Adventures of a Rydberg electron in an anisotropic world

The study of subtle interactions in atomic and molecular systems has stirred scientific curiosity since the dawn of quantum mechanics. Even today, research into perturbative long-range interactions continues to push into new territory, driven largely by the experimental capabilities of Rydberg state spectroscopy to detect effects of extremely weak interactions. While static long-range multipole interactions have been studied for years, the presence of dynamic terms that involve both position and momentum operators has been demonstrated only surprisingly recently. In this paper we document the existence of an effective vector interaction term in the long-range potential experienced by a moving charged particle in the presence of an anisotropic ionic core. In contrast to ordinary static quadrupole or dipole interaction terms, the existence of this vector interaction hinges on the motion of the distant charge as it roams beyond the confines of the core.