Fig. 3: Squeezing optimization.
a Squeezing S as a function of SQZ pump phase ϕS and AMP pump phase ϕA. The diagonal feature corresponds to SQZ and AMP squeezing along orthogonal axes, where S is optimal. b A linecut at ϕA = 0 in (a), showing the noise power PN on the I-quadrature in two scenarios: `SQZ on' and `SQZ off' (AMP is always on). Around ϕS = π/2, SQZ reduces the noise on I below the reference vacuum level. c A zoom-in around ϕS = π/2, where SQZ is maximally squeezing along the I-quadrature. The squeezed noise reaches a minimum of 7.8(2) dB below the vacuum level. d, e Maximum squeezing as a function of AMP and SQZ gain. The gain of both amplifiers was measured via the anti-squeezing of a coherent state. Arrows indicate the setpoints used for the other panels. The dashed lines are fits to a cavity input-output model, which is derived in the Supplementary Information. The un-filled data points in e deviate from the model and are excluded from the fit. ω0/2π = 6.23 GHz for AMP and SQZ in all panels with probe frequency ω = ω0. Error bars in (d) and (e) indicate the error on the mean.
