Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session J41: Interacting Bosons in Optical Lattices |
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Sponsoring Units: DAMOP Chair: Tigran Sedrakyan, University of Minnesota Room: 350 |
Tuesday, March 19, 2013 2:30PM - 2:42PM |
J41.00001: Characterizing boson density wave and valence bond orders in a lattice by its dual vortex degree of freedoms Yan Chen, Jinwu Ye A duality transformation in quantum field theory is usually established first through partition functions. It is always important to explore the dual relations between various correlation functions in the transformation. Here, we explore such a dual relation to study quantum phases and phase transitions in an extended boson Hubbard model at $1/3$ ($2/3$) filling on a triangular lattice. We develop systematically a simple and effective way to use the vortex degree of freedoms on dual lattices to characterize both the density wave and valence bond symmetry breaking patterns of the boson insulating states in the direct lattices. In addition to a checkerboard charge density wave (X-CDW) and a stripe CDW, we find a novel CDW-VBS phase which has both local CDW and local valence bond solid (VBS) orders. Implications on QMC simulations are addressed. The possible experimental realizations of cold atoms loaded on optical lattices are discussed. [Preview Abstract] |
Tuesday, March 19, 2013 2:42PM - 2:54PM |
J41.00002: Expansion dynamics of interacting bosons in homogeneous lattices Stephan Langer, Jens P. Ronzheimer, Michael Schreiber, Simon Braun, Sean Hodgman, Ian P. McCulloch, Fabian Heidrich-Meisner, Immanuel Bloch, Ulrich Schneider Due to independent real-time control of Hamiltonian parameters in optical lattices, the non-equilibrium transport properties of interacting bosons and fermions can be studied in experiments with ultra-cold atomic gases (see [1] for a sudden expansion experiment with fermions). In this work, we experimentally and numerically investigate the expansion of initially localized bosons in homogeneous one- and two-dimensional optical lattices. Dimensionality has a crucial influence, since one-dimensional systems expand ballistically both in the non-interacting and the strongly interacting limit, separated by a pronounced minimum in the expansion velocity at intermediate interaction strengths. For two-dimensional and sufficiently strongly coupled one-dimensional systems, even weak interactions lead to a dramatic suppression of the expansion, indicative of diffusive dynamics. In the case of one dimension, we find an excellent agreement between the experimental results and time-dependent density-matrix renormalization group simulations. [1] Schneider et al. Nature Phys. 8, 213 (2012) [Preview Abstract] |
Tuesday, March 19, 2013 2:54PM - 3:06PM |
J41.00003: Phase diagram of two-species hard-core bosons in a two-dimensional optical lattice Kalani Hettiarachchilage, Val\'ery Rousseau, Ka-Ming Tam, Mark Jarrell, Juana Moreno We study the finite temperature phase diagram as a function of doping for strongly correlated two-species hard-core bosons in a two-dimensional optical lattice by using Quantum Monte Carlo simulations. This model contains a repulsive interspecies interaction and different hopping terms between nearest neighbors of the two species. The phase diagram shows several competing phases such as an anti-ferromagnetically ordered Mott insulator, a coexistent, a phase separated, a superfluid and a normal liquid phases. Among them, coexistence of anti-ferromagnetic and superfluid phases near half filling and a phase separated region inside superfluid region away from half filling are of main interests. Mott behaviors of heavy species and Mott and superfluid behaviors of light species at low temperatures create this novel phase separation region. At high temperatures only a normal liquid phase appears. [Preview Abstract] |
Tuesday, March 19, 2013 3:06PM - 3:18PM |
J41.00004: Fractional charge separation in the hard-core Bose Hubbard Model on the Kagome Lattice Xue Feng Zhang, Sebastian Eggert We consider the hard core Bose Hubbard Model on a Kagome lattice with fixed (open) boundary conditions on two edges. We find that the fixed boundary conditions lift the degeneracy and freeze the system at 1/3 and 2/3 filling at small hopping. At larger hopping strengths, fractional charges spontaneously separate and are free to move to the edges of the system, which leads to a novel compressible phase with solid order. The compressibility is due to excitations on the edge which display a chrial symmetry breaking that is reminiscent of the quantum Hall effect. Large scale Monte Carlo simulations confirm the analytical calculations. [Preview Abstract] |
Tuesday, March 19, 2013 3:18PM - 3:30PM |
J41.00005: Thermodynamics of the Two-Dimensional Hubbard Model James LeBlanc, Emanuel Gull The application of a numerically exact continuous time impurity solver with the DCA dynamical mean field theory has allowed us to study the thermodynamics of the two-dimensional Hubbard model for finite, but large cluster sizes. Variation in cluster size, upwards of 50-sites, allows for extrapolation to the thermodynamic limit. We present results relevant to cold gas systems, such as entropy, double occupancy and nearest-neighbour spin correlations as well as discuss the implications of these calculations on pseudogap physics of the High-Tc Cuprate superconductors away from half filling. [Preview Abstract] |
Tuesday, March 19, 2013 3:30PM - 3:42PM |
J41.00006: Bosonic Mott Insulator with Pseudo-spin Meissner Currents Karyn Le Hur, Alexandru Petrescu We introduce a two-component bosonic Mott insulator that can support chiral Meissner edge currents as a result of time-reversal symmetry breaking due to the application of a uniform magnetic field. The key ingredient is the presence of two layers exhibiting both charge (total density) and pseudo-spin (relative density) degrees of freedom. This then allows for a Mott phase characterized by pseudospin edge currents of Meissner type [1]. A simple example can be built from a ladder system [2]. We determine the temperature scale for the existence of such a phase as a function of the interlayer Josephson coupling and interaction. We show that it is possible to probe this phase by introducing gauge fields parallel to the layers, and that in the low-field limit the system exhibits a Meissner effect, in which interlayer currents are suppressed, and the overall current circulation in the layers opposes the applied field. For higher field values the currents organize themselves in vortices, as a result of a commensurate-incommensurate transition.\\[4pt] [1] Alexandru Petrescu and Karyn Le Hur, in preparation \\[0pt] [2] E. Orignac and T. Giamarchi, Phys. Rev. B 64 p. 144515 (2001); F. Crepin, N. Laflorencie, G. Roux and P. Simon, Phys. Rev. B 84, 054517 (2011). [Preview Abstract] |
Tuesday, March 19, 2013 3:42PM - 3:54PM |
J41.00007: Experimental predictions based on LOAF theory in dilute Bose atomic gases Bogdan Mihaila We discuss possible new experimental signatures of correlations in dilute Bose gases with tunable interactions within the framework of LOAF theory. The leading-order auxiliary field (LOAF) theoretical framework is a non-perturbative approximation treating the contributions of the normal and anomalous densities on equal footing [Cooper et al. Phys. Rev. Lett. 105, 240402 (2012)]. LOAF is a conserving and gapless approximation, satisfies Goldstone's theorem, yields a Bose-Einstein transition that is second order, and can be applied outside the regime of weakly-interacting particles. [Preview Abstract] |
Tuesday, March 19, 2013 3:54PM - 4:06PM |
J41.00008: Quadrature interferometry for nonequilbrium ultracold atoms in optical lattices Philip Johnson, Eite Tiesinga We propose an interaction-based interferometric technique for making time-resolved measurements of quadrature operators of nonequilibrium ultracold atoms in optical lattices. The technique creates two subsystems of magnetic atoms in different spin states and lattice sites--the arms of the interferometer. A Feshbach resonance turns off atom-atom interactions in one spin subsystem, making it a well-characterized reference state, while atoms in the other subsystem undergo nonequilibrium many-body dynamics for a variable hold time. The nonequilibrium evolution can involve a variety of Hamiltonians, including systems with tunneling and spin-orbit couplings using artificial gauge fields. Interfering the subsystems via a second beam-splitting operation, time-resolved quadrature measurements are directly obtained by detecting relative spin populations. Analyzing a simple application of the interferometer, we obtain analytic predictions for quadratures for deep optical lattices with negligible tunneling. As a second, distinct application, we show that atom-atom interaction strengths can in principle be determined with super-Heisenberg scaling $n^{-3/2}$ in the mean number of atoms per lattice site $n$, making it possible to test the physics of interaction-based quantum metrology. [Preview Abstract] |
Tuesday, March 19, 2013 4:06PM - 4:18PM |
J41.00009: Utilizing nonequilibrium effects to probe the Mott-insulator-superfluid transition of a trapped gas of interacting bosons Lev Vidmar, S. Langer, I. McCulloch, U. Schollwoeck, U. Schneider, F. Heidrich-Meisner An increased effort has been lately devoted to explore and establish the possible links between equilibrium and nonequilibrium properties of interacting quantum many-body systems. Recent experiments on optical lattices have shown the possibility of measuring the expansion velocity of an initially trapped system, which after the sudden release of the trap expands in an empty lattice [1]. Recent theoretical studies of interacting fermions indicated that the measurement of expansion velocity may provide information about the initial state [2]. In our work, we show that measuring the expansion velocity of an initially trapped gas of interacting bosons allows one to distinguish between a superfluid and a Mott insulating state in the initial ground state in 1D. We perform time-dependent DMRG calculations of the Bose-Hubbard model in a harmonic trap and a box trap. We derive a state diagram of a trapped system as a function of Coulomb repulsion and density from the expansion velocity. The resulting diagram is consistent with the state diagram obtained by measuring equilibrium properties such as local density fluctuations and on-site compressibility [3]. [1] Schneider et al. Nature Physics 8, 213 (2012) [2] Langer et al., PRA 85, 043618 (2012) [3] Rigol et al, PRA 79, 053605 (2009) [Preview Abstract] |
Tuesday, March 19, 2013 4:18PM - 4:30PM |
J41.00010: Effects of Dissipation in a BEC Dimer T. Pudlik, H. Hennig, D. Witthaut, D.K. Campbell Recently\footnote{Holger Hennig, Dirk Witthaut, and David K. Campbell, Phys. Rev. A, to appear} we have shown that a ``global phase space'' (GPS) approach provides valuable understanding of the long-time coherence and Einstein-Podolsky-Rosen entanglement of a Bose-Einstein Condensate trapped in a two-well optical lattice (``BEC dimer''). In particular, the GPS approach allows one to distinguish purely quantum effects from those which are captured by semi-classical methods. The GPS approach in Ref. (1) was applied in the limit of zero dissipation. In the present contribution, we extend the approach to allow for dissipation and again compare the results with relevant experiments. We also report preliminary results on a BEC trimer, for which the semi-classical phase space is no longer completely integrable, in contrast to the the dimer. [Preview Abstract] |
Tuesday, March 19, 2013 4:30PM - 4:42PM |
J41.00011: Higgs boson in two dimensional superfluid and Mott insulator states Kun Chen, Yuan Huang, Longxiang Liu, Youjin Deng, Lode Pollet, Nikolay Prokof'ev We find that despite strong decay into Goldstone modes the Higgs boson survives as a well-defined resonance in the two-dimensional relativistic field theory realized in the cold atomic system near the quantum critical point between the superfluid (SF) and Mott insulator(MI) states. Using scaling analysis of analytically continued results from quantum Monte Carlo simulations we construct universal spectral functions for scalar response both for SF and MI phases and reveal that they share similar properties: a resonant peak followed by a broader secondary peak before saturating to a near plateau behavior at higher frequencies, i.e. the Higgs amplitude mode is present in the MI phase under the correlation length scale. Our simulations of a trapped system of ultra-cold $^{87}Rb$ atoms explain recent experimental data and how the signal is modified by tight confinement. [Preview Abstract] |
Tuesday, March 19, 2013 4:42PM - 4:54PM |
J41.00012: How the scaling behavior changes near the quantum phase transition point? Hao Lee, Shiang Fang, Daw-Wei Wang With unbiased quantum Monte Carlo simulation (worm algorithm), we investigate off-diagonal~long-ranged correlation and density-density correlation in two-dimensional Bose-Hubbard model. For a finite size system, we show how the Bose-Einstein condensate and the off-diagonal long-range order can appear before the presence of superfluidity in higher temperature, and demonstrate the difference of the definition of Tc for various model independent methods. Furthermore, we systematically explore the critical behaviors such as the decaying behavior of the single-particle~correlation~function near the classical (BKT)~and quantum phase transition point. We define the regime when the critical behavior works and observe how this regime changes when the critical temperature approaches zero near the quantum critical point (SF-Mott). Our results show the higher order behavior beyond the universal scaling regime, and provides a lot of insight to future experiments on critical behavior near various quantum phase transition. [Preview Abstract] |
Tuesday, March 19, 2013 4:54PM - 5:06PM |
J41.00013: Real space renormalization of the Mott-insulator to Bose-glass transition in the disordered Bose-Hubbard model Anthony Hegg, Frank Kruger, Philip Phillips We show the explicit breakdown of self-averaging, due to rare region Griffiths physics, in the disordered Bose-Hubbard model . The real space renormalization flow of the disorder is toward a Gaussian distribution with vanishing relative variance in the Mott insulator, whereas the Bose glass distribution becomes distinctly non-Gaussian with diverging relative variance. We explore distributions which correspond to a non-trivial fixed point in the renormalization group equations. [Preview Abstract] |
Tuesday, March 19, 2013 5:06PM - 5:18PM |
J41.00014: Anomalous hall phases in a bosonic Mott insulator Clement Wong, Rembert Duine Spin-orbit coupled systems that break time-reversal symmetry can exhibit the anomalous hall phase, which support a hall conductivity in the absence of a magnetic field. These topological phases are in a sense the building blocks of topological insulators and bears similarities to chiral topological superconductors. Recently, it has become possible to engineer spin-orbit couplings in cold atomic systems, making it possible to study these systems in the strongly interacting regime, for bosons and fermions. With these motivations, we study spin-orbit coupled bosons in an optical lattice in the Mott-insulating phase using a strong-coupling perturbation theory. We show that quite generally, strong interactions can induce an anomalous Hall phase even for a topologically trivial spin-orbit coupling. For the spin orbit coupling in experiment Lin et. al. [Nature (London) 471, 83 (2011)], we compute the quasiparticle dispersions, spectral weights, renormalized momentum space texture and the associated interaction-generated Berry curvature. Our results have implications for the Mott-insulating phases with textured magnetic order. [Preview Abstract] |
Tuesday, March 19, 2013 5:18PM - 5:30PM |
J41.00015: Superfluid-insulator transition in a disordered two-dimensional quantum rotor model with random on-site interactions Taeyang An, Min-Chul Cha We study the superfluid-insulator quantum phase transition in a disordered two-dimensional quantum rotor model with random on-site interactions in the presence of particle-hole symmetry. Via worm-algorithm Monte Carlo calculations of superfluid density and compressibility, we find the dynamical critical exponent $z\approx 1.13(2)$ and the correlation length critical exponent $1/\nu \approx 1.1(1)$. These exponents suggest that the insulating phase is a incompressible Mott glass rather than a Bose glass. [Preview Abstract] |
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