  We study the current flow through semiconductor quantum rings. In high
magnetic field the current is usually injected to the arm of the ring preferred
by classical magnetic forces. However, for narrow magnetic field intervals that
appear periodically on the magnetic field scale the current is injected to the
other arm of the ring. We indicate that the appearance of the anomalous --
non-classical -- current circulation results from Fano interference involving
localized resonant states. The identification of the Fano interference is based
on the comparison of the solution of the scattering problem with the results of
the stabilization method. The latter employs the bound-state type calculations
and allows to extract both the energy of metastable states localized within the
ring and the width of resonances by analysis of the energy spectrum of a finite
size system in function of its length. The Fano resonances involving states of
anomalous current circulation become extremely narrow on both magnetic field
and energy scales. This is consistent with the orientation of the Lorentz force
that tends to keep the electron within the ring and thus increases the lifetime
of the electron localization within the ring. Absence of periodic Fano
resonances in electron transfer probability through a quantum ring containing
an elastic scatterer is also explained.
