Measurement of the lifetime of the3d2D5/2state in40Ca+

We report a measurement of the lifetime of the $3d{}^2{D}_{5/2}$ metastable level in ${}^{40}{\mathrm{Ca}}^{+},$ using quantum jumps of a single cold calcium ion in a linear Paul trap. The $4s{}^2{S}_{1/2}–3d{}^2{D}_{5/2}$ transition is significant for single-ion optical frequency standards, astrophysical references, and tests of atomic structure calculations. We obtain $\tau =1.168\mathrm{}\pm 0.007$ s from observation of nearly $64000$ quantum jumps during $\sim 32$ h. Our result is more precise and significantly larger than previous measurements. Experiments carried out to quantify systematic effects included a study of a previously unremarked source of systematic error, namely, excitation by the broad background of radiation emitted by a semiconductor diode laser. Combining our result with atomic structure calculations yields $1.20\pm 0.01$ s for the lifetime of $3d{}^2{D}_{3/2}.$ We also use quantum jump observations to demonstrate photon antibunching, and to estimate background pressure and heating rates in the ion trap.