Study of frequency-modulated excitation of Rydberg potassium atoms by using B-spline

With the B-spline expansion technique and a model potential of the alkali atoms, the properties of frequency-modulated excitation of Rydberg potassium atoms in a static electric field and a microwave field are investigated by using the time-dependent two-level approach. We successfully reproduce the square wave oscillations in the low frequency, the stair step population oscillations in the intermediate frequency, and the multiphoton transitions in the high frequency with respect to the unmodulated Rabi frequency, which have been observed experimentally by Noel et al. Phys. Rev. A 58 2265 (1998)]. Furthermore, we also numerically obtain the discretized Rabi oscillations predicted in the Landau-Zener accumulation model.