We investigate the change of entanglement of photons due to propagation. We find that post-selected entanglement in general varies by propagation and, as a consequence, states with maximum bi- and tri-partite entanglement can be generated from propagation of unentangled photons. We generalize the results to n photons and show that entangled states with permutation symmetry can be generated from propagation of unentangled states. Generation of n-photon GHZ states is discussed as an example of a class of states with the desired symmetry.
@article{arxiv.0903.0389,
title = {Generation of multi-photon entanglement by propagation and detection},
author = {H. Hossein-Nejad and R. Stock and D. F. V. James},
journal= {arXiv preprint arXiv:0903.0389},
year = {2009}
}