometers Across Hybrid Air-and-Fiber Network

Insider Brief

• Researchers demonstrated quantum key distribution across an 18-kilometer free-space link connected to conventional fiber infrastructure using adaptive optics.
• The system generated secret keys at about 1,000 bits per second with superconducting detectors and 200 bits per second with room-temperature detectors.
• Faster adaptive optics and automated fiber alignment could improve performance under strong turbulence and support future terrestrial and satellite quantum networks.

Researchers demonstrated quantum key distribution across an 18-kilometer free-space link by using adaptive optics to counter atmospheric turbulence and connect the signal to conventional fiber infrastructure.

The field trial in northeastern Italy generated secret encryption keys at an average rate of about 1,000 bits per second with high-efficiency superconducting detectors and 200 bits per second with compact detectors operating at room temperature. The results suggest that quantum communication equipment built for fiber networks could also support longer free-space and satellite links without extensive changes.

The study, published in npj Quantum Information, addressed a basic problem facing future quantum networks. Such networks will likely need to move quantum signals between fiber-optic cables, open-air links and satellites. Each transmission medium has different technical demands, making it difficult to connect them without losing the fragile quantum states that carry information.