Resolving vacuum fluctuations in an electrical circuit by measuring the lamb shift Journal Article

Author(s): Fragner, A; Göppl, M; Fink, Johannes; Baur, Matthias P; Bianchetti, R; Leek, Peter J; Blais, Alexandre; Wallraff, Andreas
Article Title: Resolving vacuum fluctuations in an electrical circuit by measuring the lamb shift
Abstract: Quantum theory predicts that empty space is not truly empty. Even in the absence of any particles or radiation, in pure vacuum, virtual particles are constantly created and annihilated. In an electromagnetic field, the presence of virtual photons manifests itself as a small renormalization of the energy of a quantum system, known as the Lamb shift. We present an experimental observation of the Lamb shift in a solid-state system. The strong dispersive coupling of a superconducting electronic circuit acting as a quantum bit (qubit) to the vacuum field in a transmission-line resonator leads to measurable Lamb shifts of up to 1.4% of the qubit transition frequency. The qubit is also observed to couple more strongly to the vacuum field than to a single photon inside the cavity, an effect that is explained by taking into account the limited anharmonicity of the higher excited qubit states.
Keywords: QUANTUM THEORY; Quantum mechanics; Superconductivity; quantum dot; microwave radiation; electromagnetic field; fundamental particle; measurement method; absorption spectroscopy; solid state; superconductor
Journal Title: Science
Volume: 322
Issue 5906
ISSN: 0036-8075
Publisher: American Association for the Advancement of Science  
Date Published: 2008-11-28
Start Page: 1357
End Page: 1360
DOI: 10.1126/science.1164482
Notes: This work was supported by the Swiss National Science Foundation and ETHZ. P.J.L. was supported by the European Commission with a Marie Curie Intra-European Fellowship. A.B. was supported by the Natural Sciences and Engineering Research Council of Canada, Canadian Institute for Advanced Research, and Fonds Québécois de la Recherche sur la Nature et les Technologies
Open access: no