Nonlinear Phenomena In Coupled Bose-Einstein Condensates And Atoms & Molecule In Intense Laster Fields

Laser-atom interaction induces a lot of novel phenomena and has become one of the hotspots in the field of atomic and molecular physics. Based upon the realization of laser cooling and trapping and the application of technology of intense laser in atomic and molecular physics, we have analyzed the nonlinear phenomena in coupled Bose-Einstein condensates and atomic & molecular systems in intense laser fields.For the coupled Bose-Einstein condensates, with the coupled nonlinear Schr?dinger equations (Gross-Pitaevskii equations), we focus our investigation on the macroscopic quantum phenomena induced by the mean-field nonlinearity and the inherent coherence in Bose-Einstein condensates, we have also analyzed some related phenomena in coupled multiple Bose-Einstein condensates. The following works are enclosed in this dissertation.(I) Quasi-spin Model for Macroscopic Quantum Tunnelling between Two Coupled Bose-Einstein Condensates: The system of two coupled Bose-Einstein condensates is mapped onto an uniaxial spin with an applied magnetic field. The mean-field interaction, the coupling and the asymmetry or the detuning correspond to the anisotropy, the transverse field and the longitudinal field, respectively. The generalized Bloch's equation is derived. In the limit of low barrier, the tunneling exponent is calculated with an imaginary-time path-integral method. The dependence of the tunneling exponent on the system parameters is obtained. The crossover temperature TC from thermal regime to quantum regime is estimated. Below TC , the quantum phenomenon dominates the tunnelling, otherwise, the thermal activation dominates.(II) Conditional Spontaneous Spin Polarization and Bifurcation Delay in Coupled Two-Component Bose-Einstein Condensates: We find that the bifurcation and the spontaneous spin polarization depend not only on the system parameters, but also on the relative phase between two components. These phenomena are different from those only are determined by the parameters, we name them as conditional bifurcation and conditional spontaneous spin polarization. Through bifurcations, the system enters into the spontaneous spin polarization regime from the Rabi regime. We also find that bifurcation delay appears when the parameter is swept through the static bifurcation point.(III) Nonlinear Population Oscillation between two Coupled Bose-Einstein Condensates: We have investigated the chaotic and frequency-locked population oscillations between two coupled Bose-Einstein condensates with time-dependent asymmetric potential. Under the deterministic perturbation, there exist stable oscillations close to the separatrix solution, which are Melnikov chaotic. Numerical results reveal that, in the nondissipative regime, regular...