Study of coherent properties of Rydberg-atom systems

Atoms excited into states of high principal quantum number, Rydberg atoms, have exaggerated properties such as large size and dipole moments, long lifetimes, and high polarizabilities. These properties can be used to realize a "Rydberg excitation blockade" in narrow-band photo-excitation (∼ 1 MHz bandwidth) of laser-cooled and trapped atoms. Under ideal conditions, the blockade phenomenon leads to an inhibition of more than one Rydberg excitation in dense samples of atoms. The blockade is useful in a number of applications including quantum information processing, quantum cryptography, and atomic clocks. In this thesis, I discuss experimental investigations of the dependence of the blockade effectiveness on the principal quantum number of the excited Rydberg level, and the Rydberg excitation laser's detuning and intensity. Rydberg-atom counting statistics is used as a technique for measuring the effectiveness of the Rydberg blockade.; An important aspect in experiments on the blockade effect is the efficiency of the photo-excitation process used for Rydberg-atom generation. Therefore, the described work deals, in part, with methods of coherent excitation of atoms into and out of Rydberg states. I show that STIRAP (stimulated Raman adiabatic passage) allows us to transfer atoms into Rydberg levels with about 70% excitation efficiency, under the constraints of the present experiment. It is also seen that the excitation efficiency is insensitive to variations in laser pulse intensity and width, as expected for STIRAP. The experimental techniques used to measure the blockade effect using counting statistics and to achieve coherent excitation into Rydberg states, are important for future studies of small atomic systems blockaded to one Rydberg excitation.