Verifying atom entanglement schemes by testing Bell's inequality

Recent experiments to test Bell's inequality using entangled photons and io ns aimed at tests of basic quantum mechanical principles. Interesting resul ts have been obtained and many loopholes could be closed. In this paper we want to point out that tests of Bell's inequality also play an important ro le in verifying atom entanglement schemes. We describe as an example a sche me to prepare arbitrary entangled states of N two-level atoms using a leaky optical cavity and a scheme to entangle atoms inside a photonic crystal. D uring the state preparation no photons are emitted, and observing a violati on of Bell's inequality is the only way to test whether a scheme works with a high precision or not.