Search

Precision spectroscopy of atoms and molecules allows one to search for and to put stringent limits on the variation of fundamental constants. These experiments are typically interpreted in terms of variations of the fine structure constant α and the electron‐to‐proton mass ratio μ=me/mp. Atomic spectroscopy is usually less sensitive to other fundamental constants, unless the hyperfine structure of atomic levels is studied. However, the number of possible dimensionless constants increases when allowed for fast variations of the constants, where "fast" is determined by the time scale of the response of the studied species or experimental apparatus used. In this case, the relevant dimensionless quantity is, for example, the ratio me/⟨me⟩ and ⟨me⟩ is the time average. In this sense, one may say that the experimental signal depends on the variation of dimensionful constants (me in this example). [ABSTRACT FROM AUTHOR]

The magnetic moment of the electron, expressed by the g-factor in units of the Bohr magneton, is a key quantity in the theory of quantum electrodynamics (QED). Experiments using single particles confined in Penning traps have provided very precise values of the g-factor for the free electron as well as the electron bound in hydrogen-like ions. In this paper the status of these experiments is reviewed. The results allow testing calculations of higher order Feynman diagrams. Comparison of experimental and theoretical results for free and bound particles show no discrepancy within the limits of error, thus representing to date the most sensitive test of QED. Moreover, the g-factor provides a unique access to fundamental constants, as e.g. the electron mass or the fine structure constant. [ABSTRACT FROM AUTHOR]

Recent progress in quantum electrodynamics (QED) calculations of highly charged ions is reviewed. The theoretical predictions for the binding energies, the hyperfine splittings, and the g factors are presented and compared with available experimental data. Special attention is paid to tests of bound-state QED at strong field regime. Future prospects for tests of QED at the strongest electric and magnetic fields as well as for determination of the fine structure constant and the nuclear magnetic moments with heavy ions are discussed. [ABSTRACT FROM AUTHOR]

The fine structure constant α has a particular status in physics. Its precise determination is required to test the quantum electrodynamics (QED) theory. The constant α is also a keystone for the determination of other fundamental physical constants, especially the ones involved in the framework of the future International System of units. This paper presents Paris experiment, where the fine structure constant is determined by measuring the recoil velocity of a rubidium atom when it absorbs a photon. The impact of the recent improvement of QED calculations of the electron moment anomaly and the recent measurement of the cesium atom recoil at Berkeley will be discussed. The opportunity to provide a precise value of the ratio [ABSTRACT FROM AUTHOR]

The article discusses the derivation of the fine structure constant and discusses its most precise recent values. It reports that the value of the constant was obtained by comparing the quantum electrodynamics calculations of the g-factor (magnetic moment) of the free electron. It also mentions that the constant have also derived its values from the solid-state phenomena of the quantum hall Effect and Josephson effect and the hyperfine structure of muonium.

For more than four decades, the lowest excitation in the whole landscape of atomic nuclei, the low‐lying, isomeric state of 229Th, the so‐called thorium isomer, has challenged physicists of various disciplines. Being a solitaire with its uniquely low excitation energy of <10 eV, its predicted lifetime of a few hours results in an extremely sharp relative linewidth ΔE/E as low as 10–20. While until recently the indication of its existence was based only on indirect evidence, its unique properties inspired a multitude of potential applications, like the use of the thorium isomer as a nuclear frequency standard, potentially able to outperform even the best atomic clocks and a sensitivity‐enhanced access to potential temporal variations of fundamental constants. The various proposals to exploit the unique properties of 229mTh are presented herein, in particular focusing on its ability to serve as a test bench for time variations of fundamental constants like the fine structure constant. [ABSTRACT FROM AUTHOR]

Using an atom interferometer to measure the quotient of the reduced Planck's constant and the mass of a cesium‐133 atom ℏ/m Cs , the most accurate measurement of the fine structure constant α=1/137.035999046(27) is recorded, at an accuracy of 0.20 parts per billion (ppb). Using multiphoton interactions (Bragg diffraction and Bloch oscillations), the largest phase (12 million radians) of any Ramsey–Bordé interferometer and controlled systematic effects at a level of 0.12 ppb are demonstrated. Comparing the Penning trap measurements with the Standard Model prediction of the electron gyromagnetic anomaly ae based on the α measurement, a 2.5σ tension is observed, rejecting dark photons as the reason for the unexplained part of the muon's gyromagnetic moment discrepancy at a 99% confidence level according to frequentist statistics. Implications for dark‐sector candidates (e.g., scalar and pseudoscalar bosons, vector bosons, and axial‐vector bosons) may be a sign of physics beyond the Standard Model. A future upgrade of the cesium fountain atom interferometer is also proposed to increase the accuracy of ℏ/m Cs by 1 to 2 orders of magnitude, which would help resolve the tension. [ABSTRACT FROM AUTHOR]

Atoms and molecules can serve as sensitive probes of a possible variation of the fine structure constant α and electron‐to‐proton mass ratio μ. Two types of sensitivity coefficients are often used to quantify and compare the sensitivity of different species to the variation of fundamental constants. The dimensionless coefficients K are related to the fractional sensitivity, while dimensional factors q are related to the absolute sensitivity. Here, several common errors and misconceptions regarding these coefficients that frequently appear in the literature are discussed. [ABSTRACT FROM AUTHOR]

The magnetic moment (g‐factor) of the electron is a fundamental quantity in physics that can be measured with high accuracy by spectroscopy in Penning traps. Its value has been predicted by theory, both for the case of the free (unbound) electron and for the electron bound in a highly charged ion. Precision measurements of the electron magnetic moment yield a stringent test of these predictions and can in turn be used for a determination of fundamental constants such as the fine structure constant or the atomic mass of the electron. For the bound‐electron magnetic‐moment measurement, two complementary approaches exist, one via the so‐called "continuous Stern–Gerlach effect", applied to ions with zero‐spin nuclei, and one a spectroscopic approach, applied to ions with nonzero nuclear spin. Here, the latter approach is detailed, and an overview of the experiment and its status is given. [ABSTRACT FROM AUTHOR]

A number of atoms and ions with complex valence configurations are considered as candidates for atomic clocks with high sensitivity to the possible variation of the fine‐structure constant. Present level of the theory is not sufficient to predict frequencies of the clock transitions with accuracy, required for the experiment. Here an approach is tested, where the second‐order perturbation theory is used to iteratively saturate configuration space for valence electrons. On the examples of scandium, titanium, and iodine, it is demonstrated that this improves the efficiency of the CI+MBPT method for systems with strong configuration interaction and/or more than three valence electrons. [ABSTRACT FROM AUTHOR]