Azimuthal distinguishability of entangled photons generated in spontaneous parametric down-conversion

TL;DR

This paper experimentally shows that photons generated in different parts of a down-conversion cone exhibit distinct spatial correlations and entanglement levels due to Poynting vector walk-off, impacting quantum source design.

Contribution

It provides the first experimental demonstration of azimuthal distinguishability in entangled photons from SPDC and discusses its implications for quantum source engineering.

Findings

Photons from different cone sections have varying spatial entanglement.

Poynting vector walk-off affects the spatial correlations of generated photons.

Azimuthal distinguishability influences quantum source design for entanglement in other degrees of freedom.

Abstract

We experimentally demonstrate that paired photons generated in different sections of a down-conversion cone, when some of the interacting waves show Poynting vector walk-off, carry different spatial correlations, and therefore a different degree of spatial entanglement. This is shown to be in agreement with theoretical results. We also discuss how this azimuthal distinguishing information of the down-conversion cone is relevant for the implementation of quantum sources aimed at the generation of entanglement in other degrees of freedom, such as polarization.