Bulletin of the American Physical Society
41st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 55, Number 5
Tuesday–Saturday, May 25–29, 2010; Houston, Texas
Session Q3: Quantum Gauge Theories and Ultra-cold Atoms |
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Chair: Erich Mueller, Cornell University Room: Imperial West |
Friday, May 28, 2010 8:00AM - 8:30AM |
Q3.00001: Few-body Atomic Systems in the Fractional Quantum Hall Regime Invited Speaker: The fractional quantum hall (FQH) effect in two-dimensional electron gases represents a unique phenomenon in nature, combining aspects of strongly correlated electron gases with the statistical and topological effects unique to dimensionally reduced systems. I will discuss our attempts to generate motionally entangled states in small clusters of Bosonic atoms closely analogous to those occurring in the electronic FQH effect. By constructing an optical lattice of spinning and precisely controlled on-site potentials, small clusters of interacting atoms can be adiabatically transferred from uncorrelated states at zero angular momentum through a tabulated sequence of ground state level crossings with increasing atomic correlation and total angular momentum. Results will be shown probing these states with both time-of-flight techniques and by directly interrogating atomic correlation via photo-association to excited molecules. Comparison is made to numeric models with no free parameters. Finally, implications of these results will be presented for future experiments in the FQH regime, both probing unique features of these states, and generalizing the methods to produce macroscopic systems in the FQH limit. [Preview Abstract] |
Friday, May 28, 2010 8:30AM - 9:00AM |
Q3.00002: Simulating dense QCD matter with ultracold atomic boson-fermion mixtures Invited Speaker: We delineate, as an analog of two-flavor dense quark matter, the phase structure of a many-body mixture of ultracold atomic bosons and fermions in two internal states with a tunable boson- fermion attraction. The bosons (b) correspond to diquarks, and the fermions (f) to unpaired quarks. For weak b-f attraction, the system is a mixture of a Bose-Einstein condensate and degenerate fermions, while for strong attraction composite b-f fermions (N), analogs of the nucleon, are formed, which are superfluid due to the N-N attraction in the spin-singlet channel. We determine the symmetry breaking patterns at finite temperature as a function of the b-f coupling strength, and relate the phase diagram to that of dense QCD. [Preview Abstract] |
Friday, May 28, 2010 9:00AM - 9:30AM |
Q3.00003: Optically synthesized magnetic fields for ultracold neutral atoms Invited Speaker: Ultracold atoms hold great promise in simulating essential models in condensed matter physics. One apparent limitation is the charge neutrality of the atoms, which prevents access to a rich source of physics, for example, electrons in magnetic fields. We have circumvented this limitation by generating an effective vector potential with an optical coupling between internal states of the atoms. We have experimentally realized a synthetic magnetic field for ultracold neutral atoms, through the spatial variation of the effective vector potential. In our system, we use a two-photon Raman coupling to dress a rubidium 87 Bose-Einstein condensate (BEC), where the momentum difference between two Raman beams results in the modified energy-momentum dispersion of the dressed state, leading to an effective vector potential. We have created a synthetic magnetic field evidenced by the appearance of vortices in the BEC; this field is stable in the laboratory frame and allows for adding optical lattices with ease. Our optical approach is not subject to technical limitations of rotating systems, including the metastable nature of the rotating state, the limited maximum rotating velocity and the difficulty of applying stable rotating optical lattices. In our approach, with a suitable lattice configuration, it should be able to create sufficiently large synthetic magnetic fields in the quantum-Hall regime. Work done in collaboration with, Robert Compton, Karina Jimenez-Garcia, James Porto, and Ian Spielman, Joint Quantum Institute, National Institute of Standards and Technology, and University of Maryland. [Preview Abstract] |
Friday, May 28, 2010 9:30AM - 10:00AM |
Q3.00004: Many-body physics in optical lattices under a synthetic magnetic field Invited Speaker: Recent progress in creating artificial gauge fields for cold atom systems holds promise for experimental realization of many interesting models. In the presence of a periodic potential, the external gauge fields may be used to realize many lattice-gauge theories for the first time. We consider the simplest of such models, where an artificial magnetic field is coupled to the cold atoms and investigate various scenarios. Such an artificial magnetic field may simply be created by rotating the optical lattice, or by more elaborate means like light induced potentials. The physics of particles moving in a periodic potential in the presence of a magnetic field is rich, as it contains three parameters which control commensurate/incommensurate transitions. The first such parameter, flux quanta per plaquette of the lattice, controls the single particle physics. The energy spectrum as a function of this parameter is a fractal shape known as the Hofstadter butterfly. A second parameter is the number of particles per lattice site, which controls if certain insulating states like the Mott state are possible. The ratio of these two parameters give the filling factor, defined as the number of particles per flux quanta, which controls the quantum Hall physics. We first discuss the single particle physics where we investigate the relation between the Wannier functions and local ground states for each site. We show that the presence of the magnetic field requires a new definition of the Wannier functions, and these functions have large overlaps with local ground states. The Peirels substitution describes the hopping between sites faithfully for the lowest band. We also investigate how Peirels substitution has to be applied to higher bands such as the p-band, and discuss the resulting spectra. We then consider interacting Bosons in a rotating optical lattice and investigate the effect of the external magnetic field on the Mott Insulator- Superfluid transition. The phase boundary for this transition can be calculated exactly within mean-field theory and is shown to be controlled by the minimum eigenvalue of the Hofstadter butterfly. We argue that if one goes beyond mean field theory the Mott Insulator-Superfluid boundary is complex, and there are fractional quantum Hall phases of Bosons near every Mott lobe. As a third model we investigate the density profile for non-interacting fermions in a rotating optical lattice and find that the gaps of the Hofstadter butterfly are reflected as sharp plateaus in the density profile. Each one of these regions are topological insulators with quantized Hall conductivity. We argue that the Hall conductivity can be measured without any transport measurements, as the Streda formula relates Hall conductivity to the response of density to magnetic field change. Finally we investigate the physics of fermions with on-site attraction in a rotating optical lattice. We calculate the critical attraction strength for the transition from a topological insulator to a BCS superfluid. We also calculate the vortex lattice structures after BCS pairing takes place and investigate the transitions between different configurations of vortices. [Preview Abstract] |
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