On Bell's theorem for N-qubits

Abstract

We present a single general Bell inequality that summarizes all possible Bell type constrains on the correlation function for the N-particle system (i.e., it is a necessary and sufficient condition for the existence of local realistic models for the correlation function). It is applicable in the case when measurements on each particle can be chosen between two arbitrary dichotomic observables. We also obtain a necessary and sufficient condition for an arbitrary N-qubit mixed state to violate this general Bell inequality.