Towards the Precision Spectroscopy of a Single Molecular Ion

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This dissertation presents some development of the single molecular ion precision spectroscopy experiment including construction of the project, spectroscopy state readout, and production of ultracold molecules. Such molecular ion spectroscopy aims at testing fundamental physics such as probing the time variation of electron-proton mass ratio. The theories and characterization of ion traps are first discussed along with information regarding building the ion trapping systems. Then, routines in this project such as loading ions, Doppler laser cooling, excessive micromotion compensation, secular motion detection, and fluorescence imaging are deliberated. In the state readout experiment, the coherent motion of a single trapped barium ion resonantly driving by a radiation pressure is studied. By scattering of order only one hundred photons, the radiation pressure is able to seed a laser-cooled ion with a secular oscillation that is detectable by the Doppler velocimetry technique after proper motional amplification. This seeding method provides a mapping between the ion's internal configuration and its secular motion and can be used to read out the spectroscopy results from a single non-fluorescing ion with a partially-closed cycling transition. The work of ultracold molecule production is done with silicon monoxide ions, which has a strong vibration-conserved spontaneous decay branching. Therefore, by optically pumping the rotational cooling transitions in silicon monoxide ions with a broadband radiation, the population can be efficiently driven into the ground rotational state before falling into other manifolds. To avoid the rotational heating transition, the broadband source, derived from a femtosecond pulsed laser, is spectrally filtered using an ultrashort pulse shaper.

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  • 02/13/2018
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