Postselection-free controlled generation of a high-dimensional orbital-angular-momentum entangled state

High-dimensional entangled states in orbital angular momentum (OAM) basis offer several unique advantages for quantum information applications. However, for the optimal performance of a given application, one requires a generation technique for OAM entangled states that is completely postselection-free and fully controllable. Nonetheless, despite several efforts in the past, no such technique currently exists. In this article, we propose just such a technique and experimentally demonstrate postselection-free generation of up to about 150-dimensional OAM entangled states. We report the generation accuracy, which is a measure of the control, to be more than 98% for states with Gaussian and triangular OAM Schmidt spectra and up to 90% for the maximally-entangled OAM states, which have rectangular spectra.