![]() ![]() As each photon propagates, its wave front spreads out, like the beam from a flashlight. However, a major challenge to this form of optical communication comes from diffraction. To collect the incoming photons, each station was equipped with a telescope having a 26-mm-wide aperture and a single-photon detector. Using a high-speed tracking system, the drone directed one photon to a ground station labeled Alice and the other to a ground station labeled Bob. The drone generated pairs of infrared photons whose polarization orientations were entangled. ![]() Early last year, Xie and colleagues reported a quantum link using a single octocopter-style drone. Several teams around the world have been working on drone-based systems. The beams from one drone are visible over the testing area. Unlike a fixed tower, drones can also move around to avoid pollution or fog. “Drones can be deployed for a mobile quantum connection at any given time and location when necessary,” says Zhenda Xie from Nanjing University in China. Small drones carrying optical equipment could provide a flexible solution that could link multiple users in a quantum network. However, satellites are expensive and difficult to adapt to changing demands on the ground. More photons can survive if quantum information is transmitted through the atmosphere, as in the quantum link established using a Chinese satellite in 2018 (see Focus: Intercontinental, Quantum-Encrypted Messaging and Video). But in fibers, a large fraction of the photons scatter before reaching their destination. One of the most common methods for sending such quantum encrypted messages relies on optical fibers (see Viewpoint: Record Distance for Quantum Cryptography). For every pair, one photon would be sent to each of the users, who would be alerted to any eavesdropping by a loss of entanglement between the photons. For example, two users could exchange encrypted messages using “entangled” photons, pairs of particles with a unique quantum-mechanical relationship. Quantum communication promises fully secure message sharing. This demonstration could lead to a drone-based quantum network that could be positioned-and easily repositioned-over a city or rural area. ![]() A new experiment has used a pair of hovering drones to dole out quantum information to two ground stations separated by 1 km. The airwaves are chock full of “classical” information from cell phones, radio stations, and Wi-Fi hubs, but one day those waves could be carrying quantum encrypted messages or data input for a quantum computer. From each pair, one photon (purple beam) goes directly to the ground, while the other (pink beam) is relayed through the second drone (right). A new quantum communication system consists of a drone (left) that generates entangled photon pairs and distributes them to ground stations. ![]()
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