Sensitivity of Highly Charged Ions to Hypothetical Fifth Forces and QED Effects

Atomic probes of fundamental interactions based on precision spectroscopy have been essential for the development of quantum mechanics, nuclear physics, quantum electrodynamics, and investigations of the non-conservation of parity and the existence of an electric dipole moment of the electron. Modern techniques that allow the preparation of highly charged ions (HCIs) with a defined number of bound electrons greatly extend the periodic table in the charge dimension and make available a variety of species for spectroscopic studies covering the electromagnetic spectrum from the optical to the X-ray region, broadening the range of fundamental physics studies [1]. Recent proposals to search for the presence of the fifth force in the form of Yukawa particles using a combination of frequency metrology and King-plot methods will benefit from these properties, since HCI offer many more electromagnetic transitions with interesting properties than the usual spectroscopic species studied in laboratories. Our spectroscopic studies of Ca and Xe HCI [2,3] explore these possibilities. In addition, continuous improvements to existing experiments have allowed more rigorous tests of atomic structure theory [4] and bound-state QED [5,6].

[1] M. G. Kozlov et al., Rev. Mod. Phys. 90, 045005 (2018)
[2] N. Rehbehn et al., Phys. Rev. A 103, L040801 (2021) 
[3] N. Rehbehn et al., Phys. Rev. Lett. 131, 161803 (2023)
[4] S. Kuehn et al., Phys. Rev. Lett. 129, 245001 (2022)
[5] J. Morgner et al., Nature 622, 53 (2023)
[6] M. Togawa et al., Phys. Rev. A 110, L030802 (2024)