Test of Strong-Field QED

Abstract

This review reports on experiments addressing quantum electrodynamical (QED) effects for the ground state in hydrogen- and helium-like ions at high nuclear charges. Such experiments probe QED in the domain of the strongest possible electromagnetic fields. In a short outline, we emphasize the particularities of bound—state QED in the strong field. Experimentally we concentrate on research conducted at the ESR storage ring at GSI Darmstadt where highly charged and even bare ions at high-Z can be studied under unique experimental conditions. As a representative example, the is binding energy in H-like uranium, determined with an accuracy of 13 eV, is discussed. At present, this constitutes the most precise is Lamb shift measurement available for the high-Z regime. These is Lamb Shift studies are discussed in detail as well as the experiments aiming at a precise determination of the ground—state ionization potentials of high-Z helium like ions where the two-electron QED corrections in the strong field limit can be studied. In addition QED effects associated with the strong magnetic fields as present at high Z are reviewed. In this context, the studies of the hyperfine splitting of the ground state in H-like bismuth are presented, as measured precisely by collinear laser spectroscopy. Similar to the hyperfine splitting, highly accurate measurements of the bound state g factor in hydrogen-like ions provide a sensitive tests of bound-state QED. The measurement of the g factor of bound electrons is a new experimental approach to address QED in the strong—field domain which is accomplished by storing a single highly charged ion in an ion trap. This technique is discussed in detail and its potential for future investigations is illustrated by the presentation of a first result already obtained for the case of hydrogen-like carbon.