Transition from Lorentz to Fano Spectral Line Shapes in Non-Relativistic 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. Therefore, it is important to have control over the generation of 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.

Frequency-Dependent Sternheimer Linear-Response Formalism for Strongly Coupled Light–Matter Systems

“…Fano resonances occur due to the interference of discrete quantum states with a continuum of states. , The asymmetry is characterized as a ratio of the transition amplitude to a given discrete state and that of a transition to a continuum state . As this ratio becomes finite due to strong coupling to the continuum, this indicates the onset of a competition between constructive and destructive interference that gives rise to the asymmetric line shape . Also, the broadening of the spectra (see Figure ) and decrease in amplitude are consequences of the interference .…”

“… 69 As this ratio becomes finite due to strong coupling to the continuum, this indicates the onset of a competition between constructive and destructive interference that gives rise to the asymmetric line shape. 70 Also, the broadening of the spectra (see Figure 5 ) and decrease in amplitude are consequences of the interference. 70 These results show the changes in the spectral features of excited states of a matter system strongly coupled to the electromagnetic continuum.…”

“… 70 Also, the broadening of the spectra (see Figure 5 ) and decrease in amplitude are consequences of the interference. 70 These results show the changes in the spectral features of excited states of a matter system strongly coupled to the electromagnetic continuum. Thus, the electron–photon Sternheimer approach is a valid alternative method for studying excited-state properties of real systems strongly interacting with the quantized electromagnetic field.…”