Classical to quantum transfer of optical vortices

TL;DR

This paper demonstrates the transfer of an optical vortex beam's phase and amplitude to a heralded single photon using SPDC with a Bessel-Gauss pump, confirming the vortex nature at the single-photon level.

Contribution

It introduces a method to transfer classical optical vortex properties to single photons via SPDC with a Bessel-Gauss pump, enabling quantum vortex state generation.

Findings

Heralded single photons exhibit vortex phase structure.

The single-photon transverse intensity matches the pump's vortex pattern.

Far-field diffraction shows expected vortex-related intensity lobes.

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 singlephoton transverse intensity exhibits the expected triangular arrangement of intensity lobes associated with the presence of orbital angular momentum.