$g$ Factor of Lithiumlike Silicon: New Challenge to Bound-State QED

Abstract

The recently established agreement between experiment and theory for the $g$ factors of lithiumlike silicon and calcium ions manifests the most stringent test of the many-electron bound-state quantum electrodynamics (QED) effects in the presence of a magnetic field. In this Letter, we present a significant simultaneous improvement of both theoretical $g_{\text{th}}=2.0008898944(34)$ and experimental $g_{\text{exp}}=2.00088988845(14)$ values of the $g$ factor of lithiumlike silicon ${}^{28}$Si${}^{11+}$. The theoretical precision now is limited by the many-electron two-loop contributions of the bound-state QED. The experimental value is accurate enough to test these contributions on a few percent level.

5 pages, 1 figure