Time evolution of pairwise entanglement between two atoms

We investigate dynamics of pairwise entanglement between two atoms for various entangled initial states. The initial entanglement shows an interesting time evolution, including entanglement sudden death. The initial portion of the excited state is responsible for the sudden death of the entanglement. The initial portion of excited–ground–ground state or the initial photons in the system can induce pairwise entanglement. Meanwhile, we find that our model gives a concrete example to support the two theorems in [F. Verstraete, K. Audenaert, J. Dehaene and B. De Moor, J. Phys. A: Math. Gen. 34 (2001) 10327].