Effective magnetic fields induced by EIT in ultra-cold atomic gases

We study the influence of two resonant laser beams (to be referred to as the control and probe beams) on the centre-of-mass motion of ultra-cold atoms characterized by three energy levels of the Λ-type. The laser beams being in the electromagnetically induced transparency (EIT) configuration drive the atoms to their dark states. We impose the adiabatic approximation and obtain an effective equation of motion for the dark state atoms. The equation contains a vector potential type interaction as well as an effective trapping potential. We concentrate on the situation where the control and probe beams are co-propagating and have orbital angular momenta (OAM). The effective magnetic field is then oriented along the propagation direction of the control and probe beams. Its spatial profile can be shaped by choosing proper laser beams. We analyse several situations where the effective magnetic field exhibits a radial dependence. In particular, we study effective magnetic fields induced by Bessel beams, and demonstrate how to generate a constant effective magnetic field for a ring geometry of the atomic trap. We also discuss a possibility of creating an effective field of a magnetic monopole.