High-<i>Q</i>, Size-Independent, and Reconfigurable Optical Antennas Embedded in Zero-Index Cavities

Enhancing light-matter interactions at the nanoscale is foundational to nanophotonics, with epsilon-near-zero (ENZ) materials demonstrating significant potential. High-quality factor (<i>Q</i>) resonances that maximize these interactions are typically realized in photonic crystals requiring sub-50 nm precision nanofabrication over large areas, limiting scalability and increasing complexity. Mie resonances offer an alternative but are constrained by low <i>Q</i>-factors due to the scarcity of high-refractive index materials, necessitating large refractive index changes for effective resonance switching and limiting dynamic reconfigurability. We overcome these limitations by embedding Mie resonators within ENZ media, thereby enhancing <i>Q</i>-factors, mitigating geometric dispersion and fabrication challenges, and maximizing optical reconfigurability. We introduce three resonator-ENZ configurations: voids in AlN, Ge in SiO₂, and intrinsic InSb in doped InSb─spanning from low-loss phononic to lossy plasmonic ENZ modes. Using novel epitaxial regrowth techniques, we achieve significant <i>Q</i>-factor improvements over nonembedded resonators. An air-based Mie resonator embedded in AlN supports resonant <i>Q</i>-factors exceeding 100, with negligible geometric dispersion across sizes from 800 to 2800 nm. Additionally, we demonstrate dynamic reconfigurability of intrinsic InSb resonators by thermally tuning the ENZ wavelength over a 2 μm range in the mid-infrared (11-16 μm) wavelength regime. These results showcase the potential of Mie reonators embedded in ENZ media for high-fidelity sensors, thermal emitters, and reconfigurable metasurfaces, bridging theoretical predictions with practical applications and advancing the development of dynamic, high-<i>Q</i> optical devices.