Corrections to atomic ground state energy due to interaction between atomic electric quadrupole and optical field**Project supported by the National Natural Science Foundation of China (Grant Nos. 21503138, 11247324, 61405003, 11604225, 11404225, and 11474205) and the Fund from Beijing Education Committees, China (Grant No. KM201710028004).

Abstract

We study the ground state energy of an atom interacting with an oscillating optical field with electric dipole and quadrupole coupling. Under the rotating wave approximation, we derive the effective atomic Hamiltonians of the dipole/quadrupole coupling term within the perturbation theory up to the second order. Based on the effective Hamiltonians, we analyze the atomic ground-state energy corrections of these two processes in detail. As an application, we find that for alkali-like atoms, the energy correction from the quadrupole coupling is negligible small in comparison with that from the dipole coupling, which justifies the so-called dipole approximation used in literatures. Some special cases where the quadrupole interaction may have considerable energy corrections are also discussed. Our results would be beneficial for the study of atom–light interaction beyond dipole approximation.