Structure and Dynamics of Vortices in a Bose Condenstate with Spin Degree of Freedom

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・It is shown that a vortex can be continuously created in a Bose-Einstein condensate (BEC) of alkali atoms with |F|=1 confined in a multiply connected region by making use of a spin degree of freedom of the order parameter of a BEC.The mutiple-connecedness is realised by introducing an optical plug along the center of the vortex. The BEC stays within a weak-field seeking state during the time evolution thanks to the optical plug. This is demonstrated explicitly by solving the generalised Gross-Pitaevskii (GP) equation numerially.・This scenario is also analysed from a topological point of view. It is shown that the fundamental group π_1(SO(3))=Z_2 makes it possible to create a doubly-quantised vortex continuously from a vortex-free state.・An optical plug must be introduced in the above scenario since the weakfield seeking state and the strong-field seeking state have degenerate levels along the axis when the axial magnetic field vanishes during the creation of a vortex. It should be noted, however, that this happens only at a moment of time and at a single point in a plane. Thus it is expected that those particles taking part in the Majorana flops are negligible This conjecture is assured by solving the generalised GP equation numerically.・We also studied a BEC with |F|=2 and found that a vortex with four units of circulation is created in the present scenario.