Quantum Emitter Enhancement via Resonant Multipolar Metasurfaces on Lithium Niobate

Lithium niobate LiNbO₃ has emerged as a promising material platform for metasurfaces due to its strong nonlinear susceptibility, wide transparency window, and excellent optical quality. In this work, we design and analyze resonant multipolar metasurfaces based on thin-film LiNbO₃, demonstrating their ability to support high-Q quasi–bound states in the continuum and extreme near-field confinement. By tailoring the geometry of the nanoantennas and the array periodicity, we achieve strong electric and magnetic multipolar coupling that governs the scattering characteristics and facilitates the enhanced light–matter interaction. We further show that these resonant conditions significantly amplify the spontaneous emission rate of nearby quantum emitters through pronounced Purcell enhancement in regions of strong field localization. The interplay between multipolar resonances and material nonlinearity also enables efficient frequency conversion and dual-wavelength field enhancement. Through numerical modeling and mode analysis, we establish a connection between spatial field distributions, multipolar contributions, and macroscopic emission properties. These results indicate that LiNbO₃ metasurfaces are a versatile platform for controlling quantum emission and nonlinear optical processes in compact, high-performance photonic systems.