二能级量子体系的相干操控对于精密测量和量子信息处理非常重要,如原子钟、原子干涉仪和量子计算等。在实验上观察到相干微波-射频(MW-RF)场驱动下的铷原子超精细基态的双光子Rabi振荡现象。基于塞曼子能级之间热弛豫过程的标定和微波跃迁的测量,清晰地分辨出叠加有热弛豫过程的原子态布居相干振荡。实验测得并详细讨论了广义Rabi频率与中间态失谐和微波/射频功率的关系。当中间态失谐较大时,实验结果与等效二能级理论模型非常吻合;但当中间态失谐较小时,少量原子占据中间态造成实测的Rabi频率偏离理论值。这些结果为二能级量子系统的相干操控提供了有力的理论支持。

Coherent manipulation of a two-level quantum system is of great significance for the precision measurement and quantum information processing, such as atomic clock, atomic interferometer and quantum computing. Two-photon Rabi oscillations between hyperfine ground states of rubidium atoms simultaneously driven by microwave and radio frequency (MW-RF) fields are experimentally demonstrated. Based on the calibration of the thermal relaxation process and the measurement of the microwave transition between Zeeman sublevels, the coherent oscillations of the atomic population are distinctly distinguished in the thermal relaxation process. Moreover, the dependence of the generalized Rabi frequency on the intermediate state detuning and the power of the MW/RF fields is measured and analyzed in detail. When the intermediate state detuning is large enough, the experimental results are consistent with the equivalent two-level model. Otherwise, the measured Rabi frequency deviates from the theoretical value due to the population of the intermediate state by few atoms. These achievements provide us powerful theoretical support for the coherent manipulation of two-state quantum systems.