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 J6: Focus Session: Synthetic Gauge Fields in Cold Gases |
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Chair: Peter Engels, Washington State University Room: Delaware AB |
Wednesday, June 10, 2015 2:00PM - 2:30PM |
J6.00001: TBD Invited Speaker: Klaus Sengstock |
Wednesday, June 10, 2015 2:30PM - 3:00PM |
J6.00002: Measuring the Chern number of Hofstadter bands with bosonic atoms Invited Speaker: Monika Aidelsburger The simulation of electrons moving in periodic potentials exposed to large magnetic fields with ultracold atoms in optical lattices has motivated several successful experimental works about the realization of uniform artificial magnetic fields. One main challenge in this context is the implementation of experimental probes revealing the non-trivial topology of energy bands. Here I report about direct measurements of the transverse Hall deflection of ultracold bosonic atoms in artificially generated Hofstadter bands. In combination with the measured occupation of the different Hofstadter bands we were able to obtain an experimental value for the Chern number of the lowest band with good precision $\nu_{\mathrm{exp}}=0.99(5)$. This result constitutes the first Chern-number measurement in a non-electronic system. The artificial magnetic field was generated using a new all-optical technique, which enables flux rectification in a staggered optical superlattice based on laser-assisted tunneling. [Preview Abstract] |
Wednesday, June 10, 2015 3:00PM - 3:12PM |
J6.00003: Experimental realization of the topological Haldane model Michael Messer, Gregor Jotzu, R\'{e}mi Desbuquois, Martin Lebrat, Thomas Uehlinger, Frederik G\"{o}rg, Daniel Greif, Tilman Esslinger The Haldane model is a fundamental example of a Hamiltonian exhibiting topologically distinct phases of matter and featuring a quantum Hall effect without a net magnetic field. We report on the experimental realization of the Haldane model and the characterization of its topological band-structure, using non-interacting ultracold fermionic atoms in a periodically modulated honeycomb lattice. Here the inertial force generated by circular modulation of the lattice position breaks time-reversal symmetry and leads to complex next-nearest-neighbor tunneling. We explore the resulting Berry-curvatures of the lowest band and map out topological phase transitions connecting distinct regimes. Furthermore we extend our method to create spin dependent effective Hamiltonians by periodic modulation of a magnetic field gradient. For each spin state, the differing band structure can be characterized either by measuring the expansion of an atomic cloud in the lattice, or by a measurement of the effective mass through dipole oscillations. Our method can be used to create systems where one state is pinned to the lattice, while the other remains itinerant. [Preview Abstract] |
Wednesday, June 10, 2015 3:12PM - 3:24PM |
J6.00004: Ground State Properties of the 1/2 Flux Harper Hamiltonian Colin Kennedy, William Cody Burton, Woo Chang Chung, Wolfgang Ketterle The Harper Hamiltonian describes the motion of charged particles in an applied magnetic field - the spectrum of which exhibits the famed Hofstadter's butterfly. Recent advances in driven optical lattices have made great strides in simulating nontrivial Hamiltonians, such as the Harper model, in the time-averaged sense. We report on the realization of the ground state of bosons in the Harper Hamiltonian for 1/2 flux per plaquette utilizing a tilted two-dimensional lattice with laser assisted tunneling. We detail progress in studying various ground state properties of the 1/2 flux Harper Hamiltonian including ground state degeneracies, gauge-dependent observables, effects of micromotion, adiabatic loading schemes, and emergence and decay of coherence. Additionally, we describe prospects for flux rectification using a period-tripled superlattice and generalizations to three dimensions. [Preview Abstract] |
Wednesday, June 10, 2015 3:24PM - 3:36PM |
J6.00005: Nematic Liquid Crystals of Bosons in Kagome Lattices with Synthetic Gauge Fields Guanyu Zhu, Jens Koch, Ivar Martin We consider a family of interacting boson models based on a kagome lattice with local synthetic gauge flux, which can be realized in an optical lattice with ultra-cold atoms. Such models have a lowest flat band in the single particle spectrum. The flat band is spanned by eigenstates forming localized loops on the lattice, with the maximally compact loop states typically breaking the discrete rotational symmetry of the lattice. When populated by locally-interacting particles, the close packing of such maximally compact loop states leads to a nematic loop crystal ground state. We predict that increasing the filling beyond the close packing fraction leads to the formation of quantum liquid crystals including a nematic supersolid and a nematic superfluid phase with broken lattice rotation and $U(1)$ symmetry. We also show how the nematicity can be probed by time-of-flight experiments with ultra-cold atoms. [Preview Abstract] |
Wednesday, June 10, 2015 3:36PM - 3:48PM |
J6.00006: Synthetic spin and orbital angular momentum coupling in quantum gases Kuei Sun, Chunlei Qu, Chuanwei Zhang The recent experimental realization of synthetic spin and linear momentum (SLM) coupling for ultracold atoms (both bosons and fermions) provides a completely new platform for exploring new quantum physics in spin-orbit coupled superfluids. Nowadays, spin-orbit coupled Bose-Einstein condensates (BEC) and degenerate Fermi gases have emerged as one of the most important frontiers of ultracold atomic physics. We pioneer the route and propose a scheme to realize another important and fundamental coupling between spin and orbital angular momentum (SOAM) in ultracold atoms using higher-order Laguerre-Gaussian laser beams. We study the ground state properties of SOAM coupled BEC in various natural geometries in experiments. We find rich phase diagrams reflecting the interplay between SOAM coupling, interaction, and external trapping. Our system, unlike the SLM coupled ones in current experiments, is naturally suited for exploring strong many-body effects with spin-orbit coupling. [Preview Abstract] |
Wednesday, June 10, 2015 3:48PM - 4:00PM |
J6.00007: Proposal for generating synthetic magnetic fields in hexagonal optical lattices Binbin Tian, Manuel Endres, David Pekker We propose a new approach to generating synthetic magnetic fields in ultra cold atom systems that does not rely on either Raman transitions nor periodic drive. Instead, we consider a hexagonal optical lattice produced by the intersection of three laser beams at 120 degree angles, where the intensity of one or more of the beams is spatially non-uniform. The resulting optical lattice remains hexagonal, but has spatially varying hopping matrix elements. For atoms near the Dirac points, these spatial variations appear as a gauge field, similar to the fictitious gauge field that is induced for for electrons in strained graphene. We suggest that a robust way to generate a gauge field that corresponds to a uniform flux is to aligning three gaussian beams to intersect in an equilateral triangle. Using realistic experimental parameters, we show how the proposed setup can be used to observe cyclotron motion of an atom cloud -- the conventional Hall effect and distinct Landau levels -- the integer quantum Hall effect. [Preview Abstract] |
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