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114 W hile the spooky science of quantum mechanics underpins modern microelectronics, there’s a great deal of excitement and no doubt hype about the far less familiar field of quantum computing and its impact on comms, cryptography, sensing and other areas in which uncrewed systems are closely involved (writes Peter Donaldson). Established computer giants and ambitious start-ups alike are working on the core quantum computing technologies. The plural signifies that there are several competing core technologies – a sure sign of an industry in its infancy. Quantum mechanics describes the behaviour of matter and energy at the scale of atoms and subatomic particles. Quantum computing is based not on binary switch positions representing the 1s and 0s of conventional computing but on ‘qubits’, which can take on a combination of two values owing to a phenomenon known as quantum superposition. As theoretical physicist Sabine Hossenfelder puts it, quantum computers work by entangling qubits and shifting this entanglement around. In her words, “Entanglement is a kind of correlation, but one that does not have a non-quantum equivalent.” A working quantum computer, she says, needs qubits, a way of entangling a lot of them, and an algorithm to tell it how to move the entanglement around. There are two physical approaches to creating qubits that have been demonstrated in working machines and achieved quantum advantage, which means achieving a task that a conventional computer could not have done in a reasonable amount of time, and there are more in the works. The first involves superconducting qubits, which are tiny currents on a chip realised either by charge distribution or current flux. The chips need large, heavy and power-hungry cooling systems though to keep them at close to absolute zero to keep the qubits in their two states, and the quantum effects last only a few tens of microseconds. The second are photonic qubits, which have properties related to photons, such as the uncertainty in their state. Photonic quantum computers can work at room temperature and the quantum effects last longer, but their many optical components make them big and heavy. Quantum computing is demonstrating capabilities beyond those of the best conventional computers in a few niche applications, but they are not yet general-purpose machines. This might suggest that ‘quantum’ UAVs are a long way off, but researchers in China have demonstrated an important step towards in-flight comms secured by quantum cryptography using entangled photons. The researchers used two UAVs 200 m apart linked by free-space optical comms to each other and to different ground stations 400 m apart, named Alice and Bob in line with cryptographic tradition. One UAV generated entangled photon pairs and distributed them to Alice, while the second UAV sent them to Bob. Alice and Bob were linked by conventional comms so they could compare photon quantum states. Any difference between the states would warn that the message had been intercepted between transmission and reception, as measuring (or reading) any quantum state changes it. So should uncrewed systems developers and engineers be excited? Perhaps being excited and not excited at the same time is appropriate, as Schrodinger’s cat might say. Researchers have demonstrated an important step towards in-flight UAV comms secured by quantum cryptography using entangled photons February/March 2023 | Uncrewed Systems Technology PS | Internet of quantumUAVs? Now, here’s a thing