Corrections to atomic ground state energy due to interaction between atomic electric quadrupole and optical field
Hu Jie1, †, Chen Yu1, Bai Yi-Xiu1, He Pei-Song2, Sun Qing1, Ji An-Chun1
       

(color online) The comparison of the impacts of the electric dipole and quadrupole coupling terms on the atomic ground state manifold to second order in perturbation theory, δ quad / δ d , in terms of principle quantum number n.