  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.
