Determination of the static polarizability of the 8s²S_1∕2 state of atomic cesium

We report a precise determination of the static polarizability of the 8s²S_1∕2 state of atomic cesium, carried out jointly through experimental measurements of the dc Stark shift of the 6s²S_1∕2→8s²S_1∕2 transition using Doppler-free two-photon absorption and theoretical computations based on a relativistic all-order method. We enhance the precision of the measurement by imposing phase-modulation sidebands on the laser beam and by using a pair of vapor cells, one of which serves as a reference, and measuring the absorption spectrum in each cell with a single scan of the laser frequency. The measured value for the polarizability of the 8s state is 38,060±250a₀³, in very good agreement with our theoretical value of 38,260±290a₀³. In addition, the small difference in the Stark shift measurement for the two hyperfine states that we examine yields a variation in the polarizability due to the magnetic dipole contact interaction of 290±30a₀³.