A single ${\mathrm{Ba}}^{+}$ atom was confined in a radio-frequency ion trap and cooled by near-resonant laser light. Quantum jumps into and out of the metastable 5d ${}_{}{}^2{}_{}{}^{}D_{5/2}^{}{}_{}{}^{}$ level were observed that followed the expected exponential distribution in dark periods to good agreement. Measurement of quantum-jump distributions together with careful measurements of the absolute partial pressures of all residual gas species enabled accurate measurements of the quenched 5d ${}_{}{}^2{}_{}{}^{}D_{5/2}^{}{}_{}{}^{}$ lifetime as a function of quenching gas pressure. Measurements of quenching were observed at pressures where the mean collision rate was on the order of 1 ${\mathrm{s}}^{\mathrm{-}1}$. The results yielded quenching rate constants for the metastable level for a series of gases that typically make up the residual gas environment of ultra-high-vacuum systems (${\mathrm{H}}_2$, He, ${\mathrm{CH}}_4$, ${\mathrm{H}}_2$O, CO, ${\mathrm{N}}_2$, Ar, and ${\mathrm{CO}}_2$) together with an improved value of the $5^2$${\mathrm{D}}_{5/2}$ radiative lifetime of $t_0$=34.5±3.5 s. The above quenching rate constants were then compared with classical ion-molecule collision theory. It was found that the quenching rates for molecular gases were comparable to the classical collision rates, while the rates for atomic gases were considerably lower.

• Received 12 September 1989

DOI:https://doi.org/10.1103/PhysRevA.41.2621