  We study a non-adiabatic excitation of an electron system in a 1D quantum
ring radiated by a short THz pulse. The response of two models, a continuous
and discrete, is explored. By introducing a spatial asymmetry in the external
perturbation a net current can be generated in the ring at a zero magnetic
field. Effect of impurities and ratchets are investigated in combination with
symmetric and asymmetric external excitation.
