Spin tunnelling dynamics for spin-1 Bose-Einstein condensates in a swept magnetic field

We investigate the spin tunnelling of spin-1 Bose-Einstein condensates in a linearly swept magnetic field with a mean-field treatment. We focus on the two typical alkali Bose atoms 87Rb and 23Na condensates and study their tunnelling dynamics according to the sweep rates of the external magnetic fields. In the adiabatic (i.e. slowly sweeping) and sudden (i.e. fast sweeping) limits, no tunnelling is observed. For the case of moderate sweep rates, the tunnelling dynamics is found to be very sensitive to the sweep rates, so the plots of tunnelling probability versus sweep rate only become resolvable at a resolution of 10-4 G s-1. Moreover, a conserved quantity standing for the magnetization in experiments is found to affect dramatically the dynamics of the spin tunnelling. Theoretically we have given a complete interpretation of the above findings, and our studies could stimulate the experimental study of spinor Bose-Einstein condensates