Quantum control of vortex beams using metasurfaces

Metasurfaces are very useful to control and hybridize different degrees of freedom of light on a single interface composed of nanostructures, heading to many applications including multi-functional lenses, light-field imaging and holograms in classical optics. More recently, tremendous efforts have been made on pushing the operations of metasurfaces to the quantum optical regime. Here, we provide and experimentally demonstrate a scheme to remotely control the vortex beam structure using polarization-entangled photon pairs together with a metasurface. By adopting a heralding technique, the spin-orbit coupling provided by the metasurface directly translates to a tailor-made entanglement of the orbital angular momentum with the polarization degree of freedom in the signal arm. Then, the polarization of the heralding photon at the other end is used to remotely control the vortex structure of the signal photon, directly manifested as an orbital rotation. We further demonstrate that such heralding control can be continuous, going beyond the conventional switching applications using heralding photons. The investigations point to a versatile metasurface platform for quantum communication and information processing.