Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session N3: Frontiers in Ultra-cold Gases in Optical Lattices |
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Sponsoring Units: DAMOP Chair: Alexander Fetter, Stanford University Room: Colorado Convention Center Korbel 2A-3A |
Wednesday, March 7, 2007 8:00AM - 8:36AM |
N3.00001: Evidence for Superfluidity of Ultracold Fermions in an Optical Lattice Invited Speaker: The study of superfluid fermion pairs in a periodic potential has important ramifications for understanding superconductivity in crystalline materials. By using cold atomic gases, various models of condensed matter can be studied in a highly controllable environment. Weakly repulsive fermions in an optical lattice could undergo d-wave pairing at low temperatures, a possible mechanism for high temperature superconductivity in the copper oxides. The lattice potential could also strongly increase the critical temperature for s-wave superfluidity. Recent experimental advances in bulk atomic gases include the observation of fermion-pair condensates and high-temperature superfluidity. Experiments with fermions and bosonic bound pairs in optical lattices have been reported but have not yet addressed superfluid behavior. Here we report the observation of distinct interference peaks when a condensate of fermionic atom pairs is released from an optical lattice, implying long-range order (a property of a superfluid). Conceptually, this means that s-wave pairing and coherence of fermion pairs have now been established in a lattice potential, in which the transport of atoms occurs by quantum mechanical tunnelling and not by simple propagation. These observations were made for interactions on both sides of a Feshbach resonance. For larger lattice depths, the coherence was lost in a reversible manner, possibly as a result of a transition from superfluid to insulator. Such strongly interacting fermions in an optical lattice can be used to study a new class of hamiltonians with interband and atom-molecule couplings. [Preview Abstract] |
Wednesday, March 7, 2007 8:36AM - 9:12AM |
N3.00002: Interacting Fermions and Bose-Fermi mixtures in Optical Lattices Invited Speaker: When fermionic atoms are placed in the focus of several interfering laser beams, they feel a periodic potential and behave very much like electrons in a solid. However, the properties of this synthetic material can be changed at will. Here, we report on the realization of a strongly interacting Fermi gas in a 3D optical lattice, which opens the way to study condensed matter physics with light and atoms. For instance, the Fermi surface of the fermions in the lattice can be imaged and a dynamical transition from a band insulating state to a conductive state observed. The focus of the talk we will be on the behaviour of the system with changing interaction. By accessing a Feshbach resonance, we have formed molecules in the optical lattice and studied interaction induced coupling between the lowest Bloch bands as well as low-dimensional interacting Fermi gases. Finally, experiments with an interacting Bose-Fermi mixture in the lattice will be presented. [Preview Abstract] |
Wednesday, March 7, 2007 9:12AM - 9:48AM |
N3.00003: Doing Solid State Physics With Cold Atoms Invited Speaker: At present, there are worldwide efforts to emulate strongly correlated electronic systems using cold atoms in optical lattices. We shall discuss the necessary conditions for the success of this effort, how close current experiments are in meeting these conditions, and the new type of novel ``solid state'' phenomena unique to lattice quantum gases. [Preview Abstract] |
Wednesday, March 7, 2007 9:48AM - 10:24AM |
N3.00004: 2-D Lattices at JILA Invited Speaker: I will discuss recent developments in our work on 2-D optical lattices at JILA, in particular the interaction of vortices with a lattice, and the effects of finite-T fluctuations. [Preview Abstract] |
Wednesday, March 7, 2007 10:24AM - 11:00AM |
N3.00005: Normal State of a Polarized Fermi Gas at Unitarity Invited Speaker: I will discuss the Fermi gas at unitarity and at T=0 by assuming that, at high polarizations, it is a normal Fermi liquid composed of weakly interacting quasiparticles associated with the minority spin atoms. I will show that a quantum Monte Carlo approach can be used to calculate their effective mass and binding energy, as well as the full equation of state of the normal phase as a function of the concentration of minority atoms. We predict a first order phase transition from normal to superfluid at a concentration of 0.44 corresponding, in the presence of harmonic trapping, to a critical polarization of 77 per cent. I will discuss radii and the density profiles of both spin components in the trap and our prediction that the frequency of the spin dipole mode will be increased by a factor of 1.23 due to interactions. [Preview Abstract] |
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