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Probing the quantum vacuum with an artificial atom in front of a mirror

Abstract

Quantum fluctuations of the vacuum are both a surprising and fundamental phenomenon of nature. Understood as virtual photons, they still have a very real impact, for instance, in the Casimir effects and the lifetimes of atoms. Engineering vacuum fluctuations is therefore becoming increasingly important to emerging technologies. Here, we shape vacuum fluctuations using a superconducting circuit analogue of a mirror, creating regions in space where they are suppressed. Moving an artificial atom through these regions and measuring the spontaneous emission lifetime of the atom provides us with the spectral density of the vacuum fluctuations. Using the paradigm of waveguide quantum electrodynamics, we significantly improve over previous studies of the interaction of an atom with its mirror image, observing a spectral density as low as 0.02 quanta, a factor of 50 below the mirrorless result. This demonstrates that we can hide the atom from the vacuum, even though it is exposed in free space.

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Figure 1: An artificial atom in front of a mirror.
Figure 2: Spectroscopic measurements of the excited-state lifetime.
Figure 3: Calibrating the atom–field coupling.
Figure 4: The measured spectral density of the vacuum fluctuations S(ωa) as a function of L/λ.

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Acknowledgements

We acknowledge financial support from STINT, the Swedish Research Council, the European Union represented by the ERC and the EU project PROMISCE, NSERC of Canada, Industry Canada, and the Government of Ontario. We would also like to acknowledge J. Kimble, G. Milburn, T. Stace, J. M. Martinis, C. P. Sun and H. Dong for fruitful discussions.

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I.-C.H., A.P., C.M.W. and P.D. designed and performed the experiment. A.F.K., L.T. and G.J. provided theoretical assistance. All authors contributed to the preparation of the manuscript.

Corresponding authors

Correspondence to P. Delsing or C. M. Wilson.

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The authors declare no competing financial interests.

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Hoi, IC., Kockum, A., Tornberg, L. et al. Probing the quantum vacuum with an artificial atom in front of a mirror. Nature Phys 11, 1045–1049 (2015). https://doi.org/10.1038/nphys3484

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