Abstract
Quantum fluctuations of the electromagnetic vacuum are responsible for physical effects such as the Casimir force and the radiative decay of atoms, and set fundamental limits on the sensitivity of measurements. Entanglement between photons can produce correlations that result in a reduction of these fluctuations below the ordinary vacuum level, allowing measurements that surpass the standard quantum limit in sensitivity1,2,3,4,5. The effects of such ‘squeezed states’ of light on matter were first considered in a prediction6 of the radiative decay rates of atoms in squeezed vacuum. Despite efforts to demonstrate such effects in experiments with natural atoms7,8,9, a direct quantitative observation of this prediction has remained elusive. Here we report a twofold reduction of the transverse radiative decay rate of a superconducting artificial atom coupled to continuum squeezed vacuum. The artificial atom is effectively a two-level system formed by the strong interaction between a superconducting circuit and a microwave-frequency cavity. A Josephson parametric amplifier is used to generate quadrature-squeezed electromagnetic vacuum. The observed twofold reduction in the decay rate of the atom allows the transverse coherence time, T2, to exceed the ordinary vacuum decay limit, 2T1. We demonstrate that the measured radiative decay dynamics can be used to reconstruct the Wigner distribution of the itinerant squeezed state. Our results confirm a canonical prediction6 of quantum optics and should enable new studies of the quantum light–matter interaction.
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Acknowledgements
We thank C. Macklin, N. Roch and Lev S. Bishop for discussions. This research was supported in part (K.W.M., S.J.W. and I.S.) by the Office of Naval Research (N00014-13-1-0150) and the Office of the Director of National Intelligence (ODNI), Intelligence Advanced Research Projects Activity (IARPA), through the Army Research Office (W911NF-11-1-0029). All statements of fact, opinion or conclusions contained herein are those of the authors and should not be construed as representing the official views or policies of IARPA, the ODNI or the US government. E.G. acknowledges support from EPSRC (EP/I026231/1). K.M.B. acknowledges support from US NSF GRFP (0645960) and IGERT (0801525).
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K.W.M. and S.J.W. performed the experiment and analysed the data. S.J.W. fabricated the qubit and parametric amplifier. K.W.M. wrote the manuscript. K.M.B. helped with the experimental set-up, provided theoretical support and wrote Supplementary Information. E.G. designed the experiment and provided theoretical support. All work was carried out under the supervision of I.S.
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Murch, K., Weber, S., Beck, K. et al. Reduction of the radiative decay of atomic coherence in squeezed vacuum. Nature 499, 62–65 (2013). https://doi.org/10.1038/nature12264
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DOI: https://doi.org/10.1038/nature12264
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