Spectroscopic Probing of Retardation Effects in the Casimir-Polder Interaction: A Theoretical Study

Lennard-Jones theory describes the atom-surface interaction as the instantaneous interaction between a fluctuating dipole and its image predicting a surface induced shift of the atomic energy levels given by -C ₃ /Z ³ , where z is the atom-surface distance and C3 is the van der Waals (vdW) coefficient. In Casimir-Polder theory, demonstrated experimentally with ground state atoms in ~1μm thick metallic cavities [1], atom-surface interactions arise from the modification of vacuum fluctuations next to a dielectric boundary. More recently, Casimir-Polder theory has been tested with ground state cold atoms at intermediate distances from a dielectric surface [2]. Nevertheless, testing the limits of the van der Waals law in the extreme near field remains an important experimental challenge. Additionally, excited state atoms are also of fundamental importance, as their interaction with surfaces can also be of resonant nature. This is of particular interest when atomic dipole transitions couple resonantly to surface polaritons, allowing for exotic near field effects.