Quantum coherence generated by quantum interference

This paper deals with a system exhibiting quantum interference in the two-photon coupling between its ground state and the continuum through two quasiresonant intermediate levels by two modes of the electromagnetic field. We show that this system can generate quantum coherence among the two field modes, the internal and the external degrees of freedom. Two applications are discussed: generation of photon-number correlations between the two modes, and selection of atoms in a given velocity class.