Measurement and manipulation of ultracold bosons using microfabricated optics

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This thesis describes atomic physics experiments performed using a microfabricated photonic waveguide chip: a device that enables the interaction of cold atoms with an array of 12 microscopic light beams emitted by optical waveguides, inside a microscopic trench that has been cut into the chip, across all of the waveguides. The chip uses standard cold-atom control techniques along with readily available photonics technologies to provide an integrated atomic physics device that is not ‘scalable’ so much as already scaled. We describe experiments where atoms are driven into the trench using magneto-optical traps and magnetic traps. In the latter case, the large, homogeneous magnetic field that is present during the atom-light interaction allows us to observe polarization-dependent effects in absorption signals from the trench. Vacuum difficulties have limited the efficiency of rf-driven evaporative cooling in our magnetic trap to 0.4 (with a final phase-space density of 2× 10−5). To circumvent this issue, we have developed a novel evaporative cooling process, in which a dimple potential, comprised of an optical trap and a magnetic trap, is used to perform cycles of isentropic trap deformation and selective atom removal. Using this cooling process increases our evaporative cooling efficiency to 1.2. Various other cooling strategies that involve the dimple are also investigated. Using the dimple, we achieve a phase-space density of 0.04. Having cooled the cloud using the dimple, we move it into the trench and measure absorption signals of 50%, much larger than those achieved previously. We investigate the possibility of producing microscopic optical dipole traps in the trench by sending red-detuned light through the waveguides, and show results of preliminary experiments looking at light shifts.