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 P8: Emergent Phases in Quantum Gases |
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Chair: Wes Campbell, University of California, Los Angeles Room: Franklin CD |
Thursday, June 11, 2015 2:00PM - 2:12PM |
P8.00001: Observation of half-quantum vortices in an antiferromagnetic spinor Bose-Einstein condensate Sang Won Seo, Seji Kang, Woo Jin Kwon, Yong-il Shin We report the observation of half-quantum vortices (HQVs) in an antiferromagnetic spinor Bose-Einstein condensate. We realize the easy-plane polar or antiferromagnetic (AF) phase of the spin-1 sodium condensate by tuning the sign of the quadratic Zeeman energy with microwave dressing field. The manifold of the order parameter of this phase is given as $[U(1)\times S^1]/{Z}_2$ and HQVs are allowed as topological defects in this system. Using in-situ magnetization-sensitive imaging, we observe that a singly charged vortex splits into a pair of HQVs with ferromagnetic vortex cores of opposite magnetization. The magnetized core of the HQV is measured to be about three times of the spin healing length, which is in good agreement with mean-field predictions. [Preview Abstract] |
Thursday, June 11, 2015 2:12PM - 2:24PM |
P8.00002: Emergent phases in the spin orbit coupled spin-1 Bose Hubbard model Stefan Natu, Jedediah Pixley Motivated by recent experiments on spin orbit coupled, ultra-cold Bose gases [1], we theoretically study the spin-1 Bose Hubbard model in the presence and absence of spin orbit coupling (SOC).~ In the absence of SOC, using a spatially homogenous Gutzwiller mean field theory, we determine the phase diagram and excitation spectrum of the spin-1 Bose Hubbard model on a hyper-cubic lattice in both the polar and ferromagnetic phases. We focus on the evolution of various density, spin, and nematic order parameters across the phase diagram as a function of chemical potential and nearest neighbor hopping. We then generalize the Gutzwiller mean-field theory to incorporate spin-orbit coupling by allowing the mean-fields to be spatially inhomogeneous, which enable us to study spontaneous translational symmetry broken phases. To connect with ongoing experiments, we focus on the lattice generalization of the experimentally realized 1D spin-orbit coupling. \\[4pt] [1] Y.-J. Lin, K Jimenez-Garcia, and I. B. Spielman, Nature 471, 83 (2011). [Preview Abstract] |
Thursday, June 11, 2015 2:24PM - 2:36PM |
P8.00003: Fractional Quantum Hall Effects for Bosonic Atoms in a Chain of Rotating Traps Jianshi Zhao, Louis Jacome, Nathan Gemelke Fractional quantum Hall (FQH) physics familiar from two-dimensional electron systems has also been predicted to appear in a gas of interacting bosons that are confined to a rapidly rotating trap. Due to the emergent gauge physics, such states exhibit novel properties, including excitations with fractionalized mass and statistics. In this talk, we consider an experimental strategy of creating many FQH samples along a chain of lattice sites, coupled together via tunneling. We calculate a mean-field phase diagram and derive an effective field theory to describe this system and find that it supports novel insulator and superfluid states with localized FQH behavior. The coarse structure of the phase diagram and transport properties near phase transitions reveal novel properties of excitations in the parent FQH states, and exhibit new observable relations between thermodynamic quantities such as compressibility and moment of inertia attributable to topological constraints. We describe experimental pathways to create such states and extract new smoking gun signatures of FQH physics. [Preview Abstract] |
Thursday, June 11, 2015 2:36PM - 2:48PM |
P8.00004: Few-body treatment of the quantum Hall system Rachel Wooten, Kevin Daily, Chris H. Greene When confined to a finite, two-dimensional area and exposed to a strong magnetic field, fermions exhibit complicated, highly-correlated quantum behavior known as the quantum Hall effect [1]. At certain electron densities and magnetic fields, the system exhibits strong quantization due entirely to Coulomb interactions. Typical theoretical studies in the field consist of many-body numerical configuration interaction calculations performed in an energy-restricted single-particle Hilbert subspace. So far, quantum Hall behavior has been observed experimentally only in condensed matter systems, but there is significant interest in reproducing and studying the effect in highly-controlled cold atom systems. In light of such potential experimental developments, we approach the theoretical study of the quantum Hall system from a few-body perspective using the hyperspherical adiabatic technique [2] developed originally for atomic systems.\\[4pt] [1] D. C.~Tsui, H. L.~Stormer, and A. C.~Gossard, Phys.\ Rev.\ Lett. \textbf{48}, 1559 (1982).\\[0pt] [2] J.~Macek, J.\ Phys.\ B:.\ At.\ Mol.\ Phys., {\bf 1} 831 (1968). [Preview Abstract] |
Thursday, June 11, 2015 2:48PM - 3:00PM |
P8.00005: Geometric effects on quantum transport of ultracold atoms in optical lattices: Quantum acceleration and flat band Chih-Chun Chien, Mekena Metcalf, Massimiliano Di Ventra, Gia-Wei Chern The realizations of interesting optical lattices for ultracold atoms provide opportunities for investigating geometric effects on many-body physics. Thesquare, triangular, honeycomb, kagome lattices, and other geometries have been experimentally demonstrated. When the atoms are driven out of equilibrium by manipulations of the density or trapping potential, their quantum transport can be monitored and fundamental questions regarding transport in isolated systems can be addressed unambiguously. We found that the propagation velocity of the matter wave representing the flowing atoms can be accelerated by tuning the lattice geometry. This acceleration is a pure quantum effect because no shorter path is created as the geometry changes. For lattice geometries supporting a dispersionless flat band, the localized atoms in the flat band do not participate in transport but interfere with the mobile atoms. We found a generic insulating phase exhibiting a density jump in the profile that can be dynamically generated. Interesting spatial patterns may emerge if those flat-band lattices are manipulated, and an analogue of geometric frustration in quantum transport will be presented. [Preview Abstract] |
Thursday, June 11, 2015 3:00PM - 3:12PM |
P8.00006: strongly interacting fermions and bosons with arbitrary spin in 1D Li Yang, Liming Guan, Han Pu Under second order degenerate perturbation theory, we show that the physics of N particles, which can be either fermions or bosons, with arbitrary spin confined in one dimensional trap in the strongly interacting regime can be mapped into an effective spin model with super-exchange interaction. An effective spin-chain Hamiltonian can be obtained from this procedure. For spin-1/2 particles, this model reduces to the non-translational-symmetric Heisenberg model, where a transition between Heisenberg anti- ferromagnetic (AFM) and ferromagnetic (FM) states is expected to occur when the interaction strength is tuned from the strongly repulsive to the strongly attractive limit. We study the properties of these magnetic states. We confirm the validity of the spin-chain model by comparison with results obtained from several unbiased techniques. The spin chain model can be easily extended to arbitrary spin dependent interaction, provided the interaction between each components are strong [Preview Abstract] |
Thursday, June 11, 2015 3:12PM - 3:24PM |
P8.00007: Chiral ferromagnetism in a trapped Fermi gas with a large spin-orbit coupling Shang-Shun Zhang, Han Pu, Wu-Ming Liu A large spin-orbit (SO) coupling gives rise to a list of Landau level-like flat bands in a harmonic trap. In this work, we show that a chiral ferromagnetism in a trapped Fermi gas would appear on this flat bands for a weakly repulsive interaction. The competition between the ferromagnetic state with the strongly correlated state is studied. Due to the SO coupling, the spin ordering drives a corresponding orbital ordering, i.e., a chiral density current in the ferromagnetic phase. The experimental study of the these results obtained in this paper is discussed. [Preview Abstract] |
Thursday, June 11, 2015 3:24PM - 3:36PM |
P8.00008: Nonequilibrium quantum dynamics of partial symmetry breaking for ultracold bosons in an optical lattice ring trap Lincoln D. Carr, Miguel Angel Garcia-March, Javier Vijande, Albert Ferrando We explore the nonequilibrium quantum dynamics of partial symmetry-breaking in ring Bose-Einstein condensates described by the Bose-Hubbard Hamiltonian with an external potential. Using exact diagonalization and group theory for small systems, we establish three new concepts to predict and characterize the dynamics after a quantum quench: symmetry memory, critical symmetry-breaking strength, and the symmetry gap. Critical symmetry breaking can manifest in current reversals, but is most clearly observed in the symmetry memory operator, based on unitary rotations. [Preview Abstract] |
Thursday, June 11, 2015 3:36PM - 3:48PM |
P8.00009: Zeeman engineering in spinor Bose-Einstein condensates: topological interfaces and confined textures Magnus O. Borgh, Justin Lovegrove, Muneto Nitta, Janne Ruostekoski Engineering of the Zeeman level shifts in spinor Bose-Einstein condensates (BECs) provides a powerful tool in simulating a rich phenomenology of physical phenomena that have been encountered in cosmological or condensed-matter systems. We propose~[1] using spatial control over the Zeeman shifts as an experimentally accessible way to study defects and textures at interfaces between topologically distinct regions~[1,2]. In a spin-1 BEC, we construct spinor wave functions representing defects and textures that connect continuously between polar and ferromagnetic regions induced by nonuniform Zeeman shifts. By numerical energy minimization we characterize the core structures of energetically stable interface-crossing defects. We also show that the spatial control over the Zeeman shifts can be used to engineer states where the core of a defect confines a topologically nontrivial texture or defect of lower dimensionality. We demonstrate engineering of an energetically stable one-dimensional Skyrmion texture inside the ferromagnetic core of a vortex in the polar spin-1 BEC.\\[4pt] [1] M.~O.~Borgh, J.~Lovegrove and J.~Ruostekoski, New~J.~Phys.\ \textbf{16,} 053046 (2014).\\[0pt] [2] M.~O.~Borgh, and J.~Ruostekoski, Phys.~Rev.~Lett.\ \textbf{109,} 015302 (2012) [Preview Abstract] |
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