Increasing the dimension in high-dimensional two-photon orbital angular momentum entanglement

TL;DR

This paper demonstrates how tuning phase-matching conditions in SPDC can significantly increase the measurable dimensionality of two-photon orbital angular momentum entanglement, reaching approximately 50 dimensions.

Contribution

It introduces a method to maximize the number of entangled OAM modes by adjusting phase-matching, achieving higher-dimensional entanglement in practical experiments.

Findings

Half-width of OAM-correlation spectrum increased from 10 to 20.

Achieved approximately 50-dimensional entanglement.

Measured high concurrence values indicating strong bipartite entanglement.

Abstract

Any practical experiment utilising the innate D-dimensional entanglement of the orbital angular momentum (OAM) state space of photons is subject to the modal capacity of the detection system. We show that given such a constraint, the number of measured, entangled OAM modes in photon pairs generated by spontaneous parametric down-conversion (SPDC) can be maximised by tuning the phase-matching conditions in the SPDC process. We demonstrate a factor of 2 increase on the half-width of the OAM-correlation spectrum, from 10 to 20, the latter implying \approx 50 -dimensional two-photon OAM entanglement. Exploiting correlations in the conjugate variable, angular position, we measure concurrence values 0.96 and 0.90 for two phase-matching conditions, indicating bipartite, D-dimensional entanglement where D is tuneable.