Improved Lamb‐shift experiments

Precise measurement of the Lamb shift, the difference δ in energy between the $S1/2$ and $P1/2$ levels in single‐electron atoms and ions, is a basic test of quantum electrodynamics. Several factors limit the accuracy of experimental determinations of δ; the most important are difficulties of measuring the resonance‐line center, uncertainty about the velocity distribution of the atoms, and systematic errors, such as Stark‐effect shifts, caused by the applied electromagnetic fields.