Quantum interference and entanglement of photons which do not overlap in   time
  We discuss the possibility of quantum interferences and entanglement of photons which exist at different intervals of time, i.e., one photon being recorded before the other has been created. The corresponding two-photon correlation function is shown to violate Bell's inequalities. 
R. Wiegner, C. Thiel, J. von Zanthier and G. S. Agarwal
quant-ph