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arXiv:2309.16566

Influence of correlations in active medium on pump-induced exceptional points and strong coupling

I. S. Pashkevich, Iliya V. Doronin, A. A. Zyablovsky, E. S. Andrianov

Published Sep 28, 2023• 0 citations
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Abstract

Exceptional points show great prospects for applications such as imaging, sensing and designing lasers. Recently, systems with amplifying active medium exhibiting pump-induced exceptional points have attracted much attention due to possibility of controlling strong coupling between light and matter with the aid of pumping. In such structures, the interaction of active molecules with external degrees of freedom, such as phonons or impurities, leads to the destruction of the correlation between polarizations of different molecules. We study the effect of the correlations decay on a system behavior near pump-induced exceptional point. We show that strong coupling persists and eigenvectors together with eigenfrequencies coalesce at a negative value of population inversion, regardless of correlation decay magnitude. Thus, we show that exceptional points are robust to correlation decay, which is crucial for designing systems with exceptional points.

DOI
10.48550/arxiv.2309.16566

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Exceptional points show great prospects for applications such as imaging, sensing and designing lasers. Recently, systems with amplifying active medium exhibiting pump-induced exceptional points have attracted much attention due to possibility of controlling strong coupling between light and matter with the aid of pumping. In such structures, the interaction of active molecules with external degrees of freedom, such as phonons or impurities, leads to the destruction of the correlation between polarizations of different molecules. We study the effect of the correlations decay on a system behavior near pump-induced exceptional point. We show that strong coupling persists and eigenvectors together with eigenfrequencies coalesce at a negative value of population inversion, regardless of correlation decay magnitude. Thus, we show that exceptional points are robust to correlation decay, which is crucial for designing systems with exceptional points.
Exceptional points show great prospects for applications such as imaging, sensing, and designing lasers. Recently, systems with amplifying active medium exhibiting pump-induced exceptional points have attracted much attention due to the possibility of controlling the strong coupling between light and matter with the aid of pumping. In such structures, the interaction of the active molecules with external degrees of freedom, such as phonons or impurities, leads to the destruction of the correlations between the polarizations of different molecules. We study the effect of the correlation decay on system behavior near a pump-induced exceptional point. We show that exceptional points and strong coupling are robust to correlation decay and disappear only at very high rates of correlation decay, much larger than other relaxation rates. The obtained result is crucial for designing systems with exceptional points and strong coupling.
We propose an approach to obtain lasing without inversion, which does not require preparation of the quantum superposition of states in the active medium. We demonstrate that with periodically variable pumping, lasing is achievable even in the case when the population inversion of the active medium is always negative. This is possible due to the fact that laser in strong-coupling regime is a non-Hermitian system with an exceptional point existing at negative value of population inversion. We show that due to nonorthogonality of eigenstates near the exceptional point, the time variation of pump power can result in parametric instability in the laser and excitation of the electromagnetic field self-oscillations. These oscillations take place even when the population inversion of the active medium is always negative. Our results help to pave the way for the creation of a new class of lasers operating at negative value of population inversion.
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.
Understanding how strong correlations and dissipation combine to shape collective quantum excitations is a central challenge in many-body physics. We investigate the effect of dissipative light-matter coupling on strongly interacting exciton-polaritons in the presence of a biexciton resonance, which gives rise to polaron-polariton quasiparticles. We show that the interplay between many-body correlations and non-Hermitian coupling generates anomalous dispersion relations and exceptional points in the polaron-polariton spectrum. The location and coexistence of exceptional points are controlled by the dissipative coupling and the relative decay rates of the excitonic and photonic constituents, allowing them to emerge across different polaron-polariton branches. These results identify dissipative polaron-polaritons as a versatile platform for exploring non-Hermitian many-body physics with tunable light-matter quasiparticles.
Exceptional points (EPs) represent non-Hermitian degeneracies where eigenvalues and eigenvectors coalesce, giving rise to enhanced sensitivity and critically damped dynamics. We demonstrate that when an EP coincides with a dissipative phase transition in an extended open Dicke model of two cavities coupled to a collective spin, the critical fluctuations are strongly amplified and governed by modified critical exponents. Numerical results reveal enhanced critical scaling in both the normal and superradiant phases, in agreement with an analytical theory based on the Jordan-block structure of the linearized dynamical matrix at the EP. Our results establish EPs as a mechanism to engineer critical scaling in open quantum systems, with potential applications to critical quantum sensing.
We report on a new mechanism for electromagnetically induced transparency and opacity, which relies on the coalescence of two metastable states at an exceptional point (EP). By using two fields, a `pump,' which forms an EP, and a `probe,' which couples the EP-state to a third level, we show that small changes in the pump parameters lead to dramatic changes in the absorption of the probe; a sharp enhancement or complete inhibition. While most (if not all) of the effects associated with EPs were observed, so far, only in optics and microwave experiments, this work presents a feasible approach for measuring EP effects in atomic systems. We demonstrate these predictions for helium.