High Purity OAM Entangled Photons from SPDC with Reduced Spatial Spectral Correlations

TL;DR

This paper analyzes and optimizes SPDC sources to produce high-purity entangled photons with minimal spatial spectral correlations, enhancing high-dimensional quantum information applications.

Contribution

It identifies source configurations that significantly reduce spatial spectral correlations, enabling high-purity OAM entangled photon generation without filtering.

Findings

High-purity OAM entangled photons are achievable with optimized source parameters.

Spatial spectral coupling degrades OAM purity, but can be minimized through specific configurations.

Design parameters enable scalable, high-dimensional quantum photonic technologies.

Abstract

Entanglement generated by Spontaneous Parametric Down Conversion (SPDC) involves multiple, often mutually correlated degrees of freedom. These degrees of freedom are often treated independently, overlooking the intrinsic correlation between them. We focus on the spatial spectral correlations that, if left uncontrolled, introduce distinguishability and reduce coherence, undermining applications such as high-dimensional OAM encoding. We analyze the spatio spectral structure of the biphoton and identify source configurations enabling a strong reduction of such correlations. We then quantify how spatial spectral coupling degrades OAM spatial purity, mapping high-purity regions as functions of OAM order, crystal length, and pump/collection waists. The resulting design parameters enable engineering bright, high purity OAM entangled sources, reducing the need for loss-introducing filtering and therefore supporting scalable high-dimensional photonic quantum technologies.