Ultracold Fermions in Reduced Dimensions: Three-Body Recombination, Tomonaga-Luttinger Liquids, and a Honeycomb Lattice

Open Access
- Author:
- Marcum, Andrew
- Graduate Program:
- Physics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 14, 2019
- Committee Members:
- Kenneth M. O'Hara, Dissertation Advisor/Co-Advisor
Kenneth M. O'Hara, Committee Chair/Co-Chair
David Scott Weiss, Committee Member
Ying Liu, Committee Member
Venkatraman Gopalan, Outside Member - Keywords:
- degenerate Fermi gases
atomic gases
quasi-one dimension
three-body recombination
Luttinger liquid - Abstract:
- The physics of interacting quantum many-body systems in reduced dimensions has received a great deal of attention for many decades. Ultracold atomic gases confined to optical lattices are a superb tool with which to further the experimental investigation of these systems. Here we detail progress made on two experimental fronts of one-dimensional physics – Tomonaga-Luttinger liquids and p-wave superfluidity – using ultracold lithium-6 confined to a system of quasi-one-dimensional (1D) tubes formed by a two-dimensional (2D) square optical lattice. The realization of a p-wave superfluid in a cold-atom system has been hampered by the large inelastic losses which accompany the resonantly enhanced p-wave interactions needed for such a realization. There is strong evidence, however, that these losses are suppressed in reduced dimensions. Here we report a comparision of the three-body loss coefficient of a spin-polarized Fermi gas near a p-wave Feshbach resonance in 1D and three dimensions (3D). We find the on-resonant value in 1D is suppressed by a factor of 20 compared to the peak 3D value. This suppression is an encouraging result for the eventual realization of p-wave superfluidity in qausi-1D cold atom systems. The low-energy excitations of one-dimensional interacting fermions, and thus the transport properties of such systems, are described by Tomonaga-Luttinger liquid (TLL) theory. The elementary excitations of a TLL are collective bosonic modes, which split into independent charge modes and spin modes. This phenomenon, known as spin-charge separation, has not yet been observed directly, despite extensive experimental evidence for the existence of TLLs. Here we describe an attempt to directly observe spin-charge separation using both the frequency of dipole oscillations and the propagation of wavepackets within the quasi-1D tubes. We successfully create both types of excitations but are unable to make a statement about the existence of spin-charge separation in our system, as both types of excitations decay very quickly. We believe this decay is related to finite- temperature effects and are hopeful that improvements to our cooling techniques will allow us to observe spin-charge separation in the near future. We also report on the addition of gray molasses cooling and a painted crossed optical dipole trap to our system, which has enabled us to achieve a near state-of-the-art temperature of T = 0.06TF , where TF is the Fermi temperature of the trapped atoms,. We also discuss the implementations of high-intensity absorption imaging and phase contrast imaging, which make in situ imaging of the atom cloud possible. Finally, we give a brief overview of a proposed two-dimensional honeycomb optical lattice, which has undergone initial testing. This is a promising system for studying a wide variety of physics, including the Hubbard model, “color” superfluidity, and graphene-physics.