Probing the quantum vacuum with an artificial atom in front of a mirror
I.-C. Hoi1,2*, A.F. Kockum1, L. Tornberg1, A. Pourkabirian1, G. Johansson1, P. Delsing1, C.M. Wilson3
1Microtechnology and Nanoscience, Chalmers University of Technology, Gothenburg, Sweden
2Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
3Institute for Quantum Computing, University of Waterloo, Waterloo, Canada
* presenting author:Io-Chun Hoi,
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 present a new approach to sensing the vacuum modes, based on a setup with an artificial atom placed in front of a mirror. We embed a superconducting transmon qubit at a distance from the end of a one-dimensional (1D) transmission line. The distance between the atom and the end the line, which acts as a mirror, determines the electromagnetic (EM) environment coupled to the atom. By tuning the transition wavelength of the atom, we change the normalized distance to the mirror. As a result, the atom can be moved from a node to an antinode of the EM field. Measuring the lifetime of the atom as its transition wavelength is tuned gives information about the quantum fluctuations of the vacuum, since the lifetime is proportional to the strength of the fluctuations. We observe a change in the lifetime by a factor of 9.8, showing that we can tune the coupling to the vacuum over a large range and effectively hide the atom from the vacuum. The lower limit we observe for the strength of the vacuum fluctuations is 0.02 quanta.

Keywords: Quantum fluctuations, superconducting transmon qubit, lifetime