Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session A36: Focus Session: Novel States of Matter in Atomic Gases |
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Sponsoring Units: DAMOP DCMP Chair: Erich Mueller, Cornell University Room: LACC 510 |
Monday, March 21, 2005 8:00AM - 8:12AM |
A36.00001: Noise Correlations in one-dimensional ultra-cold atom systems Ludwig Mathey, Ashvin Vishwanath, Ehud Altman Time of flight images reflect the momentum distribution of the atoms in the trap, but the spatial noise in the image holds information on more subtle correlations. Using Bosonization, we study such noise correlations in several generic one dimensional systems of ultra cold bosons and fermions. Specifically, we show how pairing as well as spin and charge density wave correlations may be identified and extracted from the time of flight images. These incipient orders manifest themselves as power law singularities in the noise correlations, that depend on the Luttinger parameters. [Preview Abstract] |
Monday, March 21, 2005 8:12AM - 8:24AM |
A36.00002: Superfluidity of interacting bosons in one-dimension via strong disorder Noah Bray-Ali, Joel Moore We have found a novel set of superfluid and Mott insulating phases arising in strongly-disordered, one-dimensional optical lattices with large, commensurate filling of bosons. Using a spin-wave approach, we show that the bosons form a true, long-range ordered superfluid at $T=0$, provided that the on-site repulsion has a broad distribution. Such broad, power-law distributions arise naturally under real-space renormalization group flow. Furthermore, they describe the asymptotic properties of diluted two-dimensional optical lattices near percolation threshold. We discuss the possibility of true superfluidity in the diluted system. [Preview Abstract] |
Monday, March 21, 2005 8:24AM - 8:36AM |
A36.00003: Novel Superfluidity of Trapped Fermi Atoms Loaded on Optical Lattices Masahiko Machida, Susumu Yamada, Yoji Ohashi, Hideki Matsumoto We investigate a possibility of superfluidity in a trapped gas of Fermi atoms with a repulsive interaction in the presence of an optical lattice. Applying the exact diagonalization method to a one-dimensional Hubbard model including the trap potential, we find that, when the strength of the repulsive interaction exceeds a critical value, the binding energy of two Fermi atoms becomes {\it negative} below the half-filling case, indicating that an attractive interaction effectively works between Fermi atoms. In this case, a "Mott insulating core" appears in the center of the trap, where each site is occupied by one atom. The Cooper-pair correlation strongly develops between atoms in the left and right hand sides of this core. Furthermore, we show a ground-state phase diagram including the superfluidity on the trapped Fermi atoms loaded on optical lattices. [Preview Abstract] |
Monday, March 21, 2005 8:36AM - 9:12AM |
A36.00004: Novel quantum phases of interacting fermionic atoms Invited Speaker: Recent developments in ultracold atomic gases have revitalized interest in some basic qualitative questions of quantum many-body theory, because they promise to make a wide variety of conceptually interesting systems, which might previously have seemed academic or excessively special, experimentally accessible. I will describe a set of simple, idealized model systems that seem to surprisingly display new states of quantum matter. One such system is a two component fermi gas of mismatched fermi surfaces and of different masses. Our study shows it has a new kind of pairing state---breached pair superfluidity---other than the well known states of BCS and Larkin-Ovchinnikov-Fulde-Ferrell (LOFF). I will discuss when the state becomes stable and suggest ways of possible experimental realization, including a theoretical design of optical sublattices with different tunnelings (thus a spin-dependent Hubbard model). The state also contains novel signature of superfluidity in the momentum distribution of particles, which is directly observable as a first-order effect. In the presence of a steeper confining trap potential which strongly breaks the translational symmetry, our work in progress indicates that another competing new state---angular crystalline superfluid---seems to become energetically favorable. [Preview Abstract] |
Monday, March 21, 2005 9:12AM - 9:24AM |
A36.00005: Fulde-Ferrel-Larkin-Ovchinnikov paired atomic superfluids Daniel Sheehy, Leo Radzihovsky The Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) paired superfluid is a periodically modulated, finite magnetization relative of the conventional BCS superconductor. While the FFLO state has proven elusive in condensed-matter experiments, we will argue that it is naturally realized in a cloud of two species of ultra-cold fermionic atoms interacting through a Feshbach resonance, with the difference in the number of the two species playing the role of an imposed magnetization. Motivated by this possibility, we have computed the phase diagram of such atomic systems as a function of Feshbach resonance detuning, temperature and magnetization. [Preview Abstract] |
Monday, March 21, 2005 9:24AM - 9:36AM |
A36.00006: Non-equilibrium dynamics of hard-core bosons on 1D lattices: short vs large time results Marcos Rigol, Alejandro Muramatsu Based on an exact treatment we study the non-equilibrium dynamics of hard-core bosons on one-dimensional lattices. Starting from a pure Fock state we find that quasi-long range correlations develop very fast in the system, and they lead to the emergence of quasi-condensates at finite momentum [1]. The exponent observed in the power-law decay of the one-particle density matrix, which develops dynamically, is the same that has been proven to be universal in the equilibrium case [2]. We also study the time evolution of clouds of hard-core bosons when they are released from a harmonic trap. In this case we show that the momentum distribution of the free expanding hard-core bosons approaches to the one of noninteracting fermions [3], in contrast to the known behavior in equilibrium systems. [1] M. Rigol and A. Muramatsu, cond-mat/0403387, to appear in Phys. Rev. Lett. (2004). [2] M. Rigol and A. Muramatsu, Phys. Rev. A 70, 031603(R) (2004); ibid. cond-mat/0409132. [3] M. Rigol and A. Muramatsu, cond-mat/0410683. [Preview Abstract] |
Monday, March 21, 2005 9:36AM - 9:48AM |
A36.00007: Solitons in Trapped Bose-Einstein condensates in one-dimensional optical lattices Richard Scalettar, Frederic Hebert, George Batrouni We use Quantum Monte Carlo simulations to show the presence and study the properties of solitons in the one dimensional soft-core bosonic Hubbard model with near neighbor interaction in traps. We show that when the half-filled Charge Density Wave (CDW) phase is doped, solitons are produced and quasi long range order established. We discuss the implications of these results for the presence and robustness of this solitonic phase in Bose-Einstein Condensates on one dimensional optical lattices in traps and study the associated excitation spectrum. The density profile exhibits the coexistence of Mott insulator, CDW, and superfluid regions. Work supported by NSF DMR 0312261 and NSF INT 0124863. [Preview Abstract] |
Monday, March 21, 2005 9:48AM - 10:00AM |
A36.00008: Filling the Bose sea: clustered states and excitations Eddy Ardonne, Rinat Kedem, Michael Stone We explore the structure of clustered quantum states, which might be realized in `droplets' of rapidly rotating Bose Einstein condensates. We explore the underlying algebraic structure (which is that of the affine Lie algebra $su(2)_k$) and count the dimension of the space of symmetric polynomials which have the clustering property. Upon increasing the size of the droplet, the partition function of the droplet becomes a character of the underlying algebra $su(2)_k$, confirming that the system can be described by an $su(2)$ Chern-Simons theory. [Preview Abstract] |
Monday, March 21, 2005 10:00AM - 10:12AM |
A36.00009: Dynamical structure factor of one dimensional bosons in optical lattices Anibal Iucci, Miguel Cazalilla, Andrew Ho, Thierry Giamarchi We investigate a one dimensional system of cold bosonic atoms in an optical lattice subjected to a time dependent periodic potential. We study the dynamic structure factor and the excitation spectrum in different regimes: superfluid and Mott insulator. In particular the strong interactions gives rise to a continuum of excitations in the superfluid phase. We discuss the application to recent experiments on bosonic tubes. We also discuss comparisons to higher dimension situations. [Preview Abstract] |
Monday, March 21, 2005 10:12AM - 10:24AM |
A36.00010: Superfluid--Insulator Transition in Commensurate One-Dimensional Bosonic System with Off-Diagonal Disorder Kar\'en Balabanyan, Nikolay Prokof'ev, Boris Svistunov We analyze the superfluid--insulator transition in a system of one-dimensional (1D) lattice bosons with off-diagonal disorder in the limit of large commensurate filling. We argue---in contrast to the recent prediction (E.~Altman, Y.~Kafri, A.~Polkovnikov, and G.~Refael, cond-mat/0402177) of strong- randomness fixed point for this system---that at any strength of disorder the universality class of the transition on the superfluid side coincides with that of the superfluid--Mott- insulator transition in a pure system. We present results of Monte Carlo simulations for two strongly disordered models that are in excellent agreement with the advocated scenario. [Preview Abstract] |
Monday, March 21, 2005 10:24AM - 10:36AM |
A36.00011: Supersolid vs. phase separation in 2D Pinaki Sengupta, Leonid P. Pryadko, Fabien Alet, Matthias Troyer, Guido Schmid We study the nature of the ground state of the strongly-coupled two dimensional extended Bose Hubbard model on a square lattice. Strong coupling expansion and quantum Monte Carlo simulation of finite systems were used to analyse the stability of the ($\pi,\pi$) crystalline order at half-filling and the effects of doping away from it. We find that strong but finite on-site interaction along with a comparable nearest-neighbor repulsion results in a thermodynamically stable supersolid ground state just above half-filling, while the system phase separates just below half-filling. The interplay between these two interaction energies results in a rich phase diagram which is studied in detail. [Preview Abstract] |
Monday, March 21, 2005 10:36AM - 10:48AM |
A36.00012: Crystalline phases of bosons in harmonic traps Igor Romanovsky, Constantine Yannouleas, Uzi Landman Strongly repelling bosons in two-dimensional harmonic traps are described through breaking of rotational symmetry at the Hartree- Fock level and subsequent symmetry restoration via projection techniques, thus incorporating correlations beyond the Gross- Pitaevskii (GP) solution. The bosons localize and form polygonal-ring-like crystalline patterns, both for a repulsive contact potential and a Coulomb interaction, as revealed via conditional-probability-distribution analysis. For neutral bosons, the total energy of the crystalline phase saturates in contrast to the GP solution, and its spatial extent becomes smaller than that of the GP condensate. For charged bosons, the total energy and dimensions approach the values of classical point-like charges in their equilibrium configuration. For neutral bosons, the present work describes a 2D generalization of the 1D Tonks-Girardeau regime of impenetrable bosons.\footnote{Phys. Rev. Lett. (Dec. 2004); cond-mat/0410598; to see a preprint \urllink{CLICK HERE}{http://arxiv.org/abs/cond- mat/0410598}} [Preview Abstract] |
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A36.00013: Superfluid-insulator transition in moving boson lattice systems Ehud Altman, Anatoli Polkovnikov, Eugene Demler, Bertrand Halperin, Mikhail Lukin We analyze the stability of superfluid currents in a system of strongly interacting ultra-cold atoms in an optical lattice. We show that such a system undergoes a dynamic, irreversible phase transition at a critical momentum that depends upon the interaction strength between atoms. At integer filling of the lattice, the phase boundary continuously interpolates between the classical modulation instability of a weakly interacting condensate and the equilibrium quantum phase transition into a Mott insulator state at which the critical momentum vanishes. For fractional filling, the critical momentum dips to a minimum at intermediate interaction strength, but saturates to the same limiting value at both strong and weak interactions. [Preview Abstract] |
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A36.00014: Decay of superfluid currents in moving boson lattice systems Anatoli Polkovnikov, Ehud Altman, Eugene Demler, Bertrand Halperin, Mikhail Lukin Following up on the previous talk, we analyze the broadening of the dynamic superfluid-insulator transition due to quantum and thermal fluctuations. We derive asymptotic expressions for the decay rate of superfluid currents near the transition. We show that in three dimensional optical lattices the broadening of the transition is very weak. On the other hand in two and especially in one dimension the broadening is very significant unless the system is very deep in the superfluid regime. We argue that at experimentally relevant temperatures the quantum decay is stronger than the thermal and thus is straightforward to observe. [Preview Abstract] |
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