Entanglement of a multi-photon three-level atom interacting with a single-mode field in the presence of nonlinearitiesA.-S.F. Obada, S.A. Hanoura and A.A. EiedEur. Phys. J. D, 66 8 (2012) 221DOI: https://doi.org/10.1140/epjd/e2012-20658-7