Multipartite spatial entanglement generated by concurrent nonlinear processes

TL;DR

This paper explores the generation of multipartite spatial entanglement in light beams using various nonlinear optical sources, analyzing the nature of the entangled states with multiple inseparability criteria.

Contribution

It introduces a unified framework to generate and test multipartite entanglement from concurrent nonlinear processes in different photonic media.

Findings

Successful generation of non-standard 3 and 4-mode couplings

Validation of genuine multipartite entanglement using multiple criteria

Comparison of inseparability tests for complex entangled states

Abstract

Continuous variables multipartite entanglement is a key resource for quantum technologies. This works considers the multipartite entanglement generated in separated spatial modes of the same light beam by three different parametric sources: a standard $\chi^{(2)}$ medium pumped by two pumps, a single-pump nonlinear photonic crystal, and a doubly pumped nonlinear photonic crystal. These sources have in common the coexistence of several concurrent nonlinear processes in the same medium, which allows the generation of non-standard 3 and 4-mode couplings. We test the genuine nature of the multipartite entangled states thereby generated in a common framework, using both criteria based on proper bounds for the variances of nonlocal observables and on the positive partial transpose criterion. The relative simplicity of these states allows a (hopefully) useful comparison of the different inseparability tests.