Fig. 2: Experimental demonstration of frequency-dependent conditional squeezing.
From: Hybrid quantum network for sensing in the acoustic frequency range
The spin ensemble is set to the positive-mass configuration with Ωa/2π = 54 kHz (marked by the thick dashed vertical lines) and the idler field is detected at phase quadrature θi = 0°. a, Conditional noise relative to the signal shot noise for different readout angles θs. The blue and grey traces represent frequency-independent conditional squeezing and signal-field shot noise, respectively, measured by setting the Larmor frequency to 1 MHz. For each measurement phase, the dark dashed curves represent the expected theoretical noise spectra. The red data points with error bars are extracted from 60 samples around the minimal noise for each phase. The red solid curve is the conditional squeezing predicted by the model. b, Contour spectrogram of the recorded conditional squeezing, illustrating its dependence on frequency Φ(Ω), indicated by the white dashed-dotted curve. The bandwidth δΩSQL/2π ≈ 4.1 kHz over which the squeezing phase rotates from 90° to 45° is indicated in both panels by the dashed vertical lines (see comments in the text).
