Browsing by Author "Yang, Tsung-Lin"

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    3D optical lattice system for ultra-cold Lithium 6
    (2014-04-25) Yang, Tsung-Lin; Hulet, Randall G.; Killian, Thomas C.; Dai, Pengcheng
    Optical lattice experiments have proved to be a versatile tool for studying strongly correlated quantum systems. The motivation behind these experiments is to use the cold atoms to emulate a solid state system for which the Hamiltonian is analytically or numerically non-solvable. In our experiment, we construct a 3D simple cubic lattice system which realizes the Fermi-Hubbard model and provides us the opportunity to study the antiferromagnetic (AFM) insulator phase. In order to establish evaporative cooling in the optical lattice and to enlarge the size of the AFM phase, we implement a compensation potential additional to the standard lattice beam. In this thesis, I will present detailed steps to construct and calibrate the compensated 3D optical lattice system.
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    Compressibility of a Fermionic Mott Insulator of Ultracold Atoms
    (American Physical Society, 2015) Duarte, Pedro M.; Hart, Russell A.; Yang, Tsung-Lin; Liu, Xinxing; Paiva, Thereza; Khatami, Ehsan; Scalettar, Richard T.; Trivedi, Nandini; Hulet, Randall G.; Rice Quantum Institute
    We characterize the Mott insulating regime of a repulsively interacting Fermi gas of ultracold atoms in a three-dimensional optical lattice. We use inﾠsitu imaging to extract the central density of the gas and to determine its local compressibility. For intermediate to strong interactions, we observe the emergence of a plateau in the density as a function of atom number, and a reduction of the compressibility at a density of one atom per site, indicating the formation of a Mott insulator. Comparisons to state-of-the-art numerical simulations of the Hubbard model over a wide range of interactions reveal that the temperature of the gas is of the order of, or below, the tunneling energy scale. Our results hold great promise for the exploration of many-body phenomena with ultracold atoms, where the local compressibility can be a useful tool to detect signatures of different phases or phase boundaries at specific values of the filling.
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    Dynamical Response of an Interacting 1-Dimensional Fermi Gas
    (2018-05-10) Yang, Tsung-Lin; Hulet, Randall G
    Ultracold atoms with optical lattices provide a highly tunable system to measure the dynamic structure factor, $S(q,\omega)$, of an interacting one-dimensional (1D) Fermi gas. We use the two lowest hyperfine levels of the $^6$Li atom to form a pseudo-spin-1/2 system whose interactions are tunable via a Feshbach resonance. Bragg spectroscopy is used to measure the dynamic response of the 1D system to density (``charge'') mode excitations at a momentum $q$ and frequency $\omega$. In this thesis, we provide a quantitative comparison between the experimental result and the theoretical calculations based on Tomonaga-Luttinger theory.
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    Observation of antiferromagnetic correlations in the Hubbard model with ultracold atoms
    (Nature Publishing Group, 2015) Hart, Russell A.; Duarte, Pedro M.; Yang, Tsung-Lin; Liu, Xinxing; Paiva, Thereza; Khatami, Ehsan; Scalettar, Richard T.; Trivedi, Nandini; Huse, David A.; Hulet, Randall G.; Rice Quantum Institute
    Ultracold atoms in optical lattices have great potential to contribute to a better understanding of some of the most important issues in many-body physics, such as high-temperature superconductivity[1]. The Hubbard model—a simplified representation of fermions moving on a periodic lattice—is thought to describe the essential details of copper oxide superconductivity[2]. This model describes many of the features shared by the copper oxides, including an interaction-driven Mott insulating state and an antiferromagnetic (AFM) state. Optical lattices filled with a two-spin-component Fermi gas of ultracold atoms can faithfully realize the Hubbard model with readily tunable parameters, and thus provide a platform for the systematic exploration of its phase diagram[3, 4]. Realization of strongly correlated phases, however, has been hindered by the need to cool the atoms to temperatures as low as the magnetic exchange energy, and also by the lack of reliable thermometry[5]. Here we demonstrate spin-sensitive Bragg scattering of light to measure AFM spin correlations in a realization of the three-dimensional Hubbard model at temperatures down to 1.4 times that of the AFM phase transition. This temperature regime is beyond the range of validity of a simple high-temperature series expansion, which brings our experiment close to the limit of the capabilities of current numerical techniques, particularly at metallic densities. We reach these low temperatures using a compensated optical lattice technique[6], in which the confinement of each lattice beam is compensated by a blue-detuned laser beam. The temperature of the atoms in the lattice is deduced by comparing the light scattering to determinant quantum Monte Carlo simulations[7] and numerical linked-cluster expansion[8] calculations. Further refinement of the compensated lattice may produce even lower temperatures which, along with light scattering thermometry, would open avenues for producing and characterizing other novel quantum states of matter, such as the pseudogap regime and correlated metallic states of the two-dimensional Hubbard model.