Measurement of the Two-Loop Lamb Shift in Lithiumlike<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi mathvariant="normal">U</mml:mi><mml:mrow><mml:mn>89</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:math>

Using the SuperEBIT electron beam ion trap, the 2s(1/2)-2p( 1/2) transitions in U88+ and U89+ are measured and the available precision is improved by nearly an order of magnitude.

Abstract

Using the SuperEBIT electron beam ion trap, we have measured the $2{s}_{1/2}\mathrm{\text{\ensuremath{-}}}2{p}_{1/2}$ transitions in ${\mathrm{U}}^{88+}$ and ${\mathrm{U}}^{89+}$. The measured value of $280.645\ifmmode\pm\else\textpm\fi{}0.015\text{ }\text{ }\mathrm{eV}$ for Li-like ${\mathrm{U}}^{89+}$ improves the available precision by nearly an order of magnitude and establishes a new benchmark for testing the total QED contribution to the transition energy within a fractional accuracy of $3.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. We infer a value for the $2s$ two-loop Lamb shift in ${\mathrm{U}}^{89+}$ of $\ensuremath{-}0.23\text{ }\text{ }\mathrm{eV}$, from which we estimate a value of $\ensuremath{-}1.27\text{ }\text{ }\mathrm{eV}$ for the $1s$ two-loop Lamb shift in ${\mathrm{U}}^{91+}$.