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Noncommuting mixed states cannot be broadcast

H. Barnum·C. M. Caves·C. A. Fuchs·R. Jozsa·B. Schumacher
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Abstract

We show that, given a general mixed state for a quantum system, there are no physical means for {\it broadcasting\/} that state onto two separate quantum systems, even when the state need only be reproduced marginally on the separate systems. This result generalizes and extends the standard no-cloning theorem for pure states.

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H. Barnum, C. M. Caves, C. A. Fuchs, R. Jozsa, B. Schumacher. 1995-11-08. Noncommuting mixed states cannot be broadcast. https://doi.org/10.1103/physrevlett.76.2818

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