Abstract
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. Rev. Lett. \textbf{58}, 2539-2542 (1987)], demonstrating that resonance fluorescence offers a resource-efficient means to characterize squeezing in cryogenic environments.
Highlights
The accurate prediction of the fluorescence spectrum of a single atom under coherent excitation, comprising canonical phenomena such as the Mollow triplet [1,2], is a foundational success of quantum optics
We present an experimental realization of resonance fluorescence in squeezed vacuum
As the Mollow triplet provides a clear signature of coherent light-matter coupling, in recent years such spectra have been widely applied to probe quantum coherence in artificial atoms based on quantum dots [3] and superconducting qubits [4,5]
Summary
The accurate prediction of the fluorescence spectrum of a single atom under coherent excitation, comprising canonical phenomena such as the Mollow triplet [1,2], is a foundational success of quantum optics. Experiments have demonstrated that microwave-frequency squeezed light can modify the temporal radiative properties of an artificial atom, leading to phasedependent radiative decay [15] These experiments lacked a means to probe the resulting fluorescence, and predictions for the spectrum of resonance fluorescence in both the weak [6] and strong [7,8] driving regimes remain unexplored. We observe subnatural fluorescence linewidths and a strong dependence of the Mollow triplet spectrum on the relative phase of the driving and squeezed vacuum fields, in excellent agreement with theoretical predictions These results enable experimental access to the many theoretical studies on atomic spectra in squeezed reservoirs that have followed [9,10] and demonstrate the utility of resonance fluorescence for the characterization of itinerant squeezed states, an important capability for the development of proposed schemes to enhance qubit readout with microwavefrequency squeezed light [16,17]. We see a three-Lorentzian Mollow triplet spectrum, reflecting the polariton Rabi oscillations
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