Researchers look to nanosatellites for quantum communications

A nanosatellite can be used to produce a detectable quantum signal in space, researchers report.

Why it matters: Researchers envision creating global quantum communications networks, but quantum signals can't currently be transmitted long distances. Constellations of small, relatively less-expensive satellites that beam the signals from space to receivers on Earth have been proposed as a way to circumvent the problem.

How it works: In an entangled pair of photons, the state of one photon is linked to that of the other regardless of how much distance is between them — a principle of quantum mechanics that researchers want to use to distribute quantum keys for communications.

• If a message sent with a quantum key is intercepted or attempted to be intercepted, the state of the photon would be changed and the key would no longer work.
• Photons can be carried on fiber-optic cables but not for long distances because the signal can be scattered or absorbed by the cables.
• Researchers instead want to use satellites as nodes for distributing quantum signals.

What they did: Aitor Villar from the Centre for Quantum Technologies at the National University of Singapore and his colleagues built a miniature source for entangling photons and put it aboard a CubeSat, a roughly 10 x 10 x 30-centimeter nanosatellite.

• They report the source could withstand being launched on a rocket and produced a signal with the reduced power available on a nanosatellite in low-Earth orbit.
• The system, which weighs 2.6 kg and is called SpooQy-1, shines a blue laser diode on nonlinear crystals to create the entangled photon pairs.

• "This shows that entanglement technology can be deployed with minimal resources in novel operating environments, providing valuable ‘space heritage’ for different components and assembling techniques," the authors write in the journal Optica.

What it solves: A team led by Jian-Wei Pan of the University of Science and Technology in Hefei, China, has generated quantum signals on satellites, but a single satellite cannot currently cover the entire globe.

What's next: The researchers are now working on a system to send the entangled photon pair from the CubeSat to a ground receiver.

• Go deeper: China reports key advance in encrypted long-range communications (Axios)