An Optical Lattice Clock with Spin 1/2 Atoms
Massachusetts Institute of Technology Cambridge United States
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An optical lattice clock probes a spectrally narrow electronic transition in an ensemble of optically trapped, laser-cooled atoms, for use as a time and frequency standard. To date, several lattice clocks have been demonstrated with superior stability and accuracy compared to primary frequency standards based on microwave transitions. Yet, the question of which atomic system including the element and isotope performs best as a lattice clock remains unsettled. This thesis describes the first detailed investigation of an optical lattice clock using a spin-12 isotope of the ytterbium atom. A spin-12 system possesses several advantages over higher-spin systems, including a simplified level structure allowing for straightforward manipulation of the nuclear spin state and absence of any tensor light shift from the confining optical lattice. Moreover, the ytterbium atom Vb stands among the leading lattice clock candidates, offering a high performance optical clock with some degree of experimental simplicity. The frequency stability of the Yb clock is highlighted by resolving an ultra-narrow clock spectrum with a full-width at half maximum of 1 Hz, corresponding to a record quality factor Q 0 5 x 1014. Moreover, this system can be highly accurate, which is demonstrated by characterizing the Yb clock frequency at the 3 x 10-16 level of fractional uncertainty, with further progress toward a ten-fold improvement also presented. To reach this low level of uncertainty required careful consideration of important systematic errors, including the identification of the Stark-canceling wavelength, where the clocks sensitivity to the lattice intensity is minimized, a precise determination of the static polarizability of the clock transition, and the measurement and control of the atom-atom collisions.