The electron gfactor is a crucial fundamental structural parameter in atomic physics, as it reveals various mechanisms of electron interactions with external fields. Precise measurements of gfactors of electrons bound in simple atomic and molecular systems offer an effective avenue for investigating bound-state Quantum Electrodynamics (QED) theories. Especially in highly-charged heavy ions (HCIs), the strong electromagnetic interactions between the nucleus and inner-shell electrons provide unique opportunities to test QED under extremely strong fields. Accurate measurements of the gfactors of the bound-state electron are also crucial for determining nuclear effects, nuclear parameters and fundamental constants, making it a frontier topic fundamental physics. A Penning trap, which uses steady-state electromagnetic fields to confine charged particles, is utilized to perform precision g-factor measurements. This paper presents a comprehensive review of g-factor experiments for few-electron simple systems in Penning traps, covering a summary of the experimental principles, experimental setups, measurement methods, and significant research findings.
The introduction outlines the physical concept of the electron gfactor and its historical research background. The electron gfactor is considered as an effective probe to study higher-order QED effects. Through high-precision measurements of the free electron g-factor, discrepancies between the fine-structure constant and other experimental results in atomic physics have been identified. Notably, the gfactor of the 1s electron in HCIs deviates significantly from the value for free electrons as the atomic number increases. Experimental principles, including the principle of the Penning trap and the measurement principle of the bound-state electron gfactors are discussed. A double-trap experiment setup and related precision measurement techniques are also introduced.
This paper reviews several milestone experimental results including: (1) the stringent test of bound-state QED with a precision measurement of bound-state electron gfactor of ¹¹⁸Sn ⁴⁹⁺ion, (2) the g-factor measurements of lithium-like and boron-like ions and their applications, (3) the g-factor isotope shift measurement with an advanced two-ion balance technique in the Penning trap, providing insight into the QED effects in nuclear recoil. Finally, this paper summarizes the current challenges faced in the g-factor measurements of a bound-state electron in few-electron ion systems and offers an outlook on future developments in the field.