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Probability distributions consistent with a mixed state

M. A. Nielsen

quant-pharXiv:quant-ph/9909020

Abstract

A density matrix ρ may be represented in many different ways as a mixture of pure states, ρ= Σi pi |ψi ψi|. This paper characterizes the class of probability distributions (pi) that may appear in such a decomposition, for a fixed density matrix ρ. Several illustrative applications of this result to quantum mechanics and quantum information theory are given.

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