Generation of photon pairs through spontaneous four-wave mixing in subwavelength nonlinear films

TL;DR

This paper explores photon pair generation via spontaneous four-wave mixing in ultrathin amorphous silicon nitride films, demonstrating quantum correlations and analyzing material properties for integrated quantum photonics.

Contribution

It is the first to investigate SFWM in subwavelength SiN films, showing quantum correlations and measuring third-order susceptibilities based on nitrogen content.

Findings

Quantum correlations confirmed by g(2)(0) exceeding 2

Photon interference observed between SiN films and silica substrate

Third-order susceptibilities vary with nitrogen content

Abstract

Pairs of entangled photons are crucial for photonic quantum technologies. The demand for integrability and multi-functionality suggests 'flat' platforms - ultrathin layers and metasurfaces - as sources of photon pairs. Despite the success in the demonstration of spontaneous parametric down-conversion (SPDC) from such sources, there are almost no works on spontaneous four-wave mixing (SFWM) - an alternative process to generate photon pairs. Meanwhile, SFWM can be implemented in any nanostructures, including ones made of isotropic materials, which are easier to fabricate than crystalline SPDC sources. Here, we investigate photon pair generation through SFWM in subwavelength films of amorphous silicon nitride (SiN) with varying nitrogen content. For all samples, we demonstrate two-photon quantum correlations, indicated by the normalized second-order correlation function g(2)(0): it exceeds 2 and decays as the pump power increases. By observing two-photon interference between SFWM from the SiN films and the fused silica substrate, we find the third-order susceptibilities of films with different nitrogen content.