Experimental Research Of Photoassociation Of Ultracold Cs Atoms With An External Magnetic Field

Cooling molecules to the ultralow temperatures provides a foundation for the research of the abundant vibrational energy level structure of molecules,molecular reaction dynamics and molecular long-range interactions.Recently years,ultracold molecules have been wide applied for the research of quantum precision measurement,quantum chemistry,quantum computing,quantum simulation and so on,have attracted much attention of scholars from related fields.Therefore,how to prepare ultracold molecular sample efficiently has become a key problem.Photoassociation and magnetic Feshbach resonance are the most common technologies to prepare ultracold molecules.For increasing the photoassociation rate and preparing the ground state ultracold molecules,many experimental and theoretical schemes have been proposed.Combining these two technologies to explore the photoassociation of ultracold atoms near Feshbach resonance is one of the hot topics in present.The technical route of using photoassociation to manipulate the magnetic Feshbach resonance and using the magnetic Feshbach resonance to optimize the photoassociation has been developed.This paper is regarded the experimental research of photoassociation of ultracold atoms with the external magnetic field as the study objection,preparing the ultracold Cs atomic sample with the temperature of ?K order of magnitude in a high vacuum environment in the first place,then loading atoms into the levitated optical dipole trap,obtaining the ultracold Cs molecules by photoassociation,the trap loss photoassociation molecular spectroscopy manipulated by resonance magnetic field(near the d wave Feshbach resonance)and non-resonance magnetic field have been obtained by absorbing image are systematically researched.The main works in this paper can be summarized as follows: 1.Firstly,we trapping the ultracold Cs atoms in a magneto-optical trap,the temperature of the atoms was hundreds ?K order of magnitude,then compressing the magneto-optical trap to increasing the densities of the atomic sample,and applying the optical molasses technology to reduce the temperature to ~39?K.At last,the degenerated Raman sideband cooling was used to cool the atoms to a low temperature of ~1.7 ?K and polarize them in the desired F = 3,mF = 3 state.For the laser frequency stabilization in experiment,we developing a technology based on the Labview PID VI and sound card in the computer.According to reading the frequency by wavelength meter and transfer the signal to Labview procedure,we can directly stabilization laser to an arbitry frequency in a non-jumping mode range.2.In order to manipulate the interaction of the ultracold Cs atoms by magnetic field and optical field,we loading atoms into an optical dipole trap.The gravity of atoms creat a destructive potential in the vertical direction.For compensating the gravitational force,we have studied the technologies of magnetic levitated dipole trap and optical levitated dipole trap,respectively.For increasing the phase space density of the atoms,we design an optical Dimple trap,and exploring the loading of atoms into the Dimple trap with magnetic field gradient and bias magnetic field.3.We have explored the photoassociation of ultracold atoms in a non-resonance magnetic field.The Feshbach resonance position was avoided in a large range and the scattering length monotonically changing with the magnetic field.The photoassociation rate of Cs molecules was changed by altering the density of atomic pairs.We utilized the single channel square well to simulate the experimental results,and the scattering length was treated as a control parameter.4.We have measured the photoassociation spectroscopy near the d wave Feshbach resonance,the asymmetric line shape was found and confirmed as the Fano effect,the enhancement and suppression of the maximum and minimum values of Fano line shape in an ultracold atom-molecule coupling system by the external magnetic field were also observed.Compared with the standard Fano resonance observated in other physical systems,our experimental results show a very obvious small peak.For explaining this phenomenon,we developed a coupled double Fano resonance model.