MULTIPLE LANDAU-ZENER CROSSINGS AND QUANTUM INTERFERENCE IN ATOMS DRIVEN BY PHASE-MODULATED FIELDS

The excitation amplitude after multiple crossings is not a mere produc t of Landau-Zener transition probabilities at each crossing, due to co herent evolution of the system in between crossings. In the three-leve l ladder system, the trapping of population by frequency modulated fie lds ensures coherent evolution, and inclusion of phase effects for pop ulation redistribution after multiple crossings becomes necessary. The relative phase accumulated by various adiabatic states as they evolve along different paths is tailored to show the existence of quantum in terference effects. We present a method of inverting the population in a three-level system, without affecting the population in the interme diate state. We also present an all optical implementation of the thre e-level ladder system, where these effects can be realized.