  A circularly polarized light can induce a dissipationless dc current in a
quantum nanoring which is responsible for a resonant helicity-driven
contribution to magnetic moment. This current is not suppressed by thermal
averaging despite its quantum nature. We refer to this phenomenon as the
quantum resonant inverse Faraday effect. For weak electromagnetic field, when
the characteristic coupling energy is small compared to the energy level
spacing, we predict narrow resonances in the circulating current and,
consequently, in the magnetic moment of the ring. For strong fields, the
resonances merge into a wide peak with a width determined by the spectral
curvature. We further demonstrate that weak short-range disorder splits the
resonances and induces additional particularly sharp and high resonant peaks in
dc current and magnetization. In contrast, long-range disorder leads to a
chaotic behavior of the system in the vicinity of the separatrix that divides
the phase space of the system into regions with dynamically localized and
delocalized states.
