High-dimensional entanglement with orbital-angular-momentum states of light

We engineer high-dimensional orbital-angular-momentum entanglement of photon pairs that emerge from a parametric down-conversion source. By means of two angular state analysers, in essence composed of a rotatable multi-sector phase plate and a single-mode fibre, we perform selective projective measurements that maximize the Shannon dimensionality D of the measured entanglement. The multi-sector phase plates have a binary phase profile along the azimuthal coordinate, and the arc sector sizes are optimized so as to maximize D. We find that the maximum dimensionality increases linearly with the number of sectors N. The potential of our method is illustrated with an experiment for N = 4, yielding D = 16.5