Ground-State Dirac Monopole

We show theoretically that a monopole defect, analogous to the Dirac magnetic monopole, may exist as the ground state of a dilute spin-1 Bose-Einstein condensate. The ground-state monopole is not attached to a single semi-infinite Dirac string, but forms a point where the circulation of a single vortex line is reversed. Furthermore, the three-dimensional dynamics of this monopole defect are studied after the magnetic field pinning the monopole is removed and the emergence of antimonopoles is observed. Our scheme is experimentally realizable with the present-day state of the art.