LIMITATIONS ON QUANTUM LADDER CLIMBING IN COMPLEX-SYSTEMS

The use of cesium Rydberg atoms as a test system for quantum ladder cl imbing with chirped laser pulses is described. Quantum ladders can be used in the coherent control of chemical reactions; for instance, by e xciting a specific molecular bond by climbing its vibrational ladder. A Rydberg atom is an easy test system because of the large transition dipole moments between Rydberg states. The Rydberg states are easy to access and to analyze. Picosecond far-infrared laser pulses around a w avelength of 50 mu m, with peak intensities of 10(9) W/cm(2), from the free-electron laser for infrared experiments (FELIX) at Nieuwegein, T he Netherlands, were used. It is found that the complexity of the syst em puts severe Limits on the allowed intensities that are used to driv e the ladder. At high intensity the ladder is distorted due to couplin g with states outside the ladder. This distortion frustrates efficient climbing.