Bulletin of the American Physical Society
38th Annual Meeting of the Division of Atomic, Molecular, and Optical Physics
Volume 52, Number 7
Tuesday–Saturday, June 5–9, 2007; Calgary, Alberta, Canada
Session J4: Cold Atoms in Optical Lattices and Double-Well Potentials |
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Chair: I. Danshita, National Institute of Standards and Technology Room: TELUS Convention Centre Glen 206 |
Thursday, June 7, 2007 1:30PM - 1:42PM |
J4.00001: Quantum Noise Interferometry: Phase transitions and entanglement in cold atoms in optical lattices Indubala Satija, Ana Maria Rey, Charles Clark ``Intensity interferometry,'' known as Hanbury-Brown Twiss (HBT) interferometry where quantum noise is used as a tool to detect quantum correlations is emerging as a very effective tool in the study of various complexities of strongly correlated systems. The technique is based on ``bunching'' effect of bosons and corresponding ``Anti-bunching'' of fermions due to the underlying quantum statistics. In cold atomic systems HBT can be done by detailed analysis of time of flight images of the expanded atomic cloud. We demonstrate the importance of the intrinsic quantum noise in the study of quantum phase transitions such as the Anderson-type transition in strongly interacting bosons, and the magnetic phase transition in quantum Ising models. We argue that noise interferometry provides a new order parameter for characterizing quantum phase transitions and may be viewed as a measure of quantum entanglement. [Preview Abstract] |
Thursday, June 7, 2007 1:42PM - 1:54PM |
J4.00002: Stability of two-component and spinor condensates in optical lattices Zachary Dutton, Janne Ruostekoski We carry out an analysis of two-component (spin $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} )$ and spinor (spin 1) BECs in optical lattices. Using a Bogoliubov approach, we derive analytic conditions for the stability of these systems for both moving and stationary condensates in terms of the BEC interaction parameters and lattice kinetic energy. Both energy instabilities and dynamical instability conditions are derived and our results include both positive and negative interaction strengths. In both the two-component and spinor cases, we find the stability phase diagram closely reflects the free space case. [Preview Abstract] |
Thursday, June 7, 2007 1:54PM - 2:06PM |
J4.00003: Phase diagrams of the Bose-Fermi-Hubbard-Model: Analytical and numerical studies Alexander Mering, Michael Fleischhauer We present calculations for the Bose-Fermi-Hubbard model both in the limit of vanishing fermionic hopping (infinitly large mass) and large fermionic hopping (vanishing mass). In the first case, a detailed study of the fermionic ground state which minimizes the energy for the bosons allows a straight forward prediction of the phase diagram in terms of the pure Bose-Hubbard model. The resulting incompressible phases can be classified and Bose glass like phases are predicted. In the second case, the fermions act as a reservoir to the bosons and an effective hamiltonian can be derived. This hamiltonian corresponds to an extended Bose-Hubbard model with long range oscillatory density- density interactions that depend on the fermionic filling and lead e.g. to the formation of density waves. In both cases, analytic results are given and compared to numerical calculations obtained using DMRG and exact diagonalization methods. [Preview Abstract] |
Thursday, June 7, 2007 2:06PM - 2:18PM |
J4.00004: Turning back time in the optical lattice: using the Loschmidt echo as a sensor Fernando Cucchietti I will show how to perform a time reversal of the dynamics of cold bosonic atoms in an optical lattice. The time reversal creates a Loschmidt echo and is obtained by applying a linear phase imprint on the lattice and a change in magnetic field to tune the boson-boson scattering length through a Feshbach resonance. I will discuss how to use the echo as a sensor to measure intensities of external potentials (e.g. gravity, magnetic fields, etc.), and also interesting quantities such as the fidelity of the quantum simulation of the Bose-Hubbard Hamiltonian, and the critical point and exponents of the superfluid-insulator quantum phase transition in this model. [Preview Abstract] |
Thursday, June 7, 2007 2:18PM - 2:30PM |
J4.00005: Thermally activated defects in a two-dimensional lattice of Bose-Einstein condensates Volker Schweikhard, Shihkuang Tung, Eric Cornell We present a study of thermally activated phase defects in a two-dimensional (2d) Josephson junction array of Bose-Einstein condensates (BECs), created by adiabatically loading a pre-formed BEC into a 2d optical lattice. Each lattice site contains thousands of condensed atoms, so that the phase of each condensate is well-defined. Nearest-neighbor tunneling provides a Josephson coupling J which acts to keep the condensates' relative phases locked. A cloud of uncondensed atoms, in thermal equilibrium with the condensate array at a temperature T, on the other hand induces thermal fluctuations of the condensate phases. By varying the optical lattice depth we tune the Josephson coupling in the vicinity of the thermal energy, and thus induce a crossover between a phase-locked array for J$>$T and a disordered array for J$<$T. We observe phase defects by turning down the optical lattice on a timescale fast for the defects to heal, thus converting them to vortices and solitons in the reconnected condensate. The physics of this system is closely related to the Kosterlitz-Thouless transition observed in 2d superfluids and superconducting Josephson junction arrays. [Preview Abstract] |
Thursday, June 7, 2007 2:30PM - 2:42PM |
J4.00006: Breakdown of superfluid flow in a moving lattice Jongchul Mun, Patrick M. Medley, David A. Hucul, David M. Weld, David E. Pritchard, Wolfgang Ketterle The stability of superfluid currents in strongly interacting ultracold bosons was studied using a moving optical lattice. The critical momentum for a stable current was found to vary continuously from 0.5 recoil momentum in a weakly interacting superfluid (SF) to zero in the Mott insulator (MI) phase. This critical momentum was measured at various lattice depths, and the phase diagram was obtained. This measurement also enabled us to precisely determine the critical lattice depth for the SF-MI phase transition. The critical lattice depth was measured to be 13.5 recoil energy for a three- dimensional gas. When a one-dimensional gas was loaded into a moving optical lattice, a broadening of the transition between stable and unstable phases was observed. [Preview Abstract] |
Thursday, June 7, 2007 2:42PM - 2:54PM |
J4.00007: Superfluidity of Feshbach resonant atoms in an optical lattice Juha Javanainen, Tun Wang, Susanne Yelin We study atomic and molecular currents in a one-dimensional optical ring lattice for a Fermi gas in the vicinity of a Feshbach resonance by direct numerical diagonalization of small model systems. A rotational counterpart of flux quantization is used to demonstrate that a fraction of the current is carried by particles with twice the mass of an atom, which suggests pairing and superfluidity. [Preview Abstract] |
Thursday, June 7, 2007 2:54PM - 3:06PM |
J4.00008: Preparing Fermions in an Optical Lattice at Ultra-Low Temperature J.R. Williams, R. Stites, J.H. Huckans, E.L. Hazlett, K.M. O'Hara Fermionic atoms confined in an optical lattice provide an exciting opportunity for the quantum simulation of iconic models of condensed matter physics. The 2D Hubbard model, for example, which purports to describe high-temperature superconductivity in the cuprates, can be experimentally realized. Exploration of the most interesting phases (e.g. anti-ferromagnetism or {\it d}-wave superfluidity), however, will require the attainment of extremely low temperatures, or equivalently, near-zero entropy. We present a preparation method in which a cold, spin-polarized gas of fermionic atoms with a peak atomic density greater than that of the lattice site density is initially loaded into a deep 3D cubic optical lattice. The lowest band of the lattice is fully occupied, while the second band is only partially filled. Selective removal of atoms in the second band is accomplished by intensity modulation of the lattice beams which promotes atoms to a higher-lying band, from where they are allowed to escape the trapping region. The atoms that remain completely fill the lowest band and are at an extremely low temperature. We will discuss theoretical limitations on the achievable temperature and our experimental progress. [Preview Abstract] |
Thursday, June 7, 2007 3:06PM - 3:18PM |
J4.00009: Correlated tunneling dynamics of atom pairs in double well potentials Simon F\"olling, Patrick Cheinet, Stefan Trotzky, Artur Widera, Michael Feld, Torben M\"uller, Immanuel Bloch The interplay between atom-atom interaction and tunneling governs the dynamics of many strongly correlated systems of ultracold atoms. The most elementary realization of such a system is a set of two potential wells coupled via tunneling and occupied by two interacting atoms. By superimposing the periodic potentials of two standing light waves with a periodicity of 382.5nm and 765nm, respectively, we create a one-dimensional array of double well potentials for atoms with adjustable tunnel coupling and energy offset. Additional standing waves on the two orthogonal axes provide axial confinement, creating a three-dimensional array of up to $10^5$ double wells occupied by one or two $^{87}$Rb atoms each. Loading only one side of each double well before enabling the tunneling, we can directly observe the dynamics of single atoms as well as of atom pairs. Since the ratio of the tunneling matrix element $J$ and the on-site repulsive interaction $U$ between two atoms can be modified in a wide range, the crossover from a tunneling- to an interaction-dominated regime can be observed. Here, the independent motion of two atoms changes to a correlated tunnel process of the pairs. [Preview Abstract] |
Thursday, June 7, 2007 3:18PM - 3:30PM |
J4.00010: Phase Coherence of Schr\"{o}dinger Cat Sates in Gaseous BECs William Reinhardt A quantum state diffusion (QSD) numerical study, initially carried out in the simple Bose-Hubbard model, of the stability of both the creation and stability of macroscopic superposition states of gaseous Bose condensates in double well traps is reported. It is assumed that observations are made in the far-detuned quantum non-demolition regime, and that de-phasing dominates particle loss. Within the framework of these assumptions, which avoids consideration of highly pedigreed cats, we present the results of a phase space analysis of QSD, with surprising results. Presence of continuous, but far-detuned, observation destabilizes the formation of cats following pi-phase imprinting of the part of the condensate in one of the wells, but in a surprisingly predictable manner, suggesting methods for at least partially negating its influence. Further, once macroscopic superposition states are formed, there are parameter regimes where simple single shot observation of the density profiles, and in some cases even continuous monitoring, of even quite extreme macroscopic superpositions has little effect on their continuing stability. [Preview Abstract] |
Thursday, June 7, 2007 3:30PM - 3:42PM |
J4.00011: Exploring the phase diagram of a double-well optical lattice N. Lundblad, P. Lee, B. Brown, J. Sebby-Strabley, J.V. Porto, I.B. Spielman, W.D. Philliips Recent work in our group has demonstrated the creation and utility of a double-well optical lattice, consisting of a three-dimensional array of dynamically deformable lattice sites spanning the range from simple single wells to independent pairs of wells with variable barrier height and energy `tilt.' The lattice is occupied by atoms loaded from an initially Bose-condensed sample of $^{87}$Rb atoms. The various lattice parameters can be adjusted so as to create a stack of independent 2D lattices, or, in the sense of the so-called `two-leg ladder,' an array of chained double wells. We present preliminary investigations into the phase diagram of this system, which has been predicted to exhibit novel transitions between a half-filling/unit-filling Mott insulator and the superfluid phase as the chain couplings are varied. [Preview Abstract] |
Thursday, June 7, 2007 3:42PM - 3:54PM |
J4.00012: Probing atomic state coherence with a double-well optical lattice Philip Johnson, Jennifer Sebby-Strabley, Eite Tiesinga, Trey Porto, Carl Williams I will describe the theory of using the double-well optical lattice as an atom beam splitter, focusing on its ability to probe both inter-well and intra-well coherences. I will also discuss interesting effects such as the collapse-and-revival of first-order coherence occurring at \textit{twice} the on-site interaction energy (U), the role of the double well tilt, and adiabaticity requirements. We have recently implemented an atom interferometer based upon these ideas and seen clear evidence for the effects discussed above. [Preview Abstract] |
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