I will discuss experimental results where orbital angular momentum from a photon was transferred to the internal electronic degrees of freedom of a single atom. We observed strongly modified selection rules showing that an atom can absorb two quanta of angular momentum from a single photon: one from the spin and another from the spatial structure of the beam. Moreover, the results show in some cases, the longitudinal component of the field in a vortex beam plays a crucial role in determining the interaction characteristics. Furthermore, I’ll show that parasitic ac-Stark shifts from off-resonant transitions are suppressed in the center of the vortex beam. The experiments were done probing a quadrupole transition in a single trapped Calcium ion.
