Radio Frequency AC Zeeman Trapping on an Atom Chip

We demonstrate a novel spin-specific trap for ultracold neutral rubidium-87, utilizing the AC Zeeman effect near radio frequency (rf) currents on an atom chip. To our knowledge, this is the first rf AC Zeeman trap for neutral atoms, a significant step towards arbitrary state-specific trapping and manipulation. This method works at arbitrary DC magnetic field, can target any hyperfine sub-state, traps DC high- and low-field seekers, and introduces two new parameters for trap control: frequency and phase. Circularly polarized AC magnetic near-fields generate structures along with the trap that are useful as spin-targeting tools in other contexts: linear gradient regions, saddle-points, co-located traps/minima with any of these, and more. The rf trap demonstrated here (20 MHz) discriminates between hyperfine manifolds by polarization, trapping F=2 and F=1 separately, while inter-manifold transitions (6.8 GHz) would gain detuning isolation for further state targeting. We demonstrate forced evaporation in this trap, opening a path to condensation in any hyperfine sub-state or background DC magnetic field. Additionally, we present multiple techniques for imaging rf fields with atoms, and microstrip chip geometries which could serve as trapped spin-state atom interferometers. This work is funded by DTRA, NSF, VMEC, and W&M