Quantized optical vortices, or the twisted photons, may carry pre-set amounts of angular momentum along their direction of propagation, thus allowing for quantum transitions otherwise forbidden for conventional plane-wave light. In this talk I will address the question of the angular momentum transfer to internal degrees of freedom of quantum systems excited by the twisted photons, and discuss appropriate polarization observables. We will show that interactions of such beams generate parity-conserving single-spin asymmetries due to presence of an orbital angular momentum, showing in circular dichroism even in the isotropic atomic matter. We extend our theory approach to the case of semi-conductors and demonstrate associated spin-orbit effects for spin injection of photoelectrons in bulk GaAs. The developed formalism was confirmed experimentally for twisted photoexcitation of cold trapped 40Ca+ ions in Mainz University.
