Bulletin of the American Physical Society
40th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 54, Number 7
Tuesday–Saturday, May 19–23, 2009; Charlottesville, Virginia
Session K3: Optical Lattices I |
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Chair: Kaden Hazzard, Cornell University Room: Gilmer Hall 190 |
Thursday, May 21, 2009 10:30AM - 10:42AM |
K3.00001: Magnetic structure of an imbalanced two component Fermi gas on a square lattice Bernhard Wunsch, Eugene Demler, Efstratios Manousakis We study a two component Fermi gas on a two dimensional square lattice subject to a parabolic external confinement. Identifying the two components with a spin like degree of freedom we analyze the magnetic structure of this system as a function of the repulsive interaction strength, external confinement, spin imbalance and system size by means of an unrestricted Hartree Fock calculation. Recent work suggested that for imbalanced systems the system might phase separate in regions of ferromagnetic and antiferromagnetic spin order. However, while there are various competing solutions with collinear magnetization including the phase separated one, we find that for a broad parameter regime the energetically favored solution has a canted antiferromagnetic spin structure with two nonvanishing spin components, a ferromagnetic and an antiferromagnetic one. [Preview Abstract] |
Thursday, May 21, 2009 10:42AM - 10:54AM |
K3.00002: Towards studying quantum spin systems with ultracold bosons in an optical lattice Daniel Pertot, Bryce Gadway, Rene Reimann, Dominik Schneble We report on our progress towards the realization of the two-component Bose-Hubbard model using single-species ultracold bosonic atoms in a hyperfine state-dependent optical lattice. In the limit of weak hopping and unit occupancy, the two-component Bose-Hubbard model effectively mimics the spin-1/2 XXZ~Heisenberg model, which is a well-known model system in quantum magnetism. Further, the two-component Bose-Hubbard model on its own might exhibit interesting low-temperature phases. We produce Bose-Einstein condensates of $^{87}$Rb with a moving-coil transporter apparatus including a TOP trap which serves as a ``funnel'' to load a crossed optical dipole trap, where the actual condensation followed by the ramp-up of the lattice takes place. Our current work regarding the preparation of a clean Mott insulator state and the implementation of the state-dependent lattice will be discussed. [Preview Abstract] |
Thursday, May 21, 2009 10:54AM - 11:06AM |
K3.00003: Antiferromagnetic order and dynamics in lattice-trapped $^{87}$Rb Radu Chicireanu, Karl Nelson, Nathan Lundblad, Malte Schlosser, William Phillips, Trey Porto Optical lattices present an almost ideal environment in which to realize model condensed-matter systems and study strongly-correlated many-body behavior. Using an initial system ($^{87}$Rb) deep in the Mott-insulating regime, we create antiferromagnetic order in an double-well optical lattice using a effective magnetic field technique that allows spectral resolution of individual sublattices. With the use of a ``staggered field", we study spin dynamics in the lattice as the tunnel coupling in the system is increased and the staggered field is varied. [Preview Abstract] |
Thursday, May 21, 2009 11:06AM - 11:18AM |
K3.00004: Novel Pairing States in the p-orbital Honeycomb Optical Lattice Wei-Cheng Lee, Congjun Wu, Sankar Das Sarma We report on the novel pairing states of the spinless fermions in the two-dimensional honeycomb optical lattice with p orbitals. Because of the significant enhancement of the interaction effect due to the existence of two flat bands, the system could be in the pairing state even as it is away from the p-wave Feshbach resonances. We find that the gap symmetry is naturally to be f-wave and the Andreev bound state can be found under certain conditions. As the optical lattice is under rotation, although the f-wave gap symmetry is destroyed, the topological pairing states exhibiting gapless edge states could arise. The experimental setup to detect these novel pairing states will be discussed. [Preview Abstract] |
Thursday, May 21, 2009 11:18AM - 11:30AM |
K3.00005: Sign-Alternating Interaction Mediated by Strongly-Correlated Lattice Bosons Barbara Capogrosso-Sansone, Sebnem Soyler, Nikolay Prokof'ev, Boris Svistunov We reveal a generic mechanism of generating sign-alternating inter-site interactions mediated by strongly correlated lattice bosons. The ground state phase diagram of the two-component hard-core Bose-Hubbard model on a square lattice at half-integer filling factor for each component, obtained by worm algorithm Monte Carlo simulations, is strongly modified by these interactions and features the solid+superfluid phase for strong anisotropy between the hopping amplitudes. The new phase is a direct consequence of the effective nearest-neighbor repulsion between ``heavy'' atoms mediated by the ``light'' superfluid component. Due to their sign-alternating character, mediated interactions lead to a rich variety of yet to be discovered quantum phases. [Preview Abstract] |
Thursday, May 21, 2009 11:30AM - 11:42AM |
K3.00006: Thermometry in a two-component Mott insulator Patrick Medley, David Weld, Hirokazu Miyake, David Hucul, David Pritchard, Wolfgang Ketterle Ultracold atoms trapped in optical lattices offer a promising testbed for simulation of many-body Hamiltonians. However, thermometry of atoms in optical lattices remains challenging. One possible solution is to take advantage of the additional degrees of freedom offered by a two-component Mott insulator. We will present the results of experiments involving thermometry and cooling in a Mott insulator of $^{87}$Rb atoms comprising a mixture of two different hyperfine states. State-selective polarization rotation imaging can be used in conjunction with a field gradient to directly image the Boltzmann distribution of the spin states. [Preview Abstract] |
Thursday, May 21, 2009 11:42AM - 11:54AM |
K3.00007: Lattice Thermodynamics for Ultra-Cold Atoms David McKay, Brian DeMarco We report measurements on the temperature of ultra-cold $^{87}$Rb gases transferred into an optical lattice and compare to non-interacting thermodynamics for a combined lattice--parabolic potential. Absolute temperature is determined at low temperature by fitting quasi-momentum distributions obtained using bandmapping, i.e., turning off the lattice potential slowly compared with the bandgap. We show that distributions obtained at high temperature employing this technique are not quasimomentum distributions through numerical simulations. To overcome this limitation, we extract temperature using the in-trap size of the gas. [Preview Abstract] |
Thursday, May 21, 2009 11:54AM - 12:06PM |
K3.00008: New Ways to Probe Ultracold Fermions in Optical Lattices Christian Sanner, Ralf Gommers, Aviv Keshet, Yong-il Shin, Edward Su, Wolfgang Ketterle We report on new in situ methods to probe fermions in optical lattices and we discuss aspects of preparing these systems. [Preview Abstract] |
Thursday, May 21, 2009 12:06PM - 12:18PM |
K3.00009: In-Situ Imaging of an Atomic Gas in a Two-Dimensional Optical Lattice Nathan Gemelke, Chen-lung Hung, Xibo Zhang, Cheng Chin We describe studies of quantum many-body phases and few-body physics using interacting ultracold $^{133}$Cs atoms confined in optical lattices. The realization of the superfluid to Mott- insulator phase transition with neutral atoms in an optical lattice provides a tantalizing opportunity to test many-body physics with a high degree of accuracy. We report progress toward a quantitative comparison of the superfluid to Mott- insulator phase boundary with results from the Bose- Hubbard model, using in-situ imaging of Bose-condensed cesium atoms confined to a thin layer of a two-dimensional optical lattice potential. Scrutiny of this phase boundary forms a first step toward generalized quantum simulation, and promises future application to the study of quantum critical phenomena. To induce the phase transition, we employ Feshbach resonances to scan the on-site interaction energies over a wide range without modifying the tunneling rate and the overall trapping potential. High-resolution in-situ imaging of the two- dimensional density profile permits detailed studied of the compressibility of the Mott-insulating and superfluid phases, without complications from line-of-sight integration. We will discuss the extension of these results to the strongly interacting regime, and the application of insulator physics to few-body collision studies. [Preview Abstract] |
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