Combining experiments and relativistic theory for establishing accurate radiative quantities in atoms: The lifetime of the P-2(3/2) state in Ca-40(+)

We report a precise determination of the lifetime of the (4p) P-2(3/2) state of Ca-40(+), tau(p3/2) = 6.639(42) ns, using a combination of measurements of the induced light shift and scattering rate on a single trapped ion. Good agreement with the result of a recent high-level theoretical calculation, 6.69(6) ns [M. S. Safronova et al., Phys. A 83, 012503 (2011)], but a 6-sigma discrepancy with the most precise previous experimental value, 6.924(19) ns [J. Jin et al., Phys. Rev. Lett. 70, 3213 (1993)], is found. To corroborate the consistency and accuracy of the new measurements, relativistically corrected ratios of reduced-dipole-matrix elements are used to directly compare our result with a recent result for the P-1/2 state, yielding a good agreement. The application of the present method to precise determinations of radiative quantities of molecular systems is discussed.