Do all pure entangled states violate Bell's inequalities for correlation functions?

Phys Rev Lett. 2002 May 27;88(21):210402. doi: 10.1103/PhysRevLett.88.210402. Epub 2002 May 9.

Abstract

Any pure entangled state of two particles violates a Bell inequality for two-particle correlation functions (Gisin's theorem). We show that there exist pure entangled N>2 qubit states that do not violate any Bell inequality for N particle correlation functions for experiments involving two dichotomic observables per local measuring station. We also find that Mermin-Ardehali-Belinskii-Klyshko inequalities may not always be optimal for refutation of local realistic description.