  We show that, under certain conditions, the micromaser can act as an
effective source of highly correlated atoms. It is possible to create an
extended robust entanglement between two successive, initially unentangled
atoms passing through a cavity filled with with a nonlinear medium taking into
consideration a slight level shift. Information is transfered from the cavity
to the atoms in order to build up entanglement. The scheme has an advantage
over conventional creation of entanglement if the two atoms (qubits) are so far
apart that a direct interaction is difficult to achieve. The interaction of the
atoms with the micromaser occurs under the influence of a two-quantum
transition process. Interesting phenomena are observed, and an extended robust
entangled state is obtained for different values of the system parameters.
Illustrative variational calculations are performed to demonstrate the effect
within an analytically tractable two-qubit model.
