The quest for the value of the electron's atomic mass has been subject of continuing efforts over the last decades [1,2,3,4]. [5] and which are thus responsible for its predictive power, the electron mass me plays a prominent role, as it is responsible for the structure and properties of atoms and molecules. This manifests in the close link with other fundamental constants, such as the Rydberg constant R∞ and the fine-structure constant α [6]. However, the low mass of the electron considerably complicates its precise determination. In this work we present a substantial improvement by combining a very accurate 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 achieved precision of the atomic mass of the electron surpasses the current CODATA [6] value by a factor of 13. Accordingly, the result presented in this letter lays the foundation for future fundamental physics experiments [7,8] and precision tests of the SM [9,10,11] Throughout the last decades, the determination of the atomic mass of the electron has been subject to several Penning-trap experiments, as continuing experimental efforts try to further explore the scope of validity of the SM and require an exceedingly precise knowledge of me. The uniform magnetic field of these traps gives the possibility to compare the cyclotron frequency of the electron with that of another ion of known atomic mass, typically carbon ions or protons. The first such direct determination dates back to 1980, when Gräff et al. made use of a Penning trap to compare the cyclotron frequencies of a cloud of electrons with that of protons, which were alternately confined in the same magnetic field, yielding a relative precision of about 0.2 ppm [2]. Since then, a number of experiments have pushed the precision by about 3 orders of magnitude [1,12,13,4]. The latest version of the CODATA compilation of fundamental constants of 2010 lists a relative uncertainty of 4•10 -10 , resulting from the weighted average of the most precise measurements (Fig. 2). Since the cyclotron frequency of the extremely light electron is subjected to troublesome relativistic mass shifts if not held at the lowest possible energy, direct ultra-high precision mass measurements are particularly delicate. To circumvent this problem, the currently most precise measurements, including this work, pursue an indirect method which allows achieving a previously unprecedented accuracy. Among the seemingly fundamental constants which parameterize the Standard Model (SM) of physicsA single electron is bound directly to the reference ion, in this case a bare carbon nucleus (Fig. 1). In this way, it becomes possible to calibrate the magnetic field B at the very place of the electron through a measurement of the cyclotron frequency

We present a new experimental value for the magnetic moment of the electron bound in hydrogenlike carbon (12C5+): g(exp) = 2.001 041 596 (5). This is the most precise determination of an atomic g(J) factor so far. The experiment was carried out on a single 12C5+ ion stored in a Penning trap. The high accuracy was made possible by spatially separating the induction of spin flips and the analysis of the spin direction. The current theoretical value amounts to g(th) = 2.001 041 591 (7). Together experiment and theory test the bound-state QED contributions to the g(J) factor of a bound electron to a precision of 1%.

We present an experimental value for the g factor of the electron bound in hydrogenlike oxygen, which is found to be g(expt)=2.000 047 025 4 (15)(44). The experiment was performed on a single 16O7+ ion stored in a Penning trap. For the first time, the expected line shape of the g-factor resonance is calculated which is essential for minimizing the systematic uncertainties. The measurement agrees within 1.1 sigma with the predicted theoretical value g(theory)=2.000 047 020 2 (6). It represents a stringent test of bound-state quantum electrodynamics to a 0.25% level. Assuming the validity of the underlying theory, a value for the electron mass is obtained: m(e)=0.000 548 579 909 6 (4) u. This value agrees with our earlier determination on and allows a combination of both values which is about 4 times more precise than the currently accepted one.

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.

No abstract

A new independent value for the electron's mass in units of the atomic mass unit is presented, m(e) = 0.000 548 579 909 2(4) u. The value is obtained from our recent measurement of the g factor of the electron in (12)C(5+) in combination with the most recent quantum electrodynamical (QED) predictions. In the QED corrections, terms of order alpha(2) were included by a perturbation expansion in Zalpha. Our total precision is three times better than that of the accepted value for the electron's mass.

The magnetic moment μ of a bound electron, generally expressed by the g-factor μ=−g μB s ħ−1 with μB the Bohr magneton and s the electron's spin, can be calculated by bound-state quantum electrodynamics (BS-QED) to very high precision. The recent ultra-precise experiment on hydrogen-like silicon determined this value to eleven significant digits, and thus allowed to rigorously probe the validity of BS-QED. Yet, the investigation of one of the most interesting contribution to the g-factor, the relativistic interaction between electron and nucleus, is limited by our knowledge of BS-QED effects. By comparing the g-factors of two isotopes, it is possible to cancel most of these contributions and sensitively probe nuclear effects. Here, we present calculations and experiments on the isotope dependence of the Zeeman effect in lithium-like calcium ions. The good agreement between the theoretical predicted recoil contribution and the high-precision g-factor measurements paves the way for a new generation of BS-QED tests.

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.