Polarization-entangled photon pair generation from an epsilon-near-zero metasurface

TL;DR

This paper presents a nanoscale, engineered metasurface platform that efficiently generates polarization-entangled photon pairs and allows direct control over their quantum states, simplifying quantum photonic device design.

Contribution

It introduces a novel ENZ metasurface platform that enhances photon pair generation and enables direct polarization entanglement control without extra components.

Findings

Significantly boosted photon pair generation efficiency.

Direct generation of polarization-entangled Bell states.

Versatile manipulation of nonlinear susceptibility tensor.

Abstract

Polarization-entangled photon pair sources are essential for diverse quantum technologies, such as quantum communication, computation, and imaging. However, the generation of complex polarization-entangled quantum states has long been constrained by the available nonlinear susceptibility tensor of natural nonlinear crystals, necessitating a cumbersome and intricate setup for additional coherent superposition or post-selection. In this study, we introduce and experimentally demonstrate a nanoscale polarization-entangled photon pair source utilizing an artificially-engineered metamaterial platform. This platform is based on a plasmonic metasurface that is strongly coupled to an epsilon-near-zero (ENZ) material. By precisely engineering resonances at both pump and signal/idler wavelengths, and leveraging the field enhancement provided by the ENZ effect, the photon pair generation efficiency of the 68-nm-thick metasurface is significantly boosted. More notably, the ENZ metasurface platform facilitates versatile manipulation of the system's anisotropic second-order nonlinear susceptibility tensor, enabling direct control over the polarization states of the photon pairs, which leads to the generation of a polarization-entangled Bell state without the need for additional components. Our approach opens a new avenue for the simultaneous photon pair generation and quantum state engineering in a compact platform.