PUB - Publikationen an der Universität Bielefeld

Trapped Be+ ions are a leading platform for quantum information science (Gaebler et al 2016 Phys. Rev. Lett. ), but reactions with background gas species, such as H-2 and H2O, result in qubit loss. Our experiment reveals that the BeOH+ ion is the final trapped ion species when both H-2 and H2O exist in a vacuum system with cold, trapped Be+. The BeH+ product in the Be+ + H-2 reaction further reacts with H2O to form BeOH+. To understand the loss mechanism, low-temperature reactions between sympathetically cooled BeD+ ions and H2O molecules have been investigated using an integrated, laser-cooled Be+ ion trap and high-resolution time-of-flight mass spectrometer (Schneider et al 2014 Phys. Rev. Appl. ). Among all the possible products, BeH2O+, H2DO+, BeOD+, and BeOH+, only the BeOH+ molecular ion was observed experimentally, with the assumed co-product of HD. Theoretical analyses based on explicitly correlated restricted coupled cluster singles, doubles, and perturbative triples (RCCSD(T)-F12) method with the augmented correlation-consistent polarized triple zeta (AVTZ) basis set reveal that two intuitive direct abstraction product channels, Be + H2DO+ and D + BeH2O+, are not energetically accessible at the present reaction temperature (similar to 150 K). Instead, a double displacement BeOH+ + HD product channel is accessible due to a large exothermicity of 1.885 eV through a submerged barrier in the reaction pathway. While the BeOD+ + H-2 product channel has a similar exothermicity, the reaction pathway is dynamically unfavourable, as suggested by a sudden vector projection analysis. This work sheds light on the origin of the loss and contaminations of the laser-cooled Be+ ions in quantum-information experiments.