Spatial-mode two-photon interference at a beam splitter
Li-Ping Deng, Gui-Fang Dang, Kaige Wang · Physical Review A · 2006
We present a general theory on the interference of a two-photon wave packet associated with spatial modes at a beam splitter. We find that the topological symmetry of the two-photon angular spectrum governs the nature of the two-photon interference. We distinguish between the coalescence interference and anticoalescence interference according to the decrease or increase of the coincidence probability in the absence of interference, respectively, and demonstrate that the symmetric and antisymmetric two-photon angular spectra are responsible for perfect coalescence interference and anticoalescence interference, respectively. Then we prove that anticoalescence interference never occurs for two independent photons, and it turns out that anticoalescence interference is the signature of two-photon entanglement. On the basis of this feature, we propose a special Mach-Zehnder interferometer, incorporated with two spiral phase plates, which can change the interference from a coalescence to an anticoalescence type only for a two-photon entangled state. The scheme is simple and straightforward compared with a test of Bell's inequality.