Two-party Bell inequalities derived from combinatorics via triangular elimination

Abstract. Bell inequalities, originally introduced as a method to prove that some quantum states show nonlocal behavior, are now studied as a method to capture the extent of the nonlocality of quantum states. Tight Bell inequalities are considered to be more important than redundant ones. Despite the increasing importance of the study of Bell inequalities, few kinds of tight Bell inequalities have been found. Examples include the Clauser-Horne-Shimony-Holt inequality, the Immvv inequalities, the CGLMP inequalities, and the Bell inequalities in systems small enough to generate all the Bell inequalities by exhaustive search. In this paper, we establish a relation between the two-party Bell inequalities for two-valued measurements and a highdimensional convex polytope called the cut polytope in polyhedral combinatorics. Using this relation, we propose a method, triangular elimination, to derive tight Bell inequalities from facets of the cut polytope. This method gives two hundred million inequivalent tight Bell inequalities from currently known results on the cut polytope. In addition, this method gives general formulas which represent families of infinitely many Bell inequalities. These results can be used to examine general properties of Bell inequalities.