Effect of magnetic fields on the spin evolution of non-polarized 87Rb Bose-Einstein condensates

The spin mixing dynamics of spin-1 Bose-Einstein condensates with zero magnetization and under an external magnetic field is investigated. The time-dependent solutions are obtained via a diagonalization of the Hamiltonian, which has a simple form under the single mode approximation. The features of evolution are compared in detail with those with the field removed so as to emphasize the effect of the field, which can induce strong oscillation in population of atoms in spin component 0 . A new mode of oscillation characterized by a high frequency and a low frequency, is found when the field is sufficiently strong.