New phenomena have been observed by exciting ultracold ground-state atoms to Rydberg states. Starting with a dense sample of Rb atoms in a magneto-optical trap, we excite them to high Rydberg states (n = 30 - 90) with a single UV excitation pulse. Long-range molecular resonances with interatomic distances exceeding 104 a0 have been discovered. We have also observed the Rydberg excitation blockade, crucial for the implementation of quantum phase gates using neutral atoms. The physics behind these observations is attributed to the strong long-range van der Waals interactions among the Rydberg atoms. In addition, we have seen dipole (E1) forbidden but quadrupole (E2) allowed 5s → nd transitions, allowing us to determine the E2 oscillator strengths to these high Rydberg states. Our narrow-band UV pulsed laser system, with âˆ1⁄4100 MHz bandwidth, also allows us to measure the ratios of j-dependent oscillator strengths to the p and d Rydberg states.

We investigate here the characteristics of energy resonant dipole-dipole interactions between Rydberg atoms in Magneto-Optical Trap. These resonant processes occur in a kinetic energy regime in which the atoms may be considered stationary over the time scale of the experiment. Coupled with the long range of the interactions considered, this leads to multi-atom interactions becoming non-negligible. A simple model is outlined to provide insight into the effects of these multi-atom interactions which lead to some interesting behaviors. Experiments which examine the broadening of the dipole-dipole resonances and observe the time dependence of the interaction signal are discussed. Examination of adiabatic character of population transfer caused by slewing across the resonance is discussed in another experiment, as is the scaling behavior of the resonance linewidths and on-resonant signal growth rates. We end by discussing an experiment which takes advantage of some of the characteristics of these interactions to measure the tensor polarizability of Rydberg states of Rb.

Arising from a workshop, this book surveys the physics of ultracold atoms and molecules taking into consideration the latest research on ultracold phenomena, such as Bose Einstein condensation and quantum computing. Several reputed authors provide an introduction to the field, covering recent experimental results on atom and molecule cooling as well as the theoretical treatment.

This thesis describes the first demonstration of a cooperative optical non-linearity based on Rydberg excitation. Whereas in conventional non-linear optics the non-linearity arises directly from the interaction between light and matter, in a cooperative process it is mediated by dipole-dipole interactions between light-induced excitations. For excitation to high Rydberg states where the electron is only weakly bound, the dipole-dipole interactions are extremely large and long range, enabling an enormous enhancement of the non-linear effect. Consequently, cooperative non-linear optics using Rydberg excitations opens a new era for quantum optics enabling large single photon non-linearity to be accessible in free space for the first time. The thesis describes the theoretical underpinnings of the non- linear effect, the pioneering experimental results and implications for experiments in the single photon regime.