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 C5: Anti-Matter, Ion Traps, and New Experimental Techniques |
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Chair: T. Walker, University of Wisconsin Room: TELUS Convention Centre Glen 205 |
Wednesday, June 6, 2007 1:30PM - 1:42PM |
C5.00001: Measurement of the Decay Rate of the Negative Ion of Positronium (Ps$^-$) G. Gwinner, F. Fleischer, K. Degreif, M. Lestinsky, F. Plenge, D. Schwalm, V. Liechtenstein Consisting of two electrons and a positron, the negative ion of positronium (Ps $^-$) represents the simplest three-body system with a bound state. Its constituents are stable, point-like particles, and it is essentially free from perturbations by strong interaction effects. Together with the rather unique mass ratio, these properties make the positronium ion an interesting object for studying the quantum-mechanical three- body problem. We present a new determination of the decay rate, using a beam-foil method and a stripping-based detection technique. The measured value of $\Gamma = 2.089 (15)$ /ns is a factor of six more precise than the previous experimental result, and there is excellent agreement both with the latter and with the theoretical value. [Preview Abstract] |
Wednesday, June 6, 2007 1:42PM - 1:54PM |
C5.00002: Excited, Resonant, and Unnatural Parity States of Positronic Atoms and Ions Michael W.J. Bromley, Jim Mitroy, Kalman Varga Calculations have demonstrated that 11 neutral atoms can bind positrons. We report on configuration interaction (CI) calculations that have demonstrated the existence of a $^2$P$^o$ excited state of $e^+$Ca, which consists predominantly of a positronium (Ps) cluster orbiting the Ca$^+$ ion in the $L=1$ partial wave [1]. This raises the possibility of detecting the formation of positronic bound states by an optical transition to the ground ($^2$S$^e$) $e^+$Ca state. The $e^+$Mg system is shown to lack an equivalent excited state, however, by extracting phase shifts from CI pseudostate energy shifts, we show that the system has a low-energy $p$ shape resonance [2]. Finally, CI and stochastic variational method calculations of annihilation suppressed, unnatural parity $^{2,4}S^{o}$, states of PsH, LiPs, NaPs and KPs are reported [3,4]. The LiPs system being Borromean in nature. \\ $[1]$ M.W.J.Bromley and J.Mitroy Phys.~Rev.~Lett. \textbf{97} 183402 (2006) \\ $[2]$ J.Mitroy and M.W.J.Bromley Phys.~Rev. (under review)\\ $[3]$ J.Mitroy and M.W.J.Bromley Phys.~Rev.~Lett. (in press)\\ $[4]$ M.W.J.Bromley, J.Mitroy and K.Varga Phys.~Rev.~A (in preparation) [Preview Abstract] |
Wednesday, June 6, 2007 1:54PM - 2:06PM |
C5.00003: Positron Direct Annihilation in Positron-Hydrogen Colliding Systems Chi Yu Hu, Sergey Yakovlev Recent advances in theory enables the calculation of positron direct annihilation uniformly both above and below the positronium formation threshold. The direct annihilation cross section is separated out analytically in terms of various scattering amplitudes. We report and compare our new results with numerous existing calculations below the PS formation threshold. The agreement is within 1\%. Above the PS formation threshold, the annihilation cross sections are relatively smooth except at the onset of the Feshbach resonances. Resonant-like annihilation peaks are found near all the Feshbach resonances studied so far. [Preview Abstract] |
Wednesday, June 6, 2007 2:06PM - 2:18PM |
C5.00004: Traps for Antimatter: The ALPHA Antihydrogen Apparatus R. Hydomako, R.I. Thompson, M.C. Fujiwara, D.R. Gill, L. Kurchaninov, K. Olchanski, A. Olin, J.W. Storey, W.N. Hardy, D.J. Jones, M.E. Hayden, H. Malik, S. Menary Antihydrogen is the simplest atomic system composed entirely of antiparticles. Analogous to hydrogen, antihydrogen contains a positron and an antiproton. The creation and storage of antihydrogen is a challenge that combines the technologies of ion trapping (nested Penning traps to accumulate and mix the positrons and antiprotons) and atom trapping (a magnetic bottle to confine the antihydrogen atoms) with the difficulties associated with working in a particle accelerator facility. The ALPHA project is an international collaboration based at CERN's Antiproton Decelerator. ALPHA has constructed an innovative and versatile apparatus with the goal of trapping antihydrogen atoms. This talk will describe the ALPHA apparatus and its operation. Results will be given from the first run, including antihydrogen production and the storage of antimatter plasmas in the multipole trap [1]. [1] G. Andresen \textit{et al}. (ALPHA Collaboration) \textit{Phys. Rev. Lett.} \textbf{98}, 023402 (2007). [Preview Abstract] |
Wednesday, June 6, 2007 2:18PM - 2:30PM |
C5.00005: A Cooler Trap for the TITAN On-line Trapping Facility at TRIUMF G. Gwinner, Z. Ke, W. Shi, S. Toews, J. Dilling, V. Ryjkov The TITAN ion trap facility currently under construction at TRIUMF's ISAC will provide for the first time highly charged radioactive ions for precision mass measurements. Highly charged ions (HCI) extracted from the EBIT charge breeder will likely have a temperature of tens of eV/charge or more, too high for direct injection into the precision Penning trap mass spectrometer. We are currently developing an intermediate Penning cooler trap to pre-cool the HCI prior to the mass measurement. One possible route is electron cooling, where the HCI interact with a cloud of electrons, which self-cool via the emission of synchrotron radiation in the strong magnetic field of the Penning trap; another possibility is sympathetic cooling with initially cold protons provided by a cold ion source. We will present simulations of the cooling process, including the potentially detrimental effects of radiative, dielectronic, and three-body recombination. We will also present our preliminary design for a cooler Penning trap which can accommodate both electron and proton cooling. [Preview Abstract] |
Wednesday, June 6, 2007 2:30PM - 2:42PM |
C5.00006: Photoionization loading of barium ion traps. Adam Steele, Layne Churchill, Paul Griffin, Michael Chapman We demonstrate a simple and effective technique for photoionization loading barium ions into a linear trap. Photoionization allows isotope selectivity, greater loading efficiency, and eliminates the charging of insulators in the trapping region, typical of electron impact ionization. Two-step photo-ionization of barium is accomplished using an intercombination line in neutral barium ($ 5s2 {}^1S_0 \rightarrow 6s6p {}^3P_1, \lambda = 791$ nm ) followed by excitation above the ionization threshold using a nitrogen gas laser ($ \lambda = 337$ nm). Isotopic selectivity is achieved by near doppler-free excitation of the triplet $6s6p {}^3P_1$ state. Application of the technique to a barium ion-trap cavity QED experiment will be discussed. [Preview Abstract] |
Wednesday, June 6, 2007 2:42PM - 2:54PM |
C5.00007: The Development of a Passive Electrostatic Electron Recycling System (ERS). David Tessier, Ying Niu, Dominic Seccombe, Timothy Reddish, Aaron Alderman, Ben Birdsey, Peter Hammond, Frank Read The development of a completely new type of electron spectrometer, an ``Electron Recycling Spectrometer'' (ERS) is described in which low energy ($<\sim $50 eV) electrons are passively stored in a `desktop' sized ring. The orbital path for the electrons is 0.65 m long with a race-track geometry and is defined through the application of design voltages to two series of cylindrical electrostatic lenses inserted between two identical hemispherical deflector analyzers. The ERS design concept exploits the very low scattering cross sections in electron-molecule collisions, where the majority of electrons do not interact with the gaseous target. Unscattered electrons are collected, passed back through the ERS for another collision opportunity in the interaction region - i.e. they are ``recycled'' so that each electron generated in the electron source may undertake multiple passes through the interaction region. Initial results will be presented which demonstrate that the electron beam undergoes up to $\sim $1000 orbits in a time of $\sim $250 $\mu $s. The design of the system is likely to enable the storage at low kinetic energy of any type of non-relativistic charged particle, including positrons, polarized electrons, and positive {\&} negative ions. [Preview Abstract] |
Wednesday, June 6, 2007 2:54PM - 3:06PM |
C5.00008: A miniature differential atomic magnetometer based on a diverging laser beam Eleanor Hodby, Elizabeth Donley, John Kitching We demonstrate a novel atomic magnetometer that uses differential detection of the spatially diverging components of a light field to monitor the Larmor precession frequency of atoms in a thermal vapor [1]. The design is implemented in compact form with a micromachined alkali vapor cell and a naturally divergent light field emitted by a vertical cavity surface emitting laser, which serves to both optically pump the atoms and measure the transverse polarization. The size of the core physics assembly is $<$ 1cm$^{3}$. The simplicity of the experimental design makes it ideally suited for highly miniaturized implementations and wafer-level mass production. Operating the magnetometer in differential mode cancels common-mode noise and improves the sensitivity by a factor of 26 over single-channel operation. Finally, we suggest ways in which the current sensitivity of 28 pT/$\surd $Hz may be improved further without sacrificing size or simplicity. \newline [1] E. Hodby et al. To be submitted. [Preview Abstract] |
Wednesday, June 6, 2007 3:06PM - 3:18PM |
C5.00009: A portable ultrasensitive atomic magnetometer for biomagnetic measurements. Robert Wyllie, Zhimin Li, Ronald Wakai, Nicholas Proite, Peter Cook, Thad Walker We present a portable Rb cell atomic magnetometer suited for biomagnetic measurements. Working in the spin-exchange relaxation free regime, we demonstrate an initial white noise floor of 60 fT$/\sqrt {Hz} $. We show an adult magnetic cardiogram and demonstrate the feasibility of extending our measurements to fetal MCG. Based on previous experiments the noise floor can be further reduced by parametrically modulating the z-magnetic field, which also allows for the simultaneous measurement of the x and y field components using a single probe beam [1]. We will present the simple conversion of the magnetometer to a gradiometer that still uses a single probe beam. Finally, we discuss related technical advances over previous designs, including the replacement of bulky air convection heating apparatus by simple rf heating and an effective insulation material that allows 1 cm working distance from the subject at 180C temperature differential. [1] Z Li, R T Wakai, and T G Walker, Appl. Phys. Lett. 89, 134105 (2006) [Preview Abstract] |
Wednesday, June 6, 2007 3:18PM - 3:30PM |
C5.00010: Study of surface interactions of spin polarized Rb atoms in coated cells using the evanescent wave magnetometer K.F. Zhao, M. Schaden, Z. Wu We describe a new method of studying surface interactions of spin polarized rubidium atoms on silicone-coated Pyrex glass surfaces by operating the evanescent wave magnetometer in an inhomogeneous magnetic field. By analyzing the lineshape of the magnetic resonances using a theory we developed, we can estimate various parameters that characterize the surface interactions. Most interestingly, the lineshape is very sensitive to the phase shift of the Rb atom while it is on the surface. We measured for typical Surfasil(silicone) coated cells. [Preview Abstract] |
Wednesday, June 6, 2007 3:30PM - 3:42PM |
C5.00011: Spin-Exchange Optical Pumping of Solid Alkali Compounds Brian Patton, Kiyoshi Ishikawa, Yuan-Yu Jau, William Happer We demonstrate enhancement of the $^{133}$Cs nuclear polarization in a film of cesium hydride which has been placed in contact with an optically pumped cesium vapor. The maximum observed polarization at 9.4 T and 137 $^{\circ}$C is roughly 4 times the equilibrium polarization, but higher magnetizations are possible at lower magnetic fields. In an attempt to determine the mechanism of spin transfer from the alkali vapor to the solid, we have performed this experiment at intermediate magnetic fields (1-2 tesla) while pumping different optical transitions in the vapor. We will discuss the predicted spin current to the CsH layer in this regime of partial hyperfine decoupling and propose new methods for generating even higher polarizations in the solid. Potential applications of this technique will be mentioned as well as its extension to other compounds. [Preview Abstract] |
Wednesday, June 6, 2007 3:42PM - 3:54PM |
C5.00012: Intracavity Optogalvanic Spectroscopy (ICOGS) Erhan Ilkmen, Ozgur Dogru, Daniel Murnick Optogalvanic spectroscopy is a powerful technique for isotopic ratio analysis of CO$_{2}$. Isotopic lasers in resonance with specific molecular transitions in a RF glow discharge provide high specificity. Periodically modulated laser beam changes the population densities of the specific excited molecules that changes the impedance of the discharge, which then can be detected as voltage change across the electrodes. The optogalvanic signal is linear in path length and laser intensity providing a way to achieve high sensitivity. Earlier external cell studies have shown the limit of detection of $^{14}$C/$^{12}$C ratio to be of the order of $\sim $10$^{-9}$. It is now shown that placing the analyte cell directly into a $^{14}$CO$_{2}$ laser cavity greatly enhances the sensitivity - by about 10$^{6}$ which enables detection of trace amounts of $^{14}$CO$_{2}$ molecules with high signal to noise ratios. This huge improvement in sensitivity from the earlier studies is believed to be due to high internal laser power ($\sim $50W) and increase in interaction length of the laser photons with the excited molecules. The effective interaction length is of the order of the single mode laser coherence length. Unlike in intracavity laser absorption spectroscopy, the ICOGS signal does not change the laser output. [Preview Abstract] |
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