Ejection of magnetic-field-sensitive atoms from an optical dipole trap

Rubidium atoms prepared by evaporative cooling in an optical dipole trap are used in Stern-Gerlach type experiments. The analysis of the magnetic state distribution in the trap and during free fall demonstrates the possibility of ejecting all atoms with m_F≠0 from the optical dipole trap. This is achieved by applying an appropriately located inhomogeneous magnetic field. We investigate the dynamics of this cleaning process, and record the temporal history of atom positions under the combined action of magnetic field and dipole-trap potential. The experimental findings are fully supported by realistic numerical simulations of the atomic dynamics. We show that analysis of the ejected atoms provides a means for nondestructive thermometry of a trapped atom cloud.