Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session U43: Focus Session: Novel Phases in Low Dimensional Quantum Gases |
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Sponsoring Units: DAMOP Chair: M. Olshanii, University of Southern California Room: Baltimore Convention Center 346 |
Thursday, March 16, 2006 8:00AM - 8:12AM |
U43.00001: Low-Dimensional Fermi Gases Henning Moritz, Kenneth G\"uenter, Thilo St\"oferle, Michael K\"ohl, Tilman Esslinger Optical lattices are a powerful tool to create novel many-body quantum systems with ultracold atoms. They allow to study the role of interactions in the system in reduced dimensions. We have observed two-particle bound states of atoms confined in a one-dimensional matter waveguide. These bound states exist irrespective of the sign of the scattering length, contrary to the situation in free space. The strongly interacting one- dimensional Fermi gas which we create in an optical lattice represents a realization of a tunable Luttinger liquid. In a spin-polarized Fermi gas interacting via a p-wave Feshbach resonance the strong confinement allows us to restrict the asymptotic scattering states. When aligning the spins along (or perpendicular to) the axis of motion in a 1D gas, scattering into channels with the angular momentum projection of |m |=1 (or m=0) can be completely suppressed. [Preview Abstract] |
Thursday, March 16, 2006 8:12AM - 8:24AM |
U43.00002: Empirical manifestations of integrability in cold quantum gases Maxim Olshanii, Vanja Dunjko, Vladimir Yurovsky, Marcos Rigol Integrable quantum many-body systems traditionally belong to the domain of mathematical physics, with little or no connection to experiments. However, the experiments on confined quantum-degenerate gases has recently yielded faithful realizations of a number of integrable systems, thus making them phenomenologicalily relevant. We show that the presence of few-body conserved quantities in a quantum system leads to dramatic, initial-state-dependent discrepancy between the state of the system after relaxation and the predictions of thermodynamics. Using the newly introduced concept of constrained thermal equilibrium we study quantitatively the effects of the memory of the initial conditions. As objects of study we choose bosons in one-dimensional optical lattices in the deep Mott regime and spin-$0$ Bose gases confined to waveguides, both of which have been experimentally realized already. We suggest momentum distribution and chemical composition as the simplest experimental observables sensitive to the effects of integrability. Overall, we argue that the kinetic and thermodynamic properties of integrable quantum gases are so different from the usual, that they well-qualify for a new state of quantum matter. [Preview Abstract] |
Thursday, March 16, 2006 8:24AM - 8:36AM |
U43.00003: Noise and counting statistics in one-dimensional insulators Austen Lamacraft We discuss the correlation properties of current carrying states of one-dimensional insulators, which could be realized by applying an impulse to atoms loaded onto an optical lattice. While the equilibrium noise has a gapped spectrum, the quantum uncertainty encoded in the amplitudes for the Zener process gives a zero frequency contribution out of equilibrium. We derive a general expression for the generating function of the full counting statistics and find that the particle transport obeys binomial statistics. Finally, we discuss the extent to which the technique employed in a recent experiment (Phys. Rev. Lett. 95, 090404 (2005)) can be considered an ideal measurement of counting statistics. [Preview Abstract] |
Thursday, March 16, 2006 8:36AM - 9:12AM |
U43.00004: Dynamics of reduced dimension Bose gases in optical lattices Invited Speaker: We use deep optical lattices to tightly confine cold atoms in reduced dimensions. By applying shallower optical lattices in the weakly confined direction, we realize well-characterized one- and two- dimensional Bose-atom lattice gases. Transport dynamics is studied by observing motion of the atom cloud through the lattice. For a 1D quantum degenerate Bose gas, we report the observation of strongly damped dipole oscillations in a combined harmonic and optical lattice potential. Damping is significant for very shallow axial lattices (0.25 photon recoil energies), and increases dramatically with increasing lattice depth, such that the gas becomes nearly immobile for times an order of magnitude longer than the single-particle tunneling time. Surprisingly, we see no broadening of the atomic quasimomentum distribution after damped motion. [Preview Abstract] |
Thursday, March 16, 2006 9:12AM - 9:24AM |
U43.00005: The superfluid-Mott insulator transition in 2D I. B. Spielman, J. Huckans, J. Strabley, M. Anderlini, J. Kruse, J. V. Porto, W. D. Phillips Ultra-cold atoms in optical lattices have been exploited to study the Mott-insulator transition in 1, 2, and 3 dimensions; here focus on the 2D Mott-insulator transition. Initially Bose-condensed rubidium atoms are loaded into a 3D optical lattice with an average occupancy of one atom per-site. By making one lattice much deeper in one direction than the remaining two, we construct an ensemble of 2D lattice systems. These 2D systems exhibit a superfluid-insulator transition as the lattice depth is increased. In this talk I present new measurements that show that even when the conventional signature of long-range order (namely diffraction) disappears, the system is not a perfect insulator -- partially responding to an impulsive force. [Preview Abstract] |
Thursday, March 16, 2006 9:24AM - 9:36AM |
U43.00006: Crystalline phases of bosons in rotating traps: Tonks-Girardeau gas on a ring. Igor Romanovsky, Constantine Yannouleas, Uzi Landman We analyze the systems of strongly repelling bosons in two-dimensional harmonic and ring-shaped traps as a function of the rotational frequency of the trap for neutral atoms (and of an applied magnetic field for charged bosons). Our two-step approach consists of breaking the rotational symmetry at the Hartree-Fock level and of subsequent symmetry restoration via projection techniques, \footnote{Phys. Rev. Lett.{\bf 93}, 230405 (2004)} thus taking into account correlations beyond the Gross-Pitaevskii (GP) solution. The bosons localize and form crystalline patterns both for a repulsive contact potential and a Coulomb interaction, as revealed via conditional probability distribution (CPD) analysis. This behavior of the bosons in the ring-shaped traps in the strong repulsion limit is similar to the behavior of fermions and is a manifestation of the fermionization phenomenon. We present calculations for the ground state energies as a function of the rotational frequency (or the strength of the magnetic field) and as a function of the repulsion strength. [Preview Abstract] |
Thursday, March 16, 2006 9:36AM - 9:48AM |
U43.00007: Ordering and Entropy Production Across Qauntum Phase Transitions Robert Cherng, Leonid Levitov We consider the transverse field Ising spin chain swept through a quantum critical point from the disordered to the ordered phase (and vice versa) and present exact results on the ordering and entropy production. Prepared in the ground state of the initial Hamiltonian, the system evolves to a state characterized by a non-equilibrium distribution of excitations of the final Hamiltonian. We show that the evolved system, while described by a pure many-body state, possesses finite entropy if considered ``locally.'' The notion of local entropy is defined by coarse-graining in momentum space, and is linked to the properties of the system of Kibble-Zureck domain walls. Exact results obtained for the spin correlation functions are presented and used to elucidate the relationship with the Kibble-Zureck theory of critical dynamics. Possible manifestations in ultracold atoms trapped in optical lattices will be discussed. [Preview Abstract] |
Thursday, March 16, 2006 9:48AM - 10:24AM |
U43.00008: Spin 1/2 fermions on spin-dependent optical lattices Invited Speaker: We study the phase diagram of one-dimensional two-component (i.e. pseudo-``spin''-1/2) ultracold atomic Fermi gas. The two atom species can have different hopping or mass. A very rich phase diagram for equal densities of the species is found, containing Mott insulators with various quasi-long-range-order, superfluids and perhaps phase separation. We also discuss coupling such 1D systems together and the experimental signatures of the phases. In particular, we compute the ``spin''-structure factor at small momentum, which should reveal a ``spin'' gap. [Preview Abstract] |
Thursday, March 16, 2006 10:24AM - 10:36AM |
U43.00009: Quartetting and pairing instabilities in one dimensional spin 3/2 fermionic systems Congjun Wu Novel competing orders are found in spin 3/2 cold atomic systems in one-dimensional optical traps and lattices. In particular, the quartetting phase, a four-fermion counterpart of Cooper pairing, exists in a large portion of the phase diagram. The transition between the quartetting and singlet Cooper pairing phases is controlled by an Ising symmetry breaking in one of the spin channels. The singlet Cooper pairing phase also survives in the purely repulsive interaction regime. In addition, various charge and bond ordered phases are identified at commensurate fillings in lattice systems. [Preview Abstract] |
Thursday, March 16, 2006 10:36AM - 10:48AM |
U43.00010: Spinfull bosons in an optical lattice Sara Bergkvist, Ian McCulloch, Anders Rosengren We have studied the phase diagram of spinfull bosons in a one-dimensional optical lattice, using DMRG. Correlation functions and the dimerization are calculated. We also present results for energy gap to excited states and magnetization energies. We confirm the expected phase diagram with a dimerized phase in the insulating regions with an odd density and on-site singlets in the other insulating systems. [Preview Abstract] |
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