Symmetries of the Bell correlation inequalities

Abstract

Bell correlation inequalities for two sites and 2+n or 3+3 two-way measurements ("dichotomic observables") are considered. In the 2+n case, any facet of the classical experience polytope is defined by a CHSH inequality involving only two pairs of the observables. In the 3+3 case, contrary to earlier results, the action of the symmetry group reduces the set of all Bell inequalities to just 3 orbits, only one of them being "new" (not known from the 2+2 case). A detailed calculation for the singlet state of two qubits reveals the configurations of a maximal violation for this class of inequalities.