An Optical Atomic Clock Based on a Highly Charged Ion
Steven A. King1, Lukas J. Spieß1, Peter Micke1,2, Alexander Wilzewski1, Tobias Leopold1, Erik Benkler1, Richard Lange1, Nils Huntemann1, Andrey Surzhykov1,3, Vladimir A. Yerokhin1, José R. Crespo López-Urrutia2 and Piet O. Schmidt1,4
1 Physikalisch-Technische Bundesanstalt, Braunschweig, Germany
2 Max-Planck-Institut für Kernphysik, Heidelberg, Germany.
3 Technische Universität Braunschweig, Braunschweig, Germany.
4 Institut für Quantenoptik, Leibniz Universität Hannover, Germany.
Optical atomic clocks are the most accurate measurement devices ever constructed and have found many applications in fundamental science and technology. The use of highly charged ions (HCI) as a new class of references for highest accuracy clocks and precision tests of fundamental physics has long been motivated by their extreme atomic properties and reduced sensitivity to perturbations from external electric and magnetic fields compared to singly charged ions or neutral atoms. We present the first realisation of this new class of clocks, based on an optical magnetic-dipole transition in Ar13+. Its comprehensively evaluated systematic frequency uncertainty of 2.2×10-17 is comparable to that of many optical clocks in operation. From clock comparisons we improve by eight and nine orders of magnitude upon the uncertainties for the absolute transition frequency and isotope shift (40Ar vs. 36Ar), respectively. These measurements allow us to probe the largely unexplored quantum electrodynamic nuclear recoil, presented as part of improved calculations of the isotope shift which reduce the uncertainty of previous theory by a factor of three. This work establishes forbidden optical transitions in HCI as references for cutting-edge optical clocks and future high-sensitivity searches for physics beyond the standard model.