In this study, we investigate non-Hermitian optical bistability in Sm3+:BiPO4 under the influence of polarization quantization. Our work focuses on how polarization affects this bistability, especially near exceptional points (EPs) in a non-Hermitian system. We demonstrate two types of optical bistability jumps: two-step one optical bistability jump and three-step two optical bistability jumps resulting from constructive and destructive polarization quantization. One optical bistability jump, without and with a non-Hermitian self-dressing switch, is observed at destructive and constructive polarization quantization near EP region, respectively. Two optical bistability jumps via nested-cascade dressing at horizontal polarization quantization are stronger than three cascaded dressings at circular polarization quantization. In addition, two types of non-Hermitian optical bistability jumps fit the second-order eigenvector intensity splitting theoretical model. Our findings are significant in controlling optical switching in materials used for quantum technologies. Such results have potential applications in quantization phase transitions in non-Hermitian photonic systems and advanced optical devices.
In this study, we investigate non-Hermitian optical bistability in Sm3+:BiPO4 under the influence of polarization quantization. Our work focuses on how polarization affects this bistability, especially near exceptional points (EPs) in a non-Hermitian system. We demonstrate two types of optical bistability jumps: two-step one optical bistability jump and three-step two optical bistability jumps resulting from constructive and destructive polarization quantization. One optical bistability jump, without and with a non-Hermitian self-dressing switch, is observed at destructive and constructive polarization quantization near EP region, respectively. Two optical bistability jumps via nested-cascade dressing at horizontal polarization quantization are stronger than three cascaded dressings at circular polarization quantization. In addition, two types of non-Hermitian optical bistability jumps fit the second-order eigenvector intensity splitting theoretical model. Our findings are significant in controlling optical switching in materials used for quantum technologies. Such results have potential applications in quantization phase transitions in non-Hermitian photonic systems and advanced optical devices.
We report photon-phonon dressing quantization dependency on polarization. Destructive dressing polarization quantization is exhibited in fluorescence (FL) for narrowband signals, while constructive dominant dressing quantization is exhibited in fluorescence (FL) for broadband signals due to phase perturbation. Furthermore, constructive polarization quantization results due to coexistence of generation and dressing effects in strong and competitive Rabi frequency. Low power also contributes to more dressing polarization quantization, the same as in the FL region (large de-phase rate). Furthermore, linear and circular dressing quantization with polarization quantization shows inverse and direct relationships in the FL and spontaneous four-wave-mixing (SFWM) regions, respectively. Such investigations have potential in alignment of crystal field (CF) redistribution by polarization quantization at the input.
We present a comparative study of optical bistability (OB) in three-level atomic configurations, including $\Lambda $-, cascade-, and V- types under the conditions of electromagnetically induced transparency (EIT). In the steady regime, the input-output intensity relations for the OB in each configuration have been derived in analytical form. The model allows one to construct a clear picture on how the threshold intensity, and other characteristics of the OB are continuously modified with respects to controllable parameters of the laser fields, cooperation parameter, and other physical parameters of atomic system. The results showed that the threshold intensity of OB in Λ-type system is much less than the other ones and the threshold intensity of OB in V-type system is the largest one. The analytical result is convenient to choose excitation configuration for experimental observations and related applications in photonic devices.
The exploration of the effect of non-Hermitian (NH) in quantum systems is gaining renewed momentum as a result of the recent progress in experiments. It has been indicated that the ability to engineer the orders of exceptional points (EPs) can be fundamental to its applications in quantum control, such as accelerating entanglement generation; however, an initial survey of the interactions between different orders of EPs is still missing. In this work, we try to partially address this issue by employing a non-reciprocally coupled cavity system which can be experimentally realizable with a two-dimensional reconfigurable NH gauged laser array. With deliberate design, our systems display both second and third orders of EPs. The sign of a novel, purely quantum continuous entanglement phase transition is observed, which reveals how multi-EP interactions alter entanglement dynamics across different regimes while maintaining accelerated generation. Our findings reveil the genuinely quantum NH physics of higher-order EPs, which has opened up a new avenue for future investigations of the higher-order degeneracy application and the dynamic phase transitions of quantum systems.
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.
The Dicke model, which describes the collective interaction between an ensemble of atoms and a single-mode photon field, serves as a fundamental framework for studying light-matter interactions and quantum electrodynamic phenomena. In this work, we investigate the manifestation of non-Hermitian effects in a generalized Dicke model, where two dissipative atom ensembles interact with a single-mode photon field. By applying the Holstein-Primakoff transformation, we explore the system in the semiclassical limit as a non-Hermitian Dicke model, revealing rich exceptional points (EPs) and diabolic points in such a system. We find that, by introducing the nonlinear saturation gain into an atomic ensemble, higher-order EP can be induced, leading to intriguing properties. Furthermore, if the system is extended to a one-dimensional chain, then the band topology will interplay with the non-Hermitian effect. In the quantum regime, we explore the quantum signature of EPs, noting that the conditions for their emergence are influenced by discrete photon numbers. We further study the transition from photon anti-bunching to bunching at a steady state, driven by non-Hermitian dynamics. Our findings deepen the understanding of non-Hermitian physics in light-matter interaction which is instructive for the design of advanced photonic and quantum systems.