Extended Data Fig. 2: Calibration of the hybrid quantum system.
From: Hybrid quantum network for sensing in the acoustic frequency range
a, Quantum noise of light fields in the absence of the atomic spin oscillator. Teal trace, total shot noise of the signal and idler. Grey trace, shot noise of the signal. Blue trace shows 3.2 dB of conditional, frequency-independent EPR squeezing. It corresponds to ≃6 dB of entanglement of the EPR state when normalized to the total shot noise of the signal and idler fields (teal trace). Orange trace, signal-arm EPR fluctuations. b, Idler-arm noise spectra in the presence of the atomic spin oscillator. Main panel, atoms driven by vacuum fluctuations; the reconstructed quantum-backaction noise (QBAN, red area), the decoherence-associated spin thermal (TH, light-blue area) and broadband noise (BB, purple area) are shown. Left inset, ponderomotive squeezing of light by atoms observed for two different idler detection angles δθi. Right inset, atoms driven by EPR fluctuations, with (teal) and without (red) the virtual rigidity (VR) effect. Dashed curves are theoretical fits (see Methods for details). All traces are normalized to the idler shot noise.
