title: Classical to quantum transfer of optical vortices.
abstract: We show that an optical vortex beam, implemented classically, can be transferred to the transverse amplitude of a heralded single photon. For this purpose we have relied on the process of spontaneous parametric downconversion (SPDC) for the generation of signal and idler photon pairs, using a pump in the form of a Bessel-Gauss (BG) beam with orbital angular momentum (specifically, with topological charge l = 1 and l = 2). We have designed our source so that it operates within the short SPDC crystal regime for which, the amplitude and phase of the pump may be transferred to a heralded single photon. In order to verify the vortex nature of our heralded single photon, we have shown that the conditional angular spectrum and the transverse intensity at the single-photon level match similar measurements carried out for the pump. In addition, we have shown that when our heralded single photon is diffracted through a triangular aperture, the far-field single-photon transverse intensity exhibits the expected triangular arrangement of intensity lobes associated with the presence of orbital angular momentum.
authors.forename: Verónica
authors.initials: V
authors.lastname: Vicuña-Hernández
authors.forename: Héctor
authors.initials: H
authors.lastname: Cruz-Ramírez
authors.forename: Roberto
authors.initials: R
authors.lastname: Ramírez-Alarcón
authors.forename: Alfred B
authors.initials: AB
authors.lastname: U'Ren