For energy disorder simulations (Fig. ), the excitation energy for n th molecule is sampled from the Gaussian FIG. . Convergence of the lower polariton spectra with an increasing number of molecules from N = 1 to N = 10 5 , while fixing ℏΩR = 2 √ N ℏgc = 0.2 eV a constant (by decreasing gc accordingly). Here, we do not consider any type of disorder, and the cavity loss rate is set to be Γ = 20 meV.