Parametrization of spin-1 classical states
  We give an explicit parametrization of the set of mixed quantum states and of the set of mixed classical states for a spin--1. Classical states are defined as states with a positive Glauber-Sudarshan P-function. They are at the same time the separable symmetric states of two qubits. We explore the geometry of this set, and show that its boundary consists of a two-parameter family of ellipsoids. The boundary does not contain any facets, but includes straight-lines corresponding to mixtures of pure classical states. 
Olivier Giraud, Petr Braun, and Daniel Braun
quant-ph cond-mat.mes-hall cond-mat.quant-gas