Full-field mapping of spatially varying polarization entanglement generated from spontaneous parametric down-conversion

TL;DR

This paper provides a comprehensive spatial map of polarization entanglement in SPDC-generated two-photon states, revealing complex spatial-polarization couplings and high-dimensional entanglement potential for advanced quantum applications.

Contribution

It offers the first full-field spatial mapping of polarization entanglement in SPDC, uncovering rich coupling structures and high-dimensional entanglement capabilities.

Findings

Average concurrence of 0.8303 indicating near-maximal entanglement

Spatial dimensionality certified at 148, suggesting 251-dimensional hyperentanglement

Radially and linearly varying polarization states dependent on photon transverse momenta

Abstract

Two-photon states generated from spontaneous parametric down-conversion (SPDC) can display entanglement in all degrees of freedom (DoFs) of light, including spatial, temporal, and polarization. The coupling between different DoFs of a two-photon state has been shown to display rich structures that enable novel and robust information processing schemes. While existing literature has studied these couplings by post-selecting the SPDC field, a comprehensive understanding of the inherent spatial-polarization coupling produced in the SPDC process is still lacking. This work produces a full spatial map of the polarization entanglement generated across the entire SPDC field. We observe an entire class of near-maximally polarization-entangled states with an average concurrence of $0.8303\pm0.0004$, which, together with a certified spatial dimensionality of 148, could potentially offer access to a 251-dimensional hyperentanglement. The spatial-polarization coupling manifests as radially or linearly varying polarization-entangled states, whose wavefunctions are dependent on the transverse momenta of the down-converted photons and the pump beam, respectively. Our study lays important groundwork for further exploiting the coupling between entanglement in different DoFs for future quantum technologies.