One-qubit reduced states of a pure many-qubit state: polygon inequalities.
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.
Higuchi
A
A
Department of Mathematics, University of York, Heslington, York YO10 5DD, United Kingdom. ah28@york.ac.uk
Sudbery
A
A
Szulc
J
J