Bulletin of the American Physical Society
42nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 56, Number 5
Monday–Friday, June 13–17, 2011; Atlanta, Georgia
Session C5: Interacting Bose Gases |
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Chair: Mark Edwards, Georgia Southern University Room: A705 |
Tuesday, June 14, 2011 2:00PM - 2:12PM |
C5.00001: Studying Quantum Many-Particle Systems on the Single-Atom Level M. Endres, C. Weitenberg, J. Sherson, M. Cheneau, P. Schauss, T. Fukuhara, I. Bloch, S. Kuhr The reliable detection of single quantum particles has revolutionized the field of quantum optics and quantum information processing. For several years, researchers have aspired to extend such detection possibilities to larger-scale, strongly correlated quantum systems. We report on fluorescence imaging of bosonic Mott insulators in an optical lattice with single-atom and single-site resolution.\footnote{J. Sherson et al., Nature 467, 68 (2010)} From our images, we fully reconstruct the atom distribution on the lattice and identify individual excitations with high fidelity. Furthermore we will present progress towards in-situ thermometry and the detection of coherent particle-hole excitations across the superfluid-to-Mott-insulator transition. We plan to use our detection technique to study one dimensional quantum systems. In the Tonks-Girardeau regime, their strongly interacting nature can be revealed by the density-density correlation function, which should show a distinct anti-bunching of the particles. [Preview Abstract] |
Tuesday, June 14, 2011 2:12PM - 2:24PM |
C5.00002: Correlated phases of bosons in tilted, frustrated lattices Susanne Pielawa, Takuya Kitagawa, Erez Berg, Subir Sachdev We theoretically study the `tilting' of Mott insulators of bosons into metastable states, and show that there are rich possibilities for correlated phases with non-trivial entanglement of pseudospin degrees of freedom measuring the boson density. A previous study (Phys. Rev. B {\bf 66}, 075128 (2002)) examined Mott insulators on cubic lattices in 1, 2, or 3 spatial dimensions tilted along a principal cubic axis, and found quantum phases with Ising density wave order, and with superfluidity transverse to the tilt direction. The one-dimensional case has recently been realized experimentally by the Greiner group at Harvard. Here we examine a variety of lattice geometries and tilt directions in two dimensions: square, triangular, decorated square, and kagome. Frustration in these systems can be implemented by decorating the lattices. We find phases with density order, a sliding Luttinger liquid phase, and quantum liquid states with no broken symmetry; an exact liquid ground state is found for a particular correlated boson model. Reference: arXiv:1101.2897 [Preview Abstract] |
Tuesday, June 14, 2011 2:24PM - 2:36PM |
C5.00003: Atomic Magnetic Resonance Imaging in an Optical Lattice Carolyn Meldgin, Matthew Pasienski, Brian DeMarco We have developed a technique to exclusively image atoms at the center of a three-dimensional optical lattice. To achieve this, microwaves are used to transfer the central atoms into a hyperfine state that is selectively imaged. Spatial discrimination is realized using hyperfine-state-sensitive AC Stark shifts induced by crossed laser beams. We discuss how this technique will be applied to a determination of the three dimensional-disordered Bose-Hubbard (DBH) phase diagram. Direct comparison between our recent disordered optical lattice measurements and QMC predictions for the DBH model have been complicated by the inhomogeneous density profile of the trapped gas; we will explain how transport and compressibility measurements taken with this imaging technique will overcome this difficulty. [Preview Abstract] |
Tuesday, June 14, 2011 2:36PM - 2:48PM |
C5.00004: Probing Ultracold Atoms in Optical Lattices with Bragg Scattering Hirokazu Miyake, Georgios Siviloglou, Graciana Puentes, Niklas Jepsen, Ivana Dimitrova, David Weld, David Pritchard, Wolfgang Ketterle A major thrust of the field of ultracold atoms in optical lattices has been to create novel phases of matter. Developing techniques to probe these systems is as important as the realization of such phases. We have applied the technique of Bragg scattering to study quantum degenerate bosonic $^{87}$Rb atoms from the superfluid phase to the Mott insulator phase in a 3D optical lattice. Bragg scattering can allow the direct detection of new phases such as antiferromagnetic ordering in 3D, both in the spin and occupation number sector. [Preview Abstract] |
Tuesday, June 14, 2011 2:48PM - 3:00PM |
C5.00005: Bose-Einstein Condensation in the P-band of a time-dependent double well optical lattice Saurabh Paul, Eite Tiesinga We investigate the formation of a Bose Einstein Condensate in the P-band of an optical lattice [1]. The lattice traps the atoms in two dimensions while confinement in the third direction is provided by a weak harmonic trap. The lattice has shallower and deeper wells arranged in a chequerboard pattern. The 2D band structure is obtained using harmonic oscillator functions at each site, with a ground S-orbital in the shallower wells, and excited P orbitals in deeper wells. The on-site energy can be varied in real time. This allows us to study the transition from an array of 1D condensates, when the onsite energy of the S and P orbitals is off-resonant, to a 3D condensate, when the energy is resonant. We have estimated the band structure parameters and used these to perform thermodynamics on a non-interacting Bose gas. We then show for a sudden change in the lattice from the non-resonant to the resonant case, the final temperature decreases, and if the initial temperature is below the critical temperature for Bose condensation, this ensures that the final state is a 3D condensate.\\[4pt] [1] G. Wirth et al., Nature Physics doi:10.1038/nphys1857 [Preview Abstract] |
Tuesday, June 14, 2011 3:00PM - 3:12PM |
C5.00006: Exploring quantum criticality based on ultracold atoms in optical lattices Xibo Zhang, Chen-Lung Hung, Li-Chung Ha, Nathan Gemelke, Shih-Kuang Tung, Cheng Chin Critical behavior developed near a quantum phase transition offers exciting opportunities to explore the universality of strongly-correlated systems near the ground state. Cold atoms in optical lattices, in particular, represent a paradigmatic system, for which the quantum phase transition between the superfluid and Mott insulator states can be externally induced by tuning the microscopic parameters. Based on in situ density measurements, quantum criticality of cesium atoms in a two-dimensional lattice can be probed by testing critical scaling of thermodynamic observables and by extracting transport properties in the quantum critical regime. Here we present experimental progress on quantum critical scaling [1]. The thermodynamic measurement suggests that the equation of state near the critical point follows the predicted scaling law at low temperatures, and that there exists an upper limit of the temperature for which the quantum critical behavior persists. \\[4pt] [1] X. Zhang, C.-L. Hung, S.-K. Tung, N. Gemelke, and C. Chin, arXiv:1101.0284v1. [Preview Abstract] |
Tuesday, June 14, 2011 3:12PM - 3:24PM |
C5.00007: Critical temperature of a tunable trapped Bose gas Robert Smith, Naaman Tammuz, Robert Campbell, Scott Beattie, Stuart Moulder, Zoran Hadzibabic We report on high precision measurements of the critical temperature of a harmonically trapped Bose gas as a function of interaction strength. We use an ultra-cold gas of $^{39}$K atoms in which the s-wave scattering length can be tuned via a Feshbach resonance. Our measurements exclude the ideal gas result by more than five standard deviations and allow, for the first time, comparison between different mean-field and beyond- mean-field theories. [Preview Abstract] |
Tuesday, June 14, 2011 3:24PM - 3:36PM |
C5.00008: Probing the Equation of State of Strongly Correlated Bose and Fermi Gases Nir Navon, Sylvain Nascimbene, Kenneth Gunter, Benno Rem, Swann Piatecki, Werner Krauth, Frederic Chevy, Christophe Salomon We have developed and used a general method to probe with high precision the thermodynamics of homogeneous systems using trapped atomic gases. We have applied this technique to the two spin-component Fermi gas with short-range interactions. Using fermionic $^{6}$Li, one can explore a wide parameter space by changing the interaction strength, the spin-population imbalance or the temperature of the gas. This system exhibits remarkably rich physics, such as normal/superfluid phase transitions (that can be of thermal or quantum character) or Fermi liquid-type behaviour of the normal phase. We have extended this method to bosons using $^{7}$Li close to a Feshbach resonance. We have measured the EoS of the Bose gas as a function of interactions at very low temperature. For the first time in atomic Bose gases, we measured quantitatively the Lee-Huang-Yang beyond mean-field correction to the ground state energy. We compared the experimental in-situ density profiles with Monte-Carlo predictions for thermometry purpose. We have extended this study using out-of-equilibrium measurements of the Bose gas in the strongly interacting regime, which gives a first hint on properties of the hypothetical unitary Bose gas. [Preview Abstract] |
Tuesday, June 14, 2011 3:36PM - 3:48PM |
C5.00009: Dimensionality and spatial entanglement in Bose-Einstein condensates Alexandre Tacla, Carlton Caves We investigate the effects of the emergence of three-dimensional behavior on a quasi-one-dimensional Bose-Einstein condensate (BEC) trapped by a highly elongated potential. By analytically performing the Schmidt decomposition of the condensate wave function in the perturbative regime, we derive corrections to the 1D approximation due to the reshaping of the BEC in the tightly confined direction with increasing nonlinearity strength. This approach provides a straight- forward way to redefine the transverse and longitudinal wave functions as well as to calculate the amount of entanglement that arises between the two spatial directions. Numerical integration of the three-dimensional Gross-Pitaevskii equation for different trapping potentials and experimentally accessible parameters reveals good agreement with our analytical model even for relatively high nonlinearities. In particular, we show that even for such stronger nonlinearities the entanglement remains remarkably small, which allows the condensate to be well described by a separable wave function that corresponds to a single Schmidt term. [Preview Abstract] |
Tuesday, June 14, 2011 3:48PM - 4:00PM |
C5.00010: Can a Bose gas be saturated? Naaman Tammuz, Robert Smith, Robert Campbell, Scott Beattie, Stuart Moulder, Jean Dalibard, Zoran Hadzibabic In Einstein's textbook picture of an ideal gas, Bose-Einstein condensation is driven by purely statistical saturation of the excited states of the system. Experiments on dilute ultracold atomic gases are celebrated as realizations of Bose-Einstein condensation in close to its purely statistical form. Here we scrutinise this point of view using an ultracold gas of potassium ($^{39}$K) atoms, in which the strength of interactions can be tuned via a Feshbach scattering resonance. We first show that under typical experimental conditions a partially condensed atomic gas strongly deviates from the textbook concept of a saturated vapour. We then use measurements at a range of interaction strengths and temperatures to extrapolate to the non-interacting limit, and prove that in this limit the behaviour of a Bose gas is consistent with the saturation picture. [Preview Abstract] |
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