The simplest molecules in nature, molecular hydrogen ions in the form of H2(+) and HD(+), provide an important benchmark system for tests of quantum electrodynamics in complex forms of matter. Here, ...we report on such a test based on a frequency measurement of a vibrational overtone transition in HD(+) by laser spectroscopy. We find that the theoretical and experimental frequencies are equal to within 0.6(1.1) parts per billion, which represents the most stringent test of molecular theory so far. Our measurement not only confirms the validity of high-order quantum electrodynamics in molecules, but also enables the long predicted determination of the proton-to-electron mass ratio from a molecular system, as well as improved constraints on hypothetical fifth forces and compactified higher dimensions at the molecular scale. With the perspective of comparisons between theory and experiment at the 0.01 part-per-billion level, our work demonstrates the potential of molecular hydrogen ions as a probe of fundamental physical constants and laws.
We calculate ionization energies and fundamental vibrational transitions for H_{2}^{+}, D_{2}^{+}, and HD^{+} molecular ions. The nonrelativistic quantum electrodynamics expansion for the energy in ...terms of the fine structure constant α is used. Previous calculations of orders mα^{6} and mα^{7} are improved by including second-order contributions due to the vibrational motion of nuclei. Furthermore, we evaluate the largest corrections at the order mα^{8}. That allows us to reduce the fractional uncertainty to the level of 7.6×10^{-12} for fundamental transitions and to 4.5×10^{-12} for the ionization energies.
We revisit the mα^{6}(m/M) order corrections to the hyperfine splitting in the H_{2}^{+} ion and find a hitherto unrecognized second-order relativistic contribution associated with the vibrational ...motion of the nuclei. Inclusion of this correction term produces theoretical predictions which are in excellent agreement with experimental data K. B. Jefferts, Phys. Rev. Lett. 23, 1476 (1969), thereby concluding a nearly 50-year-long theoretical quest to explain the experimental results within their 1-ppm error. The agreement between the theory and experiment corroborates the proton structural properties as derived from the hyperfine structure of atomic hydrogen. Our work furthermore indicates that, for future improvements, a full three-body evaluation of the mα^{6}(m/M) correction term will be mandatory.
Recently we reported a high-precision optical frequency measurement of the (
v
,
L
): (0, 2)
→
(8, 3) vibrational overtone transition in trapped deuterated molecular hydrogen (HD
+
) ions at 10 mK ...temperature. Achieving a resolution of 0.85 parts-per-billion (p.p.b.), we found the experimental value
ν
0
= 383, 407, 177.38 (41) MHz to be in agreement with the value from molecular theory
ν
th
383, 407, 177.150 (15) MHz within 0.6 (1.1) p.p.b. (Biesheuvel et al. in Nat Commun 7:10385,
2016
). This enabled an improved test of molecular theory (including QED), new constraints on the size of possible effects due to ‘new physics,’ and the first determination of the proton–electron mass ratio from a molecule. Here, we provide the details of the experimental procedure, spectral analysis, and the assessment of systematic frequency shifts. Our analysis focuses in particular on deviations of the HD
+
velocity distribution from thermal (Gaussian) distributions under the influence of collisions with fast ions produced during (laser-induced) chemical reactions, as such deviations turn out to significantly shift the hyperfine-less vibrational frequency as inferred from the saturated and Doppler-broadened spectrum, which contains partly unresolved hyperfine structure.
Positron accumulation in the GBAR experiment Blumer, P.; Charlton, M.; Chung, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2022, Volume:
1040
Journal Article
Peer reviewed
Open access
We present a description of the GBAR positron (e+) trapping apparatus, which consists of a three stage Buffer Gas Trap (BGT) followed by a High Field Penning Trap (HFT), and discuss its performance. ...The overall goal of the GBAR experiment is to measure the acceleration of the neutral antihydrogen (H¯) atom in the terrestrial gravitational field by neutralising a positive antihydrogen ion (H¯+), which has been cooled to a low temperature, and observing the subsequent H¯ annihilation following free fall. To produce one H¯+ ion, about 1010 positrons, efficiently converted into positronium (Ps), together with about 107 antiprotons (p¯), are required. The positrons, produced from an electron linac-based system, are accumulated first in the BGT whereafter they are stacked in the ultra-high vacuum HFT, where we have been able to trap 1.4(2) × 109 positrons in 1100 s.
The GBAR (Gravitational Behavior of Antihydrogen at Rest) experiment at CERN requires efficient deceleration of 100 keV antiprotons provided by the new ELENA synchrotron ring to synthesize ...antihydrogen. This is accomplished using electrostatic deceleration optics and a drift tube that is designed to switch from -99 kV to ground when the antiproton bunch is inside – essentially a charged particle “elevator” – producing a 1 keV pulse. We describe the simulation, design, construction and successful testing of the decelerator device at -92 kV on-line with antiprotons from ELENA.
Proton–electron mass ratio from HD+ revisited
Journal of physics. B, Atomic molecular and optical physics/Journal of physics. B, Atomic, molecular and optical physics,
01/2018
Journal Article
We present a parts-per-million test of quantum electrodynamics (QED) in the HD^{+} molecular hydrogen ion, improving on previous tests based on vibrational and rotational transitions by factors of 76 ...and 1.4, respectively. The test is performed following a unified statistical approach that also produces improved constraints on physics beyond the standard model. We furthermore show how individual constraints derived from the various degrees of freedom in HD^{+} and antiprotonic helium can be combined to enhance the sensitivity, thus ruling out “fifth forces” on the Ångstrom scale that are 10^{11} times weaker than the electromagnetic interaction.
The GBAR project (Gravitational Behaviour of Anti hydrogen at Rest) at CERN, aims to measure the free fall acceleration of ultracold neutral anti hydrogen atoms in the terrestrial gravitational ...field. The experiment consists preparing anti hydrogen ions (one antiproton and two positrons) and sympathetically cooling them with B
e
+
ions to less than 10
μ
K. The ultracold ions will then be photo-ionized just above threshold, and the free fall time over a known distance measured. We will describe the project, the accuracy that can be reached by standard techniques, and discuss a possible improvement to reduce the vertical velocity spread.
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