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Probing local quantities in a strongly interacting Fermi gas and the construction of an ultracold Fermi gas apparatus

TitleProbing local quantities in a strongly interacting Fermi gas and the construction of an ultracold Fermi gas apparatus
Publication TypeThesis
Year of Publication2017
AuthorsPaudel, R
Academic DepartmentPhysics
DegreePh.D.
Number of Pages148
Date Published2017-05
UniversityUniversity of Colorado
CityBoulder, CO
Abstract

The nature of the normal phase of an ultracold Fermi gas in the BCS-BEC crossover regime is an interesting and unresolved question. As interactions increase, while the many-body ground state remains a condensate of paired fermions, the normal state must evolve from a Fermi liquid to a Bose gas of molecules. In this thesis, I present a technique to spatially select a homogeneous sample from the center of a trapped gas to explore this crossover. Combining this technique with RF spectroscopy, we locally measure Tan’s contact as a function of temperature and compare to various many-body theories. In another experiment, we measure the distribution of single-particle energies and momenta for a normal gas across the BCS-BEC crossover. We find that the data fit well to a two-part function that includes a peak corresponding to fermionic quasi particles and an “incoherent background” that is modeled using the dispersion of thermal molecules. I also describe the construction of a new-generation Fermi gas apparatus.