Variational Calculation of the Hyperfine Stark Effect in Atomic $^{87}$Rb, $^{133}$Cs, and $^{169}$Tm

Abstract: An electronically variational approach to the calculation of atomic hyperfine structure transition energies under the influence of static external electric fields is presented. The method avoids the calculation of intermediate atomic states entirely and requires only the wavefunctions of the electronic states involved in the respective hyperfine levels. These wavefunctions are obtained through relativistic general-excitation-rank configuration interaction theory. The method also enables for calculations on atoms with the most complicated of shell structures. The initial applications include $^{87}$Rb and $^{133}$Cs where very good agreement of the approach with literature results is established. For $^{169}$Tm that is used in the development of atomic clocks the differential static electric dipole polarizability between ground levels $J=\frac{7}{2}$ and $J=\frac{5}{2}$ is calculated to be $\Delta\alpha = -0.23 \pm 0.11$ \au The hyperfine Stark coefficient for the hyperfine levels belonging to the ground term with $J=\frac{7}{2}$ is found to be $k = (1.3 \pm 1.0) \times 10^{-13}$ [Hz/((V/m)$^2$)]. This coefficient is several orders of magnitude smaller than the corresponding coefficients in $^{87}$Rb and $^{133}$Cs.