Large Rabi Splitting Driven by Plasmon-Enhanced Hybrid Anapole States in Si-Au-WSe₂ Heterostructures

Exciton-polaritons arising from strong light-matter coupling are key enablers of quantum coherent phenomena, whereas large Rabi splitting is critical for ensuring their robustness and stability. However, existing microcavity photonic modes rarely combine low radiative dissipation with strong field confinement, thereby limiting large splitting strong coupling, particularly in the few-exciton regime. Here, we design a metal-dielectric hybrid cavity in which coherent hybridization among plasmon resonances, magnetic quadrupole modes, and anapole states gives rise to a plasmon-enhanced hybrid anapole state (HAS) featuring narrow linewidths (54 meV) and strong field localization (180-fold). Based on the plasmon-enhanced HAS, we realize both HAS-exciton and HAS-plasmon polaritons and further demonstrate HAS-plasmon-exciton triplex polaritons enabled by multichannel radiative coupling. The ternary system achieves a Rabi splitting of 330 meV, six times larger than the binary case, with a reduced effective exciton number of 6205 based on a characteristic excitonic volume, significantly lower than values reported for the dielectric-exciton systems under the same volume-based estimation procedure. A three-coupled oscillator model elucidates the light-matter interaction mechanism, providing a new pathway to efficient room-temperature strong coupling and a design guide for high-performance dielectric-cavity-based polariton devices.