Bulletin of the American Physical Society
43rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 57, Number 5
Monday–Friday, June 4–8, 2012; Orange County, California
Session T2: Novel Optical Lattices |
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Chair: Dan Stamper-Kurn, University of California, Berkeley Room: Grand Ballroom GF |
Friday, June 8, 2012 8:00AM - 8:12AM |
T2.00001: Creating, moving and merging Dirac points with a Fermi gas in a tunable honeycomb lattice Gregor Jotzu, Leticia Tarruell, Daniel Greif, Thomas Uehlinger, Tilman Esslinger We report on the creation of Dirac points with adjustable properties in a tunable honeycomb optical lattice. Using momentum-resolved inter-band transitions, we observe a minimum band gap inside the Brillouin zone at the position of the Dirac points. We exploit the unique tunability of our lattice potential to adjust the effective mass of the Dirac fermions by breaking the inversion symmetry of the lattice. Moreover, changing the lattice anisotropy allows us to move the position of the Dirac points inside the Brillouin zone. When increasing the anisotropy beyond a critical limit, the two Dirac points merge and annihilate each other. We map out this topological transition in lattice parameter space and fin dexcellen tagreemen twit ha biniti ocalculations .Our results pave the way to model materials where Berry phases and the topology of the band structure play a crucial role. Furthermore, they provide the possibility to explore many-body phases resulting from the interplay of complex lattice geometries with interactions. [Preview Abstract] |
Friday, June 8, 2012 8:12AM - 8:24AM |
T2.00002: Trapping of Ultracold Atoms in a 10 $\mu $m-Period Permanent Magnetic Lattice Russell McLean, Smitha Jose, Prince Surendran, Leszek Krzemien, Shannon Whitlock, Mandip Singh, Andrei Sidorov, Peter Hannaford We report the trapping of cold $^{87}$Rb atoms in a 10 $\mu $m-period 1D magnetic lattice constructed from a TbGdFeCo magnetic microstructure on an atom chip. About 3$\times $10$^{5}$ atoms, optically pumped into the $F $=1, $m_{F}$ = \textbf{-}1 ground state to reduce losses due to three body recombination, are loaded into $\sim $100 lattice sites at $\sim $10 $\mu $m below the chip surface with a trap lifetime of $\sim $12 s. Individual clouds in the lattice have been spatially resolved with in-situ absorption imaging. RF spectroscopy measurements at a specific lattice site indicate an atom temperature of 1-2 $\mu $K, close to the calculated BEC transition temperature of 1.5 $\mu $K for 2000 atoms. Besides offering potential technical advantages over optical lattices, and the ability to be mounted on an atom chip [1], magnetic lattices can potentially be tailored to arbitrary geometries such as triangular-based and honeycomb lattices [2]. In future we plan to seek a clear signature of the BEC transition in the multiple lattice traps; study decoherence times for a two-component ultracold gas close to the chip surface using by Ramsey interferometry; and implement a 2D magnetic lattice, with periods down to $\sim $1 $\mu $m and tailored geometries, using state-of-the-art magnetic microstructure technology, with a view to perform quantum tunneling experiments.\\[4pt] [1] M. Singh et al J. Phys. B \textbf{41}, 065301 (2008).\\[0pt] [2] R. Schmied et al \textit{New J. Phys}. \textbf{12}, 103029 (2010). [Preview Abstract] |
Friday, June 8, 2012 8:24AM - 8:36AM |
T2.00003: Multi-orbital and density-induced tunneling in optical lattices Dirk-Soeren Luehmann, Ole Juergensen, Klaus Sengstock We show that multi-orbital and density-induced tunneling have significant impact on the phase diagrams of atoms in optical lattices. In these systems, higher-band processes and off-site interactions constitute an important extension to the established and well-studied Hubbard model. Off-site interactions lead to density-induced hopping, so-called bond-charge interactions, which can be identified with an effective tunneling potential. We introduce dressed operators for the description of multi-orbitally renormalized tunneling, on-site, and bond-charge interactions. By means of an extended occupation-dependent Hubbard model, the phase diagrams for bosonic systems and Bose-Fermi mixtures is derived. It substantially deviates from the single-band Hubbard predictions leading to strong changes of the superfluid to Mott-insulator transition point. The presented results have direct relevance for optical lattice experiments with tunable interactions. [Preview Abstract] |
Friday, June 8, 2012 8:36AM - 8:48AM |
T2.00004: Swallowtail band structure of the superfluid Fermi Gas in an optical lattice Gentaro Watanabe, Sukjin Yoon, Dalfovo Franco We investigate the energy band structure of the superfluid flow of ultracold dilute Fermi gases in a one-dimensional optical lattice along the BCS to BEC crossover within a mean-field approach [1]. In each side of the crossover region, a loop structure (swallowtail) appears in the Bloch energy band of the superfluid above a critical value of the interaction strength. The width of the swallowtail is largest near unitarity. Across the critical value of the interaction strength, the profiles of density and pairing field change more drastically in the BCS side than in the BEC side. It is found that along with the appearance of the swallowtail, there exists a narrow band in the quasiparticle energy spectrum close to the chemical potential and the incompressibility of the Fermi gas consequently experiences a profound dip in the BCS side, unlike in the BEC side.\\[4pt] [1] G. Watanabe, S. Yoon, and F. Dalfovo, Phys.\ Rev.\ Lett. {\bf 107}, 270404 (2011). [Preview Abstract] |
Friday, June 8, 2012 8:48AM - 9:00AM |
T2.00005: Ultracold Atoms in a Tunable Optical Kagome Lattice Gyu-Boong Jo, Jennie Guzman, Claire K. Thomas, Pavan Hosur, Ashvin Vishwanath, Dan M. Stamper-Kurn Geometrically frustrated systems with a large degeneracy of low energy state are of central interest in condensed-matter physics. The ground state for the kagome antiferromagnet with a particularly high degree of frustration has been proposed to be quantum spin liquid or valence bond solid, but experimental confirmations has been hampered by the significant magnetic disorder and anisotropy of the solid-state kagome magnet. In this talk, I will present the realization of the kagome geometry in a two-dimensional optical superlattice for ultracold $^{87}$Rb atoms [1]. The kagome lattice is obtained by eliminating every fourth site from a triangular lattice of spacing a/2, with the eliminated sites forming a triangular lattice of spacing a. Our optical kagome lattice allows one to tune the lattice geometry, including kagome, one-dimensional stripe, decorated triangular lattices, thereby controlling the sensitive frustration. Our tunable lattice may offer an ideal platform not only to reveal the nature of the magnetic ground state under controlled frustration, but also to investigate possible crystalline phases in the flat band for bosons.\\[4pt] [1] Jo et al. Phys. Rev. Lett. 108, 045305 (2012) [Preview Abstract] |
Friday, June 8, 2012 9:00AM - 9:12AM |
T2.00006: Supersymmetry in Rydberg-dressed lattice fermions Hendrik Weimer, Liza Huijse, Alexey Gorshkov, Guido Pupillo, Peter Zoller, Mikhail Lukin, Eugene Demler Supersymmetry is a powerful tool that allows the characterization of strongly correlated many-body systems, in particular in the case of supersymmetric extensions of the fermionic Hubbard model [1]. At the same time, these models can exhibit rich and exotic physics on their own, such as flat bands with a vanishing dispersion relation. We show that such lattice models can be realized with Rydberg-dressed fermions in optical lattices. Strong interactions within the ground state manifold of the atoms can be realized by admixing a weak contribution of a highly excited Rydberg state [2]. We discuss the unique possbilities of ultracold atoms for the detection of supersymmetry and the effects of tuning the system away from the supersymmetric point.\\[4pt] [1] P. Fendley, K. Schoutens, J. de Boer, PRL {\bf 90}, 120402 (2003).\\[0pt] [2] J. Honer, H. Weimer, T. Pfau, H. P. B\"uchler, PRL {\bf 105}, 160404 (2010). [Preview Abstract] |
Friday, June 8, 2012 9:12AM - 9:24AM |
T2.00007: The Anderson-Higgs Amplitude Mode at the Two-Dimensional Superfluid-Mott Insulator Transition Manuel Endres, Takeshi Fukuhara, David Pekker, Marc Cheneau, Peter Schauss, Christian Gross, Eugene Demler, Stefan Kuhr, Immanuel Bloch Anderson-Higgs modes are amplitude oscillations of a quantum field and appear as collective excitations in quantum many-body systems as a consequence of spontaneous breaking of a continuous symmetry. Here we reveal and study an Anderson-Higgs mode in a two-dimensional neutral superfluid close to the transition to a Mott insulating phase. We unambiguously identify the mode by observing a resonance-like feature that shows the expected softening when approaching the quantum critical point. This was made possible by recent advances in the temperature measurement of lattice gases based on single atom detection, which allowed us to use lattice modulation spectroscopy as a sensitive tool to probe the many-body system in the linear response regime. We present an experimental and theoretical study of Anderson-Higgs excitations in our system, which also addresses the consequences of reduced dimensionality and spatial confinement. [Preview Abstract] |
Friday, June 8, 2012 9:24AM - 9:36AM |
T2.00008: Exploring a geometry-induced phase transition from a superfluid to Mott insulating state in a tunable superlattice Jennie Guzman, Gyu-Boong Jo, Claire Thomas, Pavan Hosur, Ashvin Vishwanath, Dan Stamper-Kurn Ultracold atoms in optical lattices are a promising candidate for the simulation of condensed matter systems due to the fine control over interactions and geometries. Here we present experiments probing the Mott insulator phase transition in a two-dimensional bi-chromatic superlattice using ultracold $^{87}$Rb atoms. The lattice consists of overlaying two commensurate wavelength triangular lattices. By adjusting the relative position of the two lattices, we are able to realize different lattice geometries, including the kagome, the one-dimensional stripe, and the decorated triangular lattice. The superlattice gives a new way to investigate the superfluid to Mott insulating phase transition beyond varying the ratio of the tunneling and interaction energies, J/U. Using this extra degree of control, we investigate a possible geometry-induced phase transition from a superfluid to a Mott insulating state by tuning the number of neighboring sites. [Preview Abstract] |
Friday, June 8, 2012 9:36AM - 9:48AM |
T2.00009: Exact solution of SU(4) Kondo Lattice Model for ultracold alkaline-earth atoms Solomon F. Duki, Hong Ling The recent progress in ultracold atomic physics has greatly spurred the activities aimed at using cold atoms in optical lattices as a unique platform to explore condensed matter phenomena in a highly controlled manner. For alkaline-earth atoms, there is an almost perfect decoupling of the nuclear spin from the electronic angular momentum in both the ground and the metastable states [A. V. Gorshkov et al., nature 6, 289 (2010)]. This along with the existence of relatively high nuclear spin degrees of freedom makes the cold alkaline-earth atoms an excellent candidate that one can employ to study Kondo effects with higher SU(N) spin degrees of freedom. In this work we study a mixture of two-component fermionic alkaline-earth atoms loaded in external optical lattice potentials that directly emulates the Lattice Kondo Model under suitable conditions. Using a combination of bosonization and canonical transformation, we find, for a model with SU(4) symmetry, a solvable point where the Hamiltonian of the system can be exactly diagonalized. To characterize the system, we calculate the correlation functions that are accessible by experiments such as time-of-flight. [Preview Abstract] |
Friday, June 8, 2012 9:48AM - 10:00AM |
T2.00010: Bose metals on multi-leg ladders with ring-exchange Ryan V. Mishmash, Matthew S. Block, Ribhu K. Kaul, D.N. Sheng, Olexei I. Motrunich, Matthew P.A. Fisher Accessing non-superfluid, uncondensed phases of 2D lattice bosons that conduct and break no symmetries has traditionally been very difficult. Here, we present recent work establishing compelling evidence for the stability of quasi-1D descendants of a particular example of such a ``Bose metal.'' Specifically, we focus on the so-called ``d-wave Bose metal'' (DBM), which is crucially characterized by surfaces of gapless excitations in momentum space. Motivated by a strong-coupling analysis of the gauge theory for the DBM, we study in detail a model of hard-core bosons moving on the four-leg ladder with frustrating four-site ring exchange. In this system, we have successfully identified a compressible gapless Bose metal phase with five gapless modes, one more than the number of legs [1]. We can understand the nature of this phase using slave-particle-inspired determinantal wave functions, the properties of which compare impressively well to a DMRG solution of the model Hamiltonian. This represents a significant step forward in establishing the stability of the DBM in two dimensions. Finally, we will discuss scenarios in which such Bose metal-type phases may be realized in present-day experiments on ultracold atomic gases.\\[4pt] [1] R. V. Mishmash et al., PRB 84, 245127 (2011). [Preview Abstract] |
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