Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session W10: Invited Session: Many Body Physics in Quantum Gases |
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Sponsoring Units: DCMP DAMOP Chair: Paul Goldbart, Georgia Institute of Technology Room: 309 |
Thursday, March 21, 2013 2:30PM - 3:06PM |
W10.00001: Magnetic correlations and density ordering in quantum gases Invited Speaker: Tilman Esslinger Quantum gases provide a unique avenue to study fundamental concepts in quantum many-body physics. In our research we go beyond the class of atomic many-body systems that are governed by the interplay between kinetic energy and contact interactions. Using a tunable geometry optical lattice, we create hexagonal, dimerized or anisotropic lattice structures [1]. This allows us to control the exchange energy in a repulsive two-component Fermi gas and study the formation of magnetic correlations. In a different approach, we place a Bose-Einstein condensate into a dynamic lattice potential created by the interaction of the atoms with the vacuum field of an optical cavity. This gives rise to long-range interactions, which result in a transition to a supersolid phase with a broken discrete symmetry, preceded by a mode softening [2]. In the talk I will introduce our experiments and discuss recent results.\\[4pt] [1]: L. Tarruell, D. Greif, T. Uehlinger, G. Jotzu, and T. Esslinger, Nature 483, 302--305 (2012).\\[0pt] [2]: R. Mottl, F. Brennecke, K. Baumann, R. Landig, T. Donner, and T. Esslinger, Science 336, 1570-1573 (2012). [Preview Abstract] |
Thursday, March 21, 2013 3:06PM - 3:42PM |
W10.00002: Dissipative quantum glasses in optical cavities Invited Speaker: Philipp Strack Strong light-matter interactions offer the prospects of quantum realizations of soft matter phases. We discuss how glassy phases of matter may appear with atomic ensembles in multi-mode optical cavities. Our computations show that some of these quantum optical glasses have no direct analogue in condensed matter realizations due to the photon-mediated long-range interactions and the nature of the driving and dissipation that occurs in the many-body cavity QED systems. [Preview Abstract] |
Thursday, March 21, 2013 3:42PM - 4:18PM |
W10.00003: Non-Equilibrium Dynamics of Ultra Cold Atoms and Effective Spin Models in Optical Cavities Invited Speaker: Joe Bhaseen There has been spectacular progress in exploring the properties of ultra cold atoms using light. Recent experiments [1] on Bose--Einstein condensates in optical cavities have reported a novel self-organization transition of the atom-light system. This coincides with the superradiance transition in an effective non-equilibrium Dicke model, describing two-level ``spins'' coupled to light. The light leaking out of the cavity provides valuable information on this hybrid matter-light system, and the time-dependent nature of the experiments demands consideration of the associated dynamics. We present a rich dynamical phase diagram [2,3], accessible by quench experiments, with distinct regimes of collective dynamics separated by non-equilibrium phase transitions. These findings open new directions to study the emergent dynamics and non-equilibrium phase transitions of quantum many body systems and effective spin models.\\[4pt] In collaboration with J. Keeling (University of St Andrews), J. Mayoh (University of Cambridge) and B. D. Simons (University of Cambridge).\\[4pt] [1] K. Baumann, C. Guerlin, F. Brennecke and T. Esslinger, ``Dicke Quantum Phase Transition with a Superfluid Gas in an Optical Cavity,'' Nature 464, 1301 (2010).\\[0pt] [2] J. Keeling, M. J. Bhaseen and B. D. Simons, ``Collective Dynamics of Bose--Einstein Condensates in Optical Cavities,'' Phys. Rev. Lett. 105, 043001 (2010).\\[0pt] [3] M. J. Bhaseen, J. Mayoh, B. D. Simons and J. Keeling, ``Dynamics of Nonequilibrium Dicke Models,'' Phys. Rev. A 85, 013817 (2012). [Preview Abstract] |
Thursday, March 21, 2013 4:18PM - 4:54PM |
W10.00004: Heavy Solitons in a Fermionic Superfluid Invited Speaker: Martin W. Zwierlein Topological excitations are found throughout nature, in proteins and DNA, as dislocations in crystals, as vortices and solitons in superfluids and superconductors, and generally in the wake of symmetry-breaking phase transitions. In fermionic systems, topological defects may provide bound states for fermions that often play a crucial role for the system's transport properties. Famous examples are Andreev bound states inside vortex cores, fractionally charged solitons in relativistic quantum field theory, and the spinless charged solitons responsible for the high conductivity of polymers. However, the free motion of topological defects in electronic systems is hindered by pinning at impurities. We have created long-lived solitons in a strongly interacting fermionic superfluid by imprinting a phase step into the superfluid wavefunction, and directly observed their oscillatory motion in the trapped superfluid. As the interactions are tuned from the regime of Bose-Einstein condensation (BEC) of tightly bound molecules towards the Bardeen-Cooper-Schrieffer (BCS) limit of long-range Cooper pairs, the effective mass of the solitons increases dramatically to more than 200 times their bare mass. This signals their filling with Andreev states and strong quantum fluctuations. For the unitary Fermi gas, the mass enhancement is more than fifty times larger than expectations from mean-field Bogoliubov-de Gennes theory. Our work paves the way towards the experimental study and control of Andreev bound states in ultracold atomic gases. In the presence of spin imbalance, the solitons created in our experiment represent one limit of the long sought-after Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state of mobile Cooper pairs. \\[4pt] [1] Tarik Yefsah, Ariel T. Sommer, Mark J.H. Ku, Lawrence W. Cheuk, Wenjie Ji, Waseem S. Bakr, Martin W. Zwierlein, Heavy Solitons in a Fermionic Superfluid, preprint arXiv:1302.4736 (2013) [Preview Abstract] |
Thursday, March 21, 2013 4:54PM - 5:30PM |
W10.00005: Collective Dipole Oscillations of a Spin-Orbit Coupled Bose-Einstein Condensate Invited Speaker: Shuai Chen We present an experimental study of the collective dipole oscillation of a spin-orbit coupled Bose-Einstein condensate in a harmonic trap. The dynamics of the center-of-mass dipole oscillation is studied in a broad parameter region as a function of spin-orbit coupling parameters as well as the oscillation amplitude. The anharmonic properties beyond the effective-mass approximation are revealed, such as the amplitude-dependent frequency and finite oscillation frequency at a place with a divergent effective mass. These anharmonic behaviors agree quantitatively with variational wave-function calculations. Moreover, we experimentally demonstrate a unique feature of the spin-orbit coupled system predicted by a sum-rule approach, stating that spin polarization susceptibility---a static physical quantity---can be measured via the dynamics of dipole oscillation. The divergence of polarization susceptibility is observed at the quantum phase transition that separates the magnetic nonzero-momentum condensate from the nonmagnetic zero-momentum phase. The good agreement between the experimental and theoretical results provides a benchmark for recently developed theoretical approaches. [Preview Abstract] |
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