Adiabatic passage with ultrashort laser pulses

We develop a method of executing complete population transfer between quantum states using a series of femtosecond laser pulses. The method can be applied to a large class of problems as it benefits from the high peak power and large spectral bandwidth afforded by ultrashort pulses. The new type of ``piecewise adiabaticity'' is reflected by the robustness of the degree of population transfer to a wide variation in the intensities, durations, and time delays between the pulses. The method is studied in detail for two- and three-level systems, and demonstrated experimentally in atomic rubidium where piecewise adiabatic population transfer between two electronic states is observed. Piecewise adiabatic passage offers a new set of tools for manipulating the population of atomic and molecular states on ultrashort time scale.