Photodissociation spectra of single trapped CaOH+ molecular ions

Abstract

Molecular ions that are generated by chemical reactions with trapped atomic ions can serve as an accessible testbed for developing molecular quantum technologies. On the other hand, they are also a hindrance to scaling up quantum computers based on atomic ions as unavoidable reactions with background gas destroy the information carriers. Here, we investigate the single- and two-photon dissociation processes of single $\text{CaOH}^+$ molecular ions co-trapped in $\text{Ca}^+$ ion crystals using a femtosecond laser system. We report the photodissociation cross section spectra of $\text{CaOH}^+$ for single-photon processes at $\lambda=$245 - 275$\,$nm and for two-photon processes at $\lambda=$500 - 540$\,$nm. Measurements are interpreted with quantum-chemical calculations, which predict the photodissociation threshold for $\text{CaOH}^+\to \text{Ca}^++\text{OH}$ at 265$\,$nm. This result can serve as a basis for dissociation-based spectroscopy for studying the internal structure of $\text{CaOH}^+$. The result also gives a prescription for recycling $\text{Ca}^+$ ions in large-scale trapped $\text{Ca}^+$ quantum experiments from undesired $\text{CaOH}^+$ ions formed in the presence of background water vapor.