Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session J33: Few-body and Cold Molecule Physics |
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Sponsoring Units: DAMOP Chair: Hanns-Christoph Nagerl, University of Innsbruck Room: 706 |
Tuesday, March 4, 2014 2:30PM - 2:42PM |
J33.00001: Manipulation of p-wave scattering of cold atoms in low dimensions using the magnetic field vector Shi-Guo Peng, Shina Tan, Kaijun Jiang It is well known that the magnetic Feshbach resonances of cold atoms are sensitive to the magnitude of the external magnetic field. Much less attention has been paid to the \textit{direction} of such a field. In this work we calculate the scattering properties of spin polarized fermionic atoms in reduced dimensions, near a $p$-wave Feshbach resonance. Because of spatial anisotropy of the $p$-wave interaction, the scattering has nontrivial dependence on both the magnitude and the direction of the magnetic field. In addition, we identify an inelastic scattering process which is impossible in the isotropic-interaction model; the rate of this process depends considerably on the direction of the magnetic field. Significantly, an EPR entangled pair of identical fermions may be produced during this inelastic collision. This work opens a new method to manipulate resonant cold atomic interactions. [Preview Abstract] |
Tuesday, March 4, 2014 2:42PM - 2:54PM |
J33.00002: Pairing of few Fermi atoms in one dimension Pino D'Amico, Massimo Rontani Experimental advances allow us to confine a chosen number of few quantum degenerate Li6 atoms in a trap with unit precision down to the empty-trap limit. The Heidelberg group recently observed an even-odd oscillation of the ``ionization'' energy required to subtract an atom from a one-dimensional trap in the presence of moderate attractive interactions, which was attributed to pairing [PRL 111, 175302 (2013)]. Naively, one would expect pairing to be strongly suppressed in one dimension, due to the lack of orbital degeneracies. Here we address theoretically the pairing behavior of a few Fermi atoms in a one-dimensional harmonic trap through the exact diagonalization of the fully interacting Hamiltonian. From the analysis of exact ground- and excited-state energies and wave functions we extract both the pairing gap and the Cooper pair size, reproducing the observed even-odd behavior. Our results demonstrate that pairing in one dimension is a strongly cooperative effect that significantly deviates from the behavior predicted by perturbation theory at interaction strengths within experimental reach. [Preview Abstract] |
Tuesday, March 4, 2014 2:54PM - 3:06PM |
J33.00003: Efimov physics in an ultracold Bose-Fermi gas of ~${ }^{40}K$ and ${ }^{87}Rb$ atoms Ming-Guang Hu, Ruth Bloom, Tyler Cumby, George Kotula, Deborah Jin We present measurements of Efimov physics in an ultracold Bose-Fermi gas of ${ }^{40}K$and ${ }^{87}Rb$ atoms near an interspecies Feshbach resonance. ~In particular, we measure loss rate coefficients for the trapped gas and find a resonance in the inelastic collisions of Feshbach molecules with~${ }^{87}Rb$ atoms.~However, we do not observe any E?mov-related resonances in the rates of inelastic collisions between three atoms.~ [Preview Abstract] |
Tuesday, March 4, 2014 3:06PM - 3:18PM |
J33.00004: High fidelity pseudopotentials for ultracold atomic gases Pascal Bugnion, Gareth Conduit, Richard Needs An accurate computational description of ultracold atoms interacting with effective repulsive interactions has proved elusive. Previous computational work has either used a truly repulsive potential (most often, a hard sphere potential), which fails to recover the very short-range nature of the interactions, or the excited states of an attractive potential. In this presentation, we propose a new pseudopotential, inspired by those used in electronic structure work. This potential is carefully tuned to recover the correct scattering length and effective range for a broad range of atomic energies, and does not have an undesirable bound state. This will greatly facilitate quantum Monte-Carlo and exact diagonalization simulations of cold atoms. We have used this potential to study the zero-temperature phase diagram of ultracold atomic gases at $k_Fa \ge 0$, obtaining accurate values for the ferromagnetic phase transition at different polarizations. [Preview Abstract] |
Tuesday, March 4, 2014 3:18PM - 3:30PM |
J33.00005: Universality in $s$-wave and higher partial wave Feshbach resonances: an illustration with a single atom near two scattering centers Shangguo Zhu, Shina Tan It is well-known that cold atoms near $s$-wave Feshbach resonances have universal properties that are insensitive to the short-range details of the interaction. What is less known is that atoms near higher partial wave Feshbach resonances also have remarkable universal properties. We will illustrate this with a single atom interacting resonantly with two fixed static centers. At a Feshbach resonance point with orbital angular momentum $L\ge1$, we find $2L+1$ shallow bound states whose energies behave like $1/R^{2L+1}$ when the distance $R$ between the two centers is large. This sheds additional light on the fundamental question whether Efimov effect exists for higher partial wave resonances. The effects of nonresonant partial-wave channels and the shape parameters in the effective range expansions enter as correction terms. Near $p$-wave and higher partial wave resonances, the energies can be described by a simple universal formula in terms of a parameter called ``proximity parameter.'' We will also discuss modifications of the low energy physics due to the long range Van der Waals potential. [Preview Abstract] |
Tuesday, March 4, 2014 3:30PM - 3:42PM |
J33.00006: Averaged collision and reaction rates in a two-species gas of ultracold fermions Alexander Pikovski Reactive or elastic two-body collisions in an ultracold gas are affected by quantum statistics. We study ensemble-averaged collision rates for a two-species fermionic gas, where the two species may have different masses, densities, and temperatures. It is shown in what way Fermi-averaged collision rates deviate from Boltzmann-averaged ones, particularly for a gas with strong imbalance of masses or densities. The results are independent of the details of the collision process. [Preview Abstract] |
Tuesday, March 4, 2014 3:42PM - 3:54PM |
J33.00007: A two-dimensional pseudospectral multi-configuration Hartree-Fock method for low-Z atoms in intense magnetic fields Anand Thirumalai, Kevin Schmidt, Steven Desch, Patrick Young We present here the very first two-dimensional multi-configuration Hartree-Fock studies of low-Z atoms in intense magnetic fields. The first few low-lying states are calculated in this study. The method described herein is applicable to calculations of atomic structure in magnetic fields of arbitrary strength as it exploits the natural symmetries of the problem without assumptions of any basis functions for expressing the wave functions of the electrons, or the commonly employed adiabatic approximation. A pseudospectral formulation is employed which affords considerable computational speed-up and the results obtained here are significant improvements upon earlier pseudospectral single-configuration calculations and are consistent with findings elsewhere. We also present new data for some of the states of the low-Z atoms considered here. [Preview Abstract] |
Tuesday, March 4, 2014 3:54PM - 4:06PM |
J33.00008: Hyperfine structure of OH molecules in electric and magnetic fields Kenji Maeda, Michael L. Wall, Lincoln D. Carr Ultracold polar molecules offer a unique opportunity in table-top experiments to study quantum phenomena originating from strong dipole-dipole interactions and incorporating internal degrees of freedom controllable by external electric and magnetic fields. Recently, a gas of OH molecules was evaporatively cooled at JILA to milliKelvin temperatures. However, in the presence of electric and magnetic fields, the energy spectra of OH were calculated only to energy scales of mK, far from the sub-microKelvin temperatures at which OH molecules will become quantum degenerate. We investigate single-particle energy spectra of the OH radical in the lowest rovibrational and electric ground states under combined electric and magnetic fields. In addition to the fine-structure interactions, the hyperfine interactions and centrifugal distortion effects are taken into account, yielding the zero-field spectrum of the lowest ${}^2\Pi_{3/2}$ manifold to an accuracy of less than 2kHz$\sim$100nK. We also examine level crossings and repulsions in hyperfine structures induced by applied electric and magnetic fields. We will mention many-body applications of ultracold OH molecules to simulate quantum dipolar systems. [Preview Abstract] |
Tuesday, March 4, 2014 4:06PM - 4:18PM |
J33.00009: Efimov trimers under confinement: From discrete to continuous scaling symmetry Jesper Levinsen, Pietro Massignan, Meera Parish The effect of dimensionality and confinement on the interactions between particles is key to understanding the behaviour of many quantum systems. Classic examples range from the fractional quantum Hall effect and high temperature superconductivity to the adsorption of molecules on a surface. As a general rule, one expects confinement to favour the binding of particles. However, attractively interacting bosons apparently defy this expectation: while three identical bosons in three dimensions can support an infinite tower of Efimov trimers, only two universal trimers exist in the two dimensional (2D) case. Here we reveal how these two limits are connected by investigating the problem of three bosons confined by a harmonic potential along one direction. We show that the confinement breaks the discrete Efimov scaling symmetry and destroys the weakest bound trimers. However, the deepest bound Efimov trimer persists under strong confinement and hybridizes with the quasi-two-dimensional trimers, yielding a superposition of trimer configurations that effectively involves tunnelling through a short-range repulsive barrier. Our results have immediate impact on the ongoing efforts to observe Efimov scaling in an ultracold atomic gas. [Preview Abstract] |
Tuesday, March 4, 2014 4:18PM - 4:30PM |
J33.00010: Tunneling and two particle interference with laser cooled bosons in optical tweezers Adam Kaufman, Brian Lester, Collin Reynolds, Cindy Regal We report on experiments realizing coherent tunneling of laser cooled atoms between precisely tunable optical tweezers. To verify the degree of indistinguishability achieved via laser cooling, we perform Hong-Ou-Mandel interferometry of massive bosons in tunnel-coupled tweezers. This marks the first direct observation of quantum indistinguishability with independently prepared laser cooled atoms. Our results demonstrate the viability of the tweezer plus laser cooling platform for studying few-body systems in the quantum regime, with highly tunable parameters of tunneling and interaction. [Preview Abstract] |
Tuesday, March 4, 2014 4:30PM - 4:42PM |
J33.00011: Using STM tip as electrochemical sensor for the characterization of bond vibration frequencies of a chemical analyte Shuai Chang, Chaitanya Gupta, Roger Howe Traditional electrochemical interfaces are comprised of an electrically biased electrode-electrolyte interface, where charge exchange occurs between electronic energy levels of the electrode and a redox-active ion in the electrolyte. Much of the recent progress in electrochemical sensing technology has focused on enhancing the detection limit of such sensing platforms. However, much of the molecular-level chemical information describing the non-redox active species that may also be present in the electrolyte, which is encoded in the acquired current/voltage signal, is lost as background information. In this talk, a design methodology is proposed for electrochemical interfaces that are engineered from STM tips specifically to transduce information about the intra-molecular bond vibrational frequencies of non-redox active molecular analytes. A quantum statistical model of a generalized charge transfer process, developed by the authors, will be presented as the underpinning for the design method. Minimization of electronic and nuclear entropy will be derived from the presented model, as the necessary condition required for resolving vibrational frequency information, and we will also describe select experimental strategies that may be implemented for total entropy minimization. [Preview Abstract] |
Tuesday, March 4, 2014 4:42PM - 4:54PM |
J33.00012: Electron Energy Deposition in Fast-Shock Ignition Seyed Abolfazl Ghasemi, Amir Hossein Farahbod Calculations of fast electrons penetration and energy stopping power in dense fuel show that about 25{\%} of the initial electron energy effectively reaches to the central part of the fuel if the initial electron energy is of the order $\sim$6.5 MeV. To evaluate more realistically the performance of FSI approach, we have used a quasi-two temperature electron energy distribution function of Strozzi (2012) and fast ignitor energy formula of Bellei (2013) that are consistent with 3D PIC simulations. In terms of figure of merit and for fuel mass \textgreater 1 mg, the general advantages of fast-shock ignition in comparison with shock ignition can be estimated to be better than 1.3. [Preview Abstract] |
Tuesday, March 4, 2014 4:54PM - 5:06PM |
J33.00013: Testing excited-state energy-density functionals and potentials with the ionization potential theorem Manoj Harbola, Hemanadhan Myneni, Shamim Md. The modified local spin density functional and the related local potential for excited-states are tested by employing the ionization potential theorem. The functional is constructed [1] by splitting k-space. Since its functional derivative cannot be obtained easily, the corresponding potential is given by analogy to its ground-state counterpart. Further, to calculate the highest occupied orbital energy $\epsilon_{max}$ accurately, the potential is corrected for its asymptotic behavior by employing the van Leeuwen-Barends correction [2] to it. The highest occupied orbital energy $\epsilon_{max}$ thus obtained is then compared with the $\Delta$SCF ionization energy calculated using the excited-state functional. It is shown that the two match quite accurately, demonstrating thereby that our approach of constructing excited-state functional is on sound footing. \\[4pt] [1] P. Samal and M.K. Harbola, J. Phys. B: At. Mol. Opt. Phys. 39, 4065 (2006); M. Hemanadhan and M.K. Harbola, J. Mol. Struct. Theochem \textbf{943}, 152 (2010).\\[0pt] [2] R. van Leeuwen and E.J. Baerends, Phys. Rev. A \textbf{49}, 2421 (1994). [Preview Abstract] |
Tuesday, March 4, 2014 5:06PM - 5:18PM |
J33.00014: ABSTRACT WITHDRAWN |
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