The University of Strathclyde is leading a three-year European research project to develop cold-atom quantum memories for long-distance networks spanning fiber and free-space optical links.

The Atom-Light Free-Space Quantum Optics Networking (AL FreSQO) project will investigate how quantum memories can be incorporated into repeater devices to help distribute entanglement beyond the distance possible over a direct connection. The project will also develop wavelength-conversion systems designed to connect photons traveling at telecommunications wavelengths with cold-atom memories operating at different wavelengths.

“Quantum signals are fragile and easily lost over long distances,” Daniel Oi, a professor in Strathclyde’s Department of Physics and AL FreSQO’s lead coordinator, noted in a statement. “Because they can’t be copied or amplified, we need new ways to extend their range.”

Quantum repeaters divide a long connection into shorter segments, establish entanglement across each segment, and join them using entanglement swapping. Quantum memories temporarily store quantum states while entanglement is established across other parts of the network. This buffering helps synchronize the operations required to connect the individual segments.

Connecting fiber and free-space links

AL FreSQO will combine cold-atom memories with free-space optical links, which transmit photons through the air rather than optical fiber.

Free-space links are important where fiber networks are not practical. Potential applications include quantum connections involving satellites, aircraft, ships, trains, and road vehicles.

“Frequency conversion allows us to connect free-space and fiber networks by matching different wavelengths, giving greater flexibility in how quantum networks are built,” Oi noted.

The researchers explained the selected technologies could also reduce reliance on the bulky and energy-intensive cryogenic equipment required by some alternative quantum-memory platforms.

Aidan Arnold, a reader in physics at Strathclyde, will conduct quantum non-demolition experiments intended to detect a photon without destroying it.

The project could ultimately support secure communications, clock synchronization, distributed sensing, and connections forming part of a future quantum internet.

Strathclyde is working with the universities of Southampton and Padua, Humboldt University of Berlin, Sabancı University, and University of Padua spinout ThinkQuantum.

AL FreSQO has received approximately $2.3 million through the European Commission-supported QuantERA program involving more than 40 research-funding organizations.

The project was one of 39 selected from 287 proposals submitted to the 2025 QuantERA funding call. The successful projects received approximately $61.7 million in total funding.