A simple Bell inequality for an n-particle system in a Greenberger-Horne-Zeilinger state is derived. Quantum mechanics violates this inequality by an exponentially large factor of $2^{\left(\mathit{n}\mathrm{-}2\right)/2}$ for n odd or $2^{\left(\mathit{n}\mathrm{-}1\right)/2}$ for n even.

• Received 18 May 1992

DOI:https://doi.org/10.1103/PhysRevA.46.5375