Ultracold Atom-molecule Conversion Dynamics In Periodic External Field

The study of ultracold atom molecule is a frontier subject in the field of ultracold quantum gases,which has important theoretical values and broad application prospects.The research has widely used strongly interacting superfluid,coherent molecular optics,precision measurement,and condensed-matter physics,etc.Photoassociation and magnetic resonance are widely used production techniques of ultracold atoms to molecules.This conversion process is usually described by the Landau-Zener model,but this model has some limitations in certain situations.In order to overcome these limitations,more and more models have been applied to the ultracold atom-molecule conversion.In this thesis,we mainly study ultracold atom-molecule conversion dynamics in periodic external field.Using Gaussian pulse train model and periodic modulation field to study the ultracold atom-molecule conversion and analyze corresponding dynamic behavior,as well as some interesting phenomena.The main contents and structure of this thesis are as follows:In the first chapter,the significance,common methods and relevant background knowledge of ultracold atom-molecule conversion are introduced.The basic models of ultracold diatomic molecules conversion are summarized.The application of Gaussian pulse train model and periodic modulation field in the ultracold atomic system is summarized.In the second chapter,we study the conversion dynamics of ultracold atoms to molecules in the chirped Gaussian pulse train model.Under the mean-field theory,the effects of different external field parameters such as coupling strength,sweep rate and the number of pulse trains on the conversion of ultracold atoms to molecules are studied.By adjusting these parameters,it is found that there are novel patterns of interferences in the system.In addition,the analytical expression of ultracold atom-molecule conversion efficiency is obtained by the stationary phase approximation.The result shows that the dynamic behaviors of constructive and destructive interferences can be realized by applying the Gaussian pulse train model to the ultracold atom-molecule conversion,and atommolecule conversion efficiency can be further improved by adjusting the external field.In the third chapter,we study the periodic modulation effect of ultracold atom-molecule conversion dynamics.By adjusting the external field parameters,some interesting interference and resonance phenomena are produced in the system.It is found that the interference patterns are asymmetric and the positions of the interference fringes are shifted significantly in the ultracold atom-molecule conversion system,when there is particle interaction.At the same time,we analyze the influence of coupling strength on the resonance peaks.Finally,the theoritical result is verified by numerical calculation.In the fourth chapter,the work of this thesis is summarized,and the research prospect and the further work in this field are prospected.