Increasing the dimension in high-dimensional two-photon orbital angular momentum entanglement

Any practical experiment utilizing the innate D-dimensional entanglement of the orbital angular momentum (OAM) of photons is subject to the generation capacity of the entangled photon source and the modal capacity of the detection system. We report an experimental spontaneous parametric-down-conversion system able to generate and detect tunable high-dimensional OAM entanglement. By tuning the phase matching, we demonstrate a factor of 2 increase on the half-width of the OAM-correlation spectrum, from 10 to 20. In terms of quantum mutual information capacity, this is an increase from 3.18 to 4.95 bits/photon. Furthermore, we measure correlations in the conjugate variable, angular position, and obtain concurrence values 0.96 and 0.90. The good entanglement measures in both OAM and angular position bases indicate bipartite, D-dimensional entanglement where D is tunable.