  In a recent paper Yu and Eberly [Phys. Rev. Lett. {\bf 93}, 140404 (2004)]
have shown that two initially entangled and afterwards not interacting qubits
can become completely disentangled in a finite time. We study transient
entanglement between two qubits coupled collectively to a multimode vacuum
field and find an unusual feature that the irreversible spontaneous decay can
lead to a revival of the entanglement that has already been destroyed. The
results show that this feature is independent of the coherent dipole-dipole
interaction between the atoms but it depends critically on whether or not the
collective damping is present. We show that the ability of the system to
revival entanglement via spontaneous emission relies on the presence of very
different timescales for the evolution of the populations of the collective
states and coherence between them.
