Quantum jumps and the single trapped barium ion: Determination of collisional quenching rates for the 5d2D5/2 level.

Abstract

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 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. 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\ifmmode\pm\else\textpm\fi{}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.