Sympathetic cooling of molecular ion motion to the ground state

TL;DR

This paper reports the successful sympathetic sideband cooling of a molecular ion co-trapped with an atomic ion, achieving near ground state motion in both axial modes, which advances quantum control of molecular ions.

Contribution

The study demonstrates simultaneous ground-state cooling of both axial modes of a molecular-ion and atomic-ion pair in a linear Paul trap, a novel achievement in molecular ion quantum control.

Findings

Center of mass mode cooled to $ar{n}=0.13$ quanta

Breathing mode cooled to $ar{n}=0.05$ quanta

Corresponding temperatures below 20 microkelvin

Abstract

We demonstrate sympathetic sideband cooling of a $^{40}$CaH$^{+}$ molecular ion co-trapped with a $^{40}$Ca$^{+}$ atomic ion in a linear Paul trap. Both axial modes of the two-ion chain are simultaneously cooled to near the ground state of motion. The center of mass mode is cooled to an average quanta of harmonic motion $\overline{n}_{\mathrm{COM}} = 0.13 \pm 0.03$, corresponding to a temperature of $12.47 \pm 0.03 ~\mu$K. The breathing mode is cooled to $\overline{n}_{\mathrm{BM}} = 0.05 \pm 0.02$, corresponding to a temperature of $15.36 \pm 0.01~\mu$K.