title: One-qubit reduced states of a pure many-qubit state: polygon inequalities.
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: each of them must be no greater than the sum of the others.
authors.affiliation: Department of Mathematics, University of York, Heslington, York YO10 5DD, United Kingdom. ah28@york.ac.uk
authors.forename: A
authors.initials: A
authors.lastname: Higuchi
authors.forename: A
authors.initials: A
authors.lastname: Sudbery
authors.forename: J
authors.initials: J
authors.lastname: Szulc