Quantum copies do new tricks

One of the strange features of quantum information is that, unlike almost every other type of information, it cannot be perfectly copied. For example, it is impossible to take a single photon and make a number of photons that are in the exact same quantum state. This may seem minor, but it's not. If perfect copying was possible, it would, among other things, be possible to send signals faster than the speed of light. This is forbidden by Einstein's theory of relativity.

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