  We theoretically calculate the polariton linewidth associated with the
polariton-electron scattering in a microcavity in presence of a magnetic field
perpendicular to the microcavity plane. It is shown that the polariton
linewidth oscillates as a function of the magnetic field magnitude and the
polariton-electron scattering rate can be not only decreased but also increased
by the magnetic field. The possible applications of such an effect are
discussed.
