Trapping and Ground-State Cooling of a Single H$_2^+$

TL;DR

This paper reports the successful trapping, chemical stability study, and ground-state cooling of a single H$_2^+$ ion paired with $^9$Be$^+$ in a cryogenic trap, enabling future quantum spectroscopy of light ions.

Contribution

It demonstrates co-trapping, chemical lifetime dependence on temperature, and ground-state cooling of H$_2^+$, advancing quantum logic spectroscopy capabilities for light ions.

Findings

H$_2^+$ ion lifetime up to 11 hours at 10 K

Achieved average phonon numbers of 0.07 and 0.05 in two motional modes

Cooling temperatures of approximately 22 μK and 55 μK

Abstract

We demonstrate co-trapping and sideband cooling of a H$_2^+$ - $^9$Be$^+$ ion pair in a cryogenic Paul trap. We study the chemical lifetime of H$_2^+$ and its dependence on the apparatus temperature, achieving lifetimes of up to $11^{+6}_{-3}$ h at 10 K. We demonstrate cooling of two of the modes of translational motion to an average phonon number of 0.07(1) and 0.05(1), corresponding to a temperature of 22(1) $\mu$K and 55(3) $\mu$K respectively. Our results provide a basis for quantum logic spectroscopy experiments of H$_2^+$, as well as other light ions such as HD$^+$, H$_3^+$, and He$^+$.