A group in China has made significant progress toward solving that problem, via a high accuracy pointing and tracking system. Using this method, Juan Yin and colleagues performed quantum teleportation (copying of a quantum state) using multiple entangled photons through open air between two stations 97 kilometers apart across a lake. Additionally, they demonstrated entanglement between two receivers separated by 101.8km, transmitted by a station on an island roughly halfway between them.
Though the authors do not make this clear in the paper, their method is currently limited to nighttime communication. Nevertheless, their results achieved larger distances for multi-photon teleportation and three-point entanglement than before, and the tracking system used may even enable ground-to-satellite quantum communication—at least if it happens at night.
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