Atom Chip Potential Roughness Suppression using a RF AC Zeeman Trap

Micro-fabricated wires on atom chips can sculpt complex electromagnetic fields for trapping and manipulating ultracold atoms in a compact physics package. These devices have applications in atom interferometry measurements of fundamental and inertial forces, such as sub-mm gravity or the Casimir-Polder force, as well as in the study of 1-D many-body systems. However, wire defects such as non-uniform edges and conductivity variations cause the current in the wire to deviate from a straight path. These current deviations result in additional magnetic fields generated along the wire manifesting as regions of local axial confinement in addition to the overall harmonic trapping potential. Unfortunately, this trapping potential roughness is frequently a limiting factor in experiments. We present a novel trapping scheme using AC currents of ~20 MHz in the chip wires, trapping atoms in a spin-dependent AC Zeeman (ACZ) potential using ground state intra-manifold Zeeman transitions in Rb87. Since only a given magnetic field polarization contributes to the ACZ potential it is insensitive to the additional longitudinal fields generated by the wire defects thus reducing potential roughness effects. We demonstrate this suppression experimentally by comparing the longitudinal potential roughness in identical two-wire DC and AC Zeeman chip traps, which have the same trap height and trap frequencies, and find rms suppression factors of greater than 7 in the ACZ trap.