Figure 6

Power dependence. Relative frequency shift \(\delta f_{r}=f_{r}-f_{r}(n\to 0)\) as function of average number of photons in the resonator \(\langle n_{\mathrm{ph}}\rangle \). We do not observe a noteworthy positive frequency shift in comparison with the Fig. 3 in the main text. For \(\langle n_{\mathrm{ph}}\rangle \gtrsim 10^{5}\), an increasingly negative relative frequency shift is observed which we attribute to the finite non-linearity of the resonators