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 N4: Ultracold Atoms in Optical Traps and Optical Lattices |
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Chair: P. Marzlin, University of Calgary Room: TELUS Convention Centre Macleod A1-A2 |
Friday, June 8, 2007 8:00AM - 8:12AM |
N4.00001: Cooling of individual neutral atoms in an optical lattice Michael Gibbons, Peyman Ahmadi, Kevin Fortier, Soo Kim, Michael Chapman We study the lifetime of individual neutral rubidium atoms trapped in a one-dimensional optical lattice. By using optical molasses to continuously cool the trapped atoms, we achieve vacuum-limited lifetimes greater than 200 s. Without cooling, we observe negligible atom loss within the first 5 s; thereafter, they are observed to decay with a 15 s lifetime. We use a Fokker-Planck [1] equation to simulate the evolution of the cloud in the optical lattice. By fitting the observed population remaining in the lattice to the theoretical predictions, we infer the initial temperature and heating rate of the cloud. Motivated by these results, we have developed a pulsed cooling scheme that maintains very long lifetimes with a low duty cycle ($<$1{\%}) of applied cooling. \newline [1] M.G. Gehm, K.M O'Hara, T.A. Savard, and J.E. Thomas, Phys. Rev. A \textbf{58}, 3914 (1998). [Preview Abstract] |
Friday, June 8, 2007 8:12AM - 8:24AM |
N4.00002: Echo pulses and temporal decay of motional coherence in optical lattices S. Maneshi, C. Zhuang, M. Partlow, A.M. Steinberg We study the quantized centre-of-mass motion of $^{85}$Rb atoms trapped in an optical lattice.~We have measured the coherence between the quantum vibrational states of the atoms in the lattice wells, and observe a decay of coherence. Here we present studies optimizing echo pulses and using the resulting echoes to study the properties of the sources of decoherence. To generate echo pulses, we use a combination of lattice displacements and delays in order to couple the vibrational states. Experimental results, in agreement with simulations, demonstrate that square pulses are preferable to both single-step and gaussian pulses.~We also study the coupling efficiency as a function of lattice depth, finding that this process is more efficient in shallow lattices. We will discuss a number of other avenues for further improving state coupling, including coherent control via interfering pathways, and adiabatic passage.~ We study the decay of echo amplitude over time in both 1D and 3D lattices.~ In both cases, we observe an initial exponential decay of echo amplitude followed by a plateau before a final decay.~We will discuss the relationship of these features to the time-correlation function of the well-depth fluctuations~experienced by the atoms. [Preview Abstract] |
Friday, June 8, 2007 8:24AM - 8:36AM |
N4.00003: Probing Molecular Interactions of Cs in an Optical Lattice for Quantum Information Brian Mischuck, Ivan Deutsch We describe a scheme to probe the spectrum of interacting Cs atoms in an optical lattice. Transport of the atoms to overlapping wells is achieved through a microwave drive between hyperfine levels in a polarization-gradient lattice. The spectral response of pairs of atoms to microwaves can be used to measure the effect of the interactions, even in the presence of a large background of unpaired atoms. Control of such interactions may have applications in quantum computation [Preview Abstract] |
Friday, June 8, 2007 8:36AM - 8:48AM |
N4.00004: Preparation and detection of magnetic quantum phases in optical superlattices Ana Maria Rey, Vladimir Gritsev, Eugene Demler, Mikhail Lukin By loading spinor atoms in optical lattices it is now possible to simulate quantum spin models in controlled environments and to study quantum magnetism in strongly correlated systems. In this talk we describe a technique that allows one to prepare, detect and characterize magnetic quantum phases in ultra-cold spinor atoms loaded in optical superlattices. Our technique makes use of singlet-triplet quantum spin manipulation in double-well potentials in analogy to the recently demonstrated quantum control in semiconductor double quantum dots. We shall also discuss the many-body dynamics arising from coherent coupling between singlet-triplet pairs in adjacent double-wells. In particular by deriving an effective description for such many-body system we will discuss the generation of complex magnetic states by adiabatic and non-equilibrium dynamics. [Preview Abstract] |
Friday, June 8, 2007 8:48AM - 9:00AM |
N4.00005: Species selectivity of adiabatic RF potentials Marcius H.T. Extavour, Lindsay J. LeBlanc, Thorsten Schumm, Alan Stummer, Joseph H. Thywissen We report on the successful implementation of a species-selective double-well micromagnetic trap on an atom chip. Adiabatic RF potentials have recently been used for coherent beam splitting [1], and been suggested for species-selective manipulation [2]. We report on our implementation of this suggestion for a $^{40}$K-$^{87}$Rb Bose-Fermi mixture, where the radio frequency resonances are distinct since the Lande g$_F$ factors differ between the two elements. We demonstrate, for instance, that beam splitting of $^{87}$Rb can occur while $^{40}$K remains confined in an overlapping single-well potential [3]. We also report on our progress toward direct observation of relative number squeezing in an RF beam splitter, for which indirect evidence was recently reported [4].\newline \newline Refs: [1] T. Schumm et al., Nature Phys. {\bf 1}, 57 (2005). [2] Ph.W. Courteille et al., J. Phys. B: At. Mol. Opt. Phys. {\bf 39}, 1055 (2006). [3] M. H. T. Extavour et al., Atomic Physics {\bf 20}, 241 (2006); also cond-mat/0609259. [4] G.-B. Jo et al., Phys. Rev. Lett. {\bf 98}, 030407 (2007). [Preview Abstract] |
Friday, June 8, 2007 9:00AM - 9:12AM |
N4.00006: Species-selective optical lattices L.J. LeBlanc, J.H. Thywissen In binary mixtures of ultracold alkali atoms, we consider possibilities for creating an optical lattice seen by one atomic species (the ``target'') but not the other (the ``spectator'') [1]. Two schemes for single-frequency trapping are explored and compared in terms of their trap depths and heating rates. A ``tune-in'' scheme, where the trapping frequency is nearly resonant with the target and far detuned from the spectator, is found to be preferable for fermion-boson mixtures of Li-Na Li-K and K-Na. A ``tune-out'' scheme, where the trapping frequency is chosen between the D1 and D2 lines of the spectator element, is favoured for Li-Cs, K-Rb, Rb-Cs, K-Cs and $^{39}$K-$^{40}$K mixtures. Both schemes lend themselves to a number of applications, including the creation of a lattice for the target species in the presence of a phonon-like background, the tuning of relative effective mass of the species, and the isothermal increase of phase space density in the target species. Interactions pose an upper bound on the selectivity of the lattice, since the periodically modulated density of the target can create a periodic interaction potential on the spectator. \newline \newline Ref: [1] L.\ J.\ LeBlanc and J.\ H.\ Thywissen, arXiv:cond-mat/0702034. [Preview Abstract] |
Friday, June 8, 2007 9:12AM - 9:24AM |
N4.00007: Heteronuclear molecules in a 3D optical lattice C. Ospelkaus, S. Ospelkaus, L. Humbert, P. Ernst, K. Sengstock, K. Bongs, F. Werner, F. Deuretzbacher, K. Plassmeier, D. Pfannkuche We report on experiments with Fermi-Bose mixtures confined in 3D optical lattices, especially the first production of ultracold long-lived heteronuclear molecules in a 3D optical lattice. The molecules are associated from a quantum degenerate mixture of fermionic $^{40}$K and bosonic $^{87}$Rb atoms loaded into a 3D optical lattice. Molecules are produced at a heteronuclear Feshbach resonance in the vicinity of 546.7(1)\,G. Molecule formation is studied on both the attractive and the repulsive side of the resonance. The binding energy of the heteronuclear molecules is precisely determined by rf spectroscopy and compared to a theoretical model based on a pseudopotential approach. We also characterize both the lifetime of the sample and the efficiency of rf association; comparison to the pseudopotential model results in excellent agreement. [Preview Abstract] |
Friday, June 8, 2007 9:24AM - 9:36AM |
N4.00008: Atomtronics: Realizing the behavior of electronic components in ultracold atomic systems Ron Pepino Atomtronics focuses on creating an analogy of electronic devices and circuits with ultracold atoms. Such an analogy can come from the highly tunable band structure of ultracold neutral atoms trapped in optical lattices. Solely by tuning the parameters of the optical lattice, we demonstrate that conditions can be created that cause atoms in lattices to exhibit the same behavior as electrons moving through solid state media. We present our model and show how the atomtronic diode, field effect transistor, and bipolar junction transistor can all be realized. Our analogs of these fundamental components exhibit precisely-controlled atomic signal amplification, trimming, and switching (on/off) characteristics. In addition, the evolution of dynamics of the superfluid atomic currents within these systems is completely reversible. This implies a possible use of atomtronic systems in the development of quantum computational devices. [Preview Abstract] |
Friday, June 8, 2007 9:36AM - 9:48AM |
N4.00009: Optical dipole trapping of short-lived radioactive $^{82}$Rb David Feldbaum, Haiyan Wang, Jonathan Weinstein, David Vieira, Xinxin Zhao The application of the techniques of laser cooling and trapping of radioactive atoms holds a great promise for fundamental measurements. To date only a few radioactive isotopes have been trapped in MOTs and/or in magnetic traps. All-optical trapping of radioactive atoms has not, until now, been demonstrated. Optical dipole trapping may be the most desirable method, as it introduces less systematic problems in certain cases.~ We have experimentally demonstrated the trapping of short-lived $^{82}$Rb in an optical lattice, and we plan to study the optical pumping of these atoms into a stretched state for polarization studies. Our latest results will be presented. [Preview Abstract] |
Friday, June 8, 2007 9:48AM - 10:00AM |
N4.00010: Single-beam, dark toroidal optical traps for cold atoms Spencer Olson, Matthew Terraciano, Mark Bashkansky, Zachary Dutton, Fredrik Fatemi Toroidal atom confinement has received significant attention for both fundamental and applied research. We demonstrate single-beam, blue-detuned, toroidal optical traps for cold atoms. These are created by modifying the phase of a Gaussian laser beam with a spatial light modulator (SLM). By combining a radial phase discontinuity with an azimuthal phase variation $n\phi $, where $n$ is an integer, we produce a beam containing a ring-shaped intensity null surrounded harmonically in all directions by high intensity. The SLM is used to control and optimize the propagation and trapping characteristics of these toroidal beams, which we analyze both numerically and experimentally. Finally, we demonstrate confinement of cold Rb atoms in these traps using light that is blue-detuned by $\sim $5 nm from the D2 line. [Preview Abstract] |
Friday, June 8, 2007 10:00AM - 10:12AM |
N4.00011: Quantum Coherence in a Disordered Bose-Einstein Condensate Yong P. Chen, J. Hitchcock, D. Dries, M. Junker, C. Welford, R.G. Hulet Quantum coherence underlies such phenomena as superfluids and superconductors. We have performed an experiment on a Bose-Einstein condensate (BEC) subjected to a disordered potential, and found evidence that finite quantum coherence may still exist in an insulating state. We create a large BEC of $^7$Li atoms in their (1,1) state in an elongated optical dipole trap. We then project laser speckle onto the atoms to make a disordered potential, where the disorder strength ($V_d$) is tunable by varying the laser intensity. As $V_d$ is increased, we observe a suppression of the center of mass transport (dipole motion) of the trapped BEC, signaling a transition from a superfluid to an insulator. Surprisingly, for a wide range of $V_d$, \textit{even in the insulating regime}, striking interference-like fringes are observed in the time of flight images after the atoms are released from both the trap and disordered potentials. We interpret the fringes as due to residual quantum coherence present in the disordered BEC. These fringes disappear when $V_d$ is further increased to become comparable to the chemical potential, as the BEC breaks into multiple pieces with no phase coherence between them. [Preview Abstract] |
Friday, June 8, 2007 10:12AM - 10:24AM |
N4.00012: Supersolid 4He at Low Temperature Huai-Bin Zhuang, Xi Dai, Michael Ma, Fu-Chun Zhang The observation of NCRI in solid He reported by Kim and Chan reignited interests in the existence of supersolid in nature. Though plenty of theories assume that the mechanism of the supersolid is BEC of point defects, namely vacancies and interstitials, some theories and experiments suggest that the defects cannot exist in solid He at zero temperature. Dai et al in our group proposed a solution to the quandary by introducing a low-energy bound state, called exciton, of a vacancy and an interstitial so that it is possible to have vacancy (interstitial) superfluid phase in solid He despite the high activation energy of defects in normal solid. In addition to the previous single-site meanfield treatment to the two-band Bose Hubbard model, we further retain adequate quantum fluctuations and correlations by employing a spin XY model with 'annealed vacancies' and resolving it in three-dimensional simple cubic lattice by a modified spin-wave method. We show that the supersolid phase could be favored at low temperature because of its gapless energy excitations, and that even on the zero-temperature normal solid side a 'reentrance' would occur. The results are strongly recommended by the zero-temperature exact solution and the finite-temperature mean-field outcomes from Jordan-Wigner transformation in one dimension. The method utilized could be further applicable to models dealing with spin systems, cold atoms in optical lattices and others. [Preview Abstract] |
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