Resonance fluorescence from an artificial atom in squeezed vacuum

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We present an experimental realization of resonance fluorescence in squeezed vacuum.

• We strongly couple microwave-frequency squeezed light to a superconducting artificial atom and detect the resulting fluorescence with high resolution enabled by a broadband traveling-wave parametric amplifier.
• We investigate the fluorescence spectra in the weak and strong driving regimes, observing up to 3.1 dB of reduction of the fluorescence linewidth below the ordinary vacuum level and a dramatic dependence of the Mollow triplet spectrum on the relative phase of the driving and squeezed vacuum fields.
• Our results are in excellent agreement with predictions for spectra produced by a two-level atom in squeezed vacuum [Phys.