Speaker
Description
$H_2^+$ is the simplest stable molecule, and its structure can be calculated ab initio with high precision using quantum electrodynamics. By comparing the calculations with experimental data, fundamental constants can be determined, and the validity of the theory itself can be tested. However, challenging properties such as high reactivity, low mass, and the absence of rovibrational dipole transitions have thus far strongly limited spectroscopic studies of $H_2^+$.
We trap a single $H_2^+$ molecule together with a single beryllium ion using a cryogenic Paul trap, achieving trapping lifetimes of 11 h and ground-state cooling of the shared axial motion [1]. With this platform, we have implemented quantum logic spectroscopy of $H_2^+$. The $H_2^+$ molecule is produced in a chosen rovibrational state using resonance-enhanced multiphoton ionization [2]. We use quantum-logic operations between the molecule and the beryllium ion for the preparation of single hyperfine states and non-destructive state readout [3].
I will present progress towards high precision spectroscopy of rotational and rovibrational transitions, detailing the construction of a telecom-wavelength laser system and quantum logic spectroscopy schemes for the targeted transitions. Rotational and rovibrational spectroscopy of single $H_2^+$ molecular ions could provide a more accurate determination of fundamental constants such as the proton-to-electron mass ratio and an optical molecular clock based on the simplest molecule in nature.
[1] Nick Schwegler et al., Phys. Rev. Lett 131, 133003 (2023).
[2] Ho June Kim et al., arXiv:2509.03625 (2025).
[3] David Holzapfel et al., Phys. Rev. X 15, 031009 (2025).