Strong Coupling of Molecular Excitons with QBIC and Anapole Dark States in a Single Metasurface Platform

Abstract Strong coupling between molecular vibrations and optical cavities provides an important platform for manipulating mid-infrared light-matter interactions. Strong coupling between PMMA molecular vibrations and both dielectric quasi-bound states in the continuum (QBIC) cavities and plasmonic systems has been widely investigated; however, the achievable coupling strength remains limited by field confinement capability and radiative losses. In this letter, we realize strong coupling between an Anapole state supported by a metallic metasurface and the C═O vibrational mode of PMMA, with a Rabi splitting reaching 22.2 meV. By further introducing a QBIC, we enable the coexistence of two dark resonances on the same platform. Under identical excitonic volumes, the Anapole state consistently exhibits a larger coupling strength than the QBIC, with Rabi splittings exceeding 20 meV. In contrast, the QBIC displays a longer population oscillation decay time in time-domain quantum dynamics. Combined with near-field field-distribution analysis and quantum dynamical calculations, our results reveal intrinsic differences between distinct dark states in their coupling rates and coherence preservation capabilities.