Molecular frequency metrology: ultra-high precision spectroscopy of the rotational transition of HD+
Final Report Abstract
In this project we have performed a Doppler‐free rotational spectroscopy of a cluster of trapped and sympathetically cooled molecular hydrogen ion HD+. Compared to our previous work, we have improved the signal‐to‐noise ratio by hyperfine selective dissociation of HD+, which reduced the background noise. The improved signal allowed us to reduce the spectroscopy source´s intensity, and reduce the power broadening induced by the source. Therefore, we managed to achieve unprecedented line resolution as low as 4 Hz (3×10^‐12 fractionally). The ultra‐high experimental resolution allowed to resolve transitions between individual Zeeman states. In total, 9 Zeeman components of 6 hyperfine transitions were measured, including the two unresolved stretched states of our previous work. For each Zeeman component relevant systematic effects (i.e. Zeeman shift, trap induced shift, and light shifts induced by lasers and spectroscopy source) are measured to find the unperturbed hyperfine transition frequencies. We determined the transition frequencies with relative uncertainties between 1.3×10^‐11 and 4.9×10^‐11. We employed a composite frequency approach to suppress the impact of the limited accuracy of the ab initio theory of the spin structure and determined the spin‐averaged frequency. We found an agreement between theory and experiment with relative uncertainty of 4.8×10^‐11, limited by the fundamental constants’ uncertainties. We fitted the value of a combination of fundamental constants, (m/µ)R∞, to the measured rotational frequency. We found agreement between our result and the CODATA2018 value, but our result has 2.4 times smaller uncertainty (1.9×10^‐11) than CODATA2018.
Publications
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Precise test of quantum electrodynamics and determination of fundamental constants with HD+ ions. Nature, 581(7807), 152–158.
Alighanbari, S.; Giri, G. S.; Constantin, F. L.; Korobov, V. I. & Schiller, S.
