Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session M41: Theory of Quantum Gases in Low Dimensions |
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Sponsoring Units: DAMOP Chair: Juraj Radic, University of Maryland Room: 350 |
Wednesday, March 20, 2013 8:00AM - 8:12AM |
M41.00001: Adiabatic evolution of the Fulde-Ferrell-Larkin-Ovchinnikov state of imbalanced fermionic-atom superfluids in an optical lattice of coupled tubes C.J. Bolech, Kuei Sun We study two-species imbalanced fermionic superfluids in an array of one-dimensional tubes that are coupled via particle tunneling between nearest neighbors. Incorporating the interplay of Cooper pairing, spin imbalance (or magnetization), and single-particle tunneling, we obtain imbalance profiles accompanied with oscillatory pairing reminiscent of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, and show that the magnetization of the system can undergo an incompressible-compressible transition by the tuning of the magnetic field as well as tunneling strength [Phys. Rev. A {\bf 85}, 051607 (2012)]. The system's phase diagram is well described by an effective extended Bose-Hubbard model. In addition, we discuss another viable process of pair tunneling that strongly affects the evolution of the FFLO profiles. With this new element, one can build a model describing the development of signatures characteristic of the incipience of the dimensional crossover and in partial agreement with preliminary experimental data. [Preview Abstract] |
Wednesday, March 20, 2013 8:12AM - 8:24AM |
M41.00002: Asymptotic Limit of Momentum Distribution Functions in the Sudden Expansion of a Spin-imbalanced Fermi Gas in One Dimension Fabian Heidrich-Meisner, Carlos Bolech, Stephan Langer, Ian McCulloch, Giuliano Orso, Marcos Rigol We study the sudden expansion of a spin-imbalanced Fermi gas in an optical lattice after quenching the trapping potential to zero [1], described by the attractive Hubbard model. Using time-dependent density matrix renormalization group simulations we demonstrate that the momentum distribution functions (MDFs) of majority and minority fermions become stationary after surprisingly short expansion times. We explain this via a quantum distillation mechanism [2] that results in a spatial separation of excess fermions and pairs, causing Fulde-Ferrell-Larkin-Ovchinnikov correlations to disappear rapidly. We further argue that the asymptotic form of the MDFs is determined by the integrals of motion of this integrable quantum system, namely the rapidities from the Bethe ansatz solution. We discuss the relevance of our results for the observation of Fulde-Ferrell-Larkin-Ovchinnikov correlations in 1D systems, related to recent experiments from Rice University [3].\\[4pt] [1] Bolech et al., Phys. Rev. Lett. 109, 110602 (2012)\\[0pt] [2] Heidrich-Meisner et al., Phys. Rev. A 80, 041603(R) (2009)\\[0pt] [3] Liao et al., Nature 467, 567 (2010) [Preview Abstract] |
Wednesday, March 20, 2013 8:24AM - 8:36AM |
M41.00003: Superfluidity of Bosons in Kagome Lattices with Frustration Xiao-Qi Sun, Zhu Chen, Yi-Zhuang You, Hui Zhai We consider spinless bosons in a Kagome lattice with nearest-neighbor hopping and on-site interaction, and the sign of hopping is inverted by insetting a $\pi$ flux in each triangle of Kagome lattice so that the lowest single particle band is perfectly flat. We show that in the high density limit, despite of the infinite degeneracy of the single particle ground states, interaction will select out the Bloch state at the K point of Brillouin zone for boson condensation at the lowest temperature. As temperature increases, the single boson superfluid order can be easily destroyed, while an exotic triple-boson paired superfluid order will remain. We establish that this trion superfluid exists in a broad temperature regime until the temperature is increased to the same order of hopping and then the system turns into normal phases. Finally we show that time of flight measurement of momentum distribution and its noise correlation can be used to distinguish these three phases. [Preview Abstract] |
Wednesday, March 20, 2013 8:36AM - 8:48AM |
M41.00004: The Higgs amplitude mode in superfluids of Dirac fermions Shunji Tsuchiya, Ramachandran Ganesh, Tetsuro Nikuni Motivated by recent developments of cold atom experiments in optical lattices, we study collective modes of atomic Dirac fermions on the two-dimensional honeycomb lattice. The attractive fermion Hubbard model on the honeycomb lattice was found to exhibit the quantum phase transition at half-filling between a semimetal with massless Dirac fermion excitations and a simple s-wave superfluid phase.\footnote[1]{E. Zhao and A. Paramekanti, Phys. Rev. Lett. 97, 230404 (2006).} We calculate collective modes in superfluid phase as well as in normal phase in the vicinity of the quantum critical point within the generalized random phase approximation. We find evidence for a {\it undamped} gapful Higgs amplitude mode below the two-particle continuum, together with a gapless Anderson-Bogoliubov (AB) mode in superfluid phase. As approaching the quantum critical point from the superfluid side, the energy gap of the Higgs mode decreases and eventually the Higgs mode and AB mode become degenerate at the quantum critical point. In the normal phase, we find that these collective modes split into Cooperon and exciton excitations that are particle-particle and particle-hole bound states, respectively. We discuss possibilities of observing these collective modes in optical lattice experiments. [Preview Abstract] |
Wednesday, March 20, 2013 8:48AM - 9:00AM |
M41.00005: Quantum phase-manipulation of a two-leg ladder in mixed dimensional Fermonic cold atoms Wen-Min Huang, Kyle Irwin, Shan-Wen Tsai The recent realization of mixed dimensional cold atoms has attracted intense attentions from both experimentalists and theoreticians. Exotic phases arise due to correlation effects, and the systems can be engineered with quantum phase-tunable parameters. We investigate a two-species Fermi gas: one is confined in a two-leg ladder with on-site interactions, and the other is free in a two dimensional square lattice. By integrating out the two-dimensional gas, a long-range mediated interaction in the ladder is generated due to the on-site interspecies interactions. Using the renormalization group method, we show that the mediated interactions enhance the instability of charge density waves, and can be controlled by the filling in the two-dimensional gas. Parameterizing the phase diagrams with different quantities, we discuss the possible quantum phase-manipulation of a two-leg ladder in mixed dimensional Fermionic cold atoms. [Preview Abstract] |
Wednesday, March 20, 2013 9:00AM - 9:12AM |
M41.00006: Quantum phases of cold fermions in mixed dimensions: 2D layer embedded in 3D gas Kyle Irwin, Chen-Yen Lai, Wen-Min Huang, Shan-Wen Tsai Recently two-species cold atoms in mixed dimensions have been realized experimentally, triggering lots of studies to explore new exotic phases in these systems. Inspired by this, we study the phase diagram of a mixed Fermi system, in which one species is confined in a two-dimensional square or triangular lattice with a correlation effect, and the other is free to move in three-dimensional space. By integrating out the free three-dimensional fermions, a long-range mediated interaction is generated in the two-dimensional lattice due to the interspecies interaction. We employ a functional renormalization group method to discover the possible phases, which may shed light to new exotic quantum phases created in ultracold atoms systems. [Preview Abstract] |
Wednesday, March 20, 2013 9:12AM - 9:24AM |
M41.00007: Exact Self-Consistent Condensates in (Imbalanced) quasi-1D Superfluid Fermi Gases Giacomo Marmorini, Ryosuke Yoshii, Shunji Tsuchiya, Muneto Nitta Borrowing some techniques from high-energy physics, and in particular from the study of Nambu-Jona-Lasinio model in 1+1 dimensions [1,2], we present an analytic method to approach Eilenberger equation and the associated Bogoliubov-de Gennes equation for quasi-1D fermionic gases. The problem of finding self-consistent inhomogeneous condensates is reduced to solving a certain class of nonlinear Schr\"odinger equations, whose most general solitonic solution is indeed available. Previously known solutions can be retrieved by taking appropriate limits in the parameters. The applicability of the method extends to ring geometry and to population imbalanced Fermi gases [3,4]. In particular we show exactly that fermionic zero-modes are robust against imbalance. References: \newline [1] G. Basar and G. V. Dunne, Phys. Rev. Lett. 100, 200404 (2008) \newline [2] G. Basar and G. V. Dunne, Phys. Rev. D 78, 065022 (2008) \newline [3] R. Yoshii, S. Tsuchiya, G. Marmorini and M. Nitta, Phys. Rev. B 84, 024503 (2011) \newline [4] R. Yoshii, G. Marmorini and M. Nitta, J. Phys. Soc. Jpn. 81 (2012) 094704 [Preview Abstract] |
Wednesday, March 20, 2013 9:24AM - 9:36AM |
M41.00008: Tuning the Kosterlitz-Thouless transition to zero temperature in anisotropic boson systems Jhih-Shih You, Hao Lee, Shiang Fang, Miguel A. Cazalilla, Daw-Wei Wang We study the two-dimensional Bose-Hubbard model with anisotropic hopping. Focusing on the effects of anisotropy on superfluid properties such as the helicity modulus and the normal-to-superfluid [Berezinskii-Kosterlitz-Thouless (BKT)] transition temperature, two different approaches are compared: large-scale quantumMonte Carlo simulations and the self-consistent harmonic approximation (SCHA). For the latter, two different formulations are considered, one applying near the isotropic limit and the other applying in the extremely anisotropic limit. Thus we find that the SCHA provides a reasonable description of superfluid properties of this system provided the appropriate type of formulation is employed. The accuracy of the SCHA in the extremely anisotropic limit, where the BKT transition temperature is tuned to zero (i.e., at a quantum critical point) and therefore quantum fluctuations play a dominant role, is particularly striking. [Preview Abstract] |
Wednesday, March 20, 2013 9:36AM - 9:48AM |
M41.00009: ABSTRACT WITHDRAWN |
Wednesday, March 20, 2013 9:48AM - 10:00AM |
M41.00010: Variational Matrix Product Ansatz for Interacting 1D Gases Sangwoo Chung, Kuei Sun, C.J. Bolech Shortly after the advent of the density matrix renormalization group (DMRG) method, Ostlund and Rommer [PRL 75, 3537-3540 (1995)] have demonstrated that ground states of one-dimensional lattice systems obtained with the DMRG procedure can be written in terms of products of matrices and, remarkably, that those ground states can be obtained from variational methods without making any reference to DMRG. Since then, a lot of activity ensued and recently there was some additional success in going beyond lattice models and obtaining the ground state properties of interacting bosons in the continuum. We extend those findings and discuss systems of both interacting Bosons and Fermions in one-dimension. [Preview Abstract] |
Wednesday, March 20, 2013 10:00AM - 10:12AM |
M41.00011: Revealing the breakdown of spin-charge separation in spin-imbalanced fermions in one dimension using quench dynamics Paata Kakashvili, Michael Sekania Recently, spin-imbalanced fermions in one dimension have attracted considerable attention both theoretically and experimentally. This system was successfully simulated using ultracold atoms in optical lattices. The phase diagram was measured and found to be in agreement with exact analytical calculations. It was also established theoretically that the spin-charge separation, an important property of Luttinger liquids, is absent. Low-energy bosonic excitations do not carry spin and charge separately due to the interaction between spin and charge degrees of freedom. Based on our numerical (time-dependent density matrix renormalization group method (t-DMRG)) and analytical calculations (Bethe Ansatz, Bosonization) on the Hubbard model, we propose quench experiments which not only reveal the breakdown of spin-charge separation but also make it possible to study the so called ``string'' bound states in this system. [Preview Abstract] |
Wednesday, March 20, 2013 10:12AM - 10:24AM |
M41.00012: Exploration of the Exact Bose-Fermi Mixture Phase Diagram via Quantum Monte Carlo Kyung Duk Yoon Following unprecedented success studying Bose and Fermi gases in optical lattices, atomic physicists are becoming increasingly interested in Bose-Fermi mixtures. It has been suggested that mixtures possess a complex phase diagram, containing a number of intriguing phases, including two-particle superfluids, supersolids, and density waves. Nevertheless, much of this phase diagram remains unknown because of algorithmic limitations. In this work, we explore the exact phase diagram of Bose-Fermi mixtures at finite temperatures in the hopes of uncovering Bose-Fermi density waves using a novel Auxiliary Field Quantum Monte Carlo (AFQMC) technique. Our AFQMC method expresses the Bose-Fermi partition function as a determinant that can be sampled to obtain accurate results throughout the phase diagram. Based upon this determinant, we calculate several correlation functions to look for signatures of mixture density waves. For certain system sizes and in certain parameter regimes, we compare and contrast with Exact Diagonalization and Mean Field Theory. Here, we begin this study by focusing on one-dimensional systems; future work will be extended to multidimensional systems were AFQMC is expected to be the only method capable of studying them. [Preview Abstract] |
Wednesday, March 20, 2013 10:24AM - 10:36AM |
M41.00013: Finite-size scaling of the chemical potential of bosonic quantum fluids C.M. Herdman, Adrian Del Maestro We study the finite-size scaling of the chemical potential of interacting bosonic quantum fluids using large-scale quantum Monte Carlo calculations. We consider realistic interactions for helium as well as short range repulsive interactions for bosons in one, two and three dimensions at finite temperatures. In one dimension, we compare our results to the scaling predicted by Luttinger liquid theory allowing for the identification of a parametric regime of validity for quantum linear hydrodynamics. In higher dimensions, grand canonical simulations of helium allow for the accurate computation of experimentally relevant quantities such as the chemical potential along the liquid-solid transition line at low temperatures. [Preview Abstract] |
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