An international research team led by the National University of Singapore (NUS) has generated and detected quantum entanglement onboard a CubeSat nanosatellite weighing less than 2.6 kg and orbiting Earth. CubeSats are low-resource, cost-effective satellites and are smaller than a shoebox. As a first step, the researchers needed to demonstrate that a miniaturized photon source for quantum entanglement could remain intact through the stress of launch and operate successfully in the harsh environment of space within a satellite that provides minimal energy. They examined every component of the photon-pair source that would be used to generate quantum entanglement to see if it could be made smaller or more rugged. Researchers developed a miniaturized source of quantum entanglement that measures only 20 by 10 cm. Courtesy of the Center for Quantum Technologies, National University of Singapore. “At each stage of development, we were actively conscious of the budgets for mass, size, and power," engineer Aitor Villar said. “By iterating the design through rapid prototyping and testing, we arrived at a robust, small-form factor package for all the off-shelf components needed for an entangled photon-pair source.” The new miniaturized photon-pair source consists of a blue laser diode that shines on nonlinear crystals to create pairs of photons. To achieve high-quality entanglement, the researchers had to completely redesign the mounts that currently align the nonlinear crystals with a high degree of precision and stability. To qualify the instrument for space, the researchers tested its ability to withstand the vibration and thermal changes experienced during a rocket launch and in-space operation. The photon-pair source maintained high-quality entanglement throughout the testing while preserving crystal alignment even after repeated temperature cycling from −10 to 40 °C. The researchers incorporated their new instrument into SpooQy-1, a CubeSat that was deployed into orbit from the International Space Station on June 17, 2019. The instrument successfully generated entangled photon-pairs over temperatures from 16 to 21.5 °C. The SpooQy-1 CubeSat contains a miniaturized quantum instrument that creates pairs of photons with the quantum property of entanglement. The entanglement is detected in correlations of the photons’ polarizations. Courtesy of the Center for Quantum Technologies, National University of Singapore, and NASA. “This demonstration showed that miniaturized entanglement technology can work well while consuming little power,” Villar said. “This is an important step toward a cost-effective approach to the deployment of satellite constellations that can serve global quantum networks.” The team is now working with RALSpace in England to design and build a quantum nanosatellite similar to SpooQy-1, but with the capabilities needed to beam entangled photons from space to a ground receiver. This is slated for demonstration aboard a 2022 mission. The researchers are also collaborating with other teams to improve the ability of CubeSats to support quantum networks. “In the future, our system could be part of a global quantum network transmitting quantum signals to receivers on Earth or on other spacecraft,” Villar said. “These signals could be used to implement any type of quantum communications application, from quantum key distribution for extremely secure data transmission to quantum teleportation, where information is transferred by replicating the state of a quantum system from a distance.” The research was published in Optica, a publication of OSA (The Optical Society) (www.doi.org/10.1364/OPTICA.387306).