China Researchers Use Drones to Create Prototype of Small Airborne Quantum Network

(Phys.org) A team of researchers affiliated with several institutions in China has used drones to create a prototype of a small airborne quantum network. The researchers sent entangled particles from one drone to another and from a drone to the ground.
To build a long-range quantum network, satellites appear to be the ideal solution. But for smaller networks, such as for communications between users in the same city, another option is needed. While towers can be of some use, they are subject to weather and blockage, intentional or otherwise. To get around this problem, the researchers used drones to carry the signals.
The work involved building a small laser-generating device and affixing it to one of the drones. As it fired, photons were split in two, creating entangled pairs. One of the paired photons was directed toward another drone while the other was directed to a ground station. The drone that received the entangled photon served only as a relay—after refocusing, the photon was forwarded to a third drone, which then sent it to a second ground station. Motorized devices were used on the drones to ensure transmitters and received lined up properly for transmission of the entangled photons.
The photons were sent just one kilometer, but the researchers suggest that moving the drones higher would allow for transmission over distances up to 300 kilometers. They further note both the drones and the ground stations could also be connected to a network that included satellites.