Generation of rotational-ground-state HD+ ions in an ion trap using a resonance-enhanced threshold photoionization process

Abstract

We report a method for producing ultracold ${\mathrm{HD}}^{+}$ molecular ions populated in a rotational ground state in an ion trap based on $[2+{1}^{\ensuremath{'}}]$ resonance-enhanced threshold photoionization (RETPI) and sympathetic cooling with the laser-cooled ${\mathrm{Be}}^{+}$ ions. The effects of electric field of the ion trap on the RETPI process of neutral HD molecules and the blackbody radiation (BBR) on the population evolution of rotational states of the generated polar ${\mathrm{HD}}^{+}$ ions have been studied. The initial rotational-ground-state population of ${\mathrm{HD}}^{+}$ ions is 0.93(12). After the cumulation time of 5 s, the rotational-ground-state population is reduced to 0.77(8) due to the BBR coupling. This method of generating ultracold state-selected ${\mathrm{HD}}^{+}$ ions is beneficial for the studies in precision rovibrational spectroscopy, state-controlled cold chemical reaction, and quantum logic spectroscopy.