Chemical reactions between cold trappedBa+ions and neutral molecules in the gas phase

Abstract

Using a laser-cooled ion trapping apparatus, we have investigated laser-induced chemical reactions between cold trapped ${\mathrm{Ba}}^{+}$ ions and several neutral molecular gases at room temperature, ${\mathrm{O}}_{2}$, $\mathrm{C}{\mathrm{O}}_{2}$, and ${\mathrm{N}}_{2}\mathrm{O}$, leading to the production of cold trapped $(\ensuremath{\approx}20\phantom{\rule{0.3em}{0ex}}\mathrm{mK})$ $\mathrm{Ba}{\mathrm{O}}^{+}$ ions. The $\mathrm{Ba}{\mathrm{O}}^{+}$ ions were converted back to ${\mathrm{Ba}}^{+}$ ions via reaction with room-temperature CO. Reaction rates were determined by employing molecular dynamics simulations. The cold mixed-species ion ensembles produced were used for studying the efficiency of sympathetic cooling, by variation of the ratio of laser-cooled to sympathetically cooled ion numbers. In one extreme case, 20 laser-cooled $^{138}\mathrm{Ba}^{+}$ ions were capable of maintaining the translational temperature of 120 sympathetically cooled barium isotopes $(^{135--137}\mathrm{Ba}^{+})$ and 430 $^{138}\mathrm{Ba}^{16}{\mathrm{O}}^{+}$ molecules at approximately $25\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$.