Measurement of the lifetime of the 3d2D5/2 state in 40Ca+

We report a measurement of the lifetime of the 3d 2D5/2 metastable level in 40Ca+, using quantum jumps of a single cold calcium ion in a linear Paul trap. The 4s 2S1/2-3d 2D5/2 transition is significant for single-ion optical frequency standards, astrophysical references, and tests of atomic structure calculations. We obtain τ = 1.168±0.007 s from observation of nearly 64 000 quantum jumps during ∼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±0.01 s for the lifetime of 3d 2D3/2. We also use quantum jump observations to demonstrate photon antibunching, and to estimate background pressure and heating rates in the ion trap. ©2000 The American Physical Society.