Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session R50: Quantum Gases in Reduced Dimension, Ladders, and other Novel GeometriesFocus
|
Hide Abstracts |
Sponsoring Units: DAMOP Chair: M. Rigol, Pennsylvania State University Room: Hilton Baltimore Holiday Ballroom 1 |
Thursday, March 17, 2016 8:00AM - 8:36AM |
R50.00001: Exploring Quantum Many-Body Spin Dynamics with Truncated Wigner Methods Invited Speaker: Johannes Schachenmayer Recent experiments in atomic, molecular, and optical physics offer controlled and clean environments to experimentally study non-equilibrium dynamics of large many-body quantum spin-models with variable range interactions. Thus, efficient computation of such dynamics is of great importance. While in one dimension, time-dependent density matrix renormalization group methods (t-DMRG) have proven effective under certain conditions, computing dynamics in higher dimensional systems remains an outstanding challenge. Recently we formulated the discrete truncated Wigner approximation (DTWA), a semiclassical method based on the truncated Wigner approximation (TWA) that has been proven to be surprisingly accurate in predicting quench dynamics in high-dimensional lattices with up to tens of thousands of quantum spins. Here, we introduce the DTWA and show how it can compute time-evolution of quantum states in experiments that engineer spin-models with polar molecules in optical lattices or with ions in two-dimensional Penning traps. We show, how the DTWA can provide results for the time-evolution of classical and quantum correlations in quench experiments in regimes where other numerical methods are generally unreliable. We report on progress of how to incorporate higher order corrections to the method, and how to adapt it to systems with both spin and bosonic degrees of freedom. [Preview Abstract] |
Thursday, March 17, 2016 8:36AM - 8:48AM |
R50.00002: A Quantum Dipolar Spin Liquid Norman Yao, Michael Zaletel, Dan Stamper-Kurn, Ashvin Vishwanath Quantum spin liquids are a new class of magnetic ground state in which spins are quantum mechanically entangled over macroscopic scales. Motivated by recent advances in the control of polar molecules, we show that dipolar interactions between S=1/2 moments stabilize spin liquids on the triangular and kagome lattices. In the latter case, the moments spontaneously break time-reversal, forming a chiral spin liquid with robust edge modes and emergent semions. We propose a simple route toward synthesizing a dipolar Heisenberg antiferromagnet from lattice-trapped polar molecules using only a single pair of rotational states and a constant electric field. [Preview Abstract] |
Thursday, March 17, 2016 8:48AM - 9:00AM |
R50.00003: Intrinsic topological superfluidity -- fluctuations and response K Levin, Chien-Te Wu, Brandon Anderson, Rufus Boyack Recent interest in topological superconductivity is based primarily on exploiting proximity effects to obtain this important phase. However, in cold gases it is possible to contemplate ``intrinsic" topological superfluidity produced with a synthetic spin-orbit coupling and Zeeman field. It is important for such future experiments to establish how low in temperature one needs to go to reach the ordered phase. Similarly, it will be helpful to have a probe of the normal (pseudogap) phase to determine if the ultimate superfluid order will be topological or trivial. In this talk, we address these issues by considering fluctuation effects in such a superfluid, and calculate the critical transition temperature and response functions. We see qualitative signatures of topological superfluidity in spin and charge response functions. We also explore the suppression of superfluidity due to fluctuations, and importantly find that the temperature scales necessary to reach topological superfluidity are reasonably accessible [1]. [1] Phys. Rev. B 92, 134523 (2015) [Preview Abstract] |
Thursday, March 17, 2016 9:00AM - 9:12AM |
R50.00004: Phase diagrams of spinor bosons in two-leg ladders. Jereson Silva Valencia, Roberto Franco, Marcos Sergio Figueira In the last, years different experimental groups have reported the realization of atomic ladders in the presence of a homogeneous flux [Nat. Phys. 10, 588 (2014)]. These experiments have motivated theoretical calculations on 2-leg ladders with spinless bosons under magnetic fields [PRB 91, 140406(R) (2015)]. In this paper, we consider spinor boson atoms with spin S$=$1, such as Rb and Na. Gases of these atoms can be described by the spinor Bose-Hubbard Hamiltonian which has three terms: the kinetic energy, local density-density interaction and local spin-dependent term. Using DMRG, we study S$=$1 bosons on 2-leg ladders, taking into account bothantiferromagnetic and ferromagneticspin interaction. When both legs are ferromagnetic or antiferromagnetic, we obtained Mott insulator and superfluid phases, similar to the one-dimensional case, but the insulator areas decrease due to the additional kinetic term. The even-odd asymmetry is still observed in the antiferromagnetic case. However, when the local spin interaction has a different sign on each leg, charge density waves for densities 3/2 and 5/2 appear. The Mott insulator phase for density 1 (2) correspond to the antiferromagnetic-leg (ferromagnetic-leg). [Preview Abstract] |
Thursday, March 17, 2016 9:12AM - 9:24AM |
R50.00005: XY-sliding phases -- mirage of the Renormalization Group Steven Vayl, Anatoly Kuklov, Vadim Oganesyan The so called sliding XY phases in layered systems are predicted to occur if the one loop renormalization group (RG) flow renders the interlayer Josephson coupling irrelevant, while each layer still features broken U(1) symmetry \footnote{C.S.O’Hern, et al.PRL{\bf 83},2745(1999)}. In other words, such a layered system remains essentially two-dimensional despite the presence of inter-layer Josephson coupling. We have analyzed numerically a layered system consisting of groups of asymmetric layers where the RG analysis predicts sliding phases to occur. Monte Carlo simulations of such a system have been conducted in the dual representation by Worm Algorithm \footnote{N.V.Prokof'ev ,B.V.Svistunov,PRL {\bf87},160601(2001)} in terms of the closed loops of J-currents \footnote{M.Wallin, et.al., PRB{\bf B49},12115(1994)} for layer sizes varying from 4$\times$4 to 640$\times$640 and the number of layers -- from 2 to 40. The resulting flow of the inter-layer XY-stiffness has been found to be inconsistent with the RG prediction and fully consistent with the behavior of the 3D standard XY model where the bare inter-layer Josephson coupling is much smaller than the intra-layer stiffness. This result emphasizes the importance of the compactness of the U(1) variable for 2D to 3D transformation. [Preview Abstract] |
Thursday, March 17, 2016 9:24AM - 9:36AM |
R50.00006: Spontaneous increase of magnetic flux and chiral-current reversal in bosonic ladders: Swimming against the tide Teimuraz Vekua, Sebastian Greschner, Marie Piraud, Fabain Heidrich-Meisner, Ian McCulloch, Uli Schollwoeck The interplay between the spontaneous symmetry breaking and the wave-like nature of quantum particles in lattice produces an extraordinary behavior of the chiral current of interacting bosonic particles in the presence of a uniform magnetic flux defined on a two-leg ladder. While non-interacting as well as strongly interacting particles, stirred by the magnetic field circulate along the system's boundary in the counterclockwise direction, for certain interactions between particles and at sufficiently low temperature, the circulation direction of chiral current can be spontaneously reversed in vortex lattice states. Chiral-current reversal is counter-intuitive many-body effect produced by synthetic magnetism and it can be observed up to temperatures T=0.5J, where J is a hopping rate along ladder. Besides this effect we present first numerical evidence of vortex lattice states in interacting bosonic ladders with flux and a state with spontaneously imbalanced density between the ladder legs. [Preview Abstract] |
Thursday, March 17, 2016 9:36AM - 9:48AM |
R50.00007: Dimensional phase transition from 1D behavior to a 3D Bose-Einstein condensate Axel Pelster, Denis Morath, Dominik Stra\ss el, Sebastian Eggert The emergence of new properties from low-dimensional building blocks is a universal theme in different areas in physics. The investigation of transitions between isolated and coupled low-dimensional systems promises to reveal new phenomena and exotic phases. Interacting 1D bosons, which are coupled in a two-dimensional array, are maybe the most fundamental example of a system which illustrates the concept of a dimensional phase transition. However, recent experiments using ultracold gases have shown a surprising discrepancy between theory and experiment [1] and it is far from obvious if the power laws from the underlying 1D theory can predict the transition temperature and order parameter correctly for all interaction strengths. Using a combination of large-scale Quantum Monte-Carlo simulations and chain mean-field calculations, we show that the behavior of the ordering temperature as a function of inter-chain coupling strength does not follow a universal powerlaw, but also depends strongly on the filling. [1] A. Vogler, R. Labouvie, G. Barontini, S. Eggert, V. Guarrera, and H. Ott, Phys. Rev. Lett. 113, 215301 (2014) [Preview Abstract] |
(Author Not Attending)
|
R50.00008: Solving a quantum many-body problem by experiment Thomas Schweigler, Valentin Kasper, Sebastian Erne, Bernhard Rauer, Tim Langen, Thomas Gasenzer, J\"urgen Berges, J\"org Schmiedmayer We experimentally study a pair of tunnel-coupled one-dimensional atomic superfluids, which realize the quantum sine-Gordon/massive Thirring models relevant for a wide variety of disciplines from particle to condensed-matter physics. From measured interference patterns we extract phase correlation functions and analyze if, and under which conditions, the higher-order correlation functions factorize into lower ones. This allows us to characterize the essential features of the model solely from our experimental measurements, detecting the relevant quasiparticles, their interactions and the topologically distinct vacua. Our method provides comprehensive insights into a non-trivial quantum field theory and establishes a general method to analyze quantum many-body systems through experiments. The method is also used to investigate the non-equilibrium dynamics following a quench in the tunnel-coupling between the superfluids. [Preview Abstract] |
Thursday, March 17, 2016 10:00AM - 10:12AM |
R50.00009: Meissner and Laughlin Phases in bosonic Ladders Alexandru Petrescu, Marie Piraud, Ian McCulloch, Guillaume Roux, Karyn Le Hur We introduce a hard core boson model on a ladder lattice in uniform orbital magnetic flux. This model supports the Meissner effect in the presence of insulating behavior [1,2,3]. When the ratio of particle and flux densities $\nu$ is close to 1/2, the ground state is a low-dimensional equivalent of the Laughlin state of fractional quantum Hall effect [3]. Using exact analytical methods, the density matrix renormalization group method and exact diagonalization, we identify local observables that distinguish the Laughlin phase from the surrounding vortex and Meissner phases. At $\nu = 1/2$ the antisymmetric current, currently accessible in ultracold atom experiments [5,6], saturates. Thus remnants of topological order in quasi one dimensional systems can be probed using local observables. Secondly, we show how ground state degeneracy and topology can be probed with Thouless pump experiments on the ladder geometry. [1] A. Petrescu and K. Le Hur, PRL 111, 150601 [2] M. Piraud, F. Heidrich-Meisner, I. P. McCulloch, S. Greschner, T. Vekua, and U. Schollwock, PRB 91, 140406R [3] A. Petrescu and K. Le Hur, PRB 91, 054520 [4] M. Atala et al, Nat. Phys. 10, 588; B. K. Stuhl et al, Science 349, 1514; M. Mancini et al, Science 349, 1510. [Preview Abstract] |
Thursday, March 17, 2016 10:12AM - 10:24AM |
R50.00010: Entanglement entropy of the ground state of the Lieb-Liniger model C. M. Herdman, P.-N. Roy, Roger Melko, Adrian Del Maestro We consider the entanglement between two spatial subsystems in the Lieb-Liniger model of contact interacting bosons in continuous space in one dimension. Using a continuous-space ground state path integral quantum Monte Carlo method, we numerically compute the R\'{e}nyi entropy of the reduced density matrix of the subsystem as a measure of entanglement. Our numerical algorithm is based on the replica method previously introduced by the authors, which we have extended to efficiently study large spatial subsystems using a ratio approach. We confirm a logarithmic scaling of the R\'{e}nyi entropy with subsystem size that is expected from conformal field theory and compute the non-universal sub-leading constant for interaction strengths ranging over several orders of magnitude. In the strongly interacting limit, we find agreement with the known free fermion result. [Preview Abstract] |
Thursday, March 17, 2016 10:24AM - 10:36AM |
R50.00011: Diagrammatic Monte Carlo study of Fermi-polaron systems Peter Kroiss, Lode Pollet We apply the diagrammatic Monte Carlo approach to three-dimensional Fermi-polaron systems with mass-imbalance, where an impurity interacts resonantly with a noninteracting Fermi sea whose atoms have a different mass. This method allows to go beyond frequently used variational techniques by stochastically summing all relevant impurity Feynman diagrams up to a maximum expansion order limited by the sign problem. Polaron energy and quasiparticle residue can be accurately determined over a broad range of impurity masses. The quantitative exactness of two-particle-hole wave-functions is investigated, resulting in a relative lowering of polaronic energies in the mass-imbalance phase diagram. The application of the method to two-dimensional Fermi-polaron systems is presented. [Preview Abstract] |
Thursday, March 17, 2016 10:36AM - 10:48AM |
R50.00012: Recent developments in auxiliary-field quantum Monte Carlo methods for cold atoms Hao Shi, Peter Rosenberg, Ettore Vitali, Simone Chiesa, Shiwei Zhang Exact calculations are performed on the two-dimensional strongly interacting, unpolarized, uniform Fermi gas with a zero-range attractive interaction. We describe recent advances in auxiliary-field quantum Monte Carlo techniques, which eliminate an infinite variance problem in the standard algorithm, and improve both acceptance ratio and efficiency. The new methods enable calculations on large enough lattices to reliably compute ground-state properties in the thermodynamic limit. An equation of state is obtained, with a parametrization provided, which can serve as a benchmark and allow accurate comparisons with experiments. The pressure, contact parameter, condensate fraction, and pairing gap will be presented. The same methods are also applied to obtain exact results on the two-dimensional strongly interacting Fermi gas in the presence of Rashba spin-orbit (SOC), providing insights on the interplay between pairing and SOC. [Preview Abstract] |
Thursday, March 17, 2016 10:48AM - 11:00AM |
R50.00013: Multiband effects in one-dimensional bosons in optical lattices Wei Xu, Marcos Rigol We use path integral quantum Monte Carlo simulations to study quantum phase transitions of ultracold bosons in optical lattices. We restrict our study to one-dimensional systems where, in the absence of the lattice, we recover analytic results for the Lieb-Liniger model. The latter is the model that describes one-dimensional bosons with contact interactions. We first discuss how cold finite systems need to be in order for one to observe ground state physics. We then show that, in shallow lattice potentials, higher Bloch bands lead to renormalized two-body interactions. We present a study the phase diagram of these systems at intermediate interaction strengths in shallow lattice potentials, and report a detailed comparison with the phase diagram of the one-band Bose-Hubbard model. [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