Robustness of the Floquet-assisted superradiant phase and possible laser operation

TL;DR

The paper investigates the robustness of the Floquet-assisted superradiant phase (FSP) in a parametrically driven, dissipative Dicke model motivated by light-driven graphene. By incorporating phase diffusion, inhomogeneous broadening, and realistic dissipation, the authors demonstrate drastic linewidth narrowing across the FSP transition, stability against broadening, and tolerance to dissipation up to experimentally relevant rates, with cavity loss κ identified as the most sensitive parameter. The findings indicate that the FSP can operate as a solid-state laser mechanism in the THz regime, leveraging Floquet-engineered dressed states and dissipative dynamics in two-band solids. This work broadens the landscape of lasing mechanisms by showing a robust, Floquet-driven pathway to coherent emission in solid-state platforms.

Abstract

We demonstrate the robustness of the recently established Floquet-assisted superradiant phase of the parametrically driven dissipative Dicke model, inspired by light-induced dynamics in graphene. In particular, we show the robustness of this state against key imperfections and argue for the feasibility of utilizing it for laser operation. We consider the effect of a finite linewidth of the driving field, modelled via phase diffusion. We find that the linewidth of the light field in the cavity narrows drastically across the FSP transition, reminiscent of a line narrowing at the laser transition. We then demonstrate that the FSP is robust against inhomogeneous broadening, while displaying a reduction of light intensity. We show that the depleted population inversion of near-resonant Floquet states leads to hole burning in the inhomogeneously broadened Floquet spectra. Finally, we show that the FSP is robust against dissipation processes, with coefficients up to values that are experimentally available. We conclude that the FSP presents a robust mechanism that is capable of realistic laser operation.

Figures (6)

• Figure 1: Mechanism of the Floquet-assisted superradiant phase. (a) The bare energy levels $\omega_z$ of a collection of two-level systems are dressed via strong driving field strengths $E_\mathrm{d}$ and deformed into Floquet states. Depending on the details of driving and dissipation, this process leads to population inversion in the Floquet states as indicated by the gray hatched areas. At Floquet energies that are resonant with the cavity frequency $\omega_c$, this population inversion is depleted and transferred into a coherent state in the cavity. (b) The phase diagram of the light field in the cavity shows the trivial phase (TP), the Dicke superradiant phase (DS) for small driving field strengths and the Floquet-assisted superradiant phase (FSP) for large driving field strengths around $E_\mathrm{d}^\mathrm{onset}$. The coupling strength $\lambda_c^\mathrm{FSP}$ at which the FSP emerges depends on the cavity loss rate $\kappa$ that increases with $\kappa$.
• Figure 2: Light field fluctuations across the FSP transition. Panels (a) and (b) show the root-mean-square and the standard deviation of the light field amplitude across the FSP transition as a function of the phase diffusion standard deviation $s_\phi$. The horizontal line indicates the coupling strength at which the FSP transition occurs in the absence of phase diffusion, i.e. $s_\phi=0$. Panel (c) shows the amplitude of a single-trajectory of the light field for $s_\phi=0$ (blue) and $s_\phi=0.4$ (black), as well as an inset of the driving field for the same values of $s_\phi$.
• Figure 3: Linewidth narrowing in the FSP. Panel (a) shows the power spectrum averaged over 50 phase diffusion trajectories as a function of the coupling strength $\lambda$ for $s_\phi=0.4$ on a logarithmic scale. Across the FSP transition indicated by the dashed line, the linewidth of the light field in the cavity narrows drastically. Panel (b) shows the light field amplitude across the FSP transition for the individual trajectories in light colors and their mean in solid dark blue. Panel (c) shows the power spectra for $\lambda = 0.02\lambda_c$, rescaled by a factor of $26$ for comparison, and $\lambda=\lambda_c$.
• Figure 4: Effect of inhomogeneous broadening on the FSP transition. The FSP transition at the onset driving field strength as a function of the coupling strength $\lambda$ and the inhomogeneous broadening parameter $s_\omega$. The vertical dashed line corresponds to the case that we show in Fig. \ref{['floquet']}.
• Figure 5: Two-level steady state distributions in the presence of inhomogeneous broadening. Panels (a) through (c) show the steady state distributions $n_j(\omega)$ for $N=100$ TLSs at $E_\mathrm{d}=0$ (a) and $E_\mathrm{d}=E_\mathrm{d}^\mathrm{onset}$ (b, c) as well as $\lambda=0$ (a, b) and $\lambda=\lambda_c$ (c). The distributions are concentrated at the Floquet energies of the broadened energy levels. The horizontal lines show the average level spacing $\omega_z$ and the cavity frequency $\omega_c$. Panel (d) shows the relative collective distribution $\Delta n(\omega)$ for $\lambda=\lambda_c$ (black line, white filling) and $\lambda=0$ (dark blue filling) the difference between the two (hatched filling) is the effective population inversion of Floquet states that is depleted to sustain the FSP.