We investigate dressed bound states in an open cavity with a whispering-gallery-mode microring coupled to a two-level atom and a waveguide with a mirror at the right end. We demonstrate that the non-Hermiticity of an open cavity facilitates the formation of dressed bound states, which consist of vacancylike dressed bound states and Friedrich-Wintgen dressed bound states. By deriving analytical conditions for these dressed bound states, we show that when a two-level atom couples to the standing-wave mode that corresponds to a node of the photonic wave function the vacancylike dressed bound states occur, which are characterized by null spectral density at cavity resonance. Conversely, Friedrich-Wintgen dressed bound states can be realized by continuously adjusting system parameters and are indicated by the disappearance of the Rabi peak in the emission spectrum, which is a distinctive feature in the strong-coupling regime. Moreover, we extend our analysis to the non-Markovian regime and find that our results are consistent with those obtained under the Markovian approximation in the wideband limit. In the non-Markovian regime, we analyze dressed bound states for both zero and nonzero accumulated phase factors. For zero accumulated phase factors, the non-Markovian regime exhibits higher peak values and longer relaxation times for vacancylike dressed bound states compared to the Markovian regime, where the Friedrich-Wintgen dressed bound states are absent in the non-Markovian case. Finally, we establish the correspondence between the energy spectrum and bound-state conditions for nonzero accumulated phase factors and analyze the influence of various parameters on non-Markovian bound states. Our work exhibits bound-state manipulations through non-Markovian open quantum system, which holds great potential for building high-performance quantum devices for applications such as sensing, photon storage, and nonclassical light generation.

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• Photonics
• Quantum optics