Browsing by Author "Liao, Yean-an"

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    Pairing and Phase Separation in a Polarized Fermi Gas
    (American Association for the Advancement of Science, 2006) Partridge, Guthrie B.; Li, Wenhui; Kamar, Ramsey I.; Liao, Yean-an; Hulet, Randall G.
    We report the observation of pairing in a gas of atomic fermions with unequal numbers of two components. Beyond a critical polarization, the gas separates into a phase that is consistent with a superfluid paired core surrounded by a shell of normal unpaired fermions. The critical polarization diminishes with decreasing attractive interaction. For near-zero polarization, we measured the parameter β = –0.54 ± 0.05, describing the universal energy of a strongly interacting paired Fermi gas, and found good agreement with recent theory. These results are relevant to predictions of exotic new phases of quark matter and of strongly magnetized superconductors.
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    Spin-imbalance in a one-dimensional Fermi gas
    (Nature Publishing Group, 2010) Liao, Yean-an; Rittner, Ann Sophie C.; Paprotta, Tobias; Li, Wenhui; Partridge, Guthrie B.; Hulet, Randall G.; Baur, Stefan K.; Mueller, Erich J.; Rice Quantum Institute
    Superconductivity and magnetism generally do not coexist. Changing the relative number of up and down spin electrons disrupts the basic mechanism of superconductivity, where atoms of opposite momentum and spin form Cooper pairs. Nearly forty years ago Fulde and Ferrell [1] and Larkin and Ovchinnikov [2] (FFLO) proposed an exotic pairing mechanism in which magnetism is accommodated by the formation of pairs with finite momentum. Despite intense theoretical and experimental efforts, however, polarized superconductivity remains largely elusive [3]. Unlike the three-dimensional (3D) case, theories predict that in one dimension (1D) a state with FFLO correlations occupies a major part of the phase diagram [4, 5, 6, 7, 8, 9, 10, 11, 12]. Here we report experimental measurements of density profiles of a two-spin mixture of ultracold [6] Li atoms trapped in an array of 1D tubes (a system analogous to electrons in 1D wires). At finite spin imbalance, the system phase separates with an inverted phase profile, as compared to the 3D case. In 1D, we find a partially polarized core surrounded by wings which, depending on the degree of polarization, are composed of either a completely paired or a fully polarized Fermi gas. Our work paves the way to direct observation and characterization of FFLO pairing.
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    Strongly Interacting Fermi Gases in Three Dimensions and One Dimension
    (2011) Liao, Yean-an; Hulet, Randall G.
    This thesis presents the experimental study on the two-spin component, strongly interacting 6 Li Fermi gases in 3D and 1D traps. The interaction strength is tuned from the molecular BEC regime to the BCS regime using a Feshbach resonance. The trap dimension can be tuned from 3D to 1D with the implementation of optical lattice. The evaporation of imbalanced Fermi gases in 3D trap is studied. The anisotropic and fast evaporation is the cause of the deformation observed in the 2006 Rice experiment. In a balanced Fermi system, the fraction of correlated states is measured as a function of interaction and temperature. At unitarity, the fraction of correlated states is ∼85% and exists above T c . The one-body-like photoexcitation rate can be related to the contact quantity. Lastly, the spin-imbalance in a one-dimensional Fermi gas is studied. The 1D phase diagram is mapped out. The result agrees well with the 1D theory, in which the partially polarized regime is predicted to be a FFLO phase, an exotic superfluid with pairs carrying finite center-of-mass momentum proposed almost 50 years ago.