Bulletin of the American Physical Society
43rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 57, Number 5
Monday–Friday, June 4–8, 2012; Orange County, California
Session U2: Focus Session: Universal Thermodynamics and Criticality |
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Chair: Nathan Gemelke, Pennsylvania State University Room: Grand Ballroom GF |
Friday, June 8, 2012 10:30AM - 11:00AM |
U2.00001: Quantum Monte Carlo simulations and thermometry in ultracold quantum gases Invited Speaker: Matthias Troyer Modern quantum Monte Carlo algorithms allow accurate simulations of both bosons and fermions in optical lattice at the temperatures relevant for cold atomic gases in optical lattices. These simulations allow quantitative validation of optical lattice experiments, and to use comparison to simulations for thermometry. I will review the state of the at of QMC algorithms for bosons and fermions, and present an overview of results obtained that are relevant for optical lattice experiments, including full thermodynamic data and the equation of state for the fermionic and bosonic Hubbard model. I will then focus on a proposal for universal thermometry in bosonic quantum gases [Qi Zhou and Tin-Lun Ho, PRL 106, 225301 (2011)], based on a generalized fluctuation-dissipation theorem. By applying a their scheme to our QMC results I will show that a variant of their proposal does indeed provide a reliable method for thermometry in quantum gases. [Preview Abstract] |
Friday, June 8, 2012 11:00AM - 11:12AM |
U2.00002: Quantum Criticality and Dynamics in Two-dimensional Bose Gases Xibo Zhang, Li-Chung Ha, Chen-Lung Hung, Shih-Kuang Tung, Cheng Chin Quantum criticality emerges when a many-body system is in the proximity of a continuous phase transition driven by quantum fluctuations. In the quantum critical regime, exotic, yet universal properties are anticipated; ultracold atoms provide a clean system to test these predictions. We report the observation of quantum criticality with two-dimensional (2D) Bose gases in optical lattices [1]. Based on in situ density measurements, we observe scaling behavior of the equation of state at low temperatures, locate the quantum critical point, and constrain the critical exponents ($z=2.2^{+1.0}_{-0.5}$ and $\nu=0.52^{+0.09}_{-0.10}$; the predicted values are $z=2$ and $\nu=0.5$). We observe a finite critical entropy per particle ($\sim 2k_{\mathrm{B}}$) carrying a weak dependence on the atomic interaction strength. We also study the dynamics of 2D gases by measuring the evolution of the static structure factor after quenching the atomic interaction near a Feshbach resonance. The high-resolution imaging system allows us to resolve the correlation of the density fluctuations with a spatial frequency up to 3.5 $\mu$m$^{-1}$. Our experiment provides an excellent testground to explore quantum criticality and critical dynamics with ultracold atoms.\\[4pt][1] X. Zhang et al., arXiv:1109.0344. [Preview Abstract] |
Friday, June 8, 2012 11:12AM - 11:42AM |
U2.00003: Equation of state of strongly interacting fermions Invited Speaker: Frederic Chevy Based on very general principles, Thermodynamics provides powerful tools to characterize the macroscopic properties of any physical system. Even though its origin can be traced back the XIXth century's industrial revolution, I will show how this theory provided the framework and the key ingredients leading to a precise quantitative understanding of the properties of the strongly correlated Fermi gases that were recently obtained thanks to the progress in the manipulation of ultracold atoms. [Preview Abstract] |
Friday, June 8, 2012 11:42AM - 11:54AM |
U2.00004: On a scale-invariant Fermi gas in a time-dependent harmonic potential Sergej Moroz We investigate a scale-invariant two-component Fermi gas in a time-dependent isotropic harmonic potential. The exact time evolution of density distribution in position space in any spatial dimension is obtained. Two experimentally relevant examples-- an abrupt change and a periodic modulation of a trapping frequency are solved. Consequences for experiments with ultracold quantum gases such as the excitation of a tower of undamped breathing modes and the stabilization of an antitrapped system by an AC magnetic field are discussed. Small deviations from the scale invariance and isotropy of the confinement are also considered. [Preview Abstract] |
Friday, June 8, 2012 11:54AM - 12:06PM |
U2.00005: Universal relations for Fermi gases in arbitrary dimension Manuel Valiente, Nikolaj T. Zinner, Klaus Molmer We present universal relations for Fermi gases with pairwise renormalizable contact interactions in arbitrary dimensions. The derivation of these relations is given by using the explicit form of a class of generalized functions -- Tan's selectors -- in the momentum representation. These selectors implement the short-distance boundary conditions in a straightforward manner and leads to simple derivation of the universal relations. [Preview Abstract] |
Friday, June 8, 2012 12:06PM - 12:18PM |
U2.00006: Thermodynamic properties of the SU($2N$) ultra-cold fermions in optical lattices Hsiang-hsuan Hung, Zi Cai, Lei Wang, Dong Zheng, Congjun Wu We investigate the thermodynamic properties of a half-filled SU($2N$) Fermi-Hubbard model in the two-dimensional square lattice using the determinantal quantum Monte Carlo simulation, which is free of the fermion ``sign problem''. The large number of hyperfine-spin components enhances spin fluctuations, which facilitates the Pomeranchuk cooling to temperatures comparable to the superexchange energy scale at the case of SU$(6)$. Various quantities including entropy, charge fluctuation, and spin correlations have been calculated. [Preview Abstract] |
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