We consider the exchange of spin and orbital angular momenta between a circularly polarized Laguerre–Gaussian beam of light and a single atom trapped in a two-dimensional harmonic potential. The radiation field is treated classically but the atomic centre-of-mass motion is quantized. The internal levels in the atom are taken to be Rydberg circular states. The spin and orbital angular momenta of the field are individually conserved upon absorption, with the result that the electronic and motional degrees of freedom of the atom are entangled. We suggest applications in quantum information processing.