Quantum Pair Generation in Nonlinear Metasurfaces with Mixed and Pure Photon Polarizations

TL;DR

This paper demonstrates polarization control of biphotons generated via SPDC in GaAs metasurfaces using qBIC resonances, enabling tailored quantum light with potential for quantum technology applications.

Contribution

It introduces polarization engineering of non-classical light in nonlinear metasurfaces by leveraging qBIC resonances and metasurface symmetry, advancing quantum light source development.

Findings

Polarization of emitted biphotons reflects qBIC mode properties

Control over single-photon polarization states achieved

Two-photon polarization states are nearly separable

Abstract

Metasurfaces are highly effective at manipulating classical light in the linear regime; however, effectively controlling the polarization of non-classical light generated from nonlinear resonant metasurfaces remains a challenge. Here, we present a solution by achieving polarization engineering of frequency-nondegenerate biphotons emitted via spontaneous parametric down-conversion (SPDC) in GaAs metasurfaces, where quasi-bound states in the continuum (qBIC) resonances were utilized for boosting the biphoton generation. By performing a comprehensive polarization tomography, we demonstrate that the polarization of the emitted photons directly reflects the qBIC mode's far-field properties. Furthermore, we show that both the type of qBIC mode and the symmetry of the meta-atoms can be tailored to control each single-photon polarization state, and that the subsequent two-photon polarization states are nearly separable, offering potential applications in the heralded generation of single photons with adjustable polarization. This work provides a significant step towards utilizing metasurfaces to not only generate quantum light but also engineer their polarization, a critical aspect for future quantum technologies.