Finite-Time Disentanglement via Spontaneous Emission
  We show that under the influence of pure vacuum noise two entangled qubits become completely disentangled in a finite time, and in a specific example we find the time to be given by $\ln \Big(\frac{2 +\sqrt 2}{2}\Big)$ times the usual spontaneous lifetime. 
Ting Yu and J. H. Eberly