  The entanglement character including the so-called sudden death effect
between atoms in the non-degenerate two photons Tavis-Cummings model is studied
by means of concurrence. The results show that the so-called sudden death
effect occurs only for some kind of initial states. In other words, the
phenomenon is sensitive to the initial conditions. One can expect the
resurrection of the original entanglement to occur in a periodic way following
each sudden death event. The length of the time interval for the zero
entanglement is dependent on not only the degree of entanglement of the initial
state but also the initial state. And the influence of dipole-dipole
interaction and different atomic initial states on entanglement between atoms
are discussed. The sudden death effect can be weakened by the introducing of
dipole-dipole interaction.
