Detection of the 5p – 4f orbital crossing and its optical clock transition in Pr9+

authored by
Hendrik Bekker, Anastasia Borschevsky, Zoltán Harman, Christoph H. Keitel, Thomas Pfeifer, Piet Oliver Schmidt, José R. Crespo López-Urrutia, Julian C. Berengut

Recent theoretical works have proposed atomic clocks based on narrow optical transitions in highly charged ions. The most interesting candidates for searches of physics beyond the Standard Model are those which occur at rare orbital crossings where the shell structure of the periodic table is reordered. There are only three such crossings expected to be accessible in highly charged ions, and hitherto none have been observed as both experiment and theory have proven difficult. In this work we observe an orbital crossing in a system chosen to be tractable from both sides: Pr9 +. We present electron beam ion trap measurements of its spectra, including the inter-configuration lines that reveal the sought-after crossing. With state-of-the-art calculations we show that the proposed nHz-wide clock line has a very high sensitivity to variation of the fine-structure constant, α, and violation of local Lorentz invariance; and has extremely low sensitivity to external perturbations.

Institute of Quantum Optics
CRC 1227 Designed Quantum States of Matter (DQ-mat)
External Organisation(s)
Max Planck Institute for Nuclear Physics
University of Groningen
National Metrology Institute of Germany (PTB)
University of New South Wales (UNSW)
Nature Communications
Publication date
Publication status
E-pub ahead of print
Peer reviewed
ASJC Scopus subject areas
Chemistry(all), Biochemistry, Genetics and Molecular Biology(all), Physics and Astronomy(all)
Electronic version(s) (Access: Open) (Access: Open)