Violation of Bell's inequalities implies distillability for N qubits

Abstract

We consider quantum systems composed of $N$ qubits, and the family of all Bell's correlation inequalities for two two-valued measurements per site. We show that if a $N$-qubit state $ρ$ violates any of these inequalities, then it is at least bipartite distillable. Indeed there exists a link between the amount of Bell's inequality violation and the degree of distillability. Thus, we strengthen the interpretation of Bell's inequalities as detectors of useful entanglement.

6 pages, 3 figures, REVTEX. List of authors extended. Partially rewritten, a rather qualitative explanation of the results. Conclusions unchanged