Bulletin of the American Physical Society
81st Annual Meeting of the APS Southeastern Section
Volume 59, Number 18
Wednesday–Saturday, November 12–15, 2014; Columbia, South Carolina
Session DB: Atomic, Molecular and Optical Physics II |
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Chair: John Yukich, Davidson College Room: Richland I |
Thursday, November 13, 2014 1:15PM - 1:51PM |
DB.00001: Atom Interferometry using Bose-Einstein condensates on Earth and in Space Invited Speaker: C.A. Sackett Atom interferometry is a precision measurement technique in which a quantum mechanical wave function for a particle is split into two or more parts that are separated in space. At a later time, the parts are recombined, with a result that depends on the quantum phase evolution along the different trajectories taken. This phase is sensitive to environmental effects, and it is particularly well suited to measure inertial effects like gravity or rotation. These measurements are potentially useful for inertial navigation, mineral exploration, and other applications. Terrestrial experiments have used atom interferometry to demonstrate sensing with record-breaking precision and accuracy, but the usable measurement time is limited by the particles falling in gravity. This problem is avoided in the microgravity environment of near-earth orbit, making it an ideal platform to pursue even higher precision. The application to inertial navigation is also important in space, where external navigation markers are often unavailable. The recent approval of the Cold Atom Lab aboard the International Space Station will allow preliminary tests of atom interferometry in space, using a Bose-Einstein condensate of atoms at nearly zero temperature. We will discuss the challenges and opportunities this presents. We will also describe ground-based efforts to simulate the effect of microgravity so as to improve interferometer performance. [Preview Abstract] |
Thursday, November 13, 2014 1:51PM - 2:03PM |
DB.00002: Estimation of quantum effects in atomic solids using quantum trajectory dynamics with dissipation Bing Gu, Vitaly Rassolov, Sophya Garashchuk We are interested in nuclear quantum-mechanical effects in atomic solids such as helium and para-hydrogen at low temperature. The ground state of these systems is characterized by large zero-point motion of atoms bound to their crystal cites. To make estimates of the zero-point energy (ZPE) given the anharmonicity of the potential and a typical system size of hundreds of atoms, we are developing a methodology based on the quantum trajectories evolving with dissipation. The nuclear wavefunction is represented by an ensemble of quantum trajectories evolving according to the Newtonian equations of motion under the combined influence of the external force, quantum force and friction force [1]. The external potential for solid helium-4 is computed summing up pairwise interactions, and its computation is distributed over multiple ores using Message Passing Interface. The simulation cell for solid helium, which is a $5 \times 3 \times 3$ unit cell in the hexagonal close pack (HCP) form, consists of 180 helium atoms described in Cartesian space i.e. 540 degrees of freedom. The estimated ZPE is estimated from the dynamics of 19200 trajectories. The quantum trajectory dynamics approach will be further used to study a spectrum of chlorine atom trapped in solid He matrices. [Preview Abstract] |
Thursday, November 13, 2014 2:03PM - 2:15PM |
DB.00003: Measurement of Hydrogen Balmer Series Self Absorption in Air Plasma Produced by Laser Induced Optical Breakdown Ghaneshwar Gautam, Christian Parigger Optical breakdown is induced by using Nd:YAG laser radiation. Spatially and temporally resolved spectra are collected with and without a doubling mirror by employing a Czerny-Turner spectrometer and an ICCD camera. The extent of self-absorption of the hydrogen Balmer alpha and beta lines is investigated for various time delays from plasma generation. The electron density is also determined from N$^{+}$ lines and compared with values obtained from the hydrogen Balmer series lines to further evaluate self-absorption. [Preview Abstract] |
Thursday, November 13, 2014 2:15PM - 2:27PM |
DB.00004: Molecular Dynamics of Large Systems with Quantum Corrections for Selected Nuclei Sophya Garashchuk The classical dynamics of nuclei is adequate in many situations, providing insight into chemical processes. Yet it is well-known that quantum features of nuclear behavior -- the zero-point energy, tunneling and nonadiabatic dynamics -- are sometimes important. We are interested in the regime when quantum-mechanical (QM) behavior of nuclei of a few selected bonds modestly affects reactivity while the full QM treatment is unfeasible due to exponential scaling of numerical cost with the system size for the conventional methods. To make qualitative predictions and cheap estimates of the nuclear QM effects we are developing approximate dynamics based on the quantum trajectory (QT) formulation of the Schrodinger equation. The QM effects are incorporated through the quantum potential, computed in the ``mean-field'' approximation, acting on the trajectory ensemble in addition to the classical potential. Large molecular systems are described in a mixed quantum/classical QT framework with the QM correction incorporated into selected degrees of freedom. The approach is applied to study adsorption of quantum hydrogen colliding with the graphene model, C37H15. [Preview Abstract] |
Thursday, November 13, 2014 2:27PM - 2:39PM |
DB.00005: Spatially and Temporally Resolved Aluminum Laser-Induced Breakdown Spectroscopy Measurements David Surmick, Christian Parigger Laser-induced breakdown spectroscopy measurements of a laser ablated aluminum sample are analyzed to determine the temporal evolution of aluminum containing plasma from atomic and molecular emissions. These studies facilitate the understanding of key characteristics of plasma/metal interactions. Optical breakdown is initiated by tightly focusing 12 nanosecond pulsed laser radiation onto the surface of an aluminum alloy target. Spatially and temporally resolved emission spectra are recorded with an ICCD. Aluminum atomic emissions at 396.15 and 394.4 nm are used to infer the electron density of the plasma from 0.2 to 1 $\mu $s following optical breakdown. At corresponding time delays, the plasma temperature is determined from aluminum 308.24, 309.27, 394.4 and 396.15 nm emissions using Boltzmann plot methods. At later times, from 4 to 20 $\mu $s following breakdown, atomic hydrogen Balmer series H$_{\mathrm{\alpha }}$ and H$_{\mathrm{\beta }}$ emissions are used to evaluate the electron density. The plasma temperature is further compared with results from fitting to aluminum monoxide emissions superimposed with H$_{\mathrm{\beta}}$ spectra that are recorded for time delays longer than 10 $\mu $s after optical breakdown. [Preview Abstract] |
Thursday, November 13, 2014 2:39PM - 2:51PM |
DB.00006: A Dynamically Correlated, Strongly Orthogonal, Geminal Method Without Strong Orthogonality or the Double Counting Error Brett Cagg, Vitaly Rassolov The electron correlation problem poses a significant challenge to theorists. While Hartree-Fock theory has traditionally been recognized as the foundation of computational chemistry, it suffers from an insufficient description of correlated electron motion coupled with the assumption of a single configurational, ground state wavefunction. While the remedy to both of these deficiencies is known, and is realized in the full configuration interaction method, the computational expense incurred in resolving these issues makes the exact method impractical. Thus, the most successful computational methods attempt to correct these issues without incurring undue expense. A recently developed, variationally optimized, spin-unrestricted computational method based on strongly orthogonal geminals, called USSG, accounts for most multiconfigurational correlation effects in a computationally inexpensive and well-defined manner. Unfortunately, due to the form of the wavefunction, USSG still lacks a proper description of correlated electronic motion. While the multiconfigurational correlation is certainly the most computationally difficult form of correlation to incorporate, care must be taken to properly account for the missing correlation effects without double counting those already covered in USSG. Corrections developed to account for two separate portions of missing correlation in the USSG method are presented, and the effect of these corrections on dissociation energy prediction for 38 diatomic molecules are discussed. [Preview Abstract] |
Thursday, November 13, 2014 2:51PM - 3:03PM |
DB.00007: The calculation of few-body van der Waals interactions Jianing Han, Chunyan Hu Few-body interactions offer the opportunity to study the isolated atom to few-body coupled molecules, and to condensed matter transitions. Atoms in molecules and in condensed matters are coupled by different orders of multipole-multipole interactions, which all stem from different orders of approximations from coulomb interactions between multiple charges. The lowest order multipole-multipole interaction is the dipole-dipole interaction, which is proportional to the size of the dipole. In this article, we use Rydberg atoms, which have more than 1000 times greater electric dipoles than the ground state atoms, to calculation the few-body interactions. In addition to the large dipoles, the kinetic energy of the atoms is significantly reduced by reducing the temperature, which makes these interactions stable and observable. Here we report on the 2D and 3D few-body interaction potentials and possible ways of creating semistable molecules in such an ultracold Rydberg gas with a temperature of $\approx$ 100 nK. The results reported here are useful for creating ultracold molecules. [Preview Abstract] |
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