Verification of non-classical correlation in orbital angular momentum of photons without excess components

We propose a method to detect photons in superposition of orbital angular momentum (OAM) states using a hologram and path interferometer, and its application to verification of non-classical correlation in photon pairs. The method is free from excess OAM components, and a simple assumption of classical OAM correlation between the two photons removes contributions from excess components from the coincidence curve as well, even when the proposed method is used only on one of the photons.