Reversing Hydride Ion Formation in Quantum Information Experiments with Be${}^{+}$

We demonstrate photodissociation of BeH${}^{+}$ ions within a Coulomb crystal of thousands of ${}^9$Be${}^{+}$ ions confined in a Penning trap. Because BeH${}^{+}$ ions are created via exothermic reactions between trapped, laser-cooled Be${}^{+}$(${}^2{\text{P}}_{3\mathrm{/}2}$) and background H${}_2$ within the vacuum chamber, they represent a major contaminant species responsible for infidelities in large-scale trapped-ion quantum information experiments. The rotational-state-insensitive dissociation scheme described here makes use of 157 nm photons to produce Be${}^{+}$ and H as products, thereby restoring Be${}^{+}$ ions without the need for reloading. This technique facilitates longer experiment runtimes at a given background H${}_2$ pressure, and may be adapted for removal of MgH${}^{+}$ and AlH${}^{+}$ impurities.