Development of a Microwave Atom Chip for AC Zeeman Trapping

We present work on the development of a microwave atom chip to generate AC Zeeman (ACZ) potentials for trapping and manipulation of ultra-cold atoms. ACZ potentials have applications in quantum gates, 1D many-body physics, and atom interferometry for precision measurements. Our scheme uses overlapping fields generated by RF and microwave AC currents in parallel microstrip transmission lines to produce minima in circularly polarized magnetic near-fields to confine the atoms. Axial confinement and translation are accomplished using a microwave lattice based on the ACZ or AC Stark effect. Wires below the chip allow for DC trapping. ACZ potentials are spin-specific, can be operated at any arbitrary magnetic field, and are expected to suppress roughness in the trapping potential caused by imperfections in atom chip manufacturing. We present simulations and test results for a novel broadband coupler for interfacing between SMA cables and the micro-fabricated atom chip traces. This coupler uses a tapered microstrip wedge to maintain 50 Ω impedance over a broad frequency range, with large-scale prototypes operating out to 9 GHz. This broadband behavior is useful for generating the microwave lattice and allows for the targeting of other atomic isotopes. To generate the phase-controlled microwaves needed for trapping, we have constructed an ultra-low phase noise source at 6.8 GHz based on IQ modulation with relative phase control between channels and 50 MHz of scan range.