Fractional population transfer among three-level systems in a cavity by Stark-shift-chirped rapid adiabatic passage

We show that the technique of Stark-chirped rapid adiabatic passage (SCRAP), hitherto used for complete population transfer among three states in atoms and molecules, offers a simple and robust method for creating coherent superpositions of states in the interaction of a three-level atom with cavity and laser fields. We also use this technique to generate maximally atom–photon entangled states. SCRAP in three-level systems uses three laser pulses: a strong far-off-resonant pulse modifies the transition frequencies by inducing dynamic Stark shifts and thereby creating time-dependent level crossings among the three diabatic states, while near-resonant and moderately strong pump and Stokes pulses, appropriately offset in time, drive the population between the initial and final states via adiabatic passage. In our method, the atom falls through a high-Q cavity and encounters the cavity mode and the laser beams such that the populations are transferred fractionally between two ground states (f-SCRAP). The populations of the created superposition are controlled by the detunings of the pump and cavity fields from the transition frequencies. Unlike the technique of fractional stimulated Raman adiabatic passage (f-STIRAP), f-SCRAP can be applied to one-photon as well as multiphoton transitions and it is a powerful alternative tool for f-STIRAP in the media exhibiting inhomogeneous broadening. This technique is robust against moderate variations in peak Rabi frequencies, in distance between the center of the cavity and axis of the pump and Stark laser beams and in the velocity of the atom.