  Two-photon optical transitions combined with long-range dipole-dipole
interactions can be used for the coherent manipulation of collective metastable
states composed of different atoms. We show that it is possible to induce
optical resonances accompanied by the generation of entangled superpositions of
the atomic states. Resonances of this kind can be used to implement quantum
logic gates using optically excited single atoms (impurities) in the condensed
phase.
