  We investigate the non-equilibrium charge and spin-dependent currents in a
quantum ring with a Rashba spin orbit interaction (SOI) driven by two
asymmetric picosecond electromagnetic pulses. The equilibrium persistent charge
and persistent spin-dependent currents are investigated as well. It is shown
that the dynamical charge and the dynamical spin-dependent currents vary
smoothly with a static external magnetic flux and the SOI provides a SU(2)
effective flux that changes the phases of the dynamic charge and the dynamic
spin-dependent currents. The period of the oscillation of the total charge
current with the delay time between the pulses is larger in a quantum ring with
a larger radius. The parameters of the pulse fields control to a certain extent
the total charge and the total spin-dependent currents. The calculations are
applicable to nano-meter rings fabricated in heterojuctions of III-V and II-VI
semiconductors containing several hundreds electrons.
