Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Z31: Quantum Optics and Quantum Many-body Physics in Optical Lattices |
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Sponsoring Units: DAMOP Chair: Yong Chen, Purdue University Room: E141 |
Friday, March 19, 2010 11:15AM - 11:27AM |
Z31.00001: ABSTRACT WITHDRAWN |
Friday, March 19, 2010 11:27AM - 11:39AM |
Z31.00002: Linked and knotted beams of light William Irvine, Dirk Bouwmeester Maxwell's equations allow for curious solutions having linked and knotted field lines. A particularly striking solution is one characterized by the property that {\it all} electric and magnetic field lines are closed loops with {\it any } two electric(magnetic) field lines linked. These little known solutions, are based on the Hopf fibration and have a remarkably simple representation in terms of self-dual Chandrasekhar-Kendall curl eigenstates. I will discuss their structure, time evolution, physical properties and how they may be physically realizable. [Preview Abstract] |
Friday, March 19, 2010 11:39AM - 11:51AM |
Z31.00003: Interference of Photons from a Weak Laser and a Quantum Dot David Ritchie, Anthony Bennett, Raj Patel, Christine Nicoll, Andrew Shields We demonstrate two-photon interference from two unsynchronized sources operating via different physical processes [1]. One source is spontaneous emission from the X$^{-}$ state of an electrically-driven InAs/GaAs single quantum dot with $\mu $eV linewidth, the other stimulated emission from a laser with a neV linewidth. We mix the emission from these sources on a balanced non-polarising beam splitter and measure correlations in the photons that exit using Si-avalanche photodiodes and a time-correlated counting card. By periodically switching the polarisation state of the weak laser we simultaneously measure the correlation for parallel and orthogonally polarised sources, corresponding to maximum and minimum degrees of interference. When the two sources have the same intensity, a reduction in the correlation function at time zero for the case of parallel photon sources clearly indicates this interference effect. To quantify the degree of interference, we develop a theory that predicts the correlation function. Data and experiment are then compared for a range of intensity ratios. Based on this analysis we infer a wave-function overlap of 91{\%}, which is remarkable given the fundamental differences between the two sources. \textbf{[}1] Bennett A. J \textit{et al} Nature Physics, \textbf{5}, 715--717 (2009). [Preview Abstract] |
Friday, March 19, 2010 11:51AM - 12:03PM |
Z31.00004: Photon blockade in circuit quantum electrodynamics Anthony Hoffman, Srikanth Srinivasan, Beumseok Shim, Andrew Houck Strong photon-photon interactions arise in a cavity strongly coupled to an atom or qubit, resulting in blockaded transmission[1].~ In such a system, the resonant frequency of the cavity shifts with the presence of a single photon due to the strong number-dependent nature of the cavity nonlinearity.~ Here, we investigate the photon blockade regime in superconducting circuits with integrated transmon qubits.~ To maximize the nonlinear effects, both the cavity $Q$ and qubit-cavity coupling are made extremely large by design, with $Q$ exceeding 100,000.~ Cavity transmission is characterized using a microwave generator with a controllable output bandwidth.~ Measurements of transmitted power and spectra versus incident center frequency and bandwidth are presented.~ [1] K.M. Birnbaum et al., Nature, 436, 87 (2005). [Preview Abstract] |
Friday, March 19, 2010 12:03PM - 12:15PM |
Z31.00005: Photons as phonons: Flexible crystals of atoms and light in multimode cavities Sarang Gopalakrishnan, D. Zeb Rocklin, Benjamin Lev, Paul Goldbart Condensed-matter phenomena involving the emergence and dynamics of crystal lattices can be realized using ultracold atoms confined in multimode optical cavities~[1]. The atoms locally crystallize at the antinodes of one of the cavity modes, provided the cavity is transversely pumped by a laser of sufficient intensity. The mode into which the atoms crystallize is likely to vary across the cavity, giving rise to dynamical dislocations, frustration, and possibly glassiness. The crystallization transition is a nonequilibrium quantum phase transition, involving a condensation of cavity photons that is analogous to the condensation of phonons during crystallization in solids. This photon-phonon analogy goes further: the dynamics of atoms in multimode cavities is governed by polaron-like dissipative effects. We discuss various possible kinds of quantum ordering in atom-cavity settings, their imprint on the light emitted from the cavity, and prospects for their experimental realization. [1] S. Gopalakrishnan, B.L. Lev, and P.M. Goldbart, Nature Physics 5, 845-850 (2009). [Preview Abstract] |
Friday, March 19, 2010 12:15PM - 12:27PM |
Z31.00006: Dynamical properties of Coupled Cavity Arrays and the Bose Hubbard Model Hans Gerd Evertz, Peter Pippan, Martin Hohenadler We study a system of cavity arrays coupled by photons. It can be described by a model based on the Jaynes-Cummings Hamiltonian. It resembles the Bose Hubbard model, which describes recent experiments on cold atoms in optical traps. Dynamical properties like the dynamical structure factor have recently been observed there using Bragg spectroscopy or lattice modulation. Employing an exact QMC algorithm, we calculate excitation spectra of both coupled cavities and the Bose Hubbard model. We examine the Mott insulator to superfluid phase transition and monitor single-particle excitations and polariton-density excitations. We study both the phase transition with fixed polariton density and the transition with fixed chemical potential. Finite tempererature and detuning effects are discussed. The excitation spectra of coupled cavities and the Bose Hubbard model turn out to closely resemble each other. Bose Hubbard physics can therefore be investigated in coupled cavities. [Preview Abstract] |
Friday, March 19, 2010 12:27PM - 12:39PM |
Z31.00007: Polaritons and Pairing Phenomena in Bose-Hubbard Mixtures A.O. Silver, M.J. Bhaseen, M. Hohenadler, B.D. Simons Motivated by recent experiments on cold atomic gases in ultra high finesse optical cavities, we consider the two-band Bose-Hubbard model coupled to quantum light. Photoexcitation promotes carriers between the bands and we study the interplay between Mott insulating behaviour and superfluidity. The model displays a $U(1)\times U(1)$ symmetry which supports the coexistence of Mott insulating and superfluid phases,and yields a rich phase diagram with multicritical points. This symmetry is shared by several other problems of current experimental interest, including two-component Bose gases in optical lattices, and the bosonic BEC-BCS crossover for atom-molecule mixtures induced by a Feshbach resonance. We corroborate our findings by numerical simulations. [M. J. Bhaseen, M. Hohenadler, A. O. Silver, and B. D. Simons, Phys. Rev. Lett. \textbf{102}, 135301 (2009)] [Preview Abstract] |
Friday, March 19, 2010 12:39PM - 12:51PM |
Z31.00008: Pure Mott phases in confined ultra-cold atomic systems Valery Rousseau, George Batrouni, Daniel Sheehy, Juana Moreno, Mark Jarrell We propose a novel scheme for confining atoms to optical lattices by engineering a spatially-inhomogeneous hopping matrix element in the Hubbard-model (HM) description, a situation we term off-diagonal confinement (ODC). We show, via an exact numerical solution of the boson HM with ODC, that this scheme possesses distinct advantages over the conventional method of confining atoms using an additional trapping potential, including the presence of incompressible Mott phases at commensurate filling and a phase diagram that is similar to the uniform HM. The experimental implementation of ODC will thus allow a more faithful realization of correlated phases of interest in cold atom experiments. [Preview Abstract] |
Friday, March 19, 2010 12:51PM - 1:03PM |
Z31.00009: Dynamical modulation of Optical lattices studied by a numerical investigation on response theory Zhaoxin Xu, Shiquan Su, Daniel Sheehy, Simone Chiesa, Shuxiang Yang, Juana Moreno, Mark Jarrell, Richard Scalettar The response to the dynamical modulation of optical lattice potentials is studied by Determinantal Quantum Monte Carlo combined with the Maximum Entropy method. We simulate three and two-dimensional repulsive fermionic Hubbard models within the strong coupling regime and near half-filling for a wide range of temperatures. We discuss the relation between the first and second order response \% to the dynamical modulation and the dynamical generated double occupancy and the relevance of bond order excitations near half-filling. [Preview Abstract] |
Friday, March 19, 2010 1:03PM - 1:15PM |
Z31.00010: Superflow instabilities of atomic fermion superfluids in an optical lattice Ganesh Ramachandran, Arun Paramekanti, A.A. Burkov We study the superfluid phase of the one-band attractive Hubbard model as a prototype of a strongly correlated fermionic superfluid on a lattice. We characterize its collective mode and compute the sound velocity and ``roton'' gap within a generalized random phase approximation (GRPA). At strong coupling, we perform a spin wave analysis of the appropriate pseudospin model, with our GRPA results matching onto the spin wave results. With our two-pronged understanding of the collective mode, we examine breakdown of superfluidity due to imposed supercurrent. We find several mechanisms of superflow breakdown - depairing, Landau or dynamical instabilities. The most interesting is a charge modulation dynamical instability distinct from those previously studied in Bose superfluids. The associated charge order can be of two types: (i) a commensurate checkerboard modulation driven by softening of the roton mode at the Brillouin zone corner, or (ii) an incommensurate modulation arising from flow-induced finite-momentum pairing of Bogoliubov quasiparticles. We map out a dynamical phase diagram showing critical flow momentum of the leading instability, and point out implications for experiments on cold atom superfluids in an optical lattice. [Preview Abstract] |
Friday, March 19, 2010 1:15PM - 1:27PM |
Z31.00011: Unconventional Bose-Einstein condensation with Rashba coupling in optical lattices Ian Mondragon-Shem, Boris A. Rodriguez, Congjun Wu We study the effect of Rashba spin-orbit coupling on the ground state properties of ultracold bosonic atoms in optical lattices. The Rashba coupling in the center-of-mass of the bosons is generated by spatially varying external laser fields which couple to the internal degrees of freedom of the atoms. As a result of the spin-orbit coupling, the ground state of the system acquires a finite quasi-momentum $\vec{k}_0$, which spontaneously breaks time-reversal symmetry. The Gross- Pitaevskii many-body ground state, the current density and the pseudo-spin density distributions are calculated in the high- particle-density superfluid regime, and time-of-flight calculations are carried out. In the low-particle-density regime, the phase diagram is computed showing the effect of the coupling on the Mott insulator-to-superfluid transition using a modified Bose-Hubbard model. We supplement this with the computation of the ground state of the system with a superimposed harmonic trap using a Gutzwiller ansatz, which shows the effect of the Rashba coupling on the wedding-cake structure of the system. [Preview Abstract] |
Friday, March 19, 2010 1:27PM - 1:39PM |
Z31.00012: Hubbard Model study of Off Diagonally Confined fermions in a 2D Optical Lattice Dave Cone, Simone Chiesa, Richard Scalettar, George Batrouni We report Quantum Monte Carlo simulations of a Hubbard Hamiltonian which incorporates a proposed new method for confining atoms in an optical lattice employing an inhomogeneous array of hopping matrix elements which trap atoms by going to zero at the lattice edges. This has been termed ``Off Diagonal Confinement (ODC)'' [1] to distinguish it from the more conventional use of a parabolic trap coupling to (diagonal) density operators. It has the advantage of producing systems which, while still being inhomogeneous, are entirely in the Mott phase, and allow simulations which are free of the sign problem at low temperatures. We analyze the effects of using ODC traps on the local density, density fluctuation, spin, and pairing correlation functions. Finally, we will discuss the advantages and importance of this new confinement technique for modeling correlated systems. Research supported by the Department of Energy, Office of Science SCIDAC program, DOE-DE-FC0206ER25793. [1] V.G. Rousseau {\em et al.}, arXiv:0909.3543 [Preview Abstract] |
Friday, March 19, 2010 1:39PM - 1:51PM |
Z31.00013: Spontaneous interlayer superfluidity in bilayer systems of cold polar molecules Roman Lutchyn, Enrico Rossi, Sankar Das Sarma Quantum degenerate cold-atom gases provide a remarkable opportunity to study strongly interacting systems. Recent experimental progress in producing ultracold polar molecules with a net electric dipole moment opens up new possibilities to realize novel quantum phases governed by the long-range and anisotropic dipole-dipole interactions. In this work we predict the existence of experimentally observable novel broken-symmetry states with spontaneous interlayer coherence in cold polar molecules. These exotic states appear due to strong repulsive interlayer interactions and exhibit properties of superfluids, ferromagnets and excitonic condensates. [Preview Abstract] |
Friday, March 19, 2010 1:51PM - 2:03PM |
Z31.00014: Possible critical behavior driven by the confining potential in optical lattices with ultra-cold fermions Chris Hooley, Vivaldo Campo Jr, Jorge Quintanilla A recent paper [V.L. Campo {\it et al.}, {\it Phys. Rev. Lett.} {\bf 99}, 240403 (2007)] has proposed a two-parameter scaling method to determine the phase diagram of the fermionic Hubbard model from optical lattice experiments. Motivated by this proposal, we investigate in more detail the behavior of the ground-state energy per site as a function of trap size ($L$) and confining potential ($V(x)=t\vert x/L \vert^\alpha$) in the one-dimensional case. Using the BALDA-DFT method, we find signatures of critical behavior as $\alpha \to \infty$. [Preview Abstract] |
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