Quantum interference enhancement and fluorescence spectral linewidth narrowing of a four-level system via dielectric Mie resonances

Quantum interference (QI) among different spontaneous decay channels has led to many important quantum optics applications. This effect can be strongly enhanced in an anisotropic quantum vacuum (AQV) provided by photonic nanostructures, which is promising to apply in integrated photonic quantum technologies. However, the QI effect in a dielectric Mie resonance system with a large AQV has not been studied. Here, we investigate the QI enhancement and fluorescence spectral linewidth narrowing of a four-level system with a high-index dielectric nanosphere. We find that the nearly maximum QI can be obtained due to the extreme AQV under Mie resonances. We also show that the degree of QI varies in a wide range when selecting different Mie resonances and the emitter's position. We further illustrate the subnatural-linewidth narrowing of the fluorescence spectra in the Mie resonance system, which results from large QI and a relatively small Purcell factor. These findings not only provide a scheme for quantum coherence manipulation, but also have potential applications in integrated quantum photonic devices.