Figure 5

Power spectrum measured at the output of the mixer when a signal is applied at$\mathit{\Delta }\mathit{f}\mathbf{=}{\mathit{f}}_{\mathit{s}}\mathbf{-}\mathit{f}\mathit{p}\mathbf{=}\mathbf{10}\mathbf{\text{ kHz}}$. Measurements are shown when the pump is on (blue) and when the pump is off (green), for two cases: (a) the phase shifter is tuned for maximum amplification, and (b) the phase shifter is tuned for maximum de-amplification. The measurement reveals both signal and noise gain, and the additional peaks at integer multiples of Δf are due to higher-order intermodulation products of the signal and pump.