Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session W16: Bosons in Optical Lattices I |
Hide Abstracts |
Sponsoring Units: DAMOP Chair: Selim Jochim, Max Planck Institute-Heidelberg Room: 317 |
Thursday, March 19, 2009 11:15AM - 11:27AM |
W16.00001: Generic Phase Diagram for Bose-Einstein Condensation of Weakly Interacting Symmetric Bosonic Mixtures A.B. Kuklov, T. Blanchard, B.V. Svistunov Weakly interacting Bose gas represents {\it strongly} correlated classical field within a domain (determined by the gas parameter ) of its Bose-Einstein condensation (BEC) temperature $T=T_c$. Thus, $N$-component {\it weakly} interacting mixtures representing some symmetry can potentially exhibit rich phase diagram (PD). In particular, it can feature {\it quasi-molecular} phases preceding actual formation of the ODLRO in the vicinity of $T_c$. However, realization of a specific part of the PD depends on details of interactions. As examples, we consider mixtures characterized by O(2)$\times$O(2) symmetry ($N=2$) and spin $S=1$ with the symmetry reduced to U(1)$\times$U(1) ($N=3$). Monte Carlo simulations of these systems find a {\it single} line of the respective two- and three-component BEC transitions which has tricritical point separating II and I order transitions. No {\it quasi-molecular} phases have been found despite that na\"ive mean field (with one loop correction) predicts it. We discuss how such phases can emerge above the actual $N$-component BEC transition. One suggestion relies on Feschbach resonance detuned into negative inter-specie scattering length even when the gas parameter remains small. We acknowledge support from NSF grants PHY 0653135, 0653183 and CUNY grant 80209-0914. [Preview Abstract] |
Thursday, March 19, 2009 11:27AM - 11:39AM |
W16.00002: Universal state diagrams for harmonically trapped bosons in optical lattices Marcos Rigol, George G. Batrouni, Valery G. Rousseau, Richard T. Scalettar We use quantum Monte-Carlo simulations to obtain universal zero temperature state diagrams for strongly correlated lattice bosons in one and two dimensions under the influence of a harmonic confining potential. Since harmonic traps generate a coexistence of superfluid and Mott insulating domains, we use local quantities like the quantum fluctuations of the density and a local compressibility to identify the phases present in the inhomogeneous density profiles. We emphasize the use of the 'characteristic density' to produce a universal state diagram which is relevant to experimental optical lattice systems, regardless of the number of bosons or trap curvature. We show that the critical value of U/t at which Mott insulating domains appear in the trap depends on the filling in the system, and it is in general greater than the value in the homogeneous system. Recent experimental results by Spielman et al. [Phys. Rev. Lett. 100, 120402 (2008)] are analyzed in the context of our two-dimensional state diagram, and shown to exhibit a value for the critical point in good agreement with simulations. [Preview Abstract] |
Thursday, March 19, 2009 11:39AM - 11:51AM |
W16.00003: Occupation Statistics of a Bose-Einstein Condensate in a Driven Double Well Potential K. Smith-Mannschott, M. Chuchem, M. Hiller, T. Kottos, D. Cohen We consider the occupation statistics $P_t(n)$ of a Bose-Einstein condensate consisting of $N$ particles loaded in a double-well trap with intersite coupling $K$. Two dynamical scenaria are investigated: a) wavepacket dynamics and b) linear variation of the bias between the onsite energies of the two wells. In the latter case, we resolve three different behaviors as we increase the driving rate for intermediate values of the interatomic interaction $K/N< U < NK$: quantum adiabatic, diabatic, and sudden regime. We find that during the adiabatic to diabatic crossover, many-body Landau-Zener transitions play a dominant role, resulting in oscillations of the second moment of the occupation statistics. In contrast, the crossover to the sudden regime is characterized by a broad distribution $P_n(t\rightarrow\infty)$ which is reflected in a global maximum of the second moment. [Preview Abstract] |
Thursday, March 19, 2009 11:51AM - 12:03PM |
W16.00004: Supersolidity of Cold Atomic Bose-Fermi mixtures in optical lattices Peter P. Orth, Doron L. Bergman, Karyn Le Hur An important possible mechanism for boson supersolidity in a Bose-Fermi mixture is the existence of a nested Fermi surface. Fermions then tend to exhibit a density wave at the nesting wavevector and imprint this order via boson-fermion interactions onto the bosons, which already support superfluidity. This coexistence of bosonic superfluidity and density wave order is a signature of the supersolid phase. We present new results concerning a cold mixture confined to a triangular optical lattice. For a fermionic density of $n_f=3/4$ per lattice site, the Fermi surface exhibits both a van-Hove singularity and nesting. With a Landau-Ginzburg and a microscopic mean-field analysis, we predict the supersolid parameter regime in current experimental realizations of Bose-Fermi mixtures, and make comparisons with the square lattice geometry. We also discuss competing low-temperature phases such as a phase separated and a Mott insulating regime. Finally, we consider the case of spatially anisotropic hopping, which allows us to explore a quasi 1d regime of supersolidity. [Preview Abstract] |
Thursday, March 19, 2009 12:03PM - 12:15PM |
W16.00005: Magnetic phases of two-component lattice bosons at nonzero temperature Stephen Powell The realization of magnetically-ordered phases in optical lattices is set to be one of the next major experimental advances in the field of ultracold atoms. In the limit of strong repulsion and weak tunneling between lattice sites, perturbation theory predicts that two-component fermions form a N\'eel state with a two-sublattice structure, while bosons will tend to form a ferromagnetic insulator. This perturbative approach is, however, ill-suited for describing the physics above zero temperature and away from the strong-coupling limit. Here we address the phase diagram of two-component bosons at nonzero temperature using an approach that takes as its basis the standard mean-field theory for spinless bosons. This allows spin and charge excitations to be treated on an equal footing, and elucidates the competition between the possible magnetic and superfluid orders in the lattice. [Preview Abstract] |
Thursday, March 19, 2009 12:15PM - 12:27PM |
W16.00006: Ground State Phase Diagram of the Two-Component Bose-Hubbard Model Sebnem Gunes Soyler, Barbara Capogrosso-Sansone, Nikolay Prokof'ev, Boris Svistunov We have performed path integral Monte Carlo simulations of the two-component hard-core Bose-Hubbard model on a square lattice at half-integer filling factor for each component. This system can be realized experimentally with heteronuclear bosonic mixtures in optical lattices with tunable interspecies interactions. Our results disagree with preexisting analytical treatments both quantitatively and qualitatively. We reveal the existence of an additional solid+superfluid phase for strong anisotropy between the hopping amplitudes which radically changes the topology of the ground-state phase diagram. The new phase is a direct consequence of effective interactions between ``heavy'' atoms mediated by the ``light'' superfluid component. Remarkably, mediated interactions are sign-alternating and thus lead to a rich variety of yet to be discovered quantum phases. [Preview Abstract] |
Thursday, March 19, 2009 12:27PM - 12:39PM |
W16.00007: Counterflow and paired superfluidity in one-dimensional Bose mixtures Anzi Hu, Ludwig Mathey, Ippei Danshita, Carl Williams, Charles Clark Experimental progress in recent years has made it possible to realize mixtures of cold atoms in optical lattices. In this talk,we present our work on two types of superfluidity in 1D Bose mixtures: the counterflow superfluid and the paired superfluid phase, each of which can coexist with charge-density wave order. We predict and identify these phases both with Luttinger liquid theory and with numerical simulations. Specifically, we show the phase diagram as a function of the filling fraction and the inter-species interaction. We address the question of realizability and detectability of these phases by adding a trap potential, and by calculating various quantities that can be measured in experiment. [Preview Abstract] |
Thursday, March 19, 2009 12:39PM - 12:51PM |
W16.00008: Determination of mixing or demixing state of a two-component BEC system Chao-Chun Huang, W. C. Wu In a stable ultracold trapped two-component BEC system, it is shown that the condition $U_{11}U_{22}-U_{12}^2>0$ holds as long as the intra-species $s$-wave interactions $g_{11}$ and $g_{22}$ are both repulsive. Here $U_{ij} = g_{ij} \int d{\bf r} |\Psi_i({\bf r})|^2 |\Psi_ j({\bf r})|^2$ with $\Psi_i({\bf r})$ the wave function of species $i$. The condition is valid no matter the system is in a single-trap or in an optical lattice. Based on the variational approach, the condition has been applied to determine whether the system is in mixing or demixing state, both for the single-trap and optical-lattice cases. Phonon modes of the optical-lattice system are also shown to be intimately related to the above condition. [Preview Abstract] |
Thursday, March 19, 2009 12:51PM - 1:03PM |
W16.00009: Quantum Monte Carlo simulation of disordered Bose-Hubbard model in a 3D optical lattice Fei Lin, ShengQuan Zhou, Matthew Pasienski, Brian DeMarco, David Ceperley We perform large scale quantum Monte Carlo (QMC) simulations of disordered Bose-Hubbard model defined in a 3D optical lattice and confined in a spherical harmonic trap. Our system size is comparable to the experiment ($60^3$) [1], and our simulation temperature is as low as around 3 nK. We shall show QMC results on particle density distribution inside the trap, superfluid density as a function of disorder strength, and compare our condensate fraction to the experimentally measured values [1]. [1] M. White, M. Pasienski, D. McKay, S. Zhou, D. Ceperley, and B. DeMarco, arxiv.org/abs/0807.0446 [Preview Abstract] |
Thursday, March 19, 2009 1:03PM - 1:15PM |
W16.00010: Supersolidity in a commensurate mixture of one-dimensional hardcore bosons with mass imbalance Tassilo Keilmann, Juan Ignacio Cirac, Tommaso Roscilde We report on numerical simulations of an attractive mixture of mass-imbalanced hardcore bosons in a one-dimensional optical lattice. At a commensurate filling with 2-to-1 filling ratio we observe the formation of a crystal of \emph{trimers} (made of two heavy and one light particle) which shows quasi-condensation and superfluidity for \emph{both} particle species - hence a two-species supersolid. Supersolidity is observed both in the ground state of the system, as well as out of equilibrium in the stationary state that the system attains in the Hamiltonian evolution, after having being prepared into trimers by a superlattice. These two situations correspond to two different preparation protocols (simple adiabatic loading into an optical lattice, and release from a superlattice) which can both lead to the observation of supersolidity in optical lattice experiments. [Preview Abstract] |
Thursday, March 19, 2009 1:15PM - 1:27PM |
W16.00011: A numerical study of the phase diagram and dynamics of spin 1 bosons in a one dimensional optical lattice Subroto Mukerjee, Frank Pollmann, Joel Moore We study the phase diagram and dynamics of spin 1 bosons in a one dimensional optical lattice using iTEBD (inifinite Time Evolved Block Decimation), a numerical technique that allows us to perform calculations in the thermodynamic limit. We compare our results with previous numerical work on these systems using the conventional DMRG (Density Matrix Renormalization Group) technique and analytic calculations based on the non-linear sigma model. We also investigate the possibility of the existence of a condensate of paired singlets, a Mott insulator with dimer order and a supersolid phase between the two. Our numerical technique allows us to efficiently calculate various dynamical properties of these phases to shed light on the nature of excitations. In particular, we do this for the case of one boson per site and strong interactions when the model can be mapped on to the dimerized phase of the spin-1 Heisenberg chain. [Preview Abstract] |
Thursday, March 19, 2009 1:27PM - 1:39PM |
W16.00012: Localization in a Quasi-Periodic One Dimensional System John Biddle, Donald Priour, Sankar Das Sarma We study mobility edges and Anderson-like localization in a disorder-free, one-dimensional quasi-periodic system. In particular, we study a bichromatic sinusoidal lattice potential where a primary periodic lattice is perturbed by a secondary lattice with a period that is incommensurate with that of the primary lattice. This interesting potential admits both extended and localized states without the presence of disorder. We examine the transitions between extended and localized states by numerically solving the Schrodinger equation over a broad spatial domain, and the Lyapunov exponents are obtained from the localized eigenstates. From calculations based on the single-particle eigenstates, we report how mobility edges will be manifest in cold atom experiments in bichromatic incommensurate optical lattices. [Preview Abstract] |
Thursday, March 19, 2009 1:39PM - 1:51PM |
W16.00013: Quantum gas microscope Jonathon Gillen, Waseem Bakr, Amy Peng, Simon Foelling, Markus Greiner Ultracold quantum gases in optical lattices have opened the door to studying fundamental questions of modern condensed matter physics with atomic physics experiments. The idea is to build an enlarged model of a quantum material, with ultracold atoms in the lattice playing the role of electrons or cooper pairs in real materials. In this way it becomes possible to experimentally realize condensed matter Hamiltonians and simulate for example bosonic and fermionic Hubbard models. In my talk I will focus on our new experiment in which we build a quantum gas microscope that we plan to use as a quantum simulator. This experiment will allow us to control the quantum gas on a single lattice site level, paving the way to simulating a wide variety of Hamiltonians. [Preview Abstract] |
Thursday, March 19, 2009 1:51PM - 2:03PM |
W16.00014: Observation of Coherence between Superfluid Spheres with Quantum Monte Carlo Simulation Yasuyuki Kato, Naoki Kawashima We execute quantum Monte Carlo simulation based on the directed- loop algorithm (DLA) for the Bose-Hubbard model with an external harmonic field, which is effective for modeling a cold atomic Bose gas trapped in an optical lattice. While the general idea of DLA has very broad applicability, its straight forward application to boson systems is not efficient. To simulate large systems efficiently, we modified the DLA. [1,2] We treat a system consisting of $1.8\times10^5$ particles in a $64^3$ lattice and observe a four-tiered large ``wedding-cake'' structure in Ref. [2]. These numbers are comparable to those in the pioneering experimental work by Greiner {\it et al}. We focus on cases of the two-tiered wedding-cake systems, which have two superfluid spherical regions separated by Mott insulator region at low temperature. We show an evidence of the coherence between the two superfluid spheres. [1]. Y. Kato, T. Suzuki, and N. Kawashima: Phys. Rev. E 75, 066703 (2007) [2]. Y. Kato and N. Kawashima unpublished [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700