Conservation of Angular Momentum on a Single-Photon Level
Lea Kopf, Rafael Barros, Shashi Prabhakar, Enno Giese, Robert Fickler
Abstract
Identifying conservation laws is central to every subfield of physics, as they illuminate the underlying symmetries and fundamental principles. A prime example can be found in quantum optics: the conservation of orbital angular momentum (OAM) during spontaneous parametric down-conversion (SPDC) enables the generation of a photon pair with entangled OAM. In this Letter, we report on the observation of OAM conservation in SPDC pumped on the single-photon level by a preceding SPDC process. We implement this cascaded down-conversion scheme in free space, without waveguide confinement, and thereby set the stage for experiments on the direct generation of multiphoton high-dimensional entanglement using all degrees of freedom of light.