High-precision measurement and ab initio calculation of the (6s26p2) 3P0 → 3P2 electric-quadrupole-transition amplitude in 208Pb

We have completed a measurement of the (6s(2)6p(2)) P-3(0) -> P-3(2) 939 nm electric quadrupole (E2) transition amplitude in atomic lead. Using a Faraday rotation spectroscopy technique and a sensitive polarimeter, we have measured this very weak E2 transition, and determined its amplitude to be < P-3(2) parallel to Q parallel to P-3(0)> = 8.91(9) a.u. We also present an ab initio theoretical calculation of this matrix element, determining its value to be 8.86(5) a.u., which is in excellent agreement with the experimental result. We heat a quartz vapor cell containing Pb-208 to between 800 and 940 degrees C, apply a similar to 10 G longitudinal magnetic field, and use polarization modulation and lock-in detection to measure optical rotation amplitudes of order 1 mrad with noise near 1 mu rad. We compare the Faraday rotation amplitude of the E2 transition to that of the P-3(0)-P-3(1) 1279 nm magnetic dipole (M1) transition under identical sample conditions.