Speaker
Description
Diatomic molecular hydrogen ions (MHI) such as H$_2^+$ and HD$^{+}$ are simple, single-electron systems with properties that can be calculated to high precision by ab initio theory. Comparison to precision experiments then enables stringent tests of the Standard Model and high-precision determinations of fundamental constants. Laser spectrosocopy of rovibrational transitions has now been demonstrated in both HD$^+$ [1-2] and in H$_2^+$ [3] using strings of MHI trapped in Coulomb crystals of laser cooled Be$^{+}$ ions while quantum state control of single ions has been achieved using the techniques of quantum logic spectroscopy [4]. Here, we present the results of a measurement campaign using single HD$^{+}$ ions in the Alphatrap cryogenic Penning trap [5]. The highly isolated cryogenic environment combined with image-current-based state-detection methods allows us to quickly prepare and detect ions in pure quantum states without the use of auxiliary ions. This, in turn, allowed us to perform a high-resolution determination of the ground state hyperfine structure including a comparison of the experimentally determined bound electron $g$-factor to a recent theoretical prediction with a relatively uncertainty of $2\times10^{-10}$ [6]. Recently, we have also performed laser spectroscopy of the $(v,L) = (0,0) \rightarrow (5,1)$ rovibrational transition and have achieved sub-kHz resonance linewidths that allow us to determine the transition frequency with a statistical uncertainty of less than 100 Hz, corresponding to a relative precision well below 1 ppt.
[1] S. Patra et al. Science 369, 1238 (2020).
[2] S. Alighanbari et al. Nature 581, 152 (2020).
[3] S. Alighanbari et al. Nature 644, 69 (2025).
[4] D. Holzapfel et al. Phys. Rev. X 15, 031009 (2025).
[5] Sturm, S. et al. Eur. Phys. J. Spec. Top. 227, 1425-1491 (2019).
[6] C. König et al. Phys. Rev. Lett. 134, 163001 (2025).
[7] C. König et al. Phys. Rev. Lett. accepted (2026).