Speaker: Dr. Sven Sturm (Max-Planck-Institut für Kernphysik, Heidelberg)
Title of Talk: “Precision tests of atomic physics with isolated ions in Penning traps”

Abstract: The simple structure of few- or single electron ions gives us the unique opportunity to probe the validity of Quantum Electrodynamics (QED) via a comparison of measured observables with precise predictions by theory. Single ions in Penning traps have proven to be a versatile test system for such precision measurements. The extremely good vacuum conditions we can achieve in cryogenic traps allows for very long storage of even highly charged ions, so that they can be precisely studied by measuring their motional and internal frequencies. Furthermore, in heavy highly charged ions the binding field of the nucleus can reach values up to 1016 V/cm, enabling a unique test in such extreme conditions. One prominent example is the ultra-precise determination of the g-factor of highly charged ions. While the weak-field regime has been already exquisitely tested, in the presence of strong fields higher-order contributions beyond the Standard Model might become significant. It is possible to sensitively search for such effects by measuring the Larmor- and cyclotron frequencies of single, highly charged ions in a cryogenic Penning trap with high precision. This way, by measuring the g-factor of medium heavy hydrogenlike ions with previously unprecedented precision, we have been able to perform the most stringent test of QED in strong fields. Particularly the effect of the nucleus on the g-factor of the electron is a novel and unique access to nuclear size and structure information.
To push these tests far into the strong-field, heavy ion regime we have developed and commissioned the ALPHATRAP experiment at the MPIK in Heidelberg. ALPHATRAP has recently performed the first high-precision measurement of the g-factor of a boronlike highly charged ion, 40Ar13+. This not only enables a sensitive test of multi-electron QED, but also paves the way towards a determination of the finestructure constant α. Furthermore, using a novel detection scheme also the internal atomic structure can be probed. This way, the finestructure splitting in 40Ar13+ has been measured by means of laser spectroscopy. Recent results of ALPHATRAP and future projects will be presented.

Download slides here: https://heibox.uni-heidelberg.de/f/6aefd3a64e944effb65e/?dl=1