Measurement of the scalar third-order electric polarizability of the Cs   ground state using CPT-spectroscopy in Ramsey geometry
  The AC Stark shift induced by blackbody radiation is a major source of systematic uncertainty in present-day cesium microwave frequency standards. The shift is parametrized in terms of a third-order electric polarizability $\alpha_0^{(3)}$ that can be inferred from the static electric field displacement of the clock transition resonance. In this paper, we report on an all-optical CPT pump-probe experiment measuring the differential polarizability $\Delta \alpha_0^{(3)} = \alpha_0^{(3)}(F{=}4) - \alpha_0^{(3)}(F{=}3)$ on a thermal Cs atomic beam, from which we infer $ \alpha_0^{(3)}(F{=}4) = 2.023(6)_{stat}(9)_{syst}~Hz/(kV/cm)^2$, which corresponds to a scalar Stark shift parameter $ k_{s} = -2.312(7)_{stat}(10)_{syst}~Hz/(kV/cm)^2$. The result agrees within two standard deviations with a recent measurement in an atomic fountain, and rules out another recent result obtained in a Cs vapor cell. 
Jean-Luc Robyr, Paul Knowles and Antoine Weis
physics.atom-ph