{"id":{"repo_id":"mit","oai_identifier":"oai:dspace.mit.edu:1721.1/79520"},"canonical_url":"https://search.dev.ndltd.org/etd/mit/oai:dspace.mit.edu:1721.1/79520","repository":{"repo_id":"mit","name":"MIT","base_url":"https://dspace.mit.edu/oai/request"},"display":{"title":"Ultracold Fermi gas with repulsive interactions","abstract":"This thesis presents results from experiments of ultracold atomic Fermi gases with repulsive interaction. Itinerant ferromagnetism was studied by simulating the Stoner model with a strongly interacting Fermi gas of ultracold atoms. We observed nonmonotonic behavior of lifetime, kinetic energy, and size for increasing repulsive interactions, which is in good agreement with a mean-field model for the ferromagnetic phase transition. However, later research showed the absence of enhanced spin fluctuation, which is definitive evidence against the ferromagnetic phase transition. Still, our work triggered a lot of research on repulsive interactions in ultracold Fermi gases. A quantitative approach is taken to study ultracold Fermi gases with repulsive interaction. This is done by careful measurements of density profiles in equilibrium. First, Pauli paramagnetism is observed in trapped atomic samples which have an inhomogeneous density due to the harmonic confinement potential. We experimentally measure the susceptibility of ideal Fermi gas. This research shows that ultracold atoms can serve as model systems to demonstrate well-known textbook physics in a more ideal way than other systems. Then, Fermi gases with repulsive interactions are characterized by measuring their compressibility as a function of interaction strength. The compressibility is obtained from in-trap density distributions monitored by phase contrast imaging. For interaction parameters kFa > 0.25 fast decay of the gas prevents the observation of equilibrium profiles. For smaller interaction parameters, the results are adequately described by first-order perturbation theory. A novel phase contrast imaging method compensates for dispersive distortions of the images.","abstract_html":"This thesis presents results from experiments of ultracold atomic Fermi gases with repulsive interaction. Itinerant ferromagnetism was studied by simulating the Stoner model with a strongly interacting Fermi gas of ultracold atoms. We observed nonmonotonic behavior of lifetime, kinetic energy, and size for increasing repulsive interactions, which is in good agreement with a mean-field model for the ferromagnetic phase transition. However, later research showed the absence of enhanced spin fluctuation, which is definitive evidence against the ferromagnetic phase transition. Still, our work triggered a lot of research on repulsive interactions in ultracold Fermi gases. A quantitative approach is taken to study ultracold Fermi gases with repulsive interaction. This is done by careful measurements of density profiles in equilibrium. First, Pauli paramagnetism is observed in trapped atomic samples which have an inhomogeneous density due to the harmonic confinement potential. We experimentally measure the susceptibility of ideal Fermi gas. This research shows that ultracold atoms can serve as model systems to demonstrate well-known textbook physics in a more ideal way than other systems. Then, Fermi gases with repulsive interactions are characterized by measuring their compressibility as a function of interaction strength. The compressibility is obtained from in-trap density distributions monitored by phase contrast imaging. For interaction parameters kFa > 0.25 fast decay of the gas prevents the observation of equilibrium profiles. For smaller interaction parameters, the results are adequately described by first-order perturbation theory. A novel phase contrast imaging method compensates for dispersive distortions of the images.","abstract_has_math":false,"creators":["Lee, Ye-Ryoung"],"institution":"Massachusetts Institute of Technology","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":"Massachusetts Institute of Technology. Department of Physics.","school":null,"contributors":[],"advisors":["Wolfgang Ketterle."],"committee_chairs":[],"committee_members":[],"year":2012,"date_issued":"2012","date_published":"2012","updated_at":"2026-07-22T22:21:43Z","subjects":["Physics."],"languages":["eng"],"rights":["M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission."],"rights_urls":["http://dspace.mit.edu/handle/1721.1/7582"],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/1721.1/79520","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Wolfgang Ketterle."]},{"key":"dc:contributor.department","label":"Department","values":["Massachusetts Institute of Technology. Department of Physics."]},{"key":"dc:contributor.other","label":"Dc Contributor Other","values":["Massachusetts Institute of Technology. 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They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission."]},{"key":"dc:rights.uri","label":"Rights URI","values":["http://dspace.mit.edu/handle/1721.1/7582"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/1721.1/79520"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.","Cataloged from PDF version of thesis.","Includes bibliographical references (p. 95-100)."]},{"key":"dc:description.abstract","label":"Abstract","values":["This thesis presents results from experiments of ultracold atomic Fermi gases with repulsive interaction. Itinerant ferromagnetism was studied by simulating the Stoner model with a strongly interacting Fermi gas of ultracold atoms. We observed nonmonotonic behavior of lifetime, kinetic energy, and size for increasing repulsive interactions, which is in good agreement with a mean-field model for the ferromagnetic phase transition. However, later research showed the absence of enhanced spin fluctuation, which is definitive evidence against the ferromagnetic phase transition. Still, our work triggered a lot of research on repulsive interactions in ultracold Fermi gases. A quantitative approach is taken to study ultracold Fermi gases with repulsive interaction. This is done by careful measurements of density profiles in equilibrium. First, Pauli paramagnetism is observed in trapped atomic samples which have an inhomogeneous density due to the harmonic confinement potential. We experimentally measure the susceptibility of ideal Fermi gas. This research shows that ultracold atoms can serve as model systems to demonstrate well-known textbook physics in a more ideal way than other systems. Then, Fermi gases with repulsive interactions are characterized by measuring their compressibility as a function of interaction strength. The compressibility is obtained from in-trap density distributions monitored by phase contrast imaging. For interaction parameters kFa > 0.25 fast decay of the gas prevents the observation of equilibrium profiles. For smaller interaction parameters, the results are adequately described by first-order perturbation theory. A novel phase contrast imaging method compensates for dispersive distortions of the images."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Ph.D."]},{"key":"dc:title","label":"Title","values":["Ultracold Fermi gas with repulsive interactions"]}]}],"canonical_facts":{"dc:contributor.advisor":["Wolfgang Ketterle."],"dc:contributor.department":["Massachusetts Institute of Technology. Department of Physics."],"dc:contributor.other":["Massachusetts Institute of Technology. Department of Physics."],"dc:creator":["Lee, Ye-Ryoung"],"dc:date.accessioned":["2013-07-10T14:51:25Z"],"dc:date.available":["2013-07-10T14:51:25Z"],"dc:date.issued":["2012"],"dc:description":["Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.","Cataloged from PDF version of thesis.","Includes bibliographical references (p. 95-100)."],"dc:description.abstract":["This thesis presents results from experiments of ultracold atomic Fermi gases with repulsive interaction. Itinerant ferromagnetism was studied by simulating the Stoner model with a strongly interacting Fermi gas of ultracold atoms. We observed nonmonotonic behavior of lifetime, kinetic energy, and size for increasing repulsive interactions, which is in good agreement with a mean-field model for the ferromagnetic phase transition. However, later research showed the absence of enhanced spin fluctuation, which is definitive evidence against the ferromagnetic phase transition. Still, our work triggered a lot of research on repulsive interactions in ultracold Fermi gases. A quantitative approach is taken to study ultracold Fermi gases with repulsive interaction. This is done by careful measurements of density profiles in equilibrium. First, Pauli paramagnetism is observed in trapped atomic samples which have an inhomogeneous density due to the harmonic confinement potential. We experimentally measure the susceptibility of ideal Fermi gas. This research shows that ultracold atoms can serve as model systems to demonstrate well-known textbook physics in a more ideal way than other systems. Then, Fermi gases with repulsive interactions are characterized by measuring their compressibility as a function of interaction strength. The compressibility is obtained from in-trap density distributions monitored by phase contrast imaging. For interaction parameters kFa > 0.25 fast decay of the gas prevents the observation of equilibrium profiles. For smaller interaction parameters, the results are adequately described by first-order perturbation theory. A novel phase contrast imaging method compensates for dispersive distortions of the images."],"dc:description.degree":["Ph.D."],"dc:identifier.uri":["http://hdl.handle.net/1721.1/79520"],"dc:language.iso":["eng"],"dc:publisher":["Massachusetts Institute of Technology"],"dc:rights":["M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission."],"dc:rights.uri":["http://dspace.mit.edu/handle/1721.1/7582"],"dc:subject":["Physics."],"dc:title":["Ultracold Fermi gas with repulsive interactions"],"dc:type":["Thesis"]},"updated_at":"2026-07-22T22:21:43Z"}