Bulletin of the American Physical Society
46th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 60, Number 7
Monday–Friday, June 8–12, 2015; Columbus, Ohio
Session N6: Focus Session: Magnetism & Fermions in Optical Potentials |
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Chair: John Thomas, North Carolina State University Room: Delaware AB |
Thursday, June 11, 2015 10:30AM - 11:00AM |
N6.00001: Ultracold fermions in periodic potentials: a bottom-up approach Invited Speaker: Selim Jochim During the past years we established a technique to prepare finite samples of ultracold fermions in a tightly focused optical trap with very low entropy. We are currently expanding this technique to load periodic potentials with similarly low entropies. As a starting point we have realized a double well containing two fermionic atoms in a spin-singulett configuration. We can tune on-site interaction, tunneling rate and tilt of this basic building block of the Hubbard model. In a separate effort we have realized a strongly interacting two-dimensional Fermi gas in the superfluid regime. We are now aiming to apply our low-entropy few-particle approach to this two-dimensional system to realize finite Fermi systems in tunable periodic potentials. Progress on this effort will be reported. [Preview Abstract] |
Thursday, June 11, 2015 11:00AM - 11:30AM |
N6.00002: Engineering Strongly Correlated Magnetic States with Ultracold Atoms Invited Speaker: Vito Scarola Optical lattices containing ultracold alkali atoms represent nearly ideal manifestations of Hubbard models. Hubbard models are centerpieces of solid-state physics. They can, for example, reveal intriguing magnetic states that are thought to hold the key to understanding high temperature superconductivity. Optical lattice experiments can therefore be used to study quantum states of matter of fundamental importance. Some of the work in my group uses numerical modeling to help guide ultracold atom experiments in these searches. I will review our recent work that compares with ongoing optical lattice experiments trying to realize a quantum antiferromagnet in a cubic optical lattice containing fermions in particular. I will also discuss recent work in our group that examines the impact of speckle disorder on the transport properties of ultracold fermions in a strongly correlated paramagnetic state in a trapped optical lattice. In both cases we find that the temperatures are high enough to make direct quantitative comparison with experiments. [Preview Abstract] |
Thursday, June 11, 2015 11:30AM - 11:42AM |
N6.00003: Competing chiral magnetic orders in the strongly correlated Haldane-Hubbard model Arun Paramekanti, Ciaran Hickey, Pratik Rath Motivated by recent experiments on ultracold atoms which have realized the Haldane model for a Chern insulator with synthetic gauge fields, we consider its strongly interacting limit with spin-1/2 fermions. A slave rotor mean field theory suggests the appearance of gapped or gapless chiral spin liquid Mott insulators. To study competing magnetic orders in the Mott insulator, we consider the strong coupling effective spin Hamiltonian which includes chiral three-spin exchange. We obtain its classical phase diagram, uncovering various chiral magnetic orders including tetrahedral, cone, and noncoplanar spiral states which can compete with putative chiral quantum spin liquids. We study the effect of thermal fluctuations on these states, identifying crossovers in the spin chirality, and phase transitions associated with lattice symmetry breaking. We also discuss analogous effective spin Hamiltonians for correlated spin-1/2 bosons. [Preview Abstract] |
Thursday, June 11, 2015 11:42AM - 11:54AM |
N6.00004: Magnetic-field-tunable Kondo effect in alkaline-earth cold atoms Leonid Isaev, Ana Maria Rey We study quantum magnetism in strongly interacting fermionic alkaline-earth atoms (AEAs). Due to the decoupling of electronic and nuclear degrees of freedom, AEAs in two lowest electronic states (${}^1 S_0$ and ${}^3 P_0$) obey an accurate $SU(N 2 I + 1)$ symmetry in their two-body collisions ($I$ is the nuclear spin). We consider a system that realizes the simplest $SU(2)$ case (for atoms prepared in two nuclear-spin states) in an optical lattice with two bands: one localized and one itinerant. For the fully filled narrow band (two atoms per lattice site) we demonstrate that an applied magnetic field provides an efficient control of the local ground state degeneracy due to mixing of spin and orbital two-body states. We derive an effective low-energy model that includes this magnetic-field effect as well as atomic interactions in the two optical lattice bands, and show that it exhibits a peculiar phenomenon of a magnetic field-induced Kondo effect, so far observed only in Coulomb blockaded quantum dots. We expect that our results can be tested with ultracold ${}^{173}{\rm Yb}$ or ${}^{87}{\rm Sr}$ atoms. [Preview Abstract] |
Thursday, June 11, 2015 11:54AM - 12:06PM |
N6.00005: Ferromagnetism of a Repulsive Atomic Fermi Gas in an Optical Lattice: A Quantum Monte Carlo Study Sebastiano Pilati, Ilia Zintchenko, Matthias Troyer We investigate the ferromagnetic behavior of a two-component repulsive Fermi gas under the influence of a periodic potential that describes the effect of a 3D optical lattice, using continuous-space quantum Monte Carlo simulations. We find that a shallow optical lattice below half-filling strongly favors the ferromagnetic instability compared to the homogeneous Fermi gas. Instead, in the regime of deep optical lattices and weak interactions, where the conventional description in terms of single-band tight-binding models is reliable, our results indicate that the paramagnetic state is stable, in agreement with previous quantum Monte Carlo simulations of the Hubbard model. Our findings shed light on the important role played by multi-band effects and by interaction-induced hopping in the physics of atomic gases trapped in optical lattices. [Preview Abstract] |
Thursday, June 11, 2015 12:06PM - 12:18PM |
N6.00006: Weyl points in three-dimensional optical lattices: synthetic magnetic monopoles in momentum space Hrvoje Buljan, Tena Dubcek, Colin Kennedy, Ling Lu, Wolfgang Ketterle, Marin Soljacic We show that Hamiltonians with Weyl points can be realized for ultracold atoms using laser-assisted tunneling in three-dimensional (3D) optical lattices. Weyl points are synthetic magnetic monopoles that exhibit a robust, 3D linear dispersion (e.g., see [1]). They are associated with many interesting topological states of matter, such as Weyl semimetals and chiral Weyl fermions. However, Weyl points have yet to be experimentally observed in any system. We show that this elusive goal is well-within experimental reach with an extension of the techniques recently used to obtain the Harper Hamiltonian [2]. We propose using laser assisted tunneling to create a 3D optical lattice, with specifically designed hopping between lattice sites that breaks inversion symmetry [3]. The design leads to creation of four Weyl points in the Brillouin zone of the lattice [3], which are verified to be monopoles of the synthetic magnetic field [3]. [1] L. Lu, L. Fu, J. D. Joannopoulos, and M. Solja\v{c}i\'{c}, Nature Photonics 7, 294 (2013). [2] H. Miyake, G.A. Siviloglou, C.J. Kennedy, W. Cody Burton, and W. Ketterle, Phys. Rev. Lett. 111, 185302 (2013). [3] T. Dub\v{c}ek, C.J. Kennedy, L. Lu, W. Ketterle, M. Solja\v{c}i\'{c}, H. Buljan, arXiv:1412.7615 [cond-mat.quant-gas] [Preview Abstract] |
Thursday, June 11, 2015 12:18PM - 12:30PM |
N6.00007: Vortex and Meissner phases of strongly-interacting bosons on a two-leg ladder Marie Piraud, Fabian Heidrich-Meisner, Ian P. McCulloch, Sebastian Greshner, Temo Vekua, Ulrich Schollwoeck We present the phase diagram of the strongly-interacting Bose-Hubbard model defined on a two-leg ladder geometry in the presence of a homogeneous flux. Our work was motivated by a recent experiment [1], which studied the same system, in the complementary regime of weak interactions. Based on extensive density matrix renormalization group simulations and a bosonization analysis, we have fully explored the parameter space spanned by filling, inter-leg tunneling, and flux. As a main result, we demonstrate the existence of gapless and gapped Meissner and vortex phases, with the gapped states emerging in Mott-insulating regimes [2]. We calculate experimentally accessible observables such as chiral currents and vortex patterns and study their dependence on model parameters.\\[4pt] [1] Atala et al., Nature Phys. {\bf 10}, 588 (2014)\\[0pt] [2] Piraud et al., arXiv:1409.7016 [Preview Abstract] |
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