Special Issue "High Precision Measurements of Fundamental Constants"

A special issue of Atoms (ISSN 2218-2004).

Deadline for manuscript submissions: 31 October 2018

Special Issue Editor

Guest Editor
Dr. Joseph N. Tan

National Institute of Standards & Technology (NIST), 100 Bureau Drive, Gaithersburg, MD 20899, USA
Website | E-Mail
Interests: trapping, cooling, and spectroscopy of exotic ions; order in plasmas cooled to low temperature (& driven far from equilibrium); precision measurements and tests of QED or the standard model

Special Issue Information

Dear Colleagues,

Precision experiments with atomic systems provide an important avenue for testing our understanding of the laws of nature. Along with theoretical advances, they enable significant improvement in the determination of fundamental physical constants. As an example, a 13-fold improvement in the precision of the electron mass determination (relative uncertainty of 30 ppt) was obtained by interrogating a single 12C5+ hydrogen-like ion and accounting for higher-order effects from quantum electrodynamics (QED). A direct measurement of the magnetic moment of the proton by flipping its spin in a Penning trap has now surpassed the precision of an indirect determination from the spectrum of a hydrogen maser (a 42-year-old record). The most stringent test of QED is a comparison between prediction and measurement of the anomalous magnetic moment (g-2) of an electron, with an independent value of the fine structure constant (a) coming from a cold atom interferometer. Quantum interferometry of laser-cooled atoms has also provided a precise value of the Newtonian gravitational constant (G). Some other interesting works involve exotic atomic systems (antiprotonic helium, positronium, muonic hydrogen, etc.). In keeping with the advancing precision of measurements, certain physical constants will be selected to assume a far-reaching role in metrology. In 2018, the International System of Units (SI) is scheduled to undergo a framework revision wherein a set of seven exactly-defined fundamental constants would form the new basis for defining the SI units. This Special Issue highlights recent works, innovations and challenges in high precision measurements of fundamental constants.

Dr. Joseph N. Tan
Guest Editor

Manuscript Submission Information

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Published Papers (4 papers)

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Research

Open AccessFeature PaperArticle Oriented Polar Molecules in a Solid Inert-Gas Matrix: A Proposed Method for Measuring the Electric Dipole Moment of the Electron
Received: 24 October 2017 / Revised: 21 December 2017 / Accepted: 27 December 2017 / Published: 5 January 2018
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Abstract
We propose a very sensitive method for measuring the electric dipole moment of the electron using polar molecules embedded in a cryogenic solid matrix of inert-gas atoms. The polar molecules can be oriented in the z^-direction by an applied electric field,
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We propose a very sensitive method for measuring the electric dipole moment of the electron using polar molecules embedded in a cryogenic solid matrix of inert-gas atoms. The polar molecules can be oriented in the z ^ -direction by an applied electric field, as has recently been demonstrated by Park et al. The trapped molecules are prepared into a state that has its electron spin perpendicular to z ^ , and a magnetic field along z ^ causes precession of this spin. An electron electric dipole moment d e would affect this precession due to the up to 100 GV/cm effective electric field produced by the polar molecule. The large number of polar molecules that can be embedded in a matrix, along with the expected long coherence times for the precession, allows for the possibility of measuring d e to an accuracy that surpasses current measurements by many orders of magnitude. Because the matrix can inhibit molecular rotations and lock the orientation of the polar molecules, it may not be necessary to have an electric field present during the precession. The proposed technique can be applied using a variety of polar molecules and inert gases, which, along with other experimental variables, should allow for careful study of systematic uncertainties in the measurement. Full article
(This article belongs to the Special Issue High Precision Measurements of Fundamental Constants)
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Open AccessFeature PaperArticle Proton Charge Radius from Electron Scattering
Received: 21 November 2017 / Revised: 19 December 2017 / Accepted: 20 December 2017 / Published: 30 December 2017
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Abstract
The rms-radius R of the proton charge distribution is a fundamental quantity needed for precision physics. This radius, traditionally determined from elastic electron-proton scattering via the slope of the Sachs form factor Ge(q2) extrapolated to momentum transfer q
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The rms-radius R of the proton charge distribution is a fundamental quantity needed for precision physics. This radius, traditionally determined from elastic electron-proton scattering via the slope of the Sachs form factor G e ( q 2 ) extrapolated to momentum transfer q 2 = 0 , shows a large scatter. We discuss the approaches used to analyze the e-p data, partly redo these analyses in order to identify the sources of the discrepancies and explore alternative parameterizations. The problem lies in the model dependence of the parameterized G ( q ) needed for the extrapolation. This shape of G ( q < q m i n ) is closely related to the shape of the charge density ρ ( r ) at large radii r, a quantity that is ignored in most analyses. When using our physics knowledge about this large-r density together with the information contained in the high-q data, the model dependence of the extrapolation is reduced, and different parameterizations of the pre-2010 data yield a consistent value for R = 0.887 ± 0.012 fm. This value disagrees with the more precise value 0.8409 ± 0.0004 fm determined from the Lamb shift in muonic hydrogen. Full article
(This article belongs to the Special Issue High Precision Measurements of Fundamental Constants)
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Open AccessFeature PaperArticle Long-Range Interactions for Hydrogen: 6P–1S and 6P–2S Systems
Received: 30 August 2017 / Revised: 24 October 2017 / Accepted: 16 November 2017 / Published: 23 November 2017
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Abstract
The collisional shift of a transition constitutes an important systematic effect in high-precision spectroscopy. Accurate values for van der Waals interaction coefficients are required in order to evaluate the distance-dependent frequency shift. We here consider the interaction of excited hydrogen 6P atoms
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The collisional shift of a transition constitutes an important systematic effect in high-precision spectroscopy. Accurate values for van der Waals interaction coefficients are required in order to evaluate the distance-dependent frequency shift. We here consider the interaction of excited hydrogen 6 P atoms with metastable atoms (in the 2 S state), in order to explore the influence of quasi-degenerate 2 P and 6 S states on the dipole-dipole interaction. The motivation for the calculation is given by planned high-precision measurements of the transition. Due to the presence of quasi-degenerate levels, one can use the non-retarded approximation for the interaction terms over wide distance ranges. Full article
(This article belongs to the Special Issue High Precision Measurements of Fundamental Constants)
Open AccessArticle THz/Infrared Double Resonance Two-Photon Spectroscopy of HD+ for Determination of Fundamental Constants
Received: 1 September 2017 / Revised: 1 October 2017 / Accepted: 6 October 2017 / Published: 12 October 2017
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Abstract
A double resonance two-photon spectroscopy scheme is discussed to probe jointly rotational and rovibrational transitions of ensembles of trapped HD+ ions. The two-photon transition rates and lightshifts are calculated with the two-photon tensor operator formalism. The rotational lines may be observed with
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A double resonance two-photon spectroscopy scheme is discussed to probe jointly rotational and rovibrational transitions of ensembles of trapped HD+ ions. The two-photon transition rates and lightshifts are calculated with the two-photon tensor operator formalism. The rotational lines may be observed with sub-Doppler linewidth at the hertz level and good signal-to-noise ratio, improving the resolution in HD+ spectroscopy beyond the 10−12 level. The experimental accuracy, estimated at the 10−12 level, is comparable with the accuracy of theoretical calculations of HD+ energy levels. An adjustment of selected rotational and rovibrational HD+ lines may add clues to the proton radius puzzle, may provide an independent determination of the Rydberg constant, and may improve the values of proton-to-electron and deuteron-to-proton mass ratios beyond the 10−11 level. Full article
(This article belongs to the Special Issue High Precision Measurements of Fundamental Constants)
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