Fig. 2

Resonator spectroscopy as a function of P_in and V_G a |S₂₁| (Norm.) as a function of input frequency f and input power P_in. At single photon occupancy the resonator experiences a frequency shift χ due to repulsion from an energy level above the resonator (device A). b Diagram of the Dirac cone band structure of graphene. Changing V_G to tune μ allows the dominant charge carriers to be varied between hole, charge neutral and electron-like regimes. c At single photon occupancy, |S₂₁| (Norm.) is measured as f and V_G are varied, with the voltage at CNP (V_CNP = 7.8 V) subtracted. In the p-regime, χ oscillates as V_G is varied. We extract the charge carrier density n_c d from the white linecut to generate a Fourier transform e that is consistent with Fabry-Perot oscillations in a cavity of d = 220 nm