Identifying two-photon high-dimensional entanglement in transverse patterns

We propose a scheme to explore two-photon high-dimensional entanglement associated with a transverse pattern by means of two-photon interference at a beamsplitter. We find that the topological symmetry of the angular spectrum of the two-photon state governs the nature of the two-photon interference. We prove that the anti-coalescence 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 anti-coalescence type only for a two-photon entangled state. The scheme is simple and straightforward compared with the test for a Bell inequality. (c) 2006 Elsevier B.V. All rights reserved.