Strong Superradiance of Coherently Coupled Magnetic Dipole Emitters Mediated by Whispering Gallery Modes of a Subwavelength All-Dielectric Cavity

The interaction of magnetic dipole (MD) emitters and common photonic cavities is usually weak, which is partially due to the low magnetic near field enhancements of the cavities. Here, we show that whispering gallery modes (WGMs) of a subwavelength dielectric cavity can not only greatly boost the emission rate of a MD emitter but also bring efficient couplings between coherent MD emitters. In a WGM cavity, the maximal emission rate ({\gamma}max) of a single emitter occurs at an antinode of the field pattern. The emission of the MD emitter can also be greatly affected by another coherent one depending on the magnetic field response of the WGM. The maximal contribution can also reach {\gamma}max. Notably, the cooperative emission rate of the coherent MD emitters does not decay with distance in the considered range due to the high-quality feature of a WGM. In contrast to the emission, the absorption of an emitter is hardly affected by the coherent couplings between emitters mediated by a WGM. The difference between the performances of emission and absorption is highly related to the excitation behaviors of WGMs. Our results are important for enhanced magnetic light-matter interactions.