# A single quantum cannot be cloned

@article{Wootters1982ASQ, title={A single quantum cannot be cloned}, author={William K. Wootters and Wojciech Hubert Zurek}, journal={Nature}, year={1982}, volume={299}, pages={802-803} }

If a photon of definite polarization encounters an excited atom, there is typically some nonvanishing probability that the atom will emit a second photon by stimulated emission. Such a photon is guaranteed to have the same polarization as the original photon. But is it possible by this or any other process to amplify a quantum state, that is, to produce several copies of a quantum system (the polarized photon in the present case) each having the same state as the original? If it were, the… Expand

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