Controlling quantum coherence by circularly polarized fields

In terms of analytical results, we demonstrate that, within most parts in parameter space for a two-level magnetic system, suppression of quantum coherence can be induced by the circularly polarized fields. Low-frequency driving yields a dynamical localization opposite to the case of intermediate-to-high-frequency driving. The intrinsic relation between coherent suppression and the dressed-state level-crossing resonance is revealed.