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SPIE Conference on Nonlinear Optics and its Applications

Biphoton Polarization Bell states from an InGaP nonlinear metasurface

Jinyong Ma, Tongmiao Fan, Tuomas Haggrén, Jihua Zhang, Hark Hoe Tan, C. Jagadish, Dragomir N. Neshev, Andrey A. Sukhorukov

Published Jun 20, 2024• 0 citations
Publisher

Abstract

We develop an ultrathin source of two-photon polarization Bell states based on an InGaP nonlinear metasurface. The metasurface facilitates a local optical resonance with a tailored angular dispersion, enabling the generation of polarization-entangled photon pairs through spontaneous parametric down conversion. This opens new possibilities for practical applications of integrated metasurfaces in advanced quantum technologies.

DOI
10.1117/12.3022368

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We develop an ultrathin source of two-photon polarization Bell states based on an InGaP nonlinear metasurface. The metasurface facilitates a local optical resonance with a tailored angular dispersion, enabling the generation of polarization-entangled photon pairs through spontaneous parametric down conversion. This opens new possibilities for practical applications of integrated metasurfaces in advanced quantum technologies.
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Tunable biphoton quantum entanglement generated from nonlinear flat optics is highly desirable for cutting-edge quantum technologies, yet its tunability is substantially constrained by the symmetry of material nonlinear tensors. Here, we overcome this constraint by introducing symmetry breaking in nonlinear polarization via resonant metasurfaces. While asymmetric optical responses have enabled breakthroughs in classical applications like nonreciprocal light transmission, we report the experimental demonstration of asymmetric nonlinear responses for biphoton entanglement. Using a structural-asymmetric semiconductor metasurface incorporating [110] InGaP nanoresonators, we realize continuous tuning of polarization entanglement from partially entangled states to a Bell state by adjusting the pump wavelength. We also observe pronounced spatial anti-correlations and theoretically confirm that this approach can extend to tailor hyperentanglement. Furthermore, our nanoscale entanglement source features an ultrahigh coincidence-to-accidental ratio of ≈7 × 10 4 , outperforming existing semiconductor flat optics by two orders of magnitude. Introducing asymmetric nonlinear response in quantum metasurfaces opens directions for tailoring on-demand quantum states.
Abstract Polarization Bell states are essential resources for various quantum technologies. The most common approach for generating polarization Bell states is through the spontaneous parametric down‐conversion (SPDC) in nonlinear crystals, or more recently, in ultrathin nonlinear metasurfaces. However, both platforms typically require multiplexing two SPDC processes, each producing one of the two orthogonal polarization states whose superposition results in the Bell states. Here, a Bell state source is proposed from a nonlinear metasurface by integrating a 2D and symmetrical SiO 2 nano‐grating on a LiNbO 3 film. This metasurface supports multiple high‐Q guided mode resonances and enables enhanced generation of polarization Bell states without the need of multiplexing. Furthermore, the same metasurface enables switchable generation of two distinct Bell states with high fidelity simply by switching the pump wavelength‐a capability not achievable with conventional crystal sources. This work paves an effective way toward ultrathin, multifunctional entangled photon sources, which are essential for the development of miniaturized, scalable quantum photonic systems.
Polarization-entangled photon pairs are essential resources for quantum information technologies, yet realizing compact sources with intrinsically controllable entanglement remains challenging. Van der Waals (vdW) nonlinear materials such as NbOCl2 provide atomically thin platforms for quantum light generation, yet their native crystalline anisotropies as natural materials impose limitations on accessible quantum states. Here, we develop a resonant vdW nonlinear metasurface based on NbOCl2 that exploits its intrinsic optical anisotropy to engineer polarization-dependent nonlinear responses. The anisotropic optical dispersion enables selective manipulation of resonant modes, resulting in a three-order-of-magnitude enhancement of the nonlinear response along the c axis. By further tailoring these resonant modes, we redistribute the effective second-order nonlinear susceptibility tensor between orthogonal polarization channels, balancing the spontaneous parametric down-conversion pathways along the b and c axes. This enables polarization-entangled photon generation with a measured fidelity of up to 92%. Our work establishes metasurface-enabled nonlinear optical engineering as a strategy for enhancing and controlling quantum light generation in vdW materials, providing a pathway toward scalable quantum photonic platforms.