Bulletin of the American Physical Society
15th Annual Meeting of the Northwest Section of the APS
Volume 59, Number 6
Thursday–Saturday, May 1–3, 2014; Seattle, Washington
Session C1: Atomic, Molecular and Optical Physics I |
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Chair: Daniel Steck, University of Oregon Room: Alder Commons 104 (Auditorium) |
Friday, May 2, 2014 1:30PM - 2:00PM |
C1.00001: The Life and Times of a Superfluid Vortex Ring Invited Speaker: Michael Forbes In this talk I will present an overview of superfluid dynamics in fermionic systems by telling the tale of a superfluid soliton. Starting its life as a phase imprinted domain wall in cold cloud of 6Li at MIT [1], it behaved mysteriously, moving an order of magnitude more slowly than expected. Using some of the largest computer simulations, we demonstrated [2] that the wall is rapidly promoted to a vortex ring, explaining almost all aspects of the experiment, including some subtle effects due to the imaging process. Improved observations [3] reveal that the soliton is a vortex - an early retirement of the vortex ring induced by asymmetries present in the trap. This suggests that cold atoms may provide an excellent forum for studying the microscopic nature of the vortex crossing and recombination processes at the heart of quantum turbulence. Agreement between experiment and simulation validates superfluid density functional theory (DFT), paving the path towards understanding complex superfluid dynamics in cold atoms, nuclear matter, and neutron stars.\\[4pt] In collaboration with Aurel Bugac, University of Washington; Michelle Kelley, University of Illinois; Kenneth Roche, PNNL and University of Washington; and Gabriel Wlazlowski, Warsaw University of Technology, University of Washington.\\[4pt] [1] Yefsah et al., Nature 499, 426 (2013) [arXiv:1302.4736].\\[0pt] [2] Bulgac, Forbes, et al, PRL 112, 025301 (2014) [arXiv:1306.4266].\\[0pt] [3] Ku et al. (2014) [arXiv:1402.7052]. [Preview Abstract] |
Friday, May 2, 2014 2:00PM - 2:12PM |
C1.00002: Combining Ultracold Quantum Gases of Ytterbium and Lithium Atoms Richard J. Roy, William H. Dowd, Rajendra Shrestha, Subhadeep Gupta Ultracold atomic gases are fruitful systems in which to study exotic quantum phenomena such as Bose-Einstein condensation, superfluidity, and BCS pairing of fermions like that in superconductors. In this regard, single atomic species experiments have covered significant ground in studies of few and many-body physics. However, the addition of a second species opens up a large variety of new physics to be explored. Recent advances in the field of ultracold mixtures include the coherent production of heteronuclear diatomic molecules, and the subsequent coherent control of the many molecular degrees of freedom (e.g. rotational, vibrational, and electronic) with the use of external fields. This forms the starting point for realizing a number of quantum information and computation applications and studies of controlled chemical reactions. Here we report recent progress towards the creation of ultracold molecules of lithium and ytterbium, including the successful realization of a novel, long-lived mixture of ground state lithium and metastable excited state ytterbium atoms. [Preview Abstract] |
Friday, May 2, 2014 2:12PM - 2:24PM |
C1.00003: Small harmonically trapped $N$-boson system at unitarity: Transition from $N$-body ``Efimov'' droplet to normal gas Yangqian Yan, D. Blume Using the path integral Monte Carlo technique, we study the temperature dependence of small harmonically trapped Bose systems at unitarity. At low temperature, the system behaves like a $N$-body liquid droplet whose properties are tied to Efimov trimers. At high temperature, the system behaves like a gas consisting of Boltzmann particles. We observe a sharp phase-transition-like change from the droplet to the gas state in the intermediate temperature region. The energy, specific heat, and hyperradial distribution function are monitored as the system evolves from the liquid to the gas state. The connection of the phase-transition-like feature with Efimov physics will be discussed. A simple one-parameter model yields good agreement with the path integral simulation results for the entire temperature region. We use this model to predict the transition temperature for the unitary Bose gas with large number of particles. [Preview Abstract] |
Friday, May 2, 2014 2:24PM - 2:36PM |
C1.00004: Effective and intrinsic three-body interactions in ultracold harmonically-trapped few-atom systems X.Y. Yin, D. Blume, P.R. Johnson, E. Tiesinga We derive the ground state energy for a small number of ultracold atoms in an isotropic harmonic trap using quantum field theory. Atoms are assumed to interact through pairwise energy-independent and energy-dependent delta-function potentials with strengths proportional to the scattering length $a_s$ and effective-range volume $V_\textrm{eff}$, respectively. Additionally, an intrinsic three-body potential with strength proportional to $g_3^{(0)}$ is accounted for. The calculations are performed systematically up to order $(a_\textrm{ho})^{-4}$, where $a_\textrm{ho}$ denotes the harmonic oscillator length. Effective-range volume dependent energy contributions are calculated up to order $(a_\textrm{ho})^{-5}$. We explain how our effective field theoretical results can be, if combined with independent energy calculations or measurements, used to obtain the renormalization scheme independent three-body contribution. The need for three-body counter-term interactions is discussed in the context of the effective-range volume dependent effective interactions. [Preview Abstract] |
Friday, May 2, 2014 2:36PM - 2:48PM |
C1.00005: Tunneling dynamics of two interacting one-dimensional particles Seyed Ebrahim Gharashi, D. Blume Motivated by recent cold atom experiments, the time evolution of two one-dimensional particles with attractive or repulsive short-range interaction is considered. We treat a realistic trapping potential that consists of an approximately harmonic optical trap plus a linear magnetic field gradient. This provides an ``inside region,'' where the particles are trapped, and an ``outside region,'' where the particles are free. When the barrier, which separates the two regions, is high enough, tunneling is suppressed. When the barrier is lowered, the time evolution of the system results in the loss of atoms from the trap. We find that pair tunneling dominates for strongly attractive interactions, while single-particle tunneling dominates for weak interactions. [Preview Abstract] |
Friday, May 2, 2014 2:48PM - 3:00PM |
C1.00006: Energy spectrum of harmonically trapped two-atom system with spin-orbit and Raman coupling Q. Guan, X.Y. Yin, Seyed Ebrahim Gharashi, D. Blume Ultracold atomic gases provide a novel platform with which to study spin-orbit coupling, a mechanism that plays a central role in the nuclear shell model, atomic fine structure and two-dimensional electron gases. This paper introduces a theoretical framework that allows for the efficient determination of the eigenenergies and eigenstates of a harmonically trapped two-atom system with short-range interaction subject to an equal mixture of Rashba and Dresselhaus spin-orbit coupling as well as Raman coupling. Energy spectra for experimentally relevant parameter combinations are presented and future extensions of the approach are discussed. [Preview Abstract] |
Friday, May 2, 2014 3:00PM - 3:15PM |
C1.00007: Break |
Friday, May 2, 2014 3:15PM - 3:45PM |
C1.00008: Quantum Mechanics: A Love Story Invited Speaker: Maximilian Schlosshauer Physicist Steven Weinberg once said, ``After you learn quantum mechanics, you're never really the same again.'' I became a physicist because of quantum mechanics. In this talk, I will tell you how I try to get to the bottom of what is so intriguing (and perhaps puzzling) about quantum mechanics. In particular, I will tell you about a new result that shows that whenever you jointly consider a pair of quantum systems, the whole is different from the sum of the parts. If there's time, I'll also mention experiments I have recently set up that vividly demonstrate phenomena at the heart of quantum mechanics. These are experiments that undergraduate students, and even a clumsy theoretical physicist like myself, can build on a shoestring budget. [Preview Abstract] |
Friday, May 2, 2014 3:45PM - 3:57PM |
C1.00009: Trapping Ions in a 2-pi Parabolic Mirror Chen-Kuan Chou, Gang Shu, Boris Blinov Trapped ion qubit is an excellent candidate for quantum computation and information due to its low decoherence, ease of control and detection, and ability to couple to a photon. Efficient coupling between ions and resonant photons is crucial for ion-photon and remote-ion entanglement protocols. We describe operation of an RF ion trap in which a reflective parabolic surface serves as the trap's electrodes. This parabolic mirror covers a solid angle of approximately 2 Pi around the trapped ion, while a movable needle electrode allows precise ion placement at the focal point of the parabola. We measured approximately 40{\%} solid angle fluorescence collection from a single Ba$+$ ion with this setup, with an image spot size of about twice the diffraction limit. Progress on image correction and fiber coupling will be reported. [Preview Abstract] |
Friday, May 2, 2014 3:57PM - 4:09PM |
C1.00010: Sympathetic Cooling and Reordering in Multiple Trapped Ion Species Chains John Wright, Tomasz Sakrejda, Richard Graham, Zichao Zhou, Boris Blinov Using multiple ion species allows ion-based quantum computing projects to overcome limitations of addressability and cooling in long ion chains. Namely, a single ion species would be used for quantum operations, while the other would be devoted to cooling of the entire chain. The cooling species are interspersed among the qubit ions to enable more efficient cooling while making individual addressing of the qubit ions easier. We attempt to measure and explore the effect of ion species ordering on the efficiency of the resultant cooling. Initially, the energy of spontaneous ion reordering is approximated via classical simulations. Then, the axial temperature and heating rate can be determined by measuring the time required for different length chains to reorder. Initial, approximate heating rates and work towards measuring ion species reordering effects are presented. [Preview Abstract] |
Friday, May 2, 2014 4:09PM - 4:21PM |
C1.00011: High sensitivity magnetometry with Cs vapor Rujie Li, Jiancheng Fang, Wei Quan Spin-exchange relaxation free(SERF) magnetometry based on potassium has breakdown the magnetic field sensitivity record previously kept by the superconducting quantum interference devices (SQUIDs). We describe a Cs atomic magnetometer also operating in SERF regime. Utilizing a 20$\times$20$\times$20 mm vapor cell with a relative low temperature of 106 $^{\circ}$C, we achieve the resonance linewidths 2.703Hz corresponding to an electron spin-exchange rate of 357 s$^{-1}$, and demonstrate magnetic field sensitivity of 8 fT/Hz1/2 in a single channel, as shown in fig. 1. Theoretical analysis shows that fundamental sensitivity limits of this device with a 1 cm$^3$ volume could approach 0.2 fT/Hz1/2. Taking advantage of the higher saturated vapor pressure, Cs magnetometry is particularly appropriate for lower temperatures applications. [Preview Abstract] |
Friday, May 2, 2014 4:21PM - 4:33PM |
C1.00012: Empirical Method for Measuring the Photon Scattering Rate in a Magneto-Optical Trap James Booth, Kais Jooya, Fumiei Kobayashi, Nam Musterer, Kirk Madison We have recently demonstrated an empirical technique for determining the photon scattering rate of atoms in a magneto-optical trap (MOT) [1]. This method provides a way to measure the \textit{in-situ} saturation parameter experienced by the atoms in the trap, and, as a result, to more accurately determine the atom number and the excited state fraction in the MOT. To validate the technique, we compared the atom number extracted from fluorescence measurements (which rely on the scattering rate) to an independent atom number measurement based on the absorption of an optical pumping beam. Minor deviations observed from the predictions of the generally accepted two-level atom model of light scattering led us to extend the standard analysis by describing the atoms as four-level systems. This approach incorporates the effects of the repump laser on the scattering rate and provides a better description of the observed fluorescence. The main advantage of the new technique is that it provides a straightforward, empirical method for determining the photon scattering rate of atoms in a MOT, therefore improving the atom number measurement accuracy from the fluorescence readings. \\[4pt] [1] K. Jooya, N. Musterer, K. W. Madison, and J. L. Booth, Phys. Rev. A \textbf{88}, 063401 (2013) [Preview Abstract] |
Friday, May 2, 2014 4:33PM - 4:45PM |
C1.00013: Charge Transfer Processes between H/D and Small Molecular Ions K.G. Bacani, S.L. Heczko, R.A. Strom, V.M. Andrianarijaona, D.G. Seely, C.C. Havener Charge transfer on molecule proceeds through dynamically coupled electronic, vibrational, and rotational degrees of freedom. The inelastic vibrational processes, which go along with the reaction, can be experimentally investigated by using H/D systems, which do not allow multi-electron capture. Using the upgraded ion-atom merged-beams apparatus at Oak Ridge National Laboratory, absolute direct charge transfer cross sections for H$_{2}^{+}$ , D$_{2}^{+}$, CO$^{+}$, O$_{2}^{+}$ , and H$_{3}^{+}$ are measured from keV/u collision energies where the collision is considered ``ro-vibrationally frozen'' to few eV/u energies where collision times are long enough to sample vibrational modes. The measurements presented here benchmark high energy theory and vibrationally specific adiabatic theory (Phys. Rev. A \textbf{84}, 062716, 2011).\\[4pt] Research supported by the NASA Solar {\&} Heliospheric Physics Program NNH07ZDA001N, the Office of Fusion Energy Sciences and Division of Chemical Sciences, Geosciences, and Biosciences, the Office of Basic Energy Sciences of the US Department of Energy. VA et al. is supported by the National Science Foundation through Grant No. PHY-106887. [Preview Abstract] |
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