Entanglement manipulation for mixed states in a multilevel atom   interacting with a cavity field
  We derive an explicit formula for an entanglement measure of mixed quantum states in a multi-level atom interacting with a cavity field within the framework of the quantum mutual entropy. We describe its theoretical basis and discuss its practical relevance (especially in comparison with already known pure state results). The effect of the number of levels involved on the entanglement is demonstrated via examples of three-, four- and five-level atom. Numerical calculations under current experimental conditions are performed and it is found that the number of levels present changes the general features of entanglement dramatically. 
Mahmoud Abdel-Aty, M. R. B. Wahiddin and A.-S. F. Obada