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Experiments with Bose-Einstein Condensates in a Double-Well Potential

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Experiments with Bose-Einstein Condensates in a Double-Well Potential Experiments with Bose-Einstein Condensates in a Double-Well Potential by Yong-Il Shin B.S., Physics (2000) Seoul National University Submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY February 2006 c Massachusetts Institute of Technology 2006. All rights reserved. Author............................................. ............................... Department of Physics November 17, 2005 Certified by......................................... ............................... Wolfgang Ketterle John D. MacAurthur Professor of Physics Thesis Supervisor Certified by......................................... ............................... David E. Pritchard Cecil and Ida Green Professor of Physics Thesis Supervisor Accepted by......................................... .............................. Thomas J. Greytak Professor of Physics, Associate Department Head for Education Experiments with Bose-Einstein Condensates in a Double-Well Potential by Yong-Il Shin Submitted to the Department of Physics on November 17, 2005, in partial fulfillment of the requirements for the degree of Doctor of Philosophy Abstract Trapped atom interferometry was demonstrated with Bose-Einstein condensates in an opti- cal double-well trap. Coherent splitting of trapped condensates was performed by deforming an optical single-well potential into a double-well potential, and the relative phase of the two split condensates was shown to be reproducible. Microfabricated atom chips were de- veloped with prospect for chip-based confined-atom interferometry. The same dynamical splitting scheme was implemented in a purely magnetic double-well potential on an atom chip and interference of two split condensates was observed, but not reproducible phase. Coherent optical coupling between two spatially separated condensates was realized using stimulated light scattering. The relative phase of the two condensates was continu- ously measured with an optical method, which demonstrated atom interferometry without need for a conventional beam splitter or recombiner. The Josephson-like phase dynamics of the coherent optical coupling was investigated and it was experimentally shown that the induced atomic currents depend on the relative phase of the two condensates and an additional controllable coupling phase. Condensates in an optical dipole trap were distilled into a second empty dipole trap adjacent to the first one. We showed that the distillation was driven by thermal atoms spilling over the potential barrier separating the two wells and then forming a new conden- sate. This thermodynamic relaxation process serves as a model system for metastability in condensates and provides a test for quantum kinetic theories of condensate formation. Doubly quantized vortices were topologically imprinted in spinor condensates and the stability of the vortex state was investigated. The decay of a doubly-quantized vortex core into two singly-quantized vortex cores was observed using a tomographic imaging technique. The characteristic time scale of the splitting process was found to be longer at higher atom density. Thesis Supervisor: Wolfgang Ketterle Title: John D. MacAurthur Professor of Physics Thesis Supervisor: David E. Pritchard Title: Cecil and Ida Green Professor of Physics To my parents, Kwang-Bum Shin and Young-Hee Yoon and my sister Ji-Young Acknowledgments My graduate life at MIT was enjoyable. Being a graduate student with oppressive thesis requirements, of course, is generally not an ideal way to be happy, but I can definitely say that my past four and half years in Building 26 was full of challenges and adventures through which I could observe and identify myself. Most of those challenges and adventures resulted from the struggle with super cold sodium atoms, but I know all of these were possible only because there were many people encouraging, supporting and helping me throughout the whole journey. First of all, I would like to thank Wolfgang Ketterle and Dave Pritchard for providing me with the opportunity to work with them. I was extremely lucky to have Wolfgang and Dave as thesis supervisors not only because they are great physicists but also because they really care about students’ independence as researchers. Wolfgang’s concise statement and scientific assessment on research projects always provided a clear picture of what we were doing in the lab. His considerate encouragement has been a great source of my ‘careless’ bravery in experiments. Dave showed me an example of how one can be happy with doing science. His scientific analysis on everything always inspired me. The scientific enthusiasm and the solid work ethic they showed me in the past years have set a standard for me and I believe it will work as a guideline for the rest of my research life. It has been a great privilege to join the science chamber team using MIT’s third gener- ation BEC machine. When I joined the team in September 2001, it was eight months after the first BEC with the machine. As a user and janitor of the machine, I am greatly indebted to the builders of the machine. In particular, I thank Ananth Chikkatur and Aaron Lean- hardt for teaching me how to drive this wonderful machine for scientific research. Ananth introduced me to the flavor of the BEC experiments at MIT. The patience that he showed me when I worked on my first project, the control system for the translation stage and his leadership in the ‘continuous condensate’ project really helped me to be integrated in the team. Aaron laid the solid foundation of our microtrap technique. He initiated the atom chip and the optical double well system, without which the experiments described in this thesis would have never happened. I was always fascinated by his broad knowledge of the machine and his quick evaluation of the feasibility of new experimental ideas. His working style, particularly in the lab, was so strong that sometimes it was quite hard for me to keep following him physically in a literal sense. However, I learned many things from his diligent and thrustful leadership, which essentially helped me to develop my own working style. He was also a selfless leader placing the interest of the whole team before anything. Particularly, I am deeply grateful to him for letting me lead the ‘trapped atom interferometer’ project when we had to divide our team into two subgroups. I have been benefited from working with Michele Saba, Andr´eSchirotzek, Christian San- ner, Tom Pasquini and Gyu-Boong Jo. Michele was a great labmate who could immediately compensate for the early loss of Aaron. Most of the experiments were carried out with him and his physical insight always brought an interesting spin on our experimental results. He always kindly counseled me on any problem from how to kick a soccer ball better to how to write a research proposal. He has unique and interesting opinions on any issue, so it was great fun to discuss with him, especially in a dark laboratory at around midnight. Due to the short cycle of the team projects, our team advantageously had excellent diploma students from Germany. Andr´eand Christian were diploma students who worked with us for one year. Their enthusiasm and strong motivation helped me to keep myself upright in the mid-period of my graduate life that would have possibly been a slump. Andr´ehas also been a perfect officemate with agreeable tastes in (heavy-metal) music, (Chinese truck) food, (sweaty) sports, (sleepy) classics, and etc. Having the machine run on Christmas and playing foot-volley ball at early morning with being desperate for the ‘recoil momentum’ project were small parts of my pleasant memories with him. I am looking forward to working with him in the Li lab soon. Christian was calm and very skillful almost at everything. I have enjoyed talking with him and learning from him. I believe he will make a great scientist. I thank Tom and Gyu-Boong for helping me in the lab and wish them good luck with coming research projects. Center for Ultracold Atoms was a great place for studying AMO physics. The weekly CUA seminar presented by world-leading speakers was one of the great benefits I have had from the center. Also, the big size of graduate students made it possible to ask diverse helps at various times and to make our own soccer and softball team. I thank Jamil Abo-Shaeer for organizing many unforgettable bond-enhancing gatherings, Claudiu Stan for his professional advises on various technical issues, Kaiwen Xu for discussing theoretical problems and teaching how to make a fiber tip, Deep Gupta for teaching how to change dye, Gretchen Campbell for her considerate caring for group events, Martin Zwierlein for his endless upbeat mood and organizing our soccer team, Micah Boyd for his love of Naboo, and Dave Kielpinski for showing what is the best lab-behavior. I also thank Ellenor Barish, Carol Costa, Maureen Howard, and Maxine Samuels for their administrative help and Fred Cote for his kind advises on machining. I would like to thank people who supported me outside the lab: Jaehyuk Choi who welcomed me in Cambridge with a McDonald burger for the dinner of the first night, Boguk Kim who shared a dorm apartment with me for one year and evacuated, Daihyun Lim who ruined my precious futon cover with pasting almost digested food, and Kyungjoon Lee who always emphasizes the importance of marriage and brags of his adorable baby. They are all good friends. I am grateful to Prof. Wonho Jhe for introducing atom optics experiments to me when I had to decide a graduate school. I thank Eunjong Hong and Hyungjoon Cho for their life advises, and the members of the KGSA soccer team for their ‘craziness’. Finally, I thank my family for its unconditional support and love. My parents Kwang- Bum Shin and Young-Hee Yoon have always encouraged me to live with a dream. Without their endless blessing I would not be able to become who I am.
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