Trapping paramagnetic molecules in a dynamic magnetic trap

Trapping molecules in strong-field-seeking states is particularly attractive to scientists in the field of molecular optics. If the external field is strong enough, all molecules are strong-field seekers. Contrary to the weak-field-seeking states, molecules trapping in strong-field-seeking states can avoid the loss caused by the inelastic collision which is a stumbling block for evaporative and sympathetic cooling. Unfortunately, the formation of a magnetostatic maximum in free space is forbidden according to Maxwell's equations and Earnshaw's theory. In this paper, a dynamic magnetic trap consisting of three pairs of Helmholtz coils is proposed. The time-sequence control is given together with the distribution of the magnetic field in space. The influence of the switching frequency and electric current flowing through the wires on the number of trapped molecules is investigated. We obtain the changes in the locations and the phase-space distribution within a switching cycle by trajectory simulation. Finally, the influence of the time during which the field is off on the performance of our trap is studied.