Fig. presents the linear spectra for a fixed cavity loss rate Γ = 10 meV, with an increase in coupling strength g c . The Rabi splitting of upper and lower polaritons increases. When g c = 50 cm -1 or 100 cm -1 , the strong coupling condition that g c ≫ Γ, κ is not fulfilled and there is no apparent Rabi splitting. As the g c increases, the Rabi splitting appears. The broadening of individual polariton peaks is the same in all the above cases, which is expected from the fixed cavity loss rate (which is equivalent to fixing the photon loss bath parameters that couples to the cavity mode q c , and hence the same distribution of frequencies).