Scheme for Generating a χ-Type Four-Atom Entangled State in Cavity QED

We propose a scheme for generating a χ-type four-atom entangled state in cavity QED. In the present scheme, the atoms interact simultaneously with a highly detuned cavity mode with the assistance of a strong classical field. The scheme is insensitive to the cavity decay and the thermal field, which is of importance from the experimental point of view.