Testing QED and atomic-nuclear interactions with high-Zions

Measurements of high- Z hydrogen-like ions have not yet been able to compete with the ultra-high precise test of quantum electrodynamics (QED) carried out using atomic hydrogen. However, recent advances in theory and experiment have enabled measurements involving high- Z lithium-like ions to test two-loop QED at a level similar to that achieved with atomic hydrogen. Tests of two-loop QED are limited in both cases by the uncertainties in the finite nuclear size, i.e. the uncertainties associated with the proton charge radius and the finite size of high- Z nuclei, respectively. Future experiments employing high- Z ions are described that might go beyond the present limitations. Measurements of the hyperfine splitting in highly charged ions cannot readily be described by theory, in part because of poor understanding of the finite nuclear magnetization radius. The discrepancy between measurements and theory leaves open the possibility of new physics not yet addressed by our current understanding of atomic–nuclear interactions.