The Dynamics Of The Ultracold Atom-molecules Conversion With Different External Fields

Recently, the study of the ultracold atom-molecules conversion has attracted some attentions in modern physics. The study of ultracold molecules represents an exciting new frontier for low temperature physics, atomic, and molecular physics, bring about various theory achievements, and also give rise to breakthroughs in experimental techniques. The creation of ultracold molecules is not only the further work of atom cooling but also the test and challenge of the theory and experimental techniques, therefore, the producing ultracold molecules has became the research hotspot. There are a lot of mature technology is used in the manufacture of ultracold molecules, in which the technologies of the ultracold atom-polymer molecules conversion has made great achievements. Hence, in this paper, we investigate the effect of external field shape on the ultracold atom-molecules conversion efficiency by the different technologies. By changing the external field shape and corresponding parameters, we realize stable and high-efficiency the ultracold atom-molecules conversion. The specific contents and conclusions of this paper are as follows:In the first chapter, the physical background and the related physical knowledge are briefly introduced, including The low temperature physics. Bose-Einstein Condensation, and the creation ways of ultracold atoms and ultracold molecules. We classify a vari-ety of different technologies. We introduce the basic principle of the different cooling technologies, mainly introduce the basic method of the ultracold atom-polymer molecules conversion, and the main achievements obtained are listed.In the second chapter, we present the fundamental theory about our investigation. We have worked out the Gross-Pitaevskii equations under the meanfield approximation. We construct the equivalent classical Hamiltonian for two-level system. We obtain the ultracold atom-molecules CPT state solution and derive the algebraic equations.In the third chapter, within the Feshbach resonances, we investigate the dynamics of converting ultracold bosonic atoms to molecules when the external field is a Gaussian temporal shape and a linear frequency sweep. The numerical simulation of the atom-molecules conversion efficiency is derived by using the mean-field theory, and the effect of the field parameters in the association process is analyzed. Furthermore, we derive a closed equation for the conversion efficiency in the sudden limit case. And we use quan-tum microscopic model (the Fock states) to discuss many-body effects on the conversion. Our theory indicates the Gaussian external field model can be stable and high-efficiency realization of the ultracold atom-molecules conversion.In the fourth chapter, within the Photoassociation stimulated Raman adiabatic pas-sage, we investigate the effects of external field shape to the atom-polymer conversion efficiency, by changing the Rabi frequency of the photoassociation laser and the atom-polymer coupling strength. First, we make improvements on the external filed shape is given in the reference. We introduce the concept of time-index, and discuss the influence of time-index to conversion efficiency. Then we choose a more optimized external filed shape. Under the effect of the external field, the adiabatic process almost no oscillation, the adiabatic fidelity close to 1, and the error of the system is less. And it has good parameter robustness. The external field can be stable and high-efficiency realization of the ultracold atom-polymer molecules conversion.In the fifth chapter, we summarize the main results and give an outlook of the further work.