Coherent heteronuclear spin dynamics in an ultracold spinor mixture

After more than 30 years development, ultracold atoms have become a versatile platform with a wide range of applications, from studying very fundamental physics such as basic properties of BEC, to making practical devices such as atomic clock. Among these applications, the spinor quantum gas, a quantum gas with spin degree of freedom, has attracted a lot of attentions, both experimentally and theoretically. Whereas all previous studies focus on spinor gases of single atomic species, in this thesis we present the first experimental studies of coherent spin-mixing dynamics in a spinor mixture of 87Rb and 23Na.;We produce an ultracold mixture of 87Rb and 23 Na atoms with laser cooling and evaporative cooling in magnetic and optical traps. A special spin state is prepared such that each species is in a superposition of the Zeeman sublevels in their F = 1 hyperfine ground-state manifolds. Interspecies spin-changing collisions cause the oscillation between the spin populations. We observe that the magnetization of each species oscillates while the total magnetization is conserved. We also study the effect of external magnetic field and find a resonance behavior of the dynamics. Furthermore, this resonance is found to be controllable by changing the polarization of the optical trapping light, due to the small vector light shift. The observed phenomena are in good agreement with theory developed based on the mean field Gross-Pitaevskii equation for condensate and Boltzmann equation for thermal gas.;We also study the thermal Rb spinor gas with spin either F = 1 and F = 2. Although there are differences between BEC and thermal gas in essence, the observed long-lasting coherent dynamics shows that they can be treated by unified formalism. The prediction of a factor of two in the interaction term is verified by measuring the dynamics at different atomic density.