Optical Dipole Trap For Ultracold Mixed Atoms In A Dark Magneto-optical Trap

Ultracold polar molecules have caused a wide attention of researchers for its unique features,such as degrees of freedom,rich vibrational-rotational energy level structure and inherent electric dipole moment.They have been applied in many physical fields,such as measurement of fundamental physical constants,quantum computation and quantum simulation.Recently,many groups in the world have successfully prepared kinds of ultra-cold ground polar molecules by using the Photoassciation and Feshbach resonance techniques.Unfortunately,ultracold molecule will be lost on the order of millisec-onds because of the action of gravitation and the collision with the background gas.Such a molecule sample is valueless for our study on the characteristics of ground state polar molecules and external field control.A feasible scheme is to use optical dipole trap.With the dipole trap,a potential well is formed could be used to trap the ground polar molecule.Hence,we firstly need to capture the heteronucle atoms by using dipole trap and analyze the dynamic process.In this thesis,ultacold Rb atjoms and Cs atoms were captured in a crossed dipole trap basing on the mixed dark SPOTs.Obvious improvements in the loading rate and atomic lifetime are demonstrated,comparing with the values of the atoms which are loaded dircctly from a normal magneto-optical trap.We an-alyze the atomic number as a function of time in the ODT's loading and holding processes based on the constant density and the constant volume approximations,respectively.We also demonstrate that the atomic temperature in holding pro-cess is related to the atcomic ccollisions,which consists of two-body collision and background gas induced collisions.The main works of this thesis are as follows:1.By establishing the experimental system of Cs atom dark SPOT and design-ing time sequence,we successfully capture the Cs atoms in crossed dipole trap.Obvious improvements in the loading rate and atomic lifetime are demonstrated,comparing with the values of the atoms which are loaded directly from a normal magneto-optical trap.2.We analyze the atomic number as a function of time in the ODT's loading and holding processes based on the constant density and the constant volume approximations,respectively.We also demonstrate that the atomic temperature in holding process is related to the atomic collisions,which consists of two-body collisions and background gas induced collisions.Finally the relationship between atomic collisions and optical trap depth are measured and analyzed.3.We have optically trapped ultracold mixed Rb and Cs atoms from a dark SPOT.The number of Rb atoms and Cs atoms in the trap are 2 x 108 and 3 x 108,respectively.the temperature of Rb atomic cloud and Cs atomic cloud are 150?K and 100?K respectively.4.We measured their heteronuclear collisions in the optical dipole trap.The loading and holding procedures of cold atoms in ODT are analyzed by an in-troduced phenomenological rate equation.Ultracold heteronuclear collisions rate can be derived from this equation and the increasing tendency on the trap depth is attributed to the hyperfine changing collision and photoassociation which are induced by the ODT laser with a broad linewidth.