Fig. 4: Interference between two probe tones.
From: Strong coupling between a single-photon and a two-photon Fock state
a, c Gain of the transmitted amplitude of the signal field in the n = 1 (n = 2) mode of the resonator versus the average photon number \({\overline{n}}_{{{{\rm{2(1)}}}}}\) and the phase of the control field in the n = 2 (n = 1) mode of the resonator. The average photon numbers of the signal fields in the resonator’s n = 1 and n = 2 modes are about 0.25 and 0.13, respectively. The frequencies of the probe tones are ω/2π = 4.905 GHz and 2ω/2π (at δΦext = −46 mΦ0). b, d Theoretical calculations corresponding to the plots in (a, c). The gain is defined as the ratio between the output signal amplitude at ω (2ω) when a secondary signal is applied at 2ω (ω), and the output amplitude of the same signal at ω (2ω) in the absence of the secondary signal applied at 2ω (ω). The phase shifts in the experimental data in (a, c) are an artifact due to an electronic delay.
