Optical vortices discern attosecond time delay in electron emission from   magnetic sublevels
  Photoionization from energetically distinct electronic states may have a relative time delay of tens of attoseconds. Here we demonstrate that pulses of optical vortices allow measuring such attoseconds delays from magnetic sublevels, even from a spherically symmetric target. The difference in the time delay is substantial and exhibits a strong angular dependence. Furthermore, we find an atomic scale variation in the time delays depending on the target orbital position in the laser spot. The findings offer thus a qualitatively new way for a spatio-temporal sensing of the magnetic states from which the photoelectrons originate, with a spatial resolution way below the diffraction limit of the vortex beam. Our conclusions follow from analytical considerations based on symmetry, complemented and confirmed with full numerical simulations of the quantum dynamics. 
Jonas W\"atzel and Jamal Berakdar
physics.atom-ph