We study a general theory on the interference of two-photon wavepacket in a beam splitter. We find that the symmetry of two-photon spectrum plays an important role in the manners of interference. We distinguish the coalescence and anti-coalescence interferences, and prove that the anti-coalescence interference is the signature of photon entanglement.
@article{arxiv.quant-ph/0305074,
title = {Two Photon Anti-Coalescence Interference: the Signature of Two Photon Entanglement},
author = {Kaige Wang and Shiyao Zhu},
journal= {arXiv preprint arXiv:quant-ph/0305074},
year = {2009}
}