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 G2: Synthetic Gauge Fields for Ultracold Systems |
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Chair: Ian Spielman, JQI, NIST, and University of Maryland Room: Grand Ballroom GF |
Wednesday, June 6, 2012 8:00AM - 8:12AM |
G2.00001: Superfluid Hall effect in a Bose-Einstein condensate Lindsay J. LeBlanc, Karina Jimenez-Garcia, Ross A. Williams, Matthew C. Beeler, Abigail R. Perry, William D. Phillips, Ian B. Spielman In condensed matter physics, measurement techniques exploiting the Hall effect are widely used to explore the internal properties of solids, ranging from charge-carrier concentrations in semiconductors to the quantum Hall effects in two-dimensional electron gases. While Hall physics is generally associated with the reaction of charged particles to a magnetic field, we observed a superfluid Hall effect in a BEC of neutral $^{87}$Rb atoms subjected to an artificial magnetic field $B^*$. To probe the BEC's properties, we generated an alternating atomic current and measured the cloud's dynamics as a function of $B^*$. When the artificial field is present, an effective Lorentz force acts on the atoms and the current is deflected in the direction transverse to the usual hydrodynamic flow, indicating a Hall effect. The good quantitative agreement between our measurements and a superfluid hydrodynamic model indicates that this Hall effect is associated with the BEC's irrotational superfluidity. By extending the Hall measurement technique to the realm of neutral-atom experiments, we establish this tool as a valuable probe for exploring the internal or many-body properties of ultracold gas systems. [Preview Abstract] |
Wednesday, June 6, 2012 8:12AM - 8:24AM |
G2.00002: Exotic 3D Spin-Orbit Couplings Brandon Anderson, Gediminas Juzeliunas, Victor Galitski, Ian Spielman We describe a scheme for creating an isotropic three-dimensional spin-orbit coupling, dubbed Weyl spin-orbit coupling, in systems of ultracold atoms. This coupling is induced by Raman transitions that link four internal atomic states with a tetrahedral geometry. This spin-orbit coupling gives rise to a Dirac point that is robust against environmental perturbations. We then propose a general procedure for generating exotic three-dimensional spin-orbit couplings with degenerate ground states on more complex manifolds. The procedure is applied to produce a spin-orbit coupling with a toroidal ground state manifold. Finally, we discuss the many-body implications of the exotic spin-orbit couplings. [Preview Abstract] |
Wednesday, June 6, 2012 8:24AM - 8:36AM |
G2.00003: Topological excitations of a spinor BEC by inhomogenous magnetic fields Ryan Olf, G. Edward Marti, Gabriel Dunn, Dan Stamper-Kurn Inhomogenous magnetic fields, such as those produced by the common spherical quadrupole configuration, couple spin and motional degrees of freedom in neutral spinor Bose-Einstein condensates, in direct analogy to the coupling of a magnetic field to an electric charge. Such gauge fields for neutral atoms have been of interest due to their ability to create interesting topological states, such as vortices, quantum hall and spin quantum hall states, and skyrmions. In this talk we report on the use of time-varying inhomogenous magnetic fields to create topological excitations in F=1 $^{87}$Rb confined to an optical trap. [Preview Abstract] |
Wednesday, June 6, 2012 8:36AM - 8:48AM |
G2.00004: 2D and 3D topological states of cold atoms with synthetic gauge fields Congjun Wu, Yi Li, Xiangfa Zhou We found that the synthetic gauge fields from the light-atom interaction combined with harmonic trapping potential give rise to exotic topological band structure in both 2D and 3D. Landau-level like quantizations appear with the full 2D and 3D rotational symmetry and time-reversal symmetry. Inside each band, states are labeled by their angular momenta over which energy dispersions are strongly suppressed by spin-orbit coupling to nearly flat. The radial quantization generates the energy gap between neighboring bands at the order of the harmonic frequency. Helical edge or surface states appear on open boundaries characterized by the Z2 index. These Hamiltonians can be viewed from the dimensional reduction of the high dimensional quantum Hall states in 3D and 4D flat spaces. [Preview Abstract] |
Wednesday, June 6, 2012 8:48AM - 9:00AM |
G2.00005: Effect of synthetic magnetic fields on quasi-2D gases of bosons Matthew Beeler, Karina Jimenez-Garcia, Lindsay LeBlanc, Abigail Perry, Ross Williams, Ian Spielman An ultra-cold gas of atoms can realize many different model Hamiltonians. When tightly confined in one spatial dimension, the gas can become effectively 2D. At a critical temperature, a quasi-2D Bose gas undergoes a Berezinskii-Kosterlitz-Thouless (BKT) phase transition to a superfluid as thermally excited pairs of vortices with opposite circulation bind together [1]. In general, a superfluid responds to the presence of a synthetic magnetic field with the formation of vortices [2], expected to all have the same circulation direction. These vortices induced by the synthetic magnetic field should have an effect on the microscopic mechanism behind the BKT phase transition, which may alter the properties of the quasi-2D Bose gas.\\[4pt] [1] Hadzibabic, Z. \textit{et al.}, Nature \textbf{441}, 1118--1121 (2006)\\[0pt] [2] Lin, Y.-J. \textit{et al.}, Nature \textbf{462}, 628-632 (2009). [Preview Abstract] |
Wednesday, June 6, 2012 9:00AM - 9:12AM |
G2.00006: Contact of dilute atomic Fermi gases with spin-orbit couplings Zhenhua Yu We study the contact of three dimensional spin half dilute atomic Fermi gases with spin-orbit couplings. The interatomic interaction is modeled by the contact pseudopotential. In the high temperature limit, we derive the expression for the second virial expansion of the thermodynamic potential via the ladder diagrams. When the spin-orbit couplings are small, we show that the contact between the fermions increases as the fourth power of the couplings. At zero temperature, we consider the cases where there are symmetric spin-orbit couplings in two or three dimensions. In the dilute limit, the system consists of condensed bosonic molecules; we find that the contact also becomes bigger compared to that in the absence of spin-orbit couplings. Our results indicate that generically spin-orbit couplings enhance the contact of the Fermi gases. Such enhancement can be measured via photoassociation. [Preview Abstract] |
Wednesday, June 6, 2012 9:12AM - 9:24AM |
G2.00007: Spin-orbit coupled Fermi liquid theory with magnetic dipolar interaction Yi Li, Congjun Wu We investigate the Fermi liquid properties of the ultra-cold magnetic dipolar Fermi gases in the simplest case of two-component. The magnetic dipolar interaction is invariant under the simultaneous spin-orbit rotation, but not under either spin or orbit rotation separately, thus the corresponding Fermi liquid theory is intrinsically spin-orbit coupled. The Landau interaction matrix is diagonalized in terms of the partial-wave channels of the total angular momentum $J$. The leading thermodynamic instabilities lie in the channels of ferromagnetism hybridized with the ferro-nematic order with $J=1^+$ and the spin-current mode with $J=1^-$, where $\pm$ represents even and odd parities, respectively. An exotic propagating collective mode is identified as spin-orbit coupled Fermi surface oscillations in which the spin distribution on the Fermi surface is topologically non-trivial. [Preview Abstract] |
Wednesday, June 6, 2012 9:24AM - 9:36AM |
G2.00008: Raman coupling in a Fermi gas of $^6$Li atoms Lawrence Cheuk, Ariel Sommer, Mark Ku, Waseem Bakr, Tarik Yefsah, Martin Zwierlein Entangling the spin and momentum of atoms in a Fermi gas gives rise to a variety of new tools and new physical phenomena. Its realization in cold atomic systems via Raman lasers allows spin-orbit coupling and the creation of synthetic gauge fields. Spin-orbit coupling allows realizing models of topological insulators, while synthetic gauge fields offer the prospect of realizing quantum hall states. Raman coupling can also be used to probe the excitation spectrum of a Fermi gas. Raman spectroscopy provides complementary information to the widely used radio-frequency spectroscopy. It can be used to locally map the Fermi surface in a normal Fermi gas, and to directly measure the pairing gap in a strongly interacting Fermi gas. In this talk, we present progress towards Raman dressing and Raman spectroscopy in an ultracold Fermi gas of $^6$Li atoms. [Preview Abstract] |
Wednesday, June 6, 2012 9:36AM - 9:48AM |
G2.00009: Rashba spin-orbit coupled atomic Fermi gases Lei Jiang, Xia-Ji Liu, Hui Hu, Han Pu We investigate theoretically BEC-BCS crossover physics in the presence of a Rashba spin-orbit coupling in a system of two-component Fermi gas with and without a Zeeman field that breaks the population balance between the two components. A new bound state (Rashba pair) emerges because of the spin-orbit interaction. We study the properties of Rashba pairs using a standard pair fluctuation theory. At zero temperature, the Rashba pairs condense into a macroscopic mixed spin state. We discuss in detail the experimental signatures for observing the condensation of Rashba pairs by calculating various physical observables which characterize the properties of the system and can be measured in experiment. [Preview Abstract] |
Wednesday, June 6, 2012 9:48AM - 10:00AM |
G2.00010: Hamiltonian monodromy Chen Chen, Megan Ivory, Aubin Seth, John Delos We say that a system exhibits monodromy if we take the system around a closed loop in its spectrum space, and we find that the system does not come back to its original state. We report a method for experimental realization of a newly discovered dynamical manifestation of monodromy by investigating the behavior of atoms in a trap. The trapping potential has long range attraction to and short range repulsion from the center. Calculations include two parts. First, we consider atoms as classical particles for which we can choose any desired set of initial conditions. As was shown previously for different systems, when we take the system around a monodromy circuit, a loop of initial conditions evolves into a topologically different loop. Second, we incorporate the limitations that would appear in experimental implementation. The atoms have a range of initial angles, initial angular momenta, and initial energies. Our work shows how real atoms can be driven by real forces around a monodromy circuit, and thereby shows how one can observe dynamical monodromy in a laboratory. Finally, we extend classical dynamical monodromy to quantum dynamical monodromy by examining wave function evolution under comparable conditions. [Preview Abstract] |
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