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One-qubit reduced states of a pure many-qubit state: polygon inequalities

A. Higuchi·A. Sudbery·J. Szulc
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Abstract

We show that a necessary and sufficient condition for a set of $n$ one-qubit mixed states to be the reduced states of a pure $n$-qubit state is that their smaller eigenvalues should satisfy polygon inequalities: no one of them can exceed the sum of the others.

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A. Higuchi, A. Sudbery, J. Szulc. 2003-03-18. One-qubit reduced states of a pure many-qubit state: polygon inequalities. https://doi.org/10.1103/physrevlett.90.107902

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