Trapping and Sympathetic Cooling of Boron Hydride Ions

We demonstrate the trapping and sympathetic cooling of BH$^{+}$ ions in a Coulomb crystal of laser-cooled Ca$^{+}$, which we non-destructively confirm by resonantly exciting the secular motion of the molecular ion. The BH$^{+}$ ions are loaded by ablating boron in presence of H$_{2}$ which also produces various molecular ions of the form B$_{x}$H$_{y}^{+}$ as side products. This mixture of sympathetically cooled molecular ions can then be used to perform molecular spectroscopy. Our goal is to control the internal degrees of freedom of BH$^{+}$ as a first step towards the direct Doppler cooling of a molecular ion.