Hydrogen-Deuterium Isotope Shift: From the 1S-2s-Transition Frequency to the Proton-Deuteron Charge-Radius Difference

We analyze and review the theory of the hydrogen-deuterium isotope shift for the 1S-2S transition, which is one of the most accurately measured isotope shifts in any atomic system, in view of a recently improved experiment. A tabulation of all physical effects that contribute to the isotope shift is given. These include the Dirac binding energy, quantum electrodynamic effects, including recoil corrections, and the nuclear-size effect, including the pertaining relativistic and radiative corrections. From a comparison of the theoretical result Δfth=670999566.90(66)(60)kHz (exclusive of the nonrelativistic nuclear-finite-size correction) and the experimental result Δfexpt=670994334605(15) Hz, we infer the deuteron-proton charge-radius difference (r2)d- (r2)p=3.82007(65) fm2 and the deuteron structure radius rstr=1.97507(78) fm

Mechanistic insight into proton-coupled mixed valency

Stabilisation of the mixed-valence state in [Mo2(TiPB)3(HDOP)]2+ (HTiPB = 2,4,6-triisopropylbenzoic acid, H2DOP = 3,6-dihydroxypyridazine) by electron transfer (ET) is related to the proton coordinate of the bridging ligands. Spectroelectrochemical studies suggest that ET is slower than 109 s−1. The mechanism has been probed using DFT calculations, which show that proton transfer induces a larger dipole in the molecule resulting in ET

Precision spectroscopy of helium in a magic wavelength optical dipole trap

Improvements in both theory and frequency metrology of few-electron systems such as hydrogen and helium have enabled increasingly sensitive tests of quantum electrodynamics (QED), as well as ever more accurate determinations of fundamental constants and the size of the nucleus. At the same time advances in cooling and trapping of neutral atoms have revolutionized the development of increasingly accurate atomic clocks. Here, we combine these fields to reach the highest precision on an optical tranistion in the helium atom to date by employing a Bose-Einstein condensate confined in a magic wavelength optical dipole trap. The measured transition accurately connects the ortho- and parastates of helium and constitutes a stringent test of QED theory. In addition we test polarizability calculations and ultracold scattering properties of the helium atom. Finally, our measurement probes the size of the nucleus at a level exceeding the projected accuracy of muonic helium measurements currently being performed in the context of the proton radius puzzle

QCD and strongly coupled gauge theories : challenges and perspectives

We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe