Optics Express
Mode counting in high-dimensional orbital angular momentum entanglement
Martin P. van Exter, P. S. K. Lee, S. van Doesburg, J. P. Woerdman
Abstract
We study the high-dimensional orbital angular momentum OAM) entanglement contained in the spatial profiles of two quantum-correlated photons. For this purpose, we use a multi-mode two-photon interferometer with an image rotator in one of the interferometer arms. By measuring the two-photon visibility as a function of the image rotation angle we measure the azimuthal Schmidt number, i.e., we count the number of OAM modes involved in the entanglement; in our setup this number is tunable from 1 to 8.