The Collision Cross Section Of Ultracold Rb Atoms Using Magneto-Optic And Magnetic Traps

Ultracold atomic collisional physics is a promsing field in ultracold physics, scientists play more and more attention to this area because it is significant and has the possibility of broad applications in future. The atom collisional cross section is a more popular research topic in the field of ultracold atom collision physics. In nuclear and particle physics, the concept of cross section is used to express the likelihood of interaction between particles. The informations of the trapped atom numbers of laser cooling or BEC experiments, particle loss rate, collision parameters, trap depth of cold atoms can be achieved by measured collision cross section of cold atoms. It is very important to the research on ultracold atomic physics. In this dissertation, we study the experiments of ultracold Rb atom collided with background Ar or He gas using magneto-optic and magnetic traps. A new technique to measure collision loss rate and absolute collision cross sections is proposed. An overview of both experimental and theoretical results for the case of trapped Rb and background argon or helium gas will be given. The research work has been summarized in detail as follows.We present a new technique to measure the absolute total collision cross sections for a room-temperature background gas of 40Ar using laser cooled 87Rb atoms confined in either a magneto-optic or a magnetic quadrupole trap. By using this method, loss rate of trapped atoms and the total cross section can be accurately achieved from knowledge of the background gas density. This technique can be a normative method to acquire collision cross sections of ultracold atoms with other background gases in the further work. Building up the MOT and magnetic trap is the most important task in this experiment work. Three requisite instruments are involved in this experiment, which are vacuum system, laser light systems and Rb injection system. Using software control system can turn on and off lasers to simply transfer MOT to magnetic trap.By using this new technique, we measure 85Rb or 87Rb collided with room-temperature background rgon or helium gas in the MOT and magnetic trap. The loss rates from the magneto-optic trap (MOT) and the pure magnetic trap are compared and show significant differences. The initial discussion focuses on a theoretical overview of the principles involved in atom collisional physics fields. Finally, an overview of both experimental and theoretical results including cross sections and loss rates for the case of trapped 85Rb or 87Rb and background Ar or He gas will be given. These results suggest that this theory may be a better tool for measuring total elastic collision cross section on arbitrary trap depth. Then, we present a new method for determining the trap depth of an atomic or molecular trap of any type and any depth. This method relies on measurements of the trap loss rate induced by elastic collisions of ultracold 87Rb atoms with room temperature background 40Ar gases. We compare this method with an independent technique that relies on measurements of atom loss rates during optical excitation of colliding pairs to a repulsive molecular state. The main advantage of the method presented here is its simplicity and applicability to traps of any type requiring only knowledge of the background gas pressure between the trapped particles and the background gas particles. Another advantage is that the technique is applicable to any type of traps, including the optical and magnetic traps, and at extremely low densities where intra-trap collisions are rare.Finally, cavity quantum electrodynamics is a promising research field of the cold atom physics. The entropy correlation and entanglement of a moving atom interacting with k-photon Jaynes-Cummings model are investigated. Entropy exchange, which is a form of anti-correlated behavior between atomic and field subsystems, is explored. Analytical results represents that the atomic motion, transition number k of field and field-mode structure show some influence on entropy exchange. Moreover, the relationship between entropy correlations and entanglement is also discussed.