Extrinsic orbital angular momentum of entangled photon-pairs in spontaneous parametric down-conversion

TL;DR

This paper theoretically demonstrates that entangled photon pairs generated via spontaneous parametric down-conversion can carry significant extrinsic orbital angular momentum due to spatial symmetry breaking, which is not detectable by traditional methods.

Contribution

It reveals the presence of extrinsic orbital angular momentum in entangled photon pairs and highlights the need for new measurement techniques.

Findings

Photon pairs carry non-negligible extrinsic orbital angular momentum

Traditional detection schemes cannot measure this extrinsic orbital angular momentum

Spatial symmetry breaking causes the orbital angular momentum in these systems

Abstract

Starting from the standard Hamiltonian describing the optical non-linear process of spontaneous parametric down-conversion, we theoretically show that the generated entangled photon-pairs carry non-negligible orbital angular momentum in the degrees of freedom of relative movement in the type-II cases due to spatial symmetry breaking. We also show that the orbital angular momentum carried by photon-pairs in these degrees of freedom escapes detection in the traditional measurement scheme, which demands development of new techniques for further experimental investigations.