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Quantum communications has already been proved possible over short distances. Via fiber optics, quantum key distribution (QKD) has been demonstrated over 250 km; for free-space transmission, the longest demonstrated distance has been more than 144 km.

The problem is that experts don’t expect these distances to extend to more than a few hundred kilometers with current technologies. Essentially, the technology can go only so far before markedly better devices or newer, smarter techniques have to be developed. But interesting progress is being made.

One approach is the development of quantum repeaters, devices that will store and entangle quantum states in a way that allows entanglement to be distributed over much larger distances. But these devices are still at the stage of fundamental research.

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