Bulletin of the American Physical Society
49th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 63, Number 5
Monday–Friday, May 28–June 1 2018; Ft. Lauderdale, Florida
Session C02: Quantum Gases in Optical Lattices |
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Sponsoring Units: DQI Chair: Peter Engels, Washington State University Room: Grand A |
Tuesday, May 29, 2018 10:30AM - 11:00AM |
C02.00001: Ultracold atoms in optical quasicrystals: From Many-Body Localization to Fractal Structures Invited Speaker: Ulrich Schneider Quasicrystals are a relatively novel form of solids that is non-periodic, but nonetheless long-range ordered. They can be described by fractal aperiodic tilings with more than one unit cell, similar to the celebrated Penrose tiling. Experimentally, quasicrystals give rise to diffraction patterns consisting of sharp Bragg peaks, similar to periodic crystals, but with rotational symmetries that are forbidden for periodic structures. Even though they are long-range ordered, many foundational concepts of periodic crystals such as Blochwaves or Brillouin zones are not applicable, thereby giving rise to new physics. Examples include many-body localization, phasonic degrees of freedom, fractal band structures, and a direct link to higher dimensions via cut-and-project techniques, where quasicrystals can inherit topological properties from their periodic parent’s band structures. I will first present our experimental realization of many-body localization of interacting fermions in the presence of quasi- periodic disorder in 1D and 2D, and then discuss extensions to 2D quasicrystals with high rotational symmetries. Furthermore, I will present matter-wave diffraction experiments in an eightfold symmetric optical quasicrystal that directly reveal the self- similarity of the fractal momentum-space structure. [Preview Abstract] |
Tuesday, May 29, 2018 11:00AM - 11:30AM |
C02.00002: Single-atom-resolved probing of lattice gases in momentum space Invited Speaker: David Clement Correlations between the degrees of freedom of individual quantum particles has been identified as a key resource to solve open many-body problems. So far, a large experimental effort has been devoted to the building of apparatus capable of measuring spatial and spin correlations in one and two dimensions. We will present an experiment that provides access to multi-particle correlations between the momentum degree of freedom in three-dimensional lattice systems. We produce Bose-Einstein condensates of Helium-4 atoms in a metastable state [1,2], whose internal energy (19.6 eV) is large enough to allow for an electronic detection of individual atoms in three dimensions [3,4]. Thanks to the light mass of Helium-4 and to a long time-of-flight of 330 ms, we probe the gas in the far-field regime of expansion where the atom distribution can be exactly mapped on the in-trap momentum distribution. Comparison with ab-initio Quantum-Monte Carlo calculations in the Bose-Hubbard regime qualifies our apparatus as a single-atom probe delivering momentum distributions of strongly interacting systems as large as $60\times60\times60$ sites [5]. This provides for the first time access to physical quantities of interest, like the condensed fraction and momentum correlations, which are central to phase transitions.\\ \\ In collaboration with: H. Cayla, C. Carcy, Q. Bouton, R. Chang, M. Mancini, Laboratoire Charles Fabry, Institut d’Optique, CNRS, Univ. Paris Saclay - PALAISEAU, France; G. Carleo, Institute for Theoretical Physics, ETH Zurich - ZURICH, Switzerland\\ \\References:\newline $[1]$Q. Bouton, R. Chang, L. Hoendervanger, F. Nogrette, A. Aspect, C. I. Westbrook and D. Clément, Phys. Rev. A \textbf{91} 061402(R) (2015). \newline $[2]$R. Chang, Q. Bouton, H. Cayla, C. Qu, A. Aspect, C. I. Westbrook and D. Cl\'ement, Phys. Rev. Lett. \textbf{117}, 235303 (2016). \newline $[3]$M. Schellekens, R. Hoppeler, A. Perrin, J. Viana Gomes, D. Boiron, A. Aspect, and C. I.Westbrook, Science \textbf{310}, 648 (2005).\newline $[4]$F. Nogrette, D. Heurteau, R. Chang, Q. Bouton, C. I. Westbrook, R. Sellem and D. Clément, Rev. Scient. Intrum. \textbf{86}, 113105 (2015).\newline $[5]$H. Cayla, C. Carcy, Q. Bouton, R. Chang, G. Carleo, M. Mancini and D. Clément, arXiv preprint 1710.08392 (2017). [Preview Abstract] |
Tuesday, May 29, 2018 11:30AM - 12:00PM |
C02.00003: Can quantum phase transition be a coherent process? Invited Speaker: Cheng Chin Quantum phase transitions are transitions between two distinct ground states of a many-body system. Key features of a quantum phase transition include an initial stage with rapidly growing order (called inflation), formation of topological defects, and relaxation toward new ground state. Because of its complexity, the transition is commonly described in a classical picture where quantum coherence is suppressed. Based on Bose-Einstein condensates in a shaken optical lattice, we observe strong evidences that quantum critical dynamics remains coherent during the inflation and relaxation phases. The inflation manifests in the exponential growth of density waves and momentum state populations. After the inflation, we find surprisingly that the coherent evolution, evident in both real and momentum spaces, extends over multiple domains and persists much longer than the time scale of domain formation. Reference: Coherent inflationary dynamics for Bose-Einstein condensates crossing a quantum critical point Lei Feng, Logan W. Clark, Anita Gaj, Cheng Chin, Nature Physics 14, 269 (2018). [Preview Abstract] |
Tuesday, May 29, 2018 12:00PM - 12:30PM |
C02.00004: Topology in Floquet engineered optical lattices Invited Speaker: Klaus Sengstock Topological properties lie at the heart of many fascinating phenomena in solid-state systems such as quantum Hall systems or Chern insulators. The topology of the bands can be captured by the distribution of Berry curvature, which describes the geometry of the eigenstates across the Brillouin zone. Using fermionic ultracold atoms in a hexagonal optical lattice, we engineered the Berry curvature of the Bloch bands using resonant driving and show a full momentum-resolved state tomography from which we obtain the Berry curvature and Chern number (Science 352, 1091 (2016)).\\ \\ Furthermore, we study the time-evolution of the many-body wavefunction after a sudden quench of the lattce parameters and observe the appearance, movement, and annihilation of vortices in reciprocal space. We identify their number as a dynamical topological order parameter, which suddenly changes its value at critical times. Our measurements constitute the first observation of a so called ‚dynamical topological phase transition‘, which we show to be a fruitful concept for the understanding of quantum dynamics far from equilibrium (arXiv 1608.05616).\\ \\ The talk will discuss general concepts of topology and dynamics of ultracold quantum gases in optical lattices. [Preview Abstract] |
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