High-dimensional maximally entangled photon pairs in parametric down-conversion

TL;DR

This paper presents a method to generate high-dimensional maximally entangled photon pairs using parametric down-conversion by controlling the pump beam and crystal properties, enabling direct creation of MES in specific OAM subspaces.

Contribution

It introduces a novel approach to produce high-dimensional MES without spatial filtering by manipulating pump and crystal parameters.

Findings

Successfully generated maximally entangled qutrits and ququints.

Demonstrated control over high-dimensional entanglement in OAM modes.

Enhanced potential for quantum communication protocols.

Abstract

Photon pairs generated from spontaneous parametric down-conversion are a well-established method to realize entangled bipartite photonic systems. Laguerre-Gaussian modes, which carry orbital angular momentum (OAM), are commonly exploited to engineer high-dimensional entangled quantum states. %experimentally. For Hilbert spaces with dimension d>2, maximally entangled states (MESs) help to improve the capacity and security of quantum communication protocols, among several other promising features. However, the direct generation of MES in well-defined high-dimensional subspaces of the infinite OAM basis has remained a challenge. Here, we formalize how the spatial distribution of the pump beam and the nonlinear profile of the crystal can be simultaneously utilized to generate MES without additional spatial filtering of OAM modes within a subspace. We illustrate our approach with maximally entangled qutrits (d=3) and ququints (d=5).