Testing high-Z QED with SuperEBIT: An estimate of the U91+ 1s two-loop Lamb shift based on a measurement of the 2s1/2-2p1/2 transition in U89+

Starting from the results of a recent measurement of the 2s1/2-2p1/2 transition in U89+ made on the SuperEBIT electron beam ion trap, which provided a determination of the 2s two-loop QED contribution, we estimate 1.27±0.45 eV for the two-loop contribution to the 1s level in U91+. This estimate could be improved by a factor of two or more, if the uncertainties associated with the three-photon exchange in the theoretical calculations were eliminated in the future.