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Noncommuting mixed states cannot be broadcast

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

quant-pharXiv:quant-ph/9511010

Abstract

We show that, given a general mixed state for a quantum system, there are no physical means for 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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