Bulletin of the American Physical Society
38th Annual Meeting of the Division of Atomic, Molecular, and Optical Physics
Volume 52, Number 7
Tuesday–Saturday, June 5–9, 2007; Calgary, Alberta, Canada
Session H3: Ultracold Atoms: Mott Insulators |
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Chair: B. DeMarco, University of Illinois Room: TELUS Convention Centre Glen 201-203 |
Thursday, June 7, 2007 10:30AM - 10:42AM |
H3.00001: Rotating bosonic ring lattice: Entanglement, Mott and Liftshitz-like Transitions Ana Maria Rey, Keith Burnett, Indubala Satija, Charles Clark We study the effects of rotation on one-dimensional ultra-cold bosons confined to a ring lattice. In this talk we discuss the existence of a critical rotation frequency at which an infinitesimal interatomic interaction energy fragments the ground state of integer filled (commensurate) systems into a macroscopic superposition of two states with different circulation. The formation of such an entangled cat state is accompanied by an opening of a gap in the spectrum and a sudden rearrangement of the momentum distribution. These features are reminiscent of the topological changes in the Fermi surface that occurs in the Lifshitz transition in fermionic systems. The entangled nature of the ground state induces a strong enhancement in the quantum correlations and decreases the threshold of the Mott insulator transition. In contrast to the commensurate case, the incommensurate lattice is rather insensitive to rotation. In addition we discuss the usefulness of noise correlations as tool for identifying novel physics in strongly correlated systems. [Preview Abstract] |
Thursday, June 7, 2007 10:42AM - 10:54AM |
H3.00002: Mott-insulator shells in the three-dimensional Bose-Hubbard model with harmonic confinement Makoto Yamashita Ultracold atomic gases in optical lattices provide the ideal stages for investigating the fundamental many-body problems in condensed-matter physics. Recently, the superfluid-Mott insulator (MI) transition of a Bose-Einstein condensate in a three-dimensional optical lattice was precisely measured by using a two-photon spectroscopy. It has been found that, in the strong interaction regime, the number of atoms at the lattice sites takes the integer values raging from one to five and its spatial distribution forms the shell structure, namely MI shells. To quantitatively understand these experimental results, we numerically study the ground-state properties of the three-dimensional (3D) Bose-Hubbard model with harmonic confinement. We have developed the highly efficient numerical method based on the Gutzwiller approximation, which can be applied to a large system consisting of more than one million of lattice sites. The MI shells observed in the experiments are successfully reproduced by the calculations using the appropriate parameters. We show the systematic analyses of the 3D Bose-Hubbard model and compare them with the recent experimental results. [Preview Abstract] |
Thursday, June 7, 2007 10:54AM - 11:06AM |
H3.00003: Vortices, antivortices and superfluid shells separating Mott-insulating regions Kaushik Mitra, C.J. Williams, C.A.R. Sa De Melo Atomic or molecular bosons in harmonically confined optical lattices are known to exhibit a wedding cake structure consisting of insulating (Mott) shells. We show that between the Mott regions, superfluid shells emerge as a result of fluctuations due to finite hopping. It is found that the order parameter equation in the superfluid regions is not of the Gross-Pitaeviskii type except near the insulator to superfluid boundaries. The excitation spectra in the Mott and superfluid regions are obtained, and it is shown that the superfluid shells posses low energy sound modes with spatially dependent sound velocity described by a local index of refraction directly related to the local superfluid density. Lastly, the Berezinski-Kosterlitz-Thouless transition and vortex-antivortex pairs are discussed in thin (wide) superfluid shells (rings) limited by three (two) dimensional Mott regions. The transition temperature of each superfluid region is dependent on the filling factor of the Mott shells that limit their boundaries. [Preview Abstract] |
Thursday, June 7, 2007 11:06AM - 11:18AM |
H3.00004: Many-Body Dynamics of Repulsively Bound Pairs of Particles in a Periodic Potential David Petrosyan, Bernd Schmidt, James R. Anglin, Michael Fleischhauer Recently, Winkler {\it et al.} [Nature 441, 853 (2006)] have observed repulsively bound atom pairs in an optical lattice. In a tight-binding periodic potential described by the Bose-Hubbard model, when the on-site repulsion between the particles exceeds their inter-site tunneling rate, such ``dimers'' are well localized at single sites and are stable over the time scale on which the energy dissipation is negligible. We derive an effective many-body Hamiltonian for a lattice loaded with dimers only, and discuss its implications for the dynamics of the system. We show that strong on-site repulsion and nearest-neighbor attraction favor clusters of dimers with minimum surface area and uniform, commensurate filling, representing thus incompressible ``droplets'' of a lattice liquid. [Preview Abstract] |
Thursday, June 7, 2007 11:18AM - 11:30AM |
H3.00005: Cavity QED determination of atomic number statistics in optical lattices Dominic Meiser, Wenzhou Chen, Pierre Meystre The number statistics of atoms in an optical lattice contain valuable information about their many-particle state. Usually the number statistics are difficult to measure experimentally. In this talk we present a method to measure the number statistics by means of reflection of a quantized light field off the atomic lattice inside a high-Q ring resonator. Depending on the lattice spacing, the light field is sensitive to various density-density correlations of the atoms. We discuss the cases of atoms in a Mott insulator state and atoms in a superfluid state and show how the two can be distinguished with our scheme. [Preview Abstract] |
Thursday, June 7, 2007 11:30AM - 11:42AM |
H3.00006: BCS-BEC Crossover: Critical Temperature Curve and Thermodynamics Evgeny Kozik, Barbara Capogrosso-Sansone, Nikolay Prokof'ev, Boris Svistunov The strongly-correlated regime of the BCS-BEC crossover can be realized by diluting a system of two-component fermions with a contact attractive interaction and an appropriate ultraviolet regularization. We investigate this system via a novel systematic-error-free continuous-space-time diagrammatic determinant Monte Carlo method. The results allow us to predict the universal curve $T_c/\varepsilon_F$ as a function of the parameter $k_Fa$ with the maximum on the BEC side. At unitarity, $T_c/\varepsilon_F = 0.152(7)$. We also determine the thermodynamic functions and show how the Monte Carlo results can be used for accurate thermometry. [Preview Abstract] |
Thursday, June 7, 2007 11:42AM - 11:54AM |
H3.00007: Phase diagram of the two-leg Bose-Hubbard model Ippei Danshita, James E. Williams, Carlos A. R. Sa de Melo, Charles W. Clark Recently, double-well optical lattices have been created to trap bosonic atoms [J. Sebby-Strabley {\it et al.}, Phys. Rev. A {\bf 73}, 033605 (2006)]. In the present work, we study the superfluid-to-Mott insulator transition of bosons in double-well optical lattices. Applying the time-evolving block decimation algorithm [G. Vidal, Phys. Rev. Lett. {\bf 93}, 040502 (2004); cond-mat/0605597] to the two-leg Bose-Hubbard Hamiltonian, we obtain the zero-temperature phase diagrams and find that there are the half-integer-filling and integer-filling Mott insulator regions. For symmetric double wells (no tilt), we show that the half-integer-filling Mott insulator phase is stabilized and that the integer-filling Mott insulator domain becomes smaller as the intra-double-well hopping increases. As the tilt of the double-wells increases, we find that the half-integer-filling Mott insulator phase becomes larger monotonically and approaches the integer-filling Mott phase for a single 1D lattice. In contrast, we show that the integer-filling Mott phase shows non-monotonic reentrant behaviour as a function of the tilt parameter. [Preview Abstract] |
Thursday, June 7, 2007 11:54AM - 12:06PM |
H3.00008: Heisenberg limited sensitivity via transition from a two-component Mott insulator to a superfluid Mirta Rodriguez, Stephen Clark, Dieter Jaksch We analyze the outcome of a Mott insulator to superfluid transition for a two-component Bose gas with two atoms per site in an optical lattice in the limit of slow ramping down the lattice potential. We manipulate the initial state of the atoms in the Mott insulating regime and study how local correlations between hyperfine states ofatom pairs transform into multiparticle correlations extending over the whole system. We show that under particular conditions one can create twin Fock and macroscopic superposition states and that in general, the superfluid states obtained in this way are highly depleted and present a complicated structure. [Preview Abstract] |
Thursday, June 7, 2007 12:06PM - 12:18PM |
H3.00009: Preparing and probing few-atom number states with an atom interferometer Benjamin Brown, Jennifer Sebby-Strabley, Marco Anderlini, Patricia Lee, Philip Johnson, William Phillips, Trey Porto We describe the controlled loading and measurement of
number-squeezed states and Poisson states of atoms in individual
sites of a double-well optical lattice. These states are input to
an atom interferometer that is realized by symmetrically splitting
individual lattice sites into double-wells, allowing atoms in
individual sites to evolve independently. The two paths then
interfere, creating a matter-wave double-slit diffraction pattern.
The time evolution of the double-slit diffraction pattern is used
to measure the number statistics of the input state. We present
investigations of three distinct site occupation distributions:
predominantly $N = 1$ atom per site, a Poisson distribution with
$\left |
Thursday, June 7, 2007 12:18PM - 12:30PM |
H3.00010: Transport Properties of a Mott-like State of Molecules Stephan Duerr, Niels Syassen, Dominik Bauer, Thomas Volz, Matthias Lettner, Daniel Dietze, Gerhard Rempe In Ref. [1] we showed the preparation of a Mott-like state of molecules. This state is a quantum state with exactly one molecule at each site of an optical lattice. We now study the transport properties in the Mott-like state. A molecule can tunnel with an amplitude $J_m$ to an adjacent site. If there is already another molecule at that site the molecules can collide inelastically [2], leading to loss of both molecules from the sample. This loss occurs with a rate coefficient $\Gamma$ which is typically much faster than $J_m/\hbar$. The fast on-site loss leads to a suppression of tunneling. Loss from the initial state effectively occurs with a rate $\Gamma_\textrm{eff} \propto J_m^2/\Gamma$. This effect is studied experimentally at different lattice depths and the results are compared with theoretical predictions.\\[0ex] [1] T. Volz et al. Nature Physics {\bf 2}, 692 (2006).\\[0ex] [2] N.~Syassen et al. Phys. Rev. A {\bf 74}, 062706 (2006). [Preview Abstract] |
Thursday, June 7, 2007 12:30PM - 12:42PM |
H3.00011: Measurements of Collective Modes Spanning the 3-D Superfluid to Mott-Insulator Transition David McKay, Matt White, Matt Pasienski, Yutaka Miyagawa, Brian DeMarco We report measurements on the collective modes of a $^{87}$Rb Bose-Einstein condensate transferred into a 3-D optical lattice. We measure the frequency and damping rates of dipole and quadrupole oscillations across a range of lattice depths, from the regime of pure superfluid to coexisting superfluid and Mott-insulator phases. We will discuss relevance to the transport properties of the Bose-Hubbard model, including possible bearing on the existence of a Bose metal. We will also comment on significance to recent predictions of collective mode frequencies for superfluid shells bounded by Mott-insulator phases. [Preview Abstract] |
Thursday, June 7, 2007 12:42PM - 12:54PM |
H3.00012: Progress Toward Realizing the Superfluid to Mott-Insulator Transition in the Presence of Fine-Grain Disorder Matthew Pasienski, Matthew White, David McKay, Yutaka Miyagawa, Brian DeMarco We report on experimental progress toward realizing the superfluid to Mott-insulator transition in the presence of fine-grain disorder.~ Disorder is added---using a speckle field created by a holographic diffuser---to a $^{87}$Rb Bose-Einstein condensate trapped in a 3-D optical lattice. We are able to achieve speckle sizes of 700 nm, less than twice the lattice spacing, by employing low f/{\#} optics and 532 nm light. [Preview Abstract] |
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