Transition from Lorentz to Fano Spectral Line Shapes in Nonrelativistic Quantum Electrodynamics

Abstract

Spectroscopic signatures associated with symmetric Lorentzian and asymmetric Fano line shapes are ubiquitous. Distinct features of Fano resonances in contrast with conventional symmetric resonances have found several applications in photonics such as optical switching, sensing, lasing, and nonlinear and slow-light devices. It is therefore important to effectively generate and control these resonances. In this work, we show through ab initio simulations of coupled light−matter systems that Fano interference phenomena can be realized in a multimode photonic environment by strong coupling to the electromagnetic continuum. Specifically, we show that by effectively enhancing the light−matter coupling strength to the photon continuum in an experimentally feasible way, we can achieve a transition from Lorentzian to Fano lines shapes for both electronic and polaritonic excitations. An important outcome of switching between these spectral signatures is the possibility to control the Purcell enhancement of spontaneous emission alongside electromagnetically induced transparency, which is a special case of Fano resonances. Switching from Fano back to a Lorentzian profile can be achieved by physically reducing the coupling strength to the continuum of modes. Our results hold potential for realizing tunable Fano resonances of molecules and materials interacting with the electromagnetic continuum within multimode photonic environments.

Tunable Nonlinearity and Efficient Harmonic Generation from a Strongly Coupled Light–Matter System

“…For an accurate study, it is important to employ first-principles approaches that can describe the complex interaction when light and matter strongly interact. Such first-principles methods have been developed within the framework of nonrelativistic quantum electrodynamics. − Among these methods, quantum electrodynamical density functional theory (QEDFT) is a valuable approach for describing ground- and excited-state properties of complex matter systems coupled to photons − and suitable to investigate nonlinear optical processes of strongly coupled light–matter systems.…”

Nonlinear Optical Processes in Centrosymmetric Systems by Cavity-Induced Symmetry Breaking

“…For a resonantly coupled cavity mode to a matter transition, this leads to the emergence of polaritonic states which have hybrid light–matter character. , To characterize the light–matter interaction, we deduce from eq , the light–matter coupling strength given as (see Appendix A for details) g α , i j false( k l false) = e m normalℏ 2 ε 0 ω α V false⟨ φ i k | e α · p̂ | φ j l false⟩ where |ϕ j l ⟩ are the eigenstates of the matter system. We recall that we chose the cavity frequency ω α = 24.65 meV to be resonant to the electronic transition |ϕ 1 0 ⟩ ↔ |ϕ 7 1 ⟩, and we now vary the coupling strength g α, ij ( kl ) by varying the interaction volume V as normally done in other works. − That is, the controlled cavity-induced symmetry breaking in the coupled system is linked to changing the coupling strength by reducing the cavity volume. The values of g α, ij ( kl ) are very small, since we consider very large cavity volumes.…”

Cavity-Mediated Molecular Entanglement and Generation of Non-classical States of Light

“…Over the past few years, the strong coupling of quantum light and matter via infrared or optical cavities has experienced a surge of interest in chemistry and materials science as a new approach for controlling or modifying chemical reactivity and physical properties. Seminal experimental work has demonstrated the possibility to control photochemical reactions , and energy transfer, , enhancement of harmonic generation from polaritonic states, − modification of ground-state chemical reactions via vibrational strong coupling, , or cavity-control of condensed matter properties. , In addition, for vibrational strong-coupling (VSC), it was observed that coupling to specific vibrational excitations can inhibit, steer, and enhance molecular reaction rates. Recent theoretical investigations have focused on how light and matter become entangled and what happens to the entanglement with increasing temperature.…”