A very precise measurement of the magnetic moment of a single electron bound to a carbon nucleus, combined with a state-of-the-art calculation in the framework of bound-state quantum electrodynamics, gives a new value of the atomic mass of the electron that is more precise than the currently accepted one by a factor of 13. The atomic mass of the electron is a key parameter for fundamental physics. A precise determination is a challenge because the mass is so low. Sven Sturm and colleagues report on a new determination of the electron's mass in atomic units. The authors measured the magnetic moment of a single electron bound to a reference ion (a bare nucleus of carbon-12). The results were analysed using state-of-the-art quantum electrodynamics theory to yield a mass value with a precision that exceeds the current literature value by more than an order of magnitude. The quest for the value of the electron's atomic mass has been the subject of continuing efforts over the past few decades1,2,3,4. Among the seemingly fundamental constants that parameterize the Standard Model of physics5 and which are thus responsible for its predictive power, the electron mass me is prominent, being responsible for the structure and properties of atoms and molecules. It is closely linked to other fundamental constants, such as the Rydberg constant R∞ and the fine-structure constant α (ref. 6). However, the low mass of the electron considerably complicates its precise determination. Here we combine a very precise measurement of the magnetic moment of a single electron bound to a carbon nucleus with a state-of-the-art calculation in the framework of bound-state quantum electrodynamics. The precision of the resulting value for the atomic mass of the electron surpasses the current literature value of the Committee on Data for Science and Technology (CODATA6) by a factor of 13. This result lays the foundation for future fundamental physics experiments7,8 and precision tests of the Standard Model9,10,11.

Using a phase-detection method to determine the cyclotron frequency of a single trapped ion in a Penning trap allowed us to perform a measurement of the g factor of the bound electron in hydrogenlike Si-28(13+) with a statistical uncertainty of 4 x 10(-11). Furthermore, we reevaluated the image-charge shift as the main source of uncertainty. Our result challenges bound-state quantum-electrodynamical calculations by probing two-loop contributions of order (Z alpha)(6) and paves the way towards a more precise determination of fundamental constants as the electron mass. DOI: 10.1103/PhysRevA.87.030501

The g factor of lithiumlike silicon (28)Si(11+) has been measured in a triple-Penning trap with a relative uncertainty of 1.1×10(-9) to be g(exp)=2.000 889 889 9(21). The theoretical prediction for this value was calculated to be g(th)=2.000 889 909(51) improving the accuracy to 2.5×10(-8) due to the first rigorous evaluation of the two-photon exchange correction. The measured value is in excellent agreement with the theoretical prediction and yields the most stringent test of bound-state QED for the g factor of the 1s(2)2s state and the relativistic many-electron calculations in a magnetic field.

The g factor of the electron bound in hydrogenlike28Si13+ has been measured to 10 significant digits. The valueagrees very well with bound-state quantum-electrodynamical calculations and represents todate the most stringent test of the theory. The experiment uses a single ion confined in atriple Penning trap. Here we present details of the setup, the experimental procedure andthe data evaluation.

We determined the experimental value of the g factor of the electron bound in hydrogenlike ²⁸Si¹³⁺ by using a single ion confined in a cylindrical Penning trap. From the ratio of the ion's cyclotron frequency and the induced spin flip frequency, we obtain g = 1.995 348 958 7(5)(3)(8). It is in excellent agreement with the state-of-the-art theoretical value of 1.995 348 958 0(17), which includes QED contributions up to the two-loop level of the order of (Zα)² and (Zα)⁴ and represents a stringent test of bound-state quantum electrodynamics calculations.

Individual hydrogen- and lithium-like ions with medium nuclear charge Z are confined in a cylindrical triple Penning trap for nearly unlimited time under well-controlled conditions in a small volume in space. We present progress in a project to determine the magnetic moment of the electron bound in Si13+ and Ca19+ and their Li-like counterparts. This serves for testing bound-state quantum electrodynamic calculations. Significant technical improvements will allow for higher precision than in the previous similar experiments on C5+ and O7+.

S. Sturm, A. Wagner† , K. Blaum, W. Quint, B. Schabinger, and G. Werth Institut für Physik, Johannes Gutenberg-Universität, D-55099 Mainz; MPI für Kernphysik, D-69117 Heidelberg, Germany; GSI, D-64291 Darmstadt, Germany Bound-state quantum electrodynamics (BS-QED) calculations can be tested by high-precision measurements of the gyromagnetic factor (g-factor) of the electron bound in highly-charged ions [1, 2]. Therefore, it is planned to measure the g-factor of lithiumand hydrogen-like silicon and calcium in a double Penning trap setup [3]. In the last year important steps towards the final g-factor measurement were made by developing new detection techniques and characterizing the two traps.

Individual charged atomic or molecular particles can be confined by electromagnetic fields for nearly unlimited times under well controlled conditions in a small volume in space. This allows performing spectroscopic experiments with unprecedented accuracy. We discuss a project to determine the magnetic moment of the electron bound in hydrogen-like ions with different nuclear charges. This serves for testing bound-state quantum-electrodynamics calculations with high precision. Previous results on C5+ and O7+ as well as the present status of the project with Si13+ and Ca19+ are presented in this contribution and future possibilities are discussed.

High-precision measurements of the magnetic moment of the electron bound in hydrogen-and lithium-like ions can be used to test bound-state quantum electrodynamical calculations. In the past measurements with relative experimental uncertainties as low as 2×10-9 were performed on hydrogen-like carbon and oxygen ions. In the current experiment we plan to measure the g-factor of hydrogen-like and lithium-like calcium ions. A relative uncertainty δg/g in the order of 10-9 is aspired. Here, we will give the motivation for the experiment, present the experimental techniques and first results.

Penning traps serve for the precise measurement of magnetic moments of simple atomic systems and fundamental particles. Here we present attempts to measure the magnetic moment of the electron bound in hydrogen-like or lithium-like heavy ions as well as of the proton and antiproton. While the first experiment aims for a more stringent test of bound-state quantum-electrodynamic calculations the second experiment provides a new high-precision test of the CPT theorem in the baryonic sector.

The precise determination of the anomalous magnetic moment of the electron bound in hydrogen-like ions allows for a stringent test of quantum electrodynamics (QED)in the presence of strong electric fields. g-factor measurements on the electron bound in hydrogen-like ions 12 C 5+ and 16 O 7+ , using single ions confined in a Penning trap, have yielded values in agreement with theory on the ppb level. If the QED calculations are considered correct, the results can in turn be used for a determination of fundamental constants like the electron mass m e , the fine structure constant α or nuclear parameters. We report about presentdevelopments towards g-factor measurements also in medium-heavy and heavy highly-charged ions.

The limb of the Standard Model which deals with the interaction between electrons and electromagnetic fields, quantum electrodynamics (QED), has been tested to an extremely high precision by means of different experiments. Perhaps the most outstanding agreement between theory and experiment is the result coming from the anomaly of the magnetic moment of the free electron [1], where the concordance was up to the 12 digit. Also impressive are the 9 digits of agreement between the calculations of the gfactors of the electron bound to hydrogen-like carbon and oxygen ions and their corresponding measurements performed by the collaboration between GSI and the University of Mainz [2, 3]. In this case, bound-state quantum electrodynamics (BS-QED) is the subject of the tests, which can in addition lead to a more precise determination of fundamental constants such as the mass of the electron or the fine-structure constant α. Both, the relevance of the BSQED tests and the precision of the determination of fundamental constants grow with the charge of the ions with which the experiments are performed. Therefore, a new setup has been constructed [4] with which the g-factors of hydrogenand lithium-like calcium ions are planned to be determined for two stable isotopes (masses 40 and 48). From proper comparison of these measurements, additional information can be obtained, e.g. BS-QED tests in the presence of electronic correlation effects or tests for the various methods employed in relativistic calculations of many-electron systems, as well as nuclear contributions to the magnetic moment (from the isotopic shifts in the g-factors). The measurement process, described in [5], needs to be adapted to the higher charge of calcium ions when compared to carbon or oxygen ions, since the observation of the frequency jumps from which the magnetic moment is derived is more difficult. In that sense, mainly two techniques have been developed and tested. The first one, baptized as the ’three-dip method’ [6], makes use of mode coupling of the ion motions in the Penning trap for simultaneous determination of two different frequencies. The second technique, the so-called phase sensitive detection, is based on the determination of the phase difference between two frequencies which lie very close to each other, rather than the direct measurement of both frequencies. Another new challenge is the creation of the ions, i.e. the subsequent ionization. In our case, the ions will be produced inside the trap with a mini-electron beam ion source ∗Work supported by the EU-Network HITRAP HPRI-CT-2001-50036, the BMBF, the DFG and the Helmholtz association (VH-NG-037) † alonso@uni-mainz.de (EBIS), which can be driven with an energy up to 10 keV, enough to strip all electrons from the calcium atoms. The environmental requirements are very strict, T = 4K and p ∼ 10−16 mbar. An FT-ICR (Fourier transform-ion cyclotron resonance) technique has also been implemented in order to be able to observe on-line the content of the trap, i.e. the different charge states of calcium. This tool enables the cross-section determination for electron impact ionization [7], which is only known for the noble gases and a few other elements in the periodic table.