Population dynamics of a two-level system driven by oscillating transverse and longitudinal fields

The population dynamics of a two-level system coherently driven by oscillating transverse and longitudinal fields were investigated. The condition of investigation was that the frequency of longitudinal component is much faster than the characteristic time of a population change due to the transverse component. The experiment on a coherent quantum evolution of a two-level system was conducted. It was observed a long-lasting current oscillation corresponding to the Rabi oscillation in the nanometer-scale Josephson quantum box. The system was driven by a sudden changes of the external voltage. It will be worthwhile to investigate the quantum evolution of a two-level system under ac driving fields.