Atom-photon dressed states are a basic concept of quantum optics. Here, we demonstrate that the non-Hermiticity of an open cavity can be harnessed to form the dressed bound states (DBSs) and identify two types of DBSs, the vacancylike DBS and Friedrich-Wintgen DBS, in a microring resonator operating at a chiral exceptional point. With the analytical DBS conditions, we show that the vacancylike DBS occurs when an atom couples to the standing-wave mode that is a node of the photonic wave function and characterized by null spectral density at cavity resonance. However, the Friedrich-Wintgen DBS can be accessed by continuously tuning the system parameters, such as the atom-photon detuning, and evidenced by a vanishing Rabi peak in the emission spectrum, an unusual feature in the strong-coupling anticrossing. We also demonstrate the quantum-optics applications of the proposed DBSs. Our work exhibits quantum state control through non-Hermiticity of open quantum system and presents a clear physical picture of DBSs at chiral exceptional points, which holds great potential for building high-performance quantum devices for sensing, photon storage, and nonclassical light generation.
Atom-photon dressed states are a basic concept of quantum optics. Here, we demonstrate that the non-Hermiticity of an open cavity can be harnessed to form the dressed bound states (DBSs) and identify two types of DBSs, the vacancylike DBS and Friedrich-Wintgen DBS, in a microring resonator operating at a chiral exceptional point. With the analytical DBS conditions, we show that the vacancylike DBS occurs when an atom couples to the standing-wave mode that is a node of the photonic wave function and characterized by null spectral density at cavity resonance. However, the Friedrich-Wintgen DBS can be accessed by continuously tuning the system parameters, such as the atom-photon detuning, and evidenced by a vanishing Rabi peak in the emission spectrum, an unusual feature in the strong-coupling anticrossing. We also demonstrate the quantum-optics applications of the proposed DBSs. Our work exhibits quantum state control through non-Hermiticity of open quantum system and presents a clear physical picture of DBSs at chiral exceptional points, which holds great potential for building high-performance quantum devices for sensing, photon storage, and nonclassical light generation.
We investigate the dressed bound states (DBS) 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 the DBS, which consists of the vacancy-like DBS and Friedrich-Wintgen DBS. By deriving analytical conditions for these DBS, 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 vacancy-like DBS occur, which are characterized by null spectral density at cavity resonance. Conversely, Friedrich-Wintgen DBS can be realized by continuously adjusting system parameters and 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 DBS for both zero and non-zero accumulated phase factors. For zero accumulated phase factors, the non-Markovian regime exhibits higher peak values and longer relaxation times for vacancy-like DBS compared to the Markovian regime, where the Friedrich-Wintgen DBS are absent in the non-Markovian case. Finally, we establish the correspondence between the energy spectrum and bound state conditions for non-zero 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.
An open quantum system operated at the spectral singularities where dimensionality reduces, known as exceptional points (EPs), demonstrates distinguishing behavior from the Hermitian counterpart. Here, we present an analytical description of local density of states (LDOS) for microcavity featuring chiral EPs, and unveil the anomalous spontaneous emission dynamics from a quantum emitter (QE) due to the non-Lorentzian response of EPs. Specifically, we reveal that a squared Lorentzian term of LDOS contributed by chiral EPs can destructively interfere with the linear Lorentzian profile, resulting in the null Purcell enhancement to a QE with special transition frequency, which we call EP induced transparency. While for the case of constructive interference, the squared Lorentzian term can narrow the linewidth of Rabi splitting even below that of bare components, and thus significantly suppresses the decay of Rabi oscillation. Interestingly, we further find that an open microcavity with chiral EPs supports atom-photon bound states for population trapping and decay suppression in long-time dynamics. As applications, we demonstrate the advantages of microcavity operated at chiral EPs in achieving high-fidelity entanglement generation and high-efficiency single-photon generation. Our work unveils the exotic cavity quantum electrodynamics unique to chiral EPs, which opens the door for controlling light-matter interaction at the quantum level through non-Hermiticity, and holds great potential in building high-performance quantum-optics devices.
Exceptional points (EPs) are the non-Hermitian singularities in the parameters space of open physical systems, where the eigenenergies and associated eigenstates coalesce. EPs have demonstrated great ability of manipulating eigenstates in classical systems, but the effects and applications of EPs in quantum domain remain largely unexplored. Here we show that EPs can significantly enhance the quantum coherence of atom-cavity interaction in an extended configuration of microcavity featuring chiral EPs, where the introduction of an auxiliary lossy cavity offers multiple new degrees of freedom to tailor the photonic density of states (PhDOS) of the cavities. We find from PhDOS that the proposed model can simultaneously reduce the effective linewidth of cavities and enhance the effective coupling strength of atom-cavity interaction by over one order of magnitude, leading to the prominent Rabi oscillations and improved lifetime of dressed states even the total system dissipation is increased. Our proposal thus holds great promise for building highperformance quantum devices without demanding requirement of strong atom-cavity interaction and enriches the understanding of EPs in manipulating quantum states.
Multimode cavity optomechanical systems allow light to couple otherwise non-interacting mechanical resonators, enabling non-Hermitian phenomena such as exceptional points, where eigenfrequencies and eigenvectors of coupled modes coalesce. Accessing an exceptional point and its nearby parameter space is a first step towards chiral mode dynamics and topological state transfer. Diamond optomechanical devices support strong coherent optomechanical coupling required to tune resonances to an exceptional point, as well as strain-coupling to spin-defects for hybrid quantum technologies, but have not yet been used for multimode non-Hermitian physics. Here we tune to an exceptional point in a diamond optomechanical crystal, which uses structural symmetry breaking to produce two high-frequency mechanical resonances coupled to an optical cavity. The exceptional point is reached within a stable operating window below the phonon-lasing threshold, and we observe asymmetric redistribution of optomechanical damping and anti-damping between hybridized modes. These results establish diamond optomechanical crystals as a platform for non-Hermitian optomechanics, opening routes to topological mechanical dynamics in hybrid spin-phonon interfaces.
We present a proposal to control and improve the nonclassicality of photons in a single-atom cavity-QED system with a strong coupling strength, where the atom is directly driven by external fields. Exploring the eigenvalues and the corresponding eigenstates of the system, we show that the dressed states can be optically manipulated by changing the control field intensity. In particular, tuning the control field frequency to be resonant with the one-photon excitation state, we show that the nonclassicality of cavity photons arising from the two-photon blockade can be actively controlled. We also show that there exists a magic control field Rabi frequency at which the two-photon blockade phenomenon can be significantly improved. The work presented here provides an optical method to control the statistical features of the cavity field that could find utility in nonclassical light generation, photon gateway operation, and exotic quantum-state generation.
Open photonic systems provide a versatile platform for non-Hermitian physics, enabling control over complex spectra, transport, and light-matter interactions. Exceptional points (EPs), at which eigenvalues and eigenvectors coalesce and the governing operator becomes defective, play a central role because they combine branch-point spectral topology, nonanalytic perturbative response, and controllable eigenstate conversion. This Review provides a unified framework for EP photonics by systematically distinguishing exceptional degeneracies according to the underlying operator, spectral variable, boundary conditions, and experimentally accessible observables. We discuss Hamiltonian EPs, absorbing EPs associated with scattering zeros, real-frequency scattering-matrix and Jones-matrix EPs, Bloch and Floquet EPs, and Liouvillian EPs in open quantum systems. We review their spectral topology, static and dynamical encircling, higher-order exceptional structures, and coexistence with bound states in the continuum, together with applications in sensing, lasing, coherent absorption, directional scattering, polarization and wavefront control, nonlinear optics, optical storage, nonreciprocal photonics, and quantum photonics. We also critically assess the current limitations, practical challenges, and future perspectives of EP-based photonic technologies, with particular attention to robustness, noise, scalability, and experimentally measurable performance.