Stringent test of QED with hydrogenlike tin

TL;DR

This paper reports a high-precision measurement of the electron g-factor in hydrogenlike tin ions, providing a stringent test of quantum electrodynamics in extremely strong electromagnetic fields, surpassing previous Lamb shift tests.

Contribution

The study presents the first high-precision g-factor measurement in hydrogenlike tin ions, significantly improving the accuracy of QED tests in strong fields compared to prior Lamb shift experiments.

Findings

QED validated to about 0.012% in strong fields

Achieved 0.5 ppb precision in g-factor measurement

Surpassed previous Lamb shift tests in stringency

Abstract

Inner-shell electrons naturally sense the electric field close to the nucleus, which can reach extreme values beyond $10^{15}\,\text{V}/\text{cm}$ for the innermost electrons. Especially in few-electron highly charged ions, the interaction with the electromagnetic fields can be accurately calculated within quantum electrodynamics (QED), rendering these ions good candidates to test the validity of QED in strong fields. Consequently, their Lamb shifts were intensively studied in the last decades. Another approach is the measurement of $g$ factors in highly charged ions. However, so far, either experimental accuracy or small field strength in low-$Z$ ions limited the stringency of these QED tests. Here, we report on our high-precision, high-field test of QED in hydrogenlike $^{118}$Sn$^{49+}$. The highly charged ions were produced with the Heidelberg-EBIT (electron beam ion trap) and injected into the ALPHATRAP Penning-trap setup, where the bound-electron $g$ factor was measured with a precision of 0.5 parts-per-billion. For comparison, we present state-of-the-art theory calculations, which together test the underlying QED to about $0.012\,\%$, yielding a stringent test in the strong-field regime. With this measurement, we challenge the best tests via the Lamb shift and, with anticipated advances in the $g$-factor theory, surpass them by more than an order of magnitude.