Generation of heralded vector-polarized single photons in remotely controlled topological classes

We demonstrate an experimental protocol for the preparation and control of heralded single photons in inhomogeneously polarized states, such as vector vortex and full Poincaré beam states. A laser beam is shaped by a voltage-controlled spin-to-orbital angular momentum converter q-plate device, which eliminates the need for an interferometer for the robust preparation of high-quality inhomogeneously polarized beams. Such a beam is then used as a pump in a spontaneous parametric down-conversion (SPDC) photon-pair source. We demonstrate the full pump to heralded single-photon transfer of the intensity and phase distributions, as well as of the vector polarization structure. Additionally, we show that by controlling the polarization to which the heralding idler photon is projected before detection, we can toggle between the direct and basis-switched pump-single-photon transfer. We show that this nonlocal control of the heralded single photon pertains also to the topological class of the resulting heralded single photon. We believe that our work will lead to opportunities in photon-based quantum information processing science.