Geometrical description of the convex sets of states for systems with spin-1/2 and spin-1
F. J. Bloore · Journal of Physics A Mathematical and General · 1976
The states of a quantum mechanical system form a convex set with the pure states as extremals. For a system of spin- 1 / 2 , the set is a 3-dimensional ball. For spin j, the convex set is stratified by rank r, 1<or=r