Enhanced quantum coherence of plasmonic resonances with a chiral exceptional points

While strategies to enhance the quantum coherence of plasmonic resonances have attracted a lot of attention in the past, the advent of non-Hermitian optics carries promising possibilities in this direction, mostly of which are still unexplored. In this work, we show that the quantum coherence of plasmonic resonances can be enhanced by integrating a plasmonic antenna in a photonic cavity operated at a chiral exceptional point (CEP), where the phase of light offers an additional degree of freedom for flexibly manipulating the quantum dynamics. The few-mode quantization theory is employed to demonstrate the advantages and related quantum-optics applications of the proposed hybrid cavity in both off- and on-resonance plasmon-photon coupling. For the former case, the local density of states evolves into sub-Lorentzian lineshape, resulting in reduced dissipation of polaritonic states. On resonance, we identify two mechanisms improving the quantum yield by two orders of magnitude at room temperature: the reduction of plasmonic absorption through Fano interference and the enhancement of cavity radiation through superscattering. Our results establish CEP-engineered plasmonic resonances as a promising platform for controlling quantum states and building high-performance quantum devices.