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Shuangli Du, Physics - Final Oral Dissertation Defense
 Zoom link is available upon request. Please email [[w|evwilk,Ellie]]

Title: “AC & DC Zeeman Interferometric Sensing with Ultracold Trapped Atoms on Chip”

Abstract: This thesis presents progress in developing a trapped atom interferometer on a chip, based on AC Zeeman potential. An atom interferometer is a high-precision measuring tool that can detect various types of forces and potentials. The trapped atom interferometer introduced in this thesis targets the shortcoming of traditional ballistic atom interferometers, which are typically meter-scale in height. Notably, a trapped atom interferometer has a localized atom sample, a potentially longer interferometric phase accumulation time, and the prospect of being the basis for a more compacted instrument. This thesis presents multiple projects in the developing of a trapped atom interferometer based on the AC Zeeman potentials and traps: 1) production of ultracold potassium on a chip, 2) the theory of potential roughness in chip traps, 3) microwave chip trap design, and 4) a trapped atom interferometer with rubidium atoms, based on a laser dipole trap and an AC Zeeman force. (1) Potassium is a good candidate for the atom interferometer due to its bosonic and fermionic isotopes, multiple “magic” magnetic fields, and the convenience of RF and microwave trapping. The laser cooling and trapping system were upgraded to improve the temperature and population of potassium atoms in the chip trap. On-chip cooling resulted in a significant inelastic loss, which prevented the production of a potassium Bose-Einstein condensation. (2) Numerical simulations of chip wire defects predict that the AC Zeeman trapping potential should be substantially smoother than its DC Zeeman counterparts: the suppression of the roughness is due to magnetic polarization selection rules and the AC skin effect. (3) Furthermore, the thesis presents a number of studies on the straight and curved microstrip transmission lines that form the building blocks of the microwave atom chip for the AC Zeeman trap. (4) Finally, we constructed a rubidium-based Ramsey interferometer that can be converted to an atom interferometer by applying a spin-dependent AC Zeeman force: the interferometer was used to measure DC and AC Zeeman energy shifts and fringes were observed with an AC Zeeman force. 

Bio: Shuangli Du was born in China and then moved to Japan with his parents. He spent his happy childhood in Nagoya, Aichi prefecture in Japan, and enjoyed baseball every day. He then moved back to Beijing, China, at the age of 8, and lived there for the next 14 years. In China, he gradually showed his interest in science and finally choses physics as his major for his undergraduate education at Renmin University in China. As an undergraduate researcher, he mainly worked on Angle-Resolved photoemission spectroscopy in condensed matter physics with Prof. Shancai Wang to fabricate the MoS2 crystals and measure their energy structure and electron density. In the third year of his undergraduate studies, he learned of cold atom physics in a seminar and developed a strong interest in it, which led him to his graduate studies in the Lab of Seth Aubin at the College of William & Mary. During his Ph.D. research, he developed a lot of experience in engineering physics and improved the lab apparatus, including microwave amplifiers, apparatus monitoring systems, and the potassium laser cooling and trapping system. He also made a lot of progress on physics research, including theoretical research on microstrip transmission lines and experimental research on atom interferometers. During his theoretical research, he developed an interest and talent for programming and will work on the electronic design automation software at Cadence Inc. after graduating. The experience in physics research, especially on the atom chip, will be beneficial for his new career.