  We investigate the entanglement dynamics of a quantum system consisting of
two-level atoms interacting with vacuum or thermal fields with classical
driving fields. We find that the entanglement of the system can be improved by
adjusting the classical driving field. The influence of the classical field and
the purity of the initial state on the entanglement sudden death is also
studied. It is shown that the time of entanglement sudden death can be
controlled by the classical driving fields. Particularly, the entanglement
sudden death phenomenon will disappear if the classical driving fields are
strong enough.
