Bulletin of the American Physical Society
39th Annual Meeting of the APS Division of Atomic, Molecular, and Optical Physics
Volume 53, Number 7
Tuesday–Saturday, May 27–31, 2008; State College, Pennsylvania
Session L2: Poster Session II: 4:00 pm - 6:00 pm |
Hide Abstracts |
Room: HUB-Robeson Center Alumni Hall |
|
L2.00001: ATOMIC AND MOLECULAR STRUCTURE AND PROPERTIES: THEORY |
|
L2.00002: Application of the dual-kinetic-balance sets in the relativistic many-body problem of atomic structure Kyle Beloy, Andrei Derevianko The dual-kinetic-balance (DKB) finite basis set method for solving the Dirac equation for hydrogen-like ions [V. M. Shabaev {\em et al.}, Phys. Rev. Lett. 93, 130405 (2004)] is extended to problems with a non-local spherically-symmetric Dirac-Hartree-Fock potential. We implement the DKB method using B-spline basis sets and compare its performance with the widely- employed approach of Notre Dame (ND) group [W.R. Johnson, S.A. Blundell, J. Sapirstein, Phys. Rev. A 37, 307-15 (1988)]. We compare the performance of the ND and DKB methods by computing various properties of Cs atom: energies, hyperfine integrals, the parity-non-conserving amplitude of the $6s_{1/2}-7s_{1/2}$ transition, and the second-order many-body correction to the removal energy of the valence electrons. We find that for a comparable size of the basis set the accuracy of both methods is similar for matrix elements accumulated far from the nuclear region. However, for atomic properties determined by small distances, the DKB method outperforms the ND approach. [Preview Abstract] |
|
L2.00003: Valence calculations of binding energies of mid-row lanthanides Steven M. O'Malley, Donald R. Beck Binding energies of mid-row lanthanides have been calculated by taking advantage of the $>$90\% $LS$ purity of the $4f^n$ subgroups of their neutral ground states \footnote{{\it Atomic Energy Levels -- The Rare-Earth Elements}, edited by W. C. Martin, R. Zalubas, and L. Hagan, Natl. Bur. Stand. Ref. Data Ser. Natl. Bur. Stand. (U.S.) Circ. No. 60 (U.S. GPO, Washington, D.C., 1978).}. As described in our recent work on Nd$^-$ \footnote{S. M. O'Malley and D. R. Beck, Phy. Rev. A 77, 012505 (2008).}, the $4f^n$ electrons were treated as core-like and restricted to a single $LS$ term throughout all Dirac-Fock and correlation configurations, resulting in manageable relativistic configuration-interaction calculations for these computationally complex systems. Several weakly bound $6p$ attachments ($<$200 meV) were found for each negative ion, and these were carefully analyzed with respect to approximate $LS$ total configuration as well as the $j$'s of the the $4f^n$ subgroup and $6p$ electron. [Preview Abstract] |
|
L2.00004: B-spline Galerkin methods for the Dirac equation Charlotte Froese Fischer, Oleg Zatsarinny The B-spline Galerkin method was first applied successfully to relativistic many-body theory by W. R. Johnson and J. Sapirstein in 1986. Essentially, the diagonalization of a Dirac matrix equation yielded an effectively complete but finite and orthonormal basis for bound and continuum states. Though the low-energy bound states were good approximations to solutions of the Dirac equation, no physical interpretation was important for other states. However, spurious states perturbed the spectrum and slowed the convergence properties of quantum electrodynamic (QED) calculations. Problems have also occurred with the application to relativistic R-matrix methods. In this poster we report on an investigation of Galerkin methods for eigenvalue problems represented by a pair of first-order differential equations. By selecting a simple problem, closely related to the Dirac equation, different methods are analyzed and a stable method identified. In particular, it is shown that expansions in terms of bases (B, B$^\prime$) are equivalent to the B-spline expansions investigated by Igarashi when the difference in order is unity and are similar, though simpler, than the kinetic balance bases that have been proposed. Some differences between solutions of a matrix eigenvalue problem and the the differential equation will be mentioned. Results of the application of the method to the Dirac equation will be presented. [Preview Abstract] |
|
L2.00005: Density functional calculation of ground and excited states of negative atoms Amlan K. Roy Accurate determination of negative ions pose considerable challenge in both theory and experiment. Present study extends the validity and domain of a density functional theory (DFT)-based formalism, found quite successful for a wide variety of atomic excited states, in regards to the case of ground and metastable bound excited states of atomic anions. The local work-function-based exchange and nonlocal Lee-Yang-Parr correlation potential is used, while the radial Kohn-Sham equation is solved by means of generalized pseudospectral method. A number of quantities such as total energy, radial density, density moment and transition wavelength for the anions of first and second-row atoms show reasonably good agreement with available theoretical and experimental results. For example, absolute deviation in total energy remains within 0.007-0.171\% for Li$^-$ and Be$^-$, while the transition wavelengths show absolute deviation of 0.891\% and 0.438\% relative to the experimental values. In short, this offers a simple practical route towards accurate and reliable calculation of ground and excited states of atomic negative ions. [Preview Abstract] |
|
L2.00006: Forbidden transitions among $3d^6$ levels of Fe III Narayan C. Deb, Alan Hibbert Radiative rates for electric quadrapole (E2) and magnetic dipole (M1) transitions among lowest 32 levels belonging to the $3d^6$ configuration of Fe III are calculated using the CIV3 program of Hibbert [1]. In a recent calculation we [2] reported a large scale CI calculation of E1 transitions among all J-dependent levels of the 136 LS states belonging to the $3d^6$, $3d^54s$ and $3d^54p$ configuration of Fe III. The J-dependent wavefunctions of that calculation [2] are used in the present investigation to calculate transition probabilities of all possible E2 and M1 transitions among the lowest 32 levels of the $3d^6$ configuration. These results are then compared with only a few available theoretical calculations. We find that there are some substantial disagreements among various calculations for many of the transitions. Many of the present A-values for E2 and M1 transitions are significantly higher than the corresponding values in other calculations and this has an important effect on the analysis of astrophsyical observations. \\ \noindent [1] A.Hibbert, Comput. Phys. Commun. {\bf 9} (1975) 141\\ \noindent [2] N.C.Deb and A.Hibbert, J.Phys.B {\bf 40} (2007) F251\\ [Preview Abstract] |
|
L2.00007: Optically allowed transitions among Fe IV levels belonging to lowest three configurations Narayan C. Deb, Alan Hibbert Oscillator strengths and transition rates for the dipole allowed transitions among $3d^5$, $3d^44s$ and $3d^44p$ levels of Fe IV are calculated with the CIV3 program of Hibbert [1]. Using Hartree-Fock functions up to 3d orbitals we have optimised 4s, 4p, 4d, 4f, 5s, 5p and 5d orbitals of which 4s and 4p are taken to be the spectroscopic and the remaining orbitals representing corrections to the spectroscopic orbitals or the correlation effects. The J-dependent levels of all 108 LS states are included in the calculation and relativistic effects are accounted for via the Breit-Pauli operator. Configurations are chosen in two steps: (a) two promotions were allowed from the 3p, 3d and 4l subshells, using all the above orbitals; (b) selective promotions from the 3s subshell are included, but only to the 3d, 4s and 4p orbitals. The {\it{ab initio}} fine-structure levels were then fine-tuned to reproduce the observed energy levels as closely as possible, and the wavefunctions used to calculate oscillator strengths for all possible E1 transitions. For many of these transitions, the present results show agreement between length and velocity forms to within 5\%.\\ \noindent [1] A.Hibbert, Comput. Phys. Commun. {\bf 9} (1975) 141 [Preview Abstract] |
|
L2.00008: Excitation energies, radiative and autoionization rates, dielectronic satellite lines, and dielectronic recombination rates for excited states of Na-like W from Ne-like W A.S. Safronova, U.I. Safronova, P. Beiersdorfer Energy levels, radiative transition probabilities, and autoionization rates for $2s^22p^53l'nl$, $2s2p^63l'nl$ ($n$=3- 7) and $2s^22p^54l'nl$, $2s2p^64l'nl$ ($n$=4-6) states in Na-like tungsten (W$^{63+}$) are calculated by the Cowan, HULLAC, and RMBPT codes. Autoionizing levels above the $2s^22p^6$ are threshold considered. Branching ratios relative to the first threshold and intensity factors are calculated for satellite lines, and dielectronic recombination (DR) rate coefficients are determined for the excited $2s^22p^6nl$ ($n$=3-7) states. Contributions from the excited level $2s^22p^53l'nl$, $2s2p^63l'nl$ (with $n \ge 8$) and $2s^22p^54l'nl$, $2s2p^64l'nl$ ($n \ge 7$) to the DR rate coefficients are estimated by extrapolation of all atomic parameters. The total DR rate coefficient is derived. These data as well as theoretical dielectronic satellite spectra are useful in diagnostic of high-temperature plasmas of the broad range of densities from Tokamak to HED plasmas. [Preview Abstract] |
|
L2.00009: Overview of recent results on lifetimes, rates, and line strengths of multipole transitions from $3l^{-1}4l'$ states in Ni-like ions U.I. Safronova, A.S. Safronova, P. Beiersdorfer Transition rates and line strengths are calculated for electric-multipole and magnetic-multipole transitions between $3s^23p^63d^{10}$, $3s^23p^63d^94l$, $3s^23p^53d^{10}4l$, and $3s3p^63d^{10}4l$ states in Ni-like ions with the nuclear charges ranging from $Z$ = 34 to 100. Relativistic many-body perturbation theory, including the Breit interaction, is used to evaluate retarded multipole matrix elements. Lifetimes of the $3s^23p^63d^94s$ levels are given for $Z$ = 34--100. The full set of data is given only for Ni-like W ion which is expanded to include previous work. In addition, we also give complete results for the $3d4s\ ^3D_{2} - 3d4s\ ^3D_{1}$ magnetic-dipole transition, as the transition may be observed in future experiments, which measure both transition energies and radiative rates. These atomic data are important in the modeling of radiation spectra from Ni-like multiply-charged ions generated in electron beam ion trap experiments as well as for laboratory plasma diagnostics including fusion research. [Preview Abstract] |
|
L2.00010: Energy, fine structure, hyperfine-structure, and Auger width of the core-excited states for the Li isoelectronic sequence BingCong Gou, JingJing Zhu The relativistic energies, fine structure, hyperfine-structure and Auger widths of the 1s2s$^{2 2}$S, 1s2p$^{2 2}$S, 1s(2s2p $^{3}$P$^{o})^{2}$P$^{o}$, 1s(2s2p $^{1}$P$^{o})^{2}$P$^{o}$, 1s2p$^{2 2}$D, and 1s2s2p $^{4}$P$^{o}$ states for the Li isoelectronic sequence ($Z$=2-20) are studied using the saddle-point variational method and the saddle-point complex-rotation method. Restricted variational method is carried out to extrapolate a better energy. The oscillator strengths and radiative transition rates of these states are reported. The good agreement among the oscillator strengths from the length, velocity, and acceleration results is used as the indication of the accuracy of the wavefunctions. It has been investigated that the properties such as relativistic correction, fine structure splitting, radiative and Auger rate regularly change along the Li isoelectronic sequence. The presence of autoionizing states strongly affects the character of the emission spectrum in these systems. The calculated results are compared with the available experimental and other theoretical data in the literature. [Preview Abstract] |
|
L2.00011: Term classifications and Breit-Pauli oscillator strengths of neutral tin Paul Oliver, Alan Hibbert Spectroscopic observation of embedded tin impurity is being investigated as a potential diagnostic for monitoring the erosion of vessel wall tiles in fusion power plants [1], requiring accurate estimates of the oscillator strengths (OS) of the neutral and near-neutral lines. In response to this, we have undertaken (to our knowledge) the first extensive Breit-Pauli configuration interaction (CI) calculation of transitions among the lower-lying levels in Sn I, using the atomic structure code CIV3 [2]. One-electron functions have been carefully optimised to represent accurately the main configurations, accounting for the $LS$-dependency of the orbitals, and all important correlation and polarisation effects. We present our assigned energy level term classifications, highlighting the significant inconsistencies in the literature. Present results agree favourably with other sparsely available experimental and theoretical work (mostly focusing on transitions involving the $5\rm{p}^2$ ground configuration). We observe excellent agreement in the length and velocity forms of the OS. \noindent \begin{list}{[1]}{\topsep0pt\itemsep0pt\partopsep0pt\parsep0pt} \item[{[1]}] Foster A R, Counsell G F and Summers H P 2007 {\it J. Nucl. Mater.} {\bf 363-365} 152 \item[{[2]}] Hibbert A 1975 {\it Comput. Phys. Commun.} {\bf 9} 141 \end{list} [Preview Abstract] |
|
L2.00012: Generalized Localized Hartree-Fock Density Functional Theory for Calculation of Excited-state Electronic Energies of Diatomic Molecules Zhongyuan Zhou, Shih-I Chu We present a spin-dependent localized Hartree-Fock (SLHF) density-functional theoretical (DFT) approach for the accurate calculation of electronic energies of diatomic molecular excited states. In this approach, electron spin-orbitals are obtained by solving Kohn-Sham (KS) equation with the SLHF exchange potential and Perdew-Burke-Ernzerhof (PBE) generalized-gradient correlation energy functional. A generalized pseudospectral (GPS) technique, allowing non-uniform spatial discretization, is used for high precision solution of the SLHF-KS equations. The method has been applied to the calculation of electronic energies of excited states of H$_{2}$, O$_{2}$, and N$_{2}$. The results are in good agreement with available theoretical and experimental data. [Preview Abstract] |
|
L2.00013: ABSTRACT WITHDRAWN |
|
L2.00014: A new 3D grid method for accurate electronic structure calculation of polyatomic molecules: The Voronoi-cell finite difference method Sang-Kil Son, Shih-I Chu We introduce a new computational method on \emph{unstructured} grids in the three-dimensional (3D) spaces to investigate the electronic structure of polyatomic molecules. The Voronoi-cell finite difference (VFD) method realizes a simple discrete Laplacian operator on \emph{unstructured} grids based on Voronoi cells and their natural neighbors. The feature of \emph{unstructured} grids enables us to choose intuitive pictures for an optimal molecular grid system. The new VFD method achieves highly adaptability by the Voronoi-cell diagram and yet simplicity by the finite difference scheme. It has no limitation in local refinement of grids in the vicinity of nuclear positions and provides an explicit expression at each grid without any integration. This method augmented by \emph{unstructured} molecular grids is suitable for solving the Schr\"odinger equation with the realistic 3D Coulomb potentials regardless of symmetry of molecules. For numerical examples, we test accuracies for electronic structures of one-electron polyatomic systems: linear H$_2^+$ and triangular H$_3^{++}$. We also extend VFD to the density functional theory (DFT) for many-electron polyatomic molecules. [Preview Abstract] |
|
L2.00015: Semiclassical Theory of the Structure of the Hydrogen Spectrum in Near-Perpendicular Fields: EBKM Quantization and Description of Monodromy Chris Schleif, John Delos At the 2007 DAMOP meeting we presented a talk describing the spectrum of hydrogen atoms in near-perpendicular electric and magnetic fields. We displayed a number of previously unrecognized structures in the spectrum, most of which are connected with a classical phenomenon called ``monodromy.'' At this meeting we wish to present the underlying theory which produced these results. We show that the construction of approximate classical actions by the obvious methods leads to variables that have discontinuous derivatives. Smooth continuation of these ``primitive'' action variables leads to action variables that are multivalued. We show how these multivalued actions lead to defects in the quantum spectrum. We also present a few correlation diagrams which show how quantum eigenvalues evolve from one region of near-perpendicular parameter space to another. Finally we consider the near perpendicular spectra of non-hydrogenic atoms via quantum defect theory. [Preview Abstract] |
|
L2.00016: Structure and properties of Al$^+$ Kyle Rollin, Michael Bromley, Jim Mitroy The properties of a number of states of single charged Al$^{+}$ ion are determined from a large basis configuration interaction calculation. The main focus is on the polarizabilities of the low-lying states (the $3s^2$ $^1$S$^e$, $3s3d$ $^{1,3}$D$^e$, $3s3p$ $^{1,3}$P$^o$ and $3s4s$ $^{1,3}$S$^e$ states) and the dispersion interactions of those states with the Al$^{+}$ ground state, the hydrogen atom and the rare gases. [Preview Abstract] |
|
L2.00017: PHOTON INTERACTIONS WITH ATOMS, IONS, AND MOLECULES |
|
L2.00018: Experimental studies of the interaction of atoms and molecules with intense VUV pulses Jeroen van Tilborg, Tom Allison, Marc Hertlein, Andy Aquila, Roger Falcone, Ali Belkacem We will present the latest experimental results and plans on our sub-terawatt-driven HHG sytem. Photons of energy in the 30-100 eV range are produced by propagating 40 fs, 20 mJ laser pulses through a cm-scale gas cell. After focusing of such VUV pulses, peak intensities can reach 10$^{13}$-10$^{14}$ W/cm$^{2}$, enabling nonlinear processes such as two-photon absorption to become detectable. In addition, intrinsic synchronization between laser and VUV photons allows for ultra-fast pump-probe experiments. We will discuss the details on the VUV characterization, such as spectrum, conversion efficiency, spatial profile, and energy detection. Also, we will present preliminary results from experiments in which ions from the focus of the VUV pulse (in presence of gas from a gas jet) are detected with a time-of-flight system. Fragments from dissociation of target gases such as C$_{2}$H$_{2}$, C$_{2}$H$_{4}$, N$_{2}$, Ar, and Xe are studied. [Preview Abstract] |
|
L2.00019: Solving the time-dependent Schroedinger equation with grid-based methods using exterior complex scaling Liang Tao, C. William McCurdy, Thomas N. Rescigno We show that exterior complex scaling provides a viable method for suppressing reflections in numerical simulations of the time-dependent Schroedinger equation for strong-field problems, provided the calculations are carried out in the radiation gauge. We show that numerical stability can be achieved without the {\em ad hoc} use of an untransformed external field and that recently reported instabilities [F. He, C. Ruiz and A. Becker, Phys. Rev. A 75, 053407 (2007)] can be traced to an inappropriate choice of the complex grid. Atomic simulations in 1-,2- or 3-D can be implemented using a discrete variable representation for the radial electron coordinate based on Gauss-Lobatto quadrature and finite-elements (FEM/DVR). For simulations involving diatomic molecules, cylindrical coordinates ($\rho , z$) can be used, but special care must be taken to avoid slow convergence near $\rho= 0$. We show how a proper FEM/DVR can be constructed in cylindrical coordinates. [Preview Abstract] |
|
L2.00020: Analysis of the effects of improved calculations of bremsstrahlung and other atomic processes effects on key dosimetric data. Paul Bergstrom An accurate characterization of radiative processes in certain media is a critical element in primary dosimetric standards. Depending on the energy spectrum of the radiation that is being measured, photoionization, inelastic photon-atom scattering and pair production are key processes as is electron bremsstrahlung in the atomic field. It has been nearly three decades since much of the work that serves as the foundation for this key data was established. Since that time, many developments in the evaluation of these processes have occurred. These developments are applied to understanding changes that may be necessary in primary dosimetric standards. [Preview Abstract] |
|
L2.00021: Rayleigh scattering from argon clusters in a planar expansion Mark Masters, Fredrick De Armond, Robert Dill, Joseph Suelzer Rayleigh scattering is presented as the evidence for the presence of large argon clusters formed in a planar expansion. Based on the observed scattering signal, the dependence of mean cluster size on stagnation pressure is $\left\langle N \right\rangle \propto P_0 ^{3.38}$. This is in contrast to the dependence of the mean cluster size on stagnation pressure for a symmetric expansion of $\left\langle N \right\rangle \propto P_0 ^{2.29}$. Using interferometry in conjunction with the Rayleigh scattering signal we are able to estimate the mean cluster size for clusters formed in the planar expansion. [Preview Abstract] |
|
L2.00022: AMO Instrumentation for the LCLS John Bozek The Linac Coherent Light Source (LCLS) x-ray free electron laser (FEL) facility at the Stanford Linear Accelerator Center (SLAC) is quickly nearing completion. When finished in summer 2009, the LCLS will produce ultrafast pulses of x-rays with photon energies of 800 -- 8000 eV, intensities $\ge $ 10$^{13}$ ph/s and pulse durations of $\approx $ 150 fs, at a repetition rate of 120Hz. A suite of four instruments, including one dedicated to AMO science, are currently being designed for first experiments with the LCLS source. The design of the AMO instrument is in the final stages with construction to begin later this year. Included in the AMO instrumentation are optics to focus the LCLS beam to a waist of $\sim $2$\mu $m, an experimental chamber with a supersonic pulsed gas jet, a set of five time-of-flight electron energy spectrometers, one of three ion spectrometers, and two x-ray fluorescence spectrometers, and a synchronized laser for pump-probe experiments. A downstream diagnostics chamber with instruments to measure the relevant parameters of each FEL pulse is also included. Plans for first experiments along with designs of the instrumentation will be presented. Guidance for experimental proposals for the LCLS will also be provided for prospective users. [Preview Abstract] |
|
L2.00023: Compton scattering revisited T. Suri\'{c}, V. Florescu, B.K. Chatterjee, S.C. Roy, L.A. LaJohn, R.H. Pratt Compton scattering of a photon by bound electrons is one of the fundamental processes of interaction of radiation with matter [1].Theoretical treatments of the process are often based on using impulse approximation (IA) which is, at nonrelativistic energies, obtained within ${\bf A}^{2}$ approximation of the electron-photon interaction (the ${\bf p}\cdot{\bf A}$ term is neglected). The validity of IA increases and the corrections decrease as the ratio $p_{av}/k$ of average momentum $p_{av}$ of bound electron and the photon momentum transfer $k$ becomes small. The IA is often viewed as the leading term in the $p_{av}/k$ expansion of the exact result. We examine the criteria of validity of IA for the triply differential cross section (TDCS) and for the doubly differential cross section (DDCS), which are different. We find that IA is in fair agreement with the exact expression for DDCS even when the expansion in $p_{av}/k$ is not well convergent. We also examine the importance of the inclusion of the ${\bf p}\cdot{\bf A}$ term in IA, needed at relativistic energies even in the peak region. [1] P. Eisenberger and P. M. Platzmann, Phys Rev. A 2, 415 (1970); R. Ribberfors, Phys. Rev. B 12, 2067 (1975); P. M. Bergstrom {\it et al,} Phys. Rev. A 48, 1134 (1993); R. H. Pratt {\it et al,} Nucl. Instr. and Meth. B 261, 175 (2007). [Preview Abstract] |
|
L2.00024: The Law of Photon Interaction With Matter Stewart Brekke When a photon interacts with a quantity of matter, there will be an increase in the linear, rotation and/or vibrational motion of that quantity of matter and/or emit a photon, singly or in some combination. In the Photoelectric Effect the incident photon may make the surface electron move linearly, change the spin and/or increase the vibration of the surface electron. Similarly, in the Compton effect for all kinds of particles, nuclei and molecules, the incident photon changes the linear, curvilinear, spin and/or vibrational mode of the particle, nucleus or molecule. For larger quantities of matter the incident photons at minimum may increase the molecules, ions, nuclei and/or subatomic particles such as electrons and quarks vibrations, thereby heating the quantity of matter and may increase their linear and/or orbital motions in the body of matter itself. In this manner the larger quantity of matter may move in some way. [Preview Abstract] |
|
L2.00025: Molecular Field effects investigated by Polarized Resonant Inelastic X-ray Scattering W.C. Stolte, R. Guillemin, S. Carniato, L. Journel, R. Taieb, D.W. Lindle, M. Simon Angular dependence of the Cl 2p spin-orbit components is observed experimentally in resonant inelastic x-ray scattering (RIXS) after 1s excitation in CF$_3$Cl and HCl. Theoretical analysis interprets this dependence by population differences in the 2p$_{x,y,z}$ states, and molecular-field and singlet-triplet exchange effects. Thus, polarized RIXS provides a direct measurement of the 2p$_{x,y,z}$ states populations, and a probe of the molecular environment. [Preview Abstract] |
|
L2.00026: MOLECULAR PHOTOIONIZATION, PHOTODETACHMENT, AND PHOTODISSOCIATION PROCESSES |
|
L2.00027: K-shell photodetachment of small size-selected negative ion clusters: Experiment and theory R.C. Bilodeau, N. Berrah, I. Dumitriu, O. Zatsarinny, T. Gorczyca, J.D. Bozek, N.D. Gibson, C.W. Walter, D. Toffoli, R.R. Lucchese K-shell photodetachment of atomic B$^-$ and size-selected B$_2^- $ and B$_3^-$ cluster anions have been calculated and measured, using the photon-ion beamline on the Advanced Light Source beamline 10.0.1. Absolute photodetachment cross sections of B$^- $ measured as a function of photon energy, exhibit three near- threshold shape resonances due to the $^3$S, $^3$P, and $^3$D final partial waves. The clusters exhibit bound resonances below threshold and two shape resonances above the K-shell threshold. The overall agreement between measured and calculated photodetachment cross sections is very good. However, the theoretical studies yielded additional bound resonances not observed in the experimental data and certain significant quantitative discrepancies, even in the atomic case. [Preview Abstract] |
|
L2.00028: Photodetachment Studies of the Hydrogen Molecular Anion K.C. Chartkunchand, Vernon Davis, Jeffrey Thompson, Aaron Covington Laser Photodetachment Electron Spectroscopy (LPES) has been used to study long-lived beams of the hydrogen molecular anion H$_2^-$. A photoelectron kinetic energy spectrum was measured at the photon energy of 488 nm using an intercavity crossed laser-ion beams apparatus. The energy scale of this spectrum was calibrated using the photoelectron kinetic energy spectra from the photodetachment of D$^-$ and Cu$^-$. Preliminary data and results from the analysis of this data will be presented. [Preview Abstract] |
|
L2.00029: Non-Resonant Ionization and Fragmentation Pathways in Na$_{2}$. Lutz H\"uwel, Mao Sheng Liu, Roy Anunciado With the help of molecular beam, time-of-flight (TOF) mass spectrometer, and Nd:YAG laser we have investigated multi-photon ionization and dissociation patterns of Na$_{2}$ molecules. One prominent feature of TOF spectra obtained with 532nm photons can be assigned to 3-photon ionization followed by 1-photon dissociation. This channel yields Na$^{+}$ fragments with kinetic energy of about 0.67eV, the highest kinetic energy release we found for any combination of YAG photons (1064, 532, and 355nm). In the same TOF spectra, we also observe features consistent with 2-photon dissociative excitation followed by 1-photon ionization of electronically excited Na fragments (4s, 3d, 4p). No other YAG photons produce such fragments. Finally, a broad fragment peak corresponding to low kinetic energy release is observed at all YAG wavelengths, though with subtly different line shapes. Various combinations of 532nm with other YAG photons reveal significant enhancements in some channels but not in others. We have systematically explored this behavior together with polarization and power dependence. Results of a realistic modeling based analysis of these spectra will be presented. Details of modeling and experimental approach may be found in a previous publication$^{1}$. -- $^{1}$B. Delahunty et al., Phys. Rev. A \textbf{60}, 1179 (1999) [Preview Abstract] |
|
L2.00030: Photoabsorbtion and Photoionization of Diatomic Molecules Alejandro Saenz, Irina Dumitriu The photodissociation spectra of HeH$^+$ will be presented together with photoionization cross sections of the alkali dimer cations Li$^+_2$, Na$^+_2$, and LiNa$^+$. The latter have been calculated using two methods: a time-independent perturbative method and a time-dependent non-perturbative one. The photodissociation of HeH$^+$ which is of interest for astrophysics and the tritium neutrino-mass experiments currently draws special attention because of the newly developed FEL experimental set-up FLASH in Hamburg at which dissociation of HeH$^+$ by VUV radiation has been investigated [{\it Phys. Rev. Lett.}\ {\bf 98}, 223202 (2007)]. The alkali dimer cations are presented as a first methodological step to the photoionization of the alkali dimers, but they are also interesting by themselves since no ab initio data were available for the continuum spectra. [Preview Abstract] |
|
L2.00031: Quantitative comparison of experiment and theory for intense ultrashort laser-induced dissociation of H$_{2}^{+}$ A.M. Sayler, F. Anis, J. McKenna, B. Gaire, Nora G. Johnson, K.D. Carnes, B.D. Esry, I. Ben-Itzhak Experimental measurements and theoretical calculations for intense ultrashort pulse laser-induced dissociation of H$_{2}^{+}$ were performed under near identical conditions producing results for quantitative comparison. The 3D momentum distribution was measured for the fragments of an H$_{2}^{+}$ beam after interaction with 10 fs, 790 nm pulses at intensities of 10$^{14}$, 10$^{13}$, and 10$^{12}$ W/cm$^{2}$. In parallel, the time-dependent Schr\"{o}dinger equation was solved in the Born-Oppenheimer representation including nuclear, rotational, and electronic excitation. To obtain angularly-resolved kinetic energy release distributions necessary to compare to measurements, the final wavefunctions, projected onto the scattering states, are averaged over the vibrational state, intensity volume, and thermal distribution appropriate to the experiment. The results of these measurements and calculations are contrasted, testing the quantitative agreement of theory and experiment for ultrashort pulses at these intensities. [Preview Abstract] |
|
L2.00032: Characterization of Molecular Dynamics in Ultrashort Laser Fields B. Feuerstein, T. Ergler, A. Rudenko, R. Moshammer, J. Ullrich, T. Niederhausen, U. Thumm Reaction Microscope-based, complete, and time-resolved Coulomb explosion imaging of vibrating and dissociating $D_2^2+$ molecules with femtosecond time-resolution allowed us to perform an internuclear distance (R-)dependent Fourier analysis of the corresponding wave packets. Our wave packet propagation calculations demonstrate that the obtained two-dimensional R-dependent frequency spectra enable the complete characterization of the wave packet dynamics and directly visualize the field-modified molecular potential curves in intense, ultrashort laser pulses, cf., Phys. Rev. Lett. {\bf 99} 153002 (2007). [Preview Abstract] |
|
L2.00033: Photofragmentation of Deuterated Benzene Ralf Wehlitz, Pavle Juranic, Max Young, Bethany Reilly We have measured the probability for creating various fragments of deuterated benzene (C$_{6}$H$_{3}$D$_{3}$) in the photon energy range from 12 to 160 eV at the Synchrotron Radiation Center (SRC). The fragments were detected with an improved ion time-of-flight spectrometer providing a high enough resolving power to unambiguously detect all possible photofragments of deuterated benzene. The ion fragments C$_{n}$H$_{m}$D$_{p}$ (n=2--6; m,p=0--3; note that not all combinations exist) appear in groups characterized by the number of carbon atoms. We find evidence for the existance of carbon rings with only a single hydrogen atom attched (C$_{6}$H) . We will present appearance energies and photon energy dependences of all fragments. [Preview Abstract] |
|
L2.00034: Double Photoionization of Deuterated Benzene Ralf Wehlitz, Pavle Juranic, Max Young, Bethany Reilley Previously we had noticed modulations at certain excess energies in the double-to-single photoionization ratio of C60. When those excess energies are converted into de Broglie wavelengths of an electron, then they corresponded to the inter-atomic distances of the C60 cluster\footnote{P.N.\ Juranic {\it et al.}, Phys.\ Rev.\ Lett. {\bf 96}, 023001 (2006)} such as the carbon-carbon distance, the diameter of a hexagon, and the diameter of the cluster. We attempted to observe a similar effect in benzene (C6H6). However, C6H6 can fragment creating C3H3 ions, which have the same mass-to-charge ratio as the doubly charged C6H6 ions and thus cannot be distinguished with our current ion Time-of-Flight analyzer. In order to avoid this problem we have used deuterated benzene (C6H3D3) to measure the double photoionization probability from threshold to 160 eV. [Preview Abstract] |
|
L2.00035: Production of Excited Atomic Hydrogen and Deuterium from HD Photodissociation J.R. Machacek, J.D. Bozek, J.E. Furst, T.J. Gay, H. Gould, A.L.D. Kilcoyne, K.W. McLaughlin We have measured the production of Ly$\alpha $, H$\alpha $, and H$\beta $ fluorescence from atomic H and D for the photodissociation of HD by linearly-polarized photons with energies between 20 and 66 eV. In this energy range, excited photofragments result primarily from the production of doubly-excited molecular species which promptly autoionize or dissociate into two neutrals. Theoretical calculation are not yet available for HD, but comparison between the relative cross sections for H$_{2}$, D$_{2}$ and HD targets and the available theory for H$_{2}$ and D$_{2}$ [1] allow for an estimate of the relative strength of each dissociation channel in this energy range. [1] J. D. Bozek \textit{et al.}, J. Phys. B \textbf{39}, 4871 (2006). Support provided by the NSF (Grant PHY-0653379), DOE (LBNL/ALS) and ANSTO (Access to Major Research Facilities Programme). [Preview Abstract] |
|
L2.00036: Photoelectron Spectroscopy of Doped Helium Nanodroplets Oleg Kornilov, Chia Wang, Jeong Hyun Kim, Darcy Peterka, Oliver Gessner, Daniel Neumark Helium nanodropets are unique in their ability to pick-up foreign species and facilitate formation of cryogenically cold (0.4 K) virtually unperturbed complexes. These properties stem from the droplets' superfluid nature and very weak interaction potential making helium one of the best media for matrix-isolated spectroscopy. Variety of methods has already been applied to embedded complexes including infrared, visible and UV spectroscopy. To complement this picture, in the present contribution photoelectron spectroscopy is used to conduct a systematic study of photoelectron dynamics in He droplets. Droplets doped with rare gas atoms (Ne, Ar, Kr, Xe) are investigated using tunable VUV light of Advanced Light Source at LBNL. Indirect photoionization is observed followed by both direct escape of photoelectron and energy loss mechanism of uncertain nature. Prospects for time-resolved studies of photoelectron dynamics in He droplets are discussed. [Preview Abstract] |
|
L2.00037: Momentum Imaging of the Photo Double Ionization of Ethylene Molecules: A kinematically complete experiment Sun Lee, Timur Osipov, Thorsten Weber, Ali Belkacem The direct Photo Double Ionization (PDI) is a process that arises essentially because of the electron correlation. After successfully studying the PDI of hydrogen molecules in the past our goal is to extend our knowledge from a sigma bonding system to a pi bonding system. Ethylene is an ideal candidate, because it is the simplest hydrocarbon with a pi bond. Thus we investigated the PDI of ethylene near its threshold in order to unravel unique and important intertwining of electron correlation in inter-shell and intra-shell cases and the subsequent molecular dynamics. We focused on the following reaction: C$_{2}$H$_{4}$ + hv -$>$ C$_{2}$H$_{4} \quad ^{2+}$ + 2 e$^{-}->$ 2 e$^{-}$ + CH$_{2}^{+}$ + CH$_{2}^{+ }$ Using the COLTRIMS (COLd Target Recoil Ion Momentum Spectroscopy) technique, we were able to detect two ejected electrons and nascent photo-fragments, i.e. the recoil CH$_{2}^{+ }$ions in coincidence, thus a kinematically complete experiment was performed. From this we derived the angular distributions of the emitted photoelectrons in reference to the fixed in space molecular axis and the linear polarization of the incoming light (40eV). In addition we were able to determine the electronic energy sharing as well as the internuclear distance at the instant of photo absorption. [Preview Abstract] |
|
L2.00038: Subshell-resolved ultraviolet photoionization of C$_{60}$: angular momentum versus cavity oscillations George Klenklen, Justin Schmelzer, Mohamed Madjet, Himadri Chakraborty Photoelectron intensities from the valence subshells of C$_{60}$ exhibit oscillations -- the cavity oscillations [1]. From beyond the collective plasmon energy region to the carbon K-shell ionization threshold, we calculate in the local density approximation the cross sections for ionization from all occupied subshells of C$_{60}$. Fourier transformation of the cross sections as a function of photoelectron momentum reveals four frequencies of oscillations. However, the relative strength of the signal for different oscillations is found to sensitively depend on the initial angular momentum of the electron. As an extreme example, the cross section of the highest possible angular momentum state oscillates in practically one single frequency, since signals from others are too weak. The role of the centrifugal barrier potential to determine the effect is uncovered. [1] Ruedel et al., Phys. Rev. Letts. \textbf{89}, 125503 (2002). [Preview Abstract] |
|
L2.00039: Quantum Young's double-slit-type interferences in atomic photoelectrons from atom@C$_{60}$ molecules Himadri Chakraborty, Mohamed Madjet, Jan-Michael Rost, Steve Manson The photoionization cross section of an endohedrally confined atom exhibits oscillations [1]. The effect can be best interpreted by the quantum interference of electron waves scattered from inner and outer edges of the confining shell [2]. For some atom@C$_{60}$ compounds, from beyond the collective plasmon energy region to the carbon K-shell ionization threshold, we Fourier-analyze calculated photo cross sections to determine oscillation frequencies. Since the underlying mechanism is a quantum analogue of a classical double-slit interference in photoelectron momentum space, with the central atom being the light source and the opposite sides of the shell being the slits, it is shown that the information can be used to extract geometric details. The competing role of the Coulomb and the cage potentials governs the effect. [1] J.-P. Connerade et al., \textit{J. Phys.} B \textbf{33}, 2279 (2000); [2] Ruedel et al., Phys. Rev. Letts. \textbf{89}, 125503 (2002). [Preview Abstract] |
|
L2.00040: Giant resonances of endohedral atoms M. Ya. Amusia, Arkadiy Baltenkov, Larissa Chernysheva We demonstrate for that the effect of fullerene shell upon photoionization of the ``caged'' atom in an endohedral can result in formation of Giant Endohedral Resonances or GER. This is illustrated by the concrete case of Xe@C$_{60}$ photoionization cross-section that exhibits at 17 eV a powerful resonance with total oscillator strengths of about 25. The prominent modification of the 5$p^{6}$ electron photoionization cross-section of Xe@C$_{60 }$takes place due to strong fullerene shell polarization under the action of the incoming electromagnetic wave and oscillation of this cross-section due to the reflection of the photoelectron from Xe by the C$_{60}$. These two factors transform the smoothly decreasing 5$p^{6}$ cross-section of Xe into a rather complex curve with a powerful maximum for Xe@C$_{60}$, with the oscillator strength of it being equal to 25! We present also the results for the dipole angular anisotropy parameter that is strongly affected by the reflection of the photoelectron waves but not modified by C$_{60 }$polarization. [Preview Abstract] |
|
L2.00041: Photoionization of the subvalent subshells of noble gas Endohedrals: interference of three resonances M. Ya. Amusia, A.S. Baltenkov, L.V. Chernysheva We demonstrate strong interference patterns in the photoionization cross-section of the subvalent subshells of noble gas (NG) endohedral atoms NG@F. This interference is a result of common action of three factors: the effect of neighboring atomic subshells, reflection of photoelectron waves by the fullerene F shell and resonance modification of the incoming photon beam by the complex effect under the action of the F electrons. We have considered the outer \textit{ns}-subshells for Ne, Ar, Kr and Xe noble gas atoms. The polarization of the fullerene shell is expressed via the F total photoabsorption cross section. The photoelectron reflection from the static F potential is taken into account in the frame of the so-called bubble potential that is a spherical $\delta $-type potential. As a result the NG@F photoionization cross section is presented as a product of the NG subvalent cross section and two calculated factors that account for polarization of the F electron shell and reflection of photoelectrons by the fullerene static potential. [Preview Abstract] |
|
L2.00042: Destruction and Resurrection of Atomic Giant resonances in Endohedral Atoms A@C$_{60}$ M. Ya. Amusia, A.S. Baltenkov, L.V. Chernysheva In photoabsorption by endohedral atoms some atomic Giant resonances are almost completely destroyed while the others are totally preserved due to different action on it of the fullerenes shell. As the first example we discuss the 4$d^{10}$ Giant resonance in Xe@C$_{60}$ whereas as the second serves the Giant \textit{autoionization} resonance in Eu@C$_{60}$. The qualitative difference comes from the fact that photoelectrons from the 4$d$ Giant resonance has small energies (tens of eV) and are strongly reflected by the C$_{60}$ fullerenes shell. As to the Eu@C$_{60}$, Giant autoionization leads to fast photoelectrons (about hundred eV) that go out almost untouched by the C$_{60}$ shell. As a result of the outgoing electrons energy difference the atomic Giant resonances will be largely destroyed in A@C$_{60}$ while the Giant autoionization resonance will be almost completely preserved. On the way from Xe@C$_{60}$ to Eu@C$_{60}$ the oscillation structure should disappear in cross-sections and angular anisotropy parameters. [Preview Abstract] |
|
L2.00043: Photoelectron Spectroscopy of Mixed-Metal Clusters Charles Jones, Ujjwal Gupta, Joshua Melko, Penee Clayborne, J. Ulises Reveles, Shiv Khanna, A. Welford Castleman The eventual synthesis and characterization of nanoscale materials requires an understanding of their growth mechanisms, electronic characteristics, and the dynamics of excitation and relaxation. We study the evolution of electronic and geometric stability with cluster size. The techniques of magnetic bottle photoelectron spectroscopy and velocity map imaging are employed to characterize the electronic properties of mixed-metal clusters. One direction of the studies in our laboratory focuses in on all-metal aromatic clusters (Al$_{3}$M where M = As, Sb, and Bi). These clusters have delocalized electron orbitals reminiscent of aromatic molecules like benzene. The data additionally show that these all-metal aromatics have low electron affinities, high ionization potentials, and large HOMO-LUMO gaps. Additionally, we are trying to correlate the stability of solution phase synthesized Zintl ions in the gas phase using the well-known Jellium model and 3-D aromaticity concepts. A recent example includes the presence of highly stable BiSn$_{4}^{-}$, BiSn$_{8}^{-}$ and BiSn$_{9}^{-}$ clusters in the gas phase, which can be represented by Sn$_{5}^{2-}$, Sn$_{9}^{2-}$ and Sn$_{10}^{2-}$ Zintl ions, respectively. [Preview Abstract] |
|
L2.00044: Velocity Map Imaging of Semiconductor-Metal Cluster Systems S.J. Peppernick, K.D.D. Gunaratne, A.W. Castleman Recently, a Velocity map imaging (VMI) device has been constructed to investigate the electronic nature of atoms and clusters. The VMI technique takes digitized pictures of expanding electrons from a photodetachment event. These electron snapshots can then be converted to spectra from which EAs, energy gaps, and vibrational separations can be measured. Also, VMI can capture the angular distribution of the detached electrons, whereby a quantity called the anisotropy parameter can be calculated. This parameter is useful for inferring the nature of the atomic or molecular orbital the ejected electron came from. Silicon clusters can form fullerene like cages with the addition of a single or multiple endohedral metals. Elucidating both the electronic and magnetic properties of these silicon metal clusters via the VMI technique is paramount in understanding these clusters for their potential technological applications as building blocks in cluster assembled solids. The latest experimental findings will be presented. We acknowledge funding from the Department of Energy, Building Blocks: DE-FG02-02ER46009. [Preview Abstract] |
|
L2.00045: Study of III-V Semiconductor Clusters using Anion Photoelectron Spectroscopy Ujjwal Gupta, J. Ulises Reveles, Joshua Melko, Shiv Khanna, A.W. Castleman Jr. III-V semiconductor materials are used in various electronic applications. III-V clusters are therefore a subject of extensive investigation because of the desired capability to fine tune the properties in a bottom-up approach. Evidence for band gap tunability is presented as one of the examples here. It is shown that changing the amount of gallium, changes the band gap in Bi$_{3}$Ga$_{y}^{(-)}$ clusters. Now, depending upon how stable the cluster is for a given band gap it can be used to assemble nanomaterials. It is found that Bi$_{3}$Ga$_{2}^{-}$, Bi$_{3}$Ga$_{3}$, Bi$_{3}$Ga$_{4}^{-}$ and Bi$_{3}$Ga$_{5}$ are stable with a calculated band gap ranging from 1.17 eV to 1.89 eV, using mass spectrometry, photoelectron spectroscopy and computational results. Additionally, it is shown that the electronic properties remain similar when an element from III-V cluster is replaced with another from the same group. This gives an opportunity to fine tune the material further depending upon the requisite physical properties. In this context, the example given is for gallium in Bi$_{x}$Ga$_{y}$ clusters replaced with indium to make Bi$_{x}$In$_{y}$ clusters. The electronic properties remain similar but unlike gallium, indium is not a liquid at room temperature which makes indium relatively easier to handle. [Preview Abstract] |
|
L2.00046: The Solvation and Photochemistry of HI(H$_{2}$O)$_{n}$ Clusters: Evidence of Excited State Biradical Formation and Implications to the Solvated Electron Nicholas Bianco, Darren Hydutsky, A.W. Castleman, Jr. The fundamental understanding of the dynamics of chemical reactions is an important step to a firm foundation of knowledge in many areas of science, including atmospheric chemistry. The dissolution of acids in water is one type of atmospheric reaction whose dynamics are in need of understanding, as this is a process which frees halogens, allowing them to react with and, as a result, break down ozone. In order to study this process, we employ a femtosecond laser system coupled to a time-of-flight mass spectrometer. This setup allows us to perform pump-probe experiments on a small cluster of molecules, thereby tracking the dynamics of the process. While investigating the HI(H$_{2}$O)$_{n}$ system, we observed unusual behavior associated with the iodine atoms. Upon further experimentation, we conclude that these findings provide experimental evidence for the biradical, a theoretically predicted species consisting of a halo-acid clustered to water molecules. In addition to its atmospheric relevance, the biradical is a structure that could better explain many phenomena currently thought to be the result of the cavity-bound hydrated electron. [Preview Abstract] |
|
L2.00047: ELECTRON-ATOM COLLISIONS |
|
L2.00048: MCHF studies of electron impact ionization of helium atom Hari P. Saha Recently extended multi-configuration Hartree-Fock (MCHF) method [1] for electron impact ionization of atoms have been applied to calculate triple differential cross sections for electron impact ionization of helium at excess energies $\le $ 4 eV for the coplanar geometry. The results are obtained for equal and unequal energy sharing of the two outgoing electrons in the Hartree-Fock (HF) and the MCHF approximations to determine the importance of electron correlation between the two outgoing continuum electrons. In addition, we have also performed calculation in the variationally determined screening potential approximation [2-4]. We will compare our results calculated in the three approximations with the available experimental measurements and other theoretical calculations. [1] H.P. Saha (unpublished) [2] M.R.H. Rudge and Seaton, Proc. R. Soc. London, Ser. A 283, 262(1965). [3] R.K. Peterkop, Theory of Ionization of atoms by electron impact (Colorado Associated University Press, Boulder, 1977), pp128 and 129. [4] Cheng Pan and Anthony F. Starace, Phys. Rev. Lett. 67, 185 (1991); Phys. Rev. A45, 4588 (1992). [Preview Abstract] |
|
L2.00049: Elastic Scattering using artificial confining potentials Jim Mitroy, Jun-Yi Zhang It is shown that the discrete energies of a scattering Hamiltonian calculated under the influence of an artificial confining potential can be used to determine its phase shifts. Two potentials that have the same discrete energy under the influence of the confining potential will have exactly the same phase shift at that energy when the confining potential is removed. This result can be exploited by a variety of techniques to determine the phase shifts of many-body scattering problems. Results for both model problems and real physical systems such as $e^{\pm}$-H, $e^{\pm}$-He, Ps-H, and Ps-He are presented. [Preview Abstract] |
|
L2.00050: Applications of the hybrid theory to the scattering of electrons from He$^{+}$ and Li$^{++}$ and resonances in these systems A.K. Bhatia The Hybrid theory of electron-hydrogen elastic scattering\footnote {A.K.Bhatia, Phys. Rev. A extbf75, 032713 (2007)} is applied to the S-wave scattering of electrons from He$^{+}$ and Li$^{++}$. In this method, both short-range and long-range correlations are included in the Schrodinger equation at the same time. Phase shifts obtained in this calculation have rigorous lower bounds to the exact phase shifts and they are compared with those obtained using the Feshbach projection operator formalism\footnote {A.K.Bhatia, Phys. Rev. A extbf66, 064702 (2002)}, the close-coupling approach\footnote {P.G.Burke and A.J.Taylor, J.Phys. B extbf2, 44 (1969)}, and Harris-Nesbet method\footnote {T.T.Gien, J.Phys. B extbf35, 4475 (2002); extbf36, 2291 (2003)}. The agreement among all these calculations is very good. These systems have doubly-excited or Feshbach resonances embedded in the continuum. The resonance parameters for the lowest $^{1}$S resonances in He and Li$^{+}$ are calculated and they are compared with the results obtained using the Feshbach projection operator formalism\footnote {A.K.Bhatia and A.Temkin, Phys. Rev. A extbf11, 2018 (1975)} and\footnote {A.K.Bhatia extbf15, 1315 (1977)}. It is concluded that accurate resonance parameters can be obtained by the present method, which has the advantage of including corrections due to neighboring resonances and the continuum in which these resonances are embedded. [Preview Abstract] |
|
L2.00051: A Full-Relativistic B-Spline R-Matrix Method for Electron and Photon Collisions with Atoms and Ions Oleg Zatsarinny, Klaus Bartschat We have extended our $B$-spline $R$-matrix (close-coupling) method~[1] to fully account for relativistic effects in a Dirac-Coulomb formulation. Our numerical implementation of the close-coupling method enables us to construct term-dependent, non-orthogonal sets of one-electron orbitals for the bound and continuum electrons. This is a critical aspect for complex targets, where individually optimized one-electron orbitals can significantly reduce the size of the multi-configuration expansions needed for an accurate target description. Furthermore, core-valence correlation effets are treated fully {\it ab initio}, rather than through semi-empirical, and usually local, model potentials. The method will be described in detail and illustrated by comparing our theoretical predictions for e-Cs collisions with benchmark experiments for angle-integrated and angle-differential cross sections~[2], various spin-dependent scattering asymmetries~[3], and Stokes parameters measured in superelastic collisions with laser-excited atoms~[4]. [1]~O.~Zatsarinny, Comp. Phys. Commun. {\bf 174}, 273 (2006). [2]~W.~Gehenn and E.~Reichert, J. Phys. B~{\bf 10}, 3105 (1977). [3]~G.~Baum {\it et al.}, Phys. Rev. A~{\bf 66}, 022705 (2002) and {\bf 70}, 012707 (2004). [4]~D.S.~Slaughter {\it et al.}, Phys. Rev. A~{\bf 75}, 062717 (2007). [Preview Abstract] |
|
L2.00052: Out-of-plane ($e,2e$) angular distributions and energy spectra of He autoionizating states B.A. deHarak, K. Bartschat, N.L.S. Martin Out-of-plane $(e,2e)$ measurements and calculations are reported for the helium auto\-ionizing levels $(2s^2)^1\negthinspace S$, $(2p^2)^1\negthinspace D$, $(2s2p)^1\negthinspace P$, and for direct ionization. \footnote{B.A. deHarak, K. Bartschat, and N.L.S. Martin, {\em Phys. Rev. Lett.}, In press} While the recoil peak almost vanishes in the angular distribution for direct ionization, it remains significant for the auto\-ionizing levels and exhibits a characteristic shape for each orbital angular momentum $L=0,1,2$. These findings can qualitatively be explained by an $L$-dependent addition to the ionization amplitude, but only a second-order model in the projectile$-$target interaction can quantitatively reproduce the observed magnitudes of the recoil peaks. We present the data as both angular distributions and energy spectra for the resonances. [Preview Abstract] |
|
L2.00053: Improved Potential for Distorted-Wave Electron-Impact Excitation Calculations Christopher J. Fontes, Robert D. Cowan, George Csanak Some first-order scattering theories, such as the distorted-wave approximation, permit a different potential when solving for the initial and final free-electron wavefunctions. Other methods, such as first-order many-body theory, allow only a single (initial) potential for the solution of both the initial and final continuum orbitals. In practice, however, numerical procedures have been developed whereby free-electron orbitals are considered to arise from each of the different configurations that comprise a level via configuration interaction (CI). This type of approach results in continuum orbitals that are computed from a different potential associated with each configuration, rather than from a single potential associated with the physical level in question. Our previous work on this subject considered a method for obtaining a single, consistent potential from a level that contains an arbitrary amount of CI. This approach has been implemented in the ACE collisional excitation computer code, which is part of the Los Alamos suite of atomic physics codes. Numerical results will be presented for electron-impact excitation cross sections between selected levels for a variety of atoms and ions in order to quantify the effect of this new approach and to investigate the conditions for which the aforementioned procedures are valid. This work was performed under the auspices of the US Department of Energy. [Preview Abstract] |
|
L2.00054: Relativistic distorted-wave collision strengths for the $\mathbf 16\ \Delta n=0$ optically-allowed transitions with {$\mathbf n=2$} Hong Lin Zhang, Christopher J. Fontes Relativistic distorted-wave collision strengths have been calculated for the 16 $\Delta n=0$ optically-allowed transitions with $n=2$ in the 67 Be-like ions with nuclear charge number $Z$ in the range $26 \leq Z \leq 92$. The calculations were made for the four final, or scattered, electron energies $E'$ = 0.20, 0.42, 0.80, and 1.40, where $E'$ is in units of $Z^ {2}_{\rm eff}$ Ry with $Z_{\rm eff} = Z - 2.5$. In the present calculations we used an improved ``top-up'' method, the relativistic Kummer transformation (Fontes \& Zhang, Phys.~Rev.~A {\bf 76}, 040703(R) (2007)), to obtain high partial-wave contributions, in contrast to the semi- relativistic Coulomb-Bethe approximation used by Zhang \& Sampson (ADNDT {\bf 52}, 143 (1992)). More extensive collision strengths for Be-like ions were provided in this previous publication, including data for all of the possible 45 transitions, for six scattered energies and in 85 ions with $Z$ in the range $8 \leq Z \leq 92$. The collision strengths covered in the present work should be more accurate and are presented as replacements for the corresponding results in Zhang \& Sampson (1992). [Preview Abstract] |
|
L2.00055: Electron Impact Excitation of Transitions in $C^{+}$ Swaraj Tayal The B-spline R-matrix method in the framework of Breit-Pauli approximation is used to investigate the electron impact excitation of forbidden and allowed transitions in $C^+$. An accurate description of the target wave functions has been obtained in a multiconfiguration Hartree-Fock approach with flexible nonorthogonal orbitals. The 42 fine-structure levels of the $2s^22p$, $2s2p^2$, $2s^23l$ (l = 0-2), $2p^3$, $2s^24l$ (l = 0-3), 2s2p3s and $2s^25l$ (l = 0-2) configurations have been included in the scattering calculation. A second calculation with lowest 35 levels in the close-coupling expansion has also been carried out to check channel coupling effects on collision strengths. The continuum functions have been represented by the use of B-spline basis [1]. The present cross sections for the resonance $^2P^o$ - $2s2p^2~^2D$, $^2S$ and intercombination $^2P^o$ - $2s2p^2~^4P$ transitions are in very good agreement with the electron-energy-loss merged beams experiment. Oscillator strengths and transition probabilities for C II lines normally compare very well with previous calculation. [1] O. Zatsarinny, Comput. Phys. Commun. 174, 273 (2006). [Preview Abstract] |
|
L2.00056: THE IRON PROJECT AND THE RMAX PROJECT: Radiative and CollisionalProcesses of Iron Ions - Fe~I, Fe~II, Fe~XVI, Fe~XVII Maximiliano Montenegro, Sultana Nahar, Anil Pradhan, Chiranjib Sur Results from work in progress under the Iron Project and Rmax Project on electron impact excitation and radiative processes of photo-excitations, photoionization and electron-ion recombination will be reported. Whereas the Iron Project is involved in scattering and radiative atomic processes of iron and iron-peak elements, and the Rmax Project aims particularly at the X-ray spectroscopy of astrophysical objects. We will present (i) collision strengths of Fe~II at low energies using an accurate wavefunction needed for spectral analysis of infrared region, (ii) oscillator strengths and radiative decay rates for allowed and forbidden transitions in Fe~I and Fe~II, (iii) photoionization and electron-ion recombination of ground state of Fe~XVI for over a large energy/temperature range up to and including K-shell ionization and core excitations as observed in X-ray spectra, and (iv) photoionization cross sections of large number fine structure levels (n$\leq$10 and 0 $\leq$ 10) needed for astrophysical and modeling work. Relativistic approach in the Breit-Pauli approximation is being employed to study these atomic processes. [Preview Abstract] |
|
L2.00057: An intermediate-coupling R-matrix calculation of electron-impact excitation of Fe${\rm ^{4+}}$ Donald Griffin, Connor Ballance For a number of years, there has been a major effort to calculate electron-impact excitation data for every ion stage of iron embodied by the ongoing efforts of the IRON project [1993 {\it Astron. Astrophys.} {\bf 279} 298]. Due to the complexity of the targets, calculations for the lower stages of ionization have been limited to either intermediate-coupling calculations within the ground-configurations or $LS$-coupling calculations of the ground and excited configurations. However, accurate excitation data between individual levels within both the ground and excited configurations of the low charge-state ions are urgently required for applications to both astrophysical and laboratory plasmas. Here we report on the results of the first intermediate-coupling $R$-matrix calculation of electron-impact excitation for Fe${\rm ^{4+}}$ for which the close-coupling (CC) expansion includes not only those levels of the 3d${\rm ^4}$ ground configuration, but also the levels of the {\rm 3d${\rm ^34s}$}, 3d${\rm ^34p}$, 3d${\rm ^34d}$ and ${\rm 3d^24s^2}$ excited configurations. With 359 levels in the CC expansion and over 2400 scattering channels for many of the ${\rm J\Pi}$ partial waves, this represents the largest electron-ion scattering calculation to date and it was performed on massively parallel computers using a recently developed set of relativistic parallel $R$-matrix programs. [Preview Abstract] |
|
L2.00058: Electron Impact Excitation of Ni II C.M. Cassidy, C.A. Ramsbottom, M.P. Scott, P.G. Burke, V.M. Burke, C.J. Noble Considerable demand exists for electron excitation data for the ions of Fe, Co and Ni, since lines from these elements in low ionization stages are observed in many types of astrophysical spectra. Electron scattering from these ions is complicated by the `open' 3d-shell in the target, which gives rise to hundreds of fine structure levels, and thousands of coupled channels. In this study we are using the new parallel R-matrix codes (PRMAT) to obtain Maxwellian averaged effective collisions strengths for low-lying forbidden transitions in Ni II, over a range of astrophysically significant temperatures. Latest results will be presented at the conference. [Preview Abstract] |
|
L2.00059: Electron Collisions with Astrophysically Important Ions of Fe Catherine Ramsbottom, Clare Hudson, Patrick Norrington, Penny Scott One of the outstanding problems in electron collisions with atoms and ions is the accurate calculation of cross section data for low ionisation stages of iron peak elements such as iron, nickel and cobalt. There are a number of difficulties which arise from open d-shells in the target states of these ions. Firstly, a large CI expansion is required to adequately represent electron correlation effects within the target ion, and secondly, the open d-shells give rise to a large number of target states. Futhermore, if we consider transitions between fine-structure levels, this can give rise to thousands of coupled channels. In addition, calculations must be carried out over a very fine energy mesh in order to resolve low-lying Rydberg resonances. These difficulties have necessitated a major redevelopment of the standard scalar R-matrix codes to produce the parallel PRMAT and Breit-Pauli suite of codes. These new packages are being applied to the study of electron collisions with a number of Fe ions including Fe II and Fe III. Latest collisional data will be presented at the conference. [Preview Abstract] |
|
L2.00060: Effective collision strengths for the electron impact excitation of Mg\,{\sc v} C.E. Hudson, C.A. Ramsbottom, P.H. Norrington, M.P. Scott Electron impact excitation collision strengths for fine structure transitions of Mg\,{\sc v} have been determined by a Breit-Pauli $R$-matrix calculation. The target states are represented by configuration interaction wavefunctions and consist of the 19 lowest $LS$ states, having configurations 2s$^2$2p$^4$, 2s2p$^5$, 2p$^6$, 2s$^2$2p$^3$3s and 2s$^2$2p$^3$3p. These target states give rise to 37 fine structure levels and 666 possible transitions. The effective collision strengths are calculated by averaging the electron collision strengths over a Maxwellian distribution of electron velocities. Effective collision strengths for transitions between the fine structure levels are given for electron temperatures in the range $\log_{10} T_{\rm e} ({\rm K}) = 3.0 - 7.0$. Results are compared with the previous $R$-matrix calculation of Butler \& Zeippen (AASS, 1994) and the recent Distorted Wave evaluations of Bhatia, Landi \& Eissner (ADNDT, 2006). [Preview Abstract] |
|
L2.00061: Dramatic Resonances in Low-Energy Electron Elastic Scattering from Rb, Cs, Ba, La and Fr Atoms: Signatures of Electron Affinities A.Z. Msezane, Z. Felfli, Dmitri Sokolovski We predict dramatic resonances in low-energy electron elastic total cross sections for Rb, Cs, Ba, La and Fr atoms whose energy positions are identified with the electron affinities (EA's) for these atoms, preceded by shape resonances and Ramsauer-Townsend minima. This provides a new powerful theoretical method of determining unambiguous EA values for atoms. The extracted EA values for Rb, Cs, Ba and La atoms agree very well with the most recently measured values, but our value for Fr disagrees significantly with existing calculated values (there are no experimental EA's for the Fr atom). The calculation used the recent Regge-pole methodology [1] with a Thomas-Fermi potential incorporating the vital core- polarization interaction. Results will be compared with other available data.\newline [1] D. Sokolovski, Z. Felfli, S. Yu. Ovchinnikov, J. H. Macek and A. Z. Msezane, Phys. Rev. A {\bf 76}, 012705 (2007) [Preview Abstract] |
|
L2.00062: Simple method for Calculating Electron Affinity: Results for Ca, Sr and Ce Z. Felfli, A.Z. Msezane, Dmitri Sokolovski We have benchmarked the recently developed Regge-pole methodology for electron- atom elastic scattering on the most recent measurement of the electron affinity (EA) of the Ca atom [1]. The predictive power of the methodology is then demonstrated by calculating the binding energy of the ground state of the very complicated Ce$^-$ ion, with a g-orbital attachment, a shape resonance at 0.37 eV and a Ramsauer-Townsend minimum at about 0.09~eV [2]. Our calculated EA for Ce agrees very well with the latest measured value [3], but disagrees with that of Ref. [4]. Low-energy electron scattering partial, total and differential cross sections for e$^-$-Ca, e$^-$-Sr and e$^-$-Ce will be presented and discussed.\\ $[1]$ V. V. Petrunin, H. H. Andersen, P. Balling and T. Andersen, Phys. Rev. Lett. {\bf 76}, 744 (1996)\\ $[2]$ Z. Felfli, A. Z. Msezane and D. Sokolovski, J. Phys. B {\bf 41}, Fast Track,At Press (2008)\\ $[3]$ C. W. Walter {\it et al}, Phys. Rev. A {\bf 76}, 052702 (2007)\\ $[4]$ V. T. Davis and J. S. Thompson, Phys. Rev. Lett. {\bf 88}, 073003 (2002) [Preview Abstract] |
|
L2.00063: Electron Impact K-shell Ionization of Atomic Targets Bidhan Saha, Arun K. Basak, M. Alfaz Uddin, A.A.R. Patoary In spite of considerable progress -both theoretically and experimentally- recently in evaluating accurate K-shell ionization cross sections that play a decisive role for quantitative analyses using (i) electron probe microanalysis, (ii) Auger electron spectroscopy and (iii) electron energy loss spectra, attempts are still continuing to search for a model that can easily generate reliable cross sections for a wide range of energies and for various targets needed for plasma modeling code We report few modifications of the widely used binary encounter approximation (BEA) [1,2] and have tested by evaluating the electron impact K-shell ionization of few neutral targets at various projectile energies. Details will be presented at the meeting. [1] M. Gryziniski, Phys. Rev. A \textbf{138}, 336 (1965); [2] L. Vriens, Proc. Phys. Soc. (London) \textbf{89}, 13, (1966). [3M. A. Uddin , A. K. F. Haque, M. M. Billah, A. K. Basak, K, R, Karim and B. C. Saha, ,Phys. Rev. A \textbf{71},032715 (2005); [4] M. A. Uddin, A. K. Basak, and B. C. Saha, Int. J. Quan. Chem \textbf{100}, 184 (2004).] [Preview Abstract] |
|
L2.00064: Dielectronic Recombination of Al-Like Ions Shahin Abdel-Naby, Dragan Nikolic, Thomas W. Gorczyca, Nigel R. Badnell, Daniel W. Savin Accurate dielectronic recombination (DR) data are important for cosmic and laboratory plasma modeling. Over the past few years, our group has computed reliable DR data for all isoelectronic sequences up through Mg-like ions. Recently, we have focused our work on the complex third-row M-shell isoelectronic sequences, especially Al-like. Previous calculations for the DR rate coefficient for S$^{3+}$ were performed only within a non-relativistic LS-coupling approximation. Fe$^{13+}$ DR calculations, including semi-relativistic effects, have been completed and tested against the Heidelberg heavy-ion Test Storage Ring facility measurements. Here we present semi-relativistic DR rate coefficient calculations for a wide range of Al-like ions using AUTOSTRUCTURE, a level-resolved distorted-wave program package. The important effect of fine structure splitting in the Al-like ground state will be discussed. Finally, our results are fitted into a simple formula for use by astrophysical plasma modelers.\newline This work was funded in part by NASA (APRA), NASA (SHP) SR\&T, and UK PPARC grants. [Preview Abstract] |
|
L2.00065: Stable Bound States of Yb and Pr Negative Ions A.Z. Msezane, Z. Felfli, D. Sokolovski Andersen {\it et al} [1] concluded, through careful experimental investigation, that the electron affinity (EA) of Yb should be less than 3 meV and the accuracy of the theoretical calculations was deemed insufficient to provide a definitive answer to whether a stable bound state of the negative Yb ion exists. Such a small EA value for Yb is suitable for quenching Rydberg states, going through the formation of a temporary negative ion by ground state atoms with low EA's [2]. Our result obtained using the recent Regge- pole methodology [3] in which a Thomas-Fermi potential incorporates the important core- polarization potential, contradicts the conclusion in [1] by predicting a binding energy of 28~meV for the Yb$^-$ ion with a d-orbital electron attachment, including a Ramsauer-Townsend minimum at 20 meV and an s-wave Wigner threshold behavior of the total elastic cross section. Results for the e$^-$-Pr scattering will also be presented and contrasted with those for e$^-$-Yb scattering. \\$[1]$ H. H. Andersen, T. Andersen and U. V. Petersen, J. Phys. B {\bf 31}, 2239 (1998)\\$[2]$ I. I. Fabrikant and V. S. Lebedev, J. Phys. B {\bf 33}, 1521 (2000)\\$[3]$ D.Sokolovski {\it et al}, Phys. Rev. A {\bf 76}, 012705 (2007) [Preview Abstract] |
|
L2.00066: Resonances in Near-Threshold Electron Elastic Scattering Cross Sections for Au and Pt: Identification of Electron Affinities. Z. Felfli, A.Z. Msezane, D. Sokolovski The near-threshold electron attachment in Au and Pt atoms is investigated as Regge resonances using our recent Regge-pole methodology [1] together with a Thomas-Fermi potential which incorporates the crucial core-polarization interaction. The resultant stable negative ion states are found to have the discernable characteristic of very small imaginary parts of the Regge poles, which translates into long-lived resonances. The near-threshold electron elastic total cross sections for both Au and Pt are characterized by multiple resonances from which we extract the electron affinity (EA) values through the scrutiny of the imaginary part of the relevant complex angular momentum. For Au$^-$ and Pt$^-$ the extracted binding energies of 2.262 eV and 2.163 eV, respectively, are in excellent agreement with the most recently measured EA values for Au [2] and Pt [3]. Ramsauer-Townsend minima, shape resonances and the Wigner threshold behavior are identified in both Au$^-$ and Pt$^-$ ions.\\$[1]$ D. Sokolovski {\it et al}, Phys. Rev. A {\bf 76}, 012705 (2007)\\$[2]$ H. Hotop and W. C. Lineberger, J. Chem. Ref. Data {\bf 14}, 731 (1985)\\$[3]$ R. C. Bilodeau {\it et al}, Phys. Rev. A {\bf 61}, 012505 (1999) [Preview Abstract] |
|
L2.00067: Signature of Ericson Fluctuations in helium inelastic scattering cross sections near the double ionization threshold Junliang Xu, Anh Thu Le, Toru Morishita, Chii-Dong Lin We calculated the inelastic electron impact excitation cross sections of He$^{+}$ by electrons for a model helium atom to examine the onset of the signature of quantum chaotic scattering in this simple system. We find Ericson fluctuations (EF) in the calculated inelastic scattering cross sections only when the impact energies lie within about 0.25 eV below the double ionization threshold. We also discuss the stringent requirements and the proper methods for analyzing the inelastic scattering cross sections in order to observe EF experimentally. [Preview Abstract] |
|
L2.00068: ATOM OPTICS |
|
L2.00069: Towards Experimental Realization of an Atom Transistor Evan Salim, Dana Anderson, Ho-Chaio(Rick) Chuang, Victor Bright, Alex Zozulya, Jeffrey DeNatale, Robert Mihailovich We present theoretical and experimental progress towards an atom transistor using ultra-cold Rb87 atoms. Our transistor system will use a three well potential where tunneling between the two outside wells is controlled by the number of atoms in central well. In order to achieve realistic tunneling rates in the device, we create the potentials less than 1 micrometer away from an atom chip patterned with sub-micron wires. This scheme presents a host of technical challenges, including fabrication of chip features with adequate resolution and managing surface effects due to the proximity of the chip and the atoms. Noise limits of the system are discussed for both field fluctuations and atom number noise. [Preview Abstract] |
|
L2.00070: Optical One-Way Barrier for Atoms Elizabeth Schoene, Jeremy Thorn, Tao Li, Daniel Steck We demonstrate an asymmetric optical potential barrier for ultracold $^{87}$Rb atoms using laser light tuned near the D$_2$ transition. Such a one-way barrier, where atoms impinging on one side are transmitted but reflected from the other, is a literal realization of Maxwell's demon and has important implications for cooling atomic species not amenable to standard laser-cooling techniques. In our experiment, atoms are confined to a far-detuned dipole trap consisting of a single focused Gaussian beam, which is divided near the focus by the barrier. The one-way barrier consists of two focused laser beams oriented normal to the dipole trap. The first barrier beam is tuned between the $F=1\longrightarrow F'$ and the $F=2\longrightarrow F'$ families of hyperfine transitions, and presents a barrier only for atoms in the $F=2$ ground state, while letting $F=1$ atoms pass. The second beam pumps the atoms to $F=2$ on the reflecting side of the barrier, thus producing the asymmetry. We study experimentally the reflection and transmission dynamics of atoms in the presence of the one-way barrier. [Preview Abstract] |
|
L2.00071: Quantum ratchet using a delta kicked accelerator Vijayashankar Ramareddy, Ishan Talukdar, Gil Summy, Itzhack Dana A Quantum ratchet is a directed transport of particles in a spatially periodic system arising from the asymmetry between the initial distribution and the spatially periodic potential. A quantum $\delta$-kicked rotor has already been utilized to realize a ratchet [1]. When a quantum $\delta$-kicked accelerator is used instead of a kicked rotor, the ratchet acceleration is found to be generally suppressed [2]. Furthermore the ratchet arises only for special values of the acceleration. We use accelerated standing wave pulses on an atomic state prepared with a Bragg pulse on a BEC to realize the $\delta$-kicked accelerator and to study the ratchet. [1]I. Dana et. al., Phys. Rev. Lett. 100, 024103 (2008). [2]I. Dana et. al., Phys. Rev. E 76, 015201(R) (2007) [Preview Abstract] |
|
L2.00072: Observing matter-wave stability under small displacements with an atom interferometer Saijun Wu, Edward J. Su, Eric J. Heller, Mara G. Prentiss We discuss a recently-developed 4-pulse atom interferometry scheme in terms of spatial-displacement echoes, and experimentally study the stability of matter-wave dynamics in a magnetic guiding potential as a function of small spatial displacements. We observe that the displacement-induced dephasing factor saturates to a constant value at long interrogation time, and can be almost completely suppressed when the displacement across the guide is smaller than the coherence length of the atomic sample. Our observations illustrate the insensitivity of matter-wave dynamics to small spacial displacements as well as the feasibility of manipulating magnetically-guided atoms with optical pulses at high fidelity. We also demonstrate an interferometric method for in situ probing of the coherence length of confined atomic sample. [Preview Abstract] |
|
L2.00073: Spatial light modulators for cold atom manipulation Laurence Pruvost, Michael Mestre, Fabienne Diry, Bruno Viaris de Lesegno Spatial Light Modulators (SLM's) are programmable optical elements that can act as dynamical holograms, providing flexible control over the light intensity of a laser in a given plane. Thus, the operator can manipulate small objects using the forces that arise from the dipole force. They are being used for a wide range of applications, including biology, condensed matter physics, quantum optics and atomic physics. Our group is performing experiments using SLM's for cold atom manipulation. First we have focused on response time and diffraction pattern quality issues. We have demonstrated a device involving a SLM and an acousto-optic modulator (AOM/SLM) with a refresh time of some micro-seconds and without bleed effect during the hologram changes [1]. This device would be well-suited for cold atom manipulation with time-dependent dipole potentials. We have experimented with cold rubidium atom guiding using hollow Laguerre-Gaussian beams obtained by applying helical-phase holograms to laser beam. Future applications of this technique will be presented and discussed in the context of cold atoms or Bose-Einstein condensates experiments. [1] Fast reconfigurable and transient-less holographic beam-shaping realized by a AOM-SLM device, M. Mestre, B. Viaris de Lesegno, R. Farcy, L. Pruvost, J. Bourderionnet, A. Delboulbe, B. Loiseaux, and, D. Dolfi, Eur. Phys. J. Appl. Phys. \textbf{40}, 269--274 (2007). [Preview Abstract] |
|
L2.00074: Single- and Multi-Mode Channels for Neutral Atom Ensembles, N. Chattrapiban, S. Mitra, I.V. Arakelyan, W.T. Hill, III An ability to move coherent ensembles of neutral atoms through single-mode channels is key to realizing a host of future applications ranging from atom interferometry to quantum computing. While a number of promising chip-based approaches for guiding and splitting thermal and coherent atomic clouds have been demonstrated recently, they lack some flexibility offered by all-optical approaches -- an ability to create optical elements that can be co-located with atom traps and to rearrange them in real time. We have investigated various ways to create single-mode channels with blue-detuned tunnels. In particular, we have calculated the energy levels in a tunnel with an impenetrable wall (i.e., infinite potential) as well as in a finite Bessel potential, $V_0 J_m^2 (\kappa r)$. Our results show that single-mode operation should be possible at condensate temperatures for tunnels diameters $\sim $ 1 $\mu $m. At the same time, the degeneracy between energy levels could provide a platform for generating interesting spatial superpositions, which can be controlled by the Bessel order, $m$, and $V_0 $, which depends on the optical field intensity. [Preview Abstract] |
|
L2.00075: MATTER WAVE INTERFEROMETRY |
|
L2.00076: Observation of on-chip, atom interferometric phase coherence with 710 $\mu $m and 200 ms packet separation Quentin Diot, Stephen R. Segal, Eric A. Cornell, Alex A. Zozulya, Dana Z. Anderson We report on an atom chip Bose-Einstein condensate interferometer with long arm length and coherence time. In our experiment, a standing wave of light splits a condensate into two packets that counter-propagate in a waveguide potential with weak axial confinement. We vary the relative phase of the packets by applying a magnetic field gradient during propagation. We apply the splitting light a second time after the packets have propagated for one axial trap period in order to read out the relative phase. The packets are separated for a total of 200 ms and achieve a maximum spatial separation of 710 $\mu $m; these parameters compare favorably with those of similar experiments. To extract the phase shift due to the applied magnetic field, we must carefully control apparatus vibrations. We compare the noise in our results to the expected contribution from quantum phase diffusion. [Preview Abstract] |
|
L2.00077: Matter-Wave Interferometery at BYU Christopher Erickson, James Archibald, Jeremey Birrell, Dan Christensen, Marshall Van Zijll, Dallin Durfee We report on the progress of two matter-wave interferometers at BYU. The first device is a thermal-beam Ramsey-Bord\a'e calcium interferometer. This device will be used to improve long-term stability of atom-interferometer inertial force sensors and optical frequency standards, and for measurements of relativistic effects in extremely non-relativistic limits. In the future this device will be upgraded to a dual species Ca/Sr interferometer for measurements of time-varying constants. The second device is an ion interferometer based on a laser-cooled $^{87}$Sr$^+$ beam which will be split and recombined using stimulated Raman transitions. The ion interferometer will be used to test Coulomb's inverse-square law and the possibility of a finite photon rest mass. We will also present several pieces of precision instrumentation developed for these experiments. [Preview Abstract] |
|
L2.00078: Confinement effects in guided-wave atom interferometer with mm-scale arm separation J.H.T. Burke, B. Deissler, K.J. Hughes, C.A. Sackett Guided-wave atom interferometers measure interference effects using atoms held in a confining potential. In one common implementation, the confinement is primarily two-dimensional, and the atoms move along the nearly free dimension after being manipulated by an off-resonant standing wave laser beam. In this configuration, residual confinement along the nominally free axis can introduce a phase gradient to the atoms that limits the arm separation of the interferometer. We experimentally investigate this effect in detail, and show that it can be alleviated by having the atoms undergo a more symmetric motion in the guide. This can be achieved by either using additional laser pulses or by allowing the atoms to freely oscillate in the potential. With these techniques, we demonstrate interferometer measurement times up to 72~ms and arm separations up to 0.42 mm with a well controlled phase, or times of 0.91~s and separations of 1.7 mm with an uncontrolled phase. [Preview Abstract] |
|
L2.00079: Quantum-noise limits in matter wave interferometry with anyons Frank Corvino, Ivana Djuric, J.D. Mancini, Christopher Search Here we consider a generalized Mach-Zehnder interferometer for matter waves with fractional quantum statistics, so called anyons. First, the input-output relations are derived for a lossless beam splitter with two input arms and two output arms using anyon commutation relations. By studying the scattering of multi-particle states by the beam splitter we are able to elucidate the role of quantum statistics and compare the output statistics of bosons, fermions, anyons, and classical particles. In addition, we study the quantum noise in the output statistics for the full interferometer and compare the results with anyons to the standard quantum limit for the sensitivity of the interferometer. Finally, we suggest methods for achieving Heisenberg limited sensitivity in an anyonic matter wave interferometry. [Preview Abstract] |
|
L2.00080: Noise limits on Bose-Einstein condensate gyroscope performance Stephen R. Segal, Dana Z. Anderson, Alex A. Zozulya We present a theoretical study of the impact of several noise sources on the sensitivity and performance of an atom-based Sagnac gyroscope. We consider a device that uses Bose condensed atoms that are split by light fields and counter-propagate around a loop produced by magnetic potentials created with an atom chip. In addition to atom shot noise and atom interactions, electrical current shot noise and Johnson noise impose fundamental limits on device performance. Magnetic field fluctuations and vibrations from external sources also introduce noise. We examine how these effects impact the performance of the gyroscope. [Preview Abstract] |
|
L2.00081: Structure and interference of ultracold atoms in circular waveguides Martin Kandes, Oscar Salazar, Michael Bromley Simple circular waveguides promise to be an ideal architecture for building high-precision matter-wave interferometers that exploit the coherent source of atoms provided by Bose-Einstein condensates (BECs). We perform numerical calculations of the time-dependent Gross-Pitaevskii equation in one and two dimensions to simulate gravity-induced quantum interference for counterpropagating BECs in a circular waveguide. The emphasis being on the role that nonlinear interactions have on the feasibility of interferometric measurements. Our results vividly illustrate the many challenges in performing the corresponding experiments. [Preview Abstract] |
|
L2.00082: Apparatus for Ultra-Cold Fermion Interferometry Seth Aubin, Aiyana Garcia, Brian DeSalvo We present progress on the construction of an apparatus for ultra-cold fermion interferometry experiments. The apparatus consists of two connected glass vacuum cells: Fermionic potassium ($^{40}$K) and bosonic rubidium ($^{87}$Rb) atoms are cooled and collected in a dual-species magneto-optical trap (MOT) in the first cell and are then transported magnetically to the second cell, where they are loaded into a micro-magnetic chip trap. We use radio-frequency (RF) evaporation to cool the rubidium atoms, which in turn sympathetically cool the potassium atoms. The apparatus takes advantage of the rapid cooling inherent to micro-magnetic traps, while also benefiting from the ultra high vacuum achievable with a two chamber vacuum system. In describing our experimental approach, we address the experimental challenges and possible force-sensing applications of fermion interferometers on chips. [Preview Abstract] |
|
L2.00083: QUANTUM INFORMATION |
|
L2.00084: Entanglement of a Laguerre-Gaussian cavity mode with a rotating mirror P.-L. Giscard, M. Bhattacharya, P. Meystre It is known that the exchange of linear momentum between an optical cavity field mode and a vibrating mirror can entangle them together [1]. We consider here the rotational analog of this situation and show that radiation torque can entangle a Laguerre-Gaussian cavity field mode with a rotating mirror [2]. We present the arrangement used to generate the entanglement and study its robustness against temperature, showing that it persists up to $100K$ for experimentally accessible parameters. We further study the dependence of the entanglement with angular momentum and the detuning from the cavity resonance. Finally we observe a strong correlation between the behavior of the entanglement at low temperature and the mean number of thermal phonons at the mirror rotation frequency, a consequence of the black-body law for the phonons. \newline \newline [1] D. Vitali \textit{et al.}, Phys. Rev. Lett. \textbf{98}, 030405 (2007). \newline [2] M. Bhattacharya, P. -L. Giscard, P. Meystre, Phys. Rev. A \textbf{77}, 013827 (2008). [Preview Abstract] |
|
L2.00085: Robust preparation of Dicke-states by multi-ion STIRAP Ian Linington, Nikolay Vitanov We present a simple technique for the generation of arbitrary-sized Dicke states in a chain of trapped ions. The method uses global addressing of the entire chain by two pairs of laser pulses in order to engineer collective adiabatic passage along a multi-ion dark state -- a unique eigenstate of the Hamiltonian in which decaying energy levels are not populated in any ion. In the adiabatic limit, the system resides in the dark state at all times and hence spontaneous emission is completely avoided. Dicke state preparation is achieved in only two stages of collective adiabatic passage, in between which the system resides in a vibrational Fock state. As well as an extremely simple experimental implementation, our technique also possesses the following advantages: (i) dynamical and geometric phases acquired during the entire preparation procedure are both identically zero; (ii) the proposed technique is adiabatic in nature and hence it is robust against fluctuations in the intensity and timing of the laser pulses; (iii) there is no decoherence arising from spontaneous emission in the adiabatic limit, regardless of the decay rate from the upper level -- this allows the use of resonant laser pulses which in turn allows shorter pulse durations; (iv) because only two, very rapid, interaction steps are required, the effects of heating are almost negligible under realistic experimental conditions. For a Dicke state of ten ions sharing two excitations, we predict a fidelity approaching $99\%$. [Preview Abstract] |
|
L2.00086: Coherent control of entangled states of atomic ensembles Scott B. Papp, Kyung S. Choi, Hui Deng, H. Jeff Kimble The realization of quantum communication protocols over a scalable quantum network depends on precise control of entangled states. Recent experimental progress toward a scalable quantum network has included the demonstration of heralded entanglement creation and the distribution of entanglement amongst the nodes of a network. In our system quantum nodes are realized with a pair of atomic ensembles of laser cooled Cs atoms. We will discuss recent developments including the storage and retrieval of entanglement into and out of a quantum memory [1] and an investigation of the processes by which entanglement decays in our system [2]. [1] K. S. Choi, H. Deng, J. Laurat, and H. J. Kimble, arXiv:0712.3571v2 (2008). [2] J. Laurat, K. S. Choi, H. Deng, C.-W. Chou, and H. J. Kimble, Phys. Rev. Lett. \textbf{99}, 180504 (2007). [Preview Abstract] |
|
L2.00087: QUANTUM COMPUTATION |
|
L2.00088: Experimental Progress Towards the Development of Neutral Atom Quantum Computing Architecture Based on 2D Optical Lattices on a Chip Rajani Ayachitula, Andrew Morss, Katharina Gillen, Gregory Lafyatis In previous theoretical work, we showed that optical lattices can be created above an optical waveguide by destructively interfering laser light in two different waveguide modes. Single atoms can be tightly trapped at the nodes of a lattice, serving as individually addressable qubits of a quantum memory. Theoretically, we have examined moving the atoms within the lattice. We have also studied ways to carry out one- and two-qubit gates. In subsequent experimental work, we developed and characterized optical waveguides suitable for making these optical lattices. We measure losses $\mathbin{\lower.3ex\hbox{$\buildrel<\over {\smash{\scriptstyle\sim}\vphantom{_x}}$}} $1db/cm for TE0 and TE1 modes. To address individual modes, we couple light into the waveguide modes using gratings fabricated on the waveguide surface. We have observed $>$15{\%} coupling efficiency. Our initial scientific studies characterize samples of cold atoms dropped onto the waveguide. We will discuss recent experimental progress. [Preview Abstract] |
|
L2.00089: Towards Spin Photon Entanglement Using Nitrogen Vacancy Center in Diamond Emre Togan, Yiwen Chu, Alexey Trifonov, M.V. Gurudev Dutt, Liang Jiang, Lily Childress, Alexander S. Zibrov, Philip Hemmer, Mikhail Lukin In recent years there has been an increase in demand for using small, few qubit systems for optically scalable quantum information processing. Earlier work indicates that an ideal candidate is using qubits formed by individual nuclear spin state of $^{13}$C in diamond that can be addressed and manipulated using electronic spin state of a nearby Nitrogen Vacancy (NV) center. Demonstrations so far have been in manipulating both the NV and some nearby $^{13}$C nuclear spins. Here we describe the progress that we've made towards entangling two separate NVs, allowing isolated few qubit systems to be scaled up. To entangle two NVs one needs to isolate emission from single NV centers that are sufficiently narrow in bandwidth, and understand the underlying selection rules for this emission process. In this work we estimate emission linewidth of the zero phonon line of several different NVs. We also show by using resonant absorption spectroscopy on single NVs one can selectively excite different optical transitions and study their selection rules. Finally we propose and evaluate a method to demonstrate spin-photon entanglement, to act as an initial step to entangle two NVs. [Preview Abstract] |
|
L2.00090: Repulsive shield between polar molecules Alexey Gorshkov, Mikhail Lukin, Peter Zoller, Hans Peter B\"uchler We propose and analyze a technique that allows to suppress inelastic collisions and simultaneously enhance elastic interactions between cold polar molecules. The main idea is to cancel the leading dipole-dipole interaction with a suitable combination of static electric and microwave fields in such a way that the remaining repulsive van-der-Waals-type potential forms a repulsive shield with controllable range. We analyze in detail the elastic and inelastic scattering cross sections, and outline a method towards efficient evaporative cooling of polar molecules. Furthermore, we show that this setup is suitable for the realization of three-dimensional crystalline structures. [Preview Abstract] |
|
L2.00091: Ion transport through an X-intersection trap array Brad Blakestad, J.M. Amini, J.W. Britton, K.R. Brown, R.J. Epstein, J.P. Home, J.D. Jost, E. Knill, C. Langer, D. Leibfried, C. Ospelkaus, R. Ozeri, S. Seidelin, A. VanDevender, J.H. Wesenberg, D.J. Wineland Scaling up traps to control numerous atomic ions is an important step towards large-scale trapped-ion quantum information processing, and likely will require two-dimensional junctions such as T-({\#}) or X-intersections. An 18-zone ion trap array that incorporates such an X-intersection has been demonstrated. One issue that impedes travel through this structure is the RF pseudopotential bumps that occur at the junction. With the use of 9Be+ and 24Mg+ ions, we explore the movement of ions through this junction while maintaining reasonable trapping frequencies and minimizing motional excitation. Current experiments are devoted to exploring the tradeoffs between transport duration and ion heating. (Work supported by IARPA.) ({\#})W. K. Hensinger, et al; \textbf{App. Phys. Lett.} 88, 034101 (2006). [Preview Abstract] |
|
L2.00092: A scheme for enhanced light collection from a trapped ion Jonathan Sterk, Peter Maunz, Andrew Manning, Chris Monroe By coupling a trapped ion to an optical cavity, fluorescence into a single mode can be dramatically enchanced. This not only boosts the fidelity and speed of trapped ion qubit measurement, but it also can greatly improve probabilistic entangling schemes that rely on the collection and interference of single photons~[1]. We present progress towards an ion--cavity system for 369nm photon collection from a trapped Yb$^{+}$ ion. The ion will reside in a microtrap inside an optical cavity, where the ion--electrode spacing is smaller than the ion--cavity distance, which may mitigate the effect of stray fields from charged mirrors~[2,3]. A single-atom cooperativity of $C\sim0.4$ should be achievable in a one-sided cavity, yielding $10$ times the number of photons collected from a free-space ion. This would permit significantly faster detection and a $100$-fold increase for heralded two-photon entanglement events~[1]. \\ $[1]$ D. L. Moehring, et. al. \emph{Nature} \textbf{449}, 68 (2007)\\ $[2]$ G. Guthorlein, \textit{et al.}, {\it Nature} {\bf 414}, 49 (2001)\\ $[3]$ A. B. Mundt, \textit{et al.} \textit{Phys. Rev. Lett.}, \textbf{89}, 103001, (2002) [Preview Abstract] |
|
L2.00093: Simulating Quantum Spin Models with Trapped Ytterbium Ions$^1$ M.-S. Chang, K. Kim, S. Korenblit, K.R. Islam, J.D. Sterk, A. Chew, R. Slusher$^{\dagger}$, C. Monroe Simulating large quantum many-body systems is practically impossible with classical computers, as it requires resources exponential in the system size. An array of cold trapped ions has recently been identified as a promising candidate for exploring many-body spin Hamiltonians. This is due to superb control of their quantum states and interactions, high-fidelity spin state detection of each and every ion, and very long coherence time. We will initially work with less than 10 ions, but will speculate on how this may be scaled up to larger numbers of spins. We will report the recent progress toward quantum simulations of Heisenberg-like spin Hamiltonians [1] with trapped Ytterbium ions in a linear Paul trap. \\ \\ $[1]$ D. Porras and J. I. Cirac, Phys. Rev. Lett. {\bf 92}, 207901 (2004) \\ \\ $^1$This work is supported by the DARPA OLE Program under ARO Award W911NF-07-1-0576, IARPA under ARO contract W911NF-04-1-0234, and the NSF PIF Program under grant PHY-0601255. [Preview Abstract] |
|
L2.00094: Experimental Progress Towards Scalable Quantum Computation using Dual Atomic Species in Optical Lattices Arjun Sharma, Scott Waitukaitis, Daniel Rivas, Kathy-Anne Brickman, Nathan Gemelke, Cheng Chin We propose a new method for implementing quantum entaglement with neutral atoms. In our scheme, ultracold fermionic lithium atoms ($^{6}$Li) and bosonic cesium atoms ($^{133}$Cs) will be loaded into two independent optical lattices. The Cs lattice will be sparsely filled (1atom/1000sites) relative to uniformly filled Li lattice. Each lattice frequency is carefully chosen so that one specie's lattice does not influence the other species. Precise phase control with electro-optic modulators will enable translation of the Cs lattice so that a single Cs atom can interact with any Li atom. Through this interaction, and transportation of the Cs atoms among the Li atoms, entanglement of distant Li atoms may be realized. We are fabricating a vacuum system with two chambers. Each atomic species will be Bose-condensed in its own chamber. The Li atoms will then be transported to the Cs chamber. Initial experiments will conduct the first studies into the cold collision properties between Li and Cs quantum gases. The results will allow us to determine the best strategy to implement the above entangling operations. [Preview Abstract] |
|
L2.00095: QUANTUM MEASUREMENT |
|
L2.00096: Nanoscale magnetometry with nitogen-vacancy color centers in diamond Jonathan Hodges, Sungkun Hong, Jeronimo Maze, Paul Stanwix, Paola Cappellaro, Liang Jiang, M.V. Gurudev Dutt, Emre Togan, Amir Yacoby, Philip R. Hemmer, Ronald Walsworth, Mikhail D. Lukin The ability to sense and spatially resolve magnetic fields at nanometer dimensions is key to understanding many fundamental physical processes and has a wide range of applications in materials science, biology, and medicine. Our novel approach to nanoscale sensing is based on coherent control of individual electronic spins associated with the nitrogen-vacany (NV) center in diamond. In this work, we describe proof-of-principle experimental measurements of time-varying magnetic fields using single NV$^{-}$ centers in bulk crystalline diamond and sub-100 nm diamond nanocrystals. Using spin echo spectroscopy techniques on the spin triplet electronic ground state, we sense magnetic fields with frequencies from 3kHz to 15 kHz to a resolution approaching 100 $\mu$Gauss. [Preview Abstract] |
|
L2.00097: Progress toward continuous measurement and feedback-stabilization of Pauli operators in an optical qubit. Tom Jones, Thomas Loyd, JM Geremia We describe progress toward an optical qubit implementation of continuous measurement and real-time quantum feedback, with the ultimate objective to achieve complete control over single-shot polarization-basis Pauli measurements performed on the qubit. Current work has focussed on the production of high-quality optical qubits by cavity-enhanced degenerate type II downconversion of light from 426nm to 852nm. Weak measurement of Pauli operators in the polarization basis will be performed by heterodyne detection. Our objective is to analyze the near quantum-limited continuous measurement data using techniques from real-time quantum filtering theory to enable us to feedback on the qubit polarization in order to obtain a deterministic outcome of the Pauli measurement being performed. [Preview Abstract] |
|
L2.00098: LOW TEMPERATURE PLASMAS |
|
L2.00099: Structure and dynamics in ultra-cold Rydberg gases and cold plasmas Duncan Tate, Alexander Gill, Cristian Vesa, William Whitledge In this presentation, we will discuss recent experiments using ultra-cold Rydberg atoms. We create dense samples of cold Rydberg atoms ($n \sim 1 \times 10^{10}$ cm$^{-3}$, $T \approx 100 \mu$K) from $5p \ ^2P_{3/2}$ rubidium atoms in a MOT using a narrow bandwidth ($\approx 100$ MHz) 480 nm light pulses. This light is generated by an amplified diode laser system whose output is frequency-doubled by a potassium niobate crystal. We are pursuing three avenues of research. First, we are investigating the effect of the cold Rydberg atoms on the electron temperature of an ultra-cold plasma, which is created by direct photoionization of the $^2P_{3/2}$ Rb atoms using a Littman dye laser. The Rydberg atoms (produced as described above) are then ``embedded'' in the plasma from 1-10 $\mu$s later. Second, we are performing mm-wave and optical spectroscopy of the dense Rydberg samples in a search for long-range molecular species. Third, we are improving the performance of a ``dark SPOT'' trap with the ultimate goal of increasing the achievable Rydberg density in the experiments described above. [Preview Abstract] |
|
L2.00100: Fluorescence Imaging of Ultracold Neutral Plasmas Jose Castro, Hong Gao, Thomas Killian Spatially-resolved fluorescence imaging of Ultracold Neutral Plasmas (UNP) produces a spectrum that is Doppler-broadened due to the thermal ion velocity and shifted due to the ion expansion velocity. Furthermore, sheet excitation of the plasma allows for localized analysis of the system without density variation. Using this technique, adiabatic cooling, electron-ion collisions, kinetic energy oscillations and velocity-changing collisions are studied for Ultracold Neutral Plasmas. [Preview Abstract] |
|
L2.00101: BOSE-EINSTEIN CONDENSATES |
|
L2.00102: Bose-Einstein Condensate ``Level'': a tool box for precesion measurement Satyan Bhongale, Eddy Timmermans A trapped, phase separated, two component Bose-Einstein condensate (BEC) can be configured to give a single BEC bubble that floats freely in the surrounding BEC. We point out that this system gives a unique template to carry out mesoscopic quantum studies and to detect weak forces. We demonstrate the detection capabilities by proposing and studying a ``Quantum Level'' for fundamental quantum fluctuation studies and for mapping the potential energy landscape near a surface with exquisite accuracy. The above method open up a new avenue for research where the quantum state of a trapped ultra-cold gases such as a BEC is cast as a measurement-tool rather than a system-under-investigation. [Preview Abstract] |
|
L2.00103: On the Application of Group Theoretical and Graphical Techniques in Pursuit of the General, Interacting N-body Problem W. Blake Laing, Martin Dunn, David W. Kelle, Deborah K. Watson We use group theoretical and graphical techniques to develop a method that does not require intensive numerical effort when solving for systems with arbitrary interactions where N may be large (such as a BEC or a superfluid helium droplet). This method generalizes an N-body dimensional perturbation theory to higher order and is a significant advancement in our long-term project to analytically describe beyond-mean-field effects in confined, large-N quantum systems. We use symmetry properties and group representation theory, and have developed a graphical technique to analytically derive the next-order, N-body wave function for a fully-interacting confined quantum system. This method makes no assumptions concerning the number of particles or the strength of interparticle interactions and holds promise for applications to experimental systems such as a BEC with ``tunable'' interactions. [Preview Abstract] |
|
L2.00104: Stochastic Variational Method for Atomic Gases Martin Th{\O}gersen, Dmitri Fedorov, Aksel Jensen We have applied the stochastic variational method [1] to trapped cold gases and calculated energies, densities, correlation functions and condensate fractions as function of scattering length and particle number [2]. We also investigated the $N$-body Efimov effect for systems with $N=3, 4, 5, 6,$ and $7$ bosons at infinite scattering length and obtained the characteristic exponential scaling factors for the energies and densities [3]. We have also compared the finite-range three-body model with the zero-range model [4] and determined the validity region of, and the effective range corrections to, the latter.\newline [1] H.H. Sorensen, D.V. Fedorov and A.S. Jensen, AIP Conference Proc. {\bf 777} (2005) 12; K. Varga and Y. Suzuki, Comput. Phys. Commun. {\bf 106} (1997) 157.\newline [2] M. Th{\o}gersen, D.V. Fedorov and A.S. Jensen, Europhys. Lett. {\bf 79} (2007) 40002.\newline [3] M. Th{\o}gersen, D.V. Fedorov and A.S. Jensen, submitted to Europhys. Lett.\newline [4] E. Braaten and H.-W. Hammer, Phys. Rep. {\bf 428} (2006) 259; T. Kraemer et al., Nature {\bf 440} (2006) 315. [Preview Abstract] |
|
L2.00105: The ground and resonant states of three self-gravitating bosons and fermions Yew Kam Eugene Ho, Sabyasachi Kar Recently, a new property of the Bose-Einstein condensates (BECs) has been proposed [1] that it is self bound for sufficiently strong self-gravitation, opening up a door to study self-gravitating systems with attractive $1/r$ potentials. Such an attractive potential can simulate gravity between the quantum systems. In the usual strong anisotropy regime, the inter-atomic potential takes a form of --u/r, where u is the coupling constant dependent on the laser intensity. Recently, we have investigated the ground state, excited states, and resonance states for three self-gravitating bosons and fermions using highly correlated exponential basis functions [2]. Our calculated bound states energies are lower than the earlier results in the literature [3]. We have also employed the complex-coordinate rotation method [4] to calculate the energies and widths for resonances lying below the $N=$2 and $N=$3 thresholds of the two-body subsystems [2]. [1] D. O'Dell\textit{ et al}., Phys. Rev. Lett. \textbf{84}, 5687 (2000); Phys. Rev. A \textbf{63}, 031603 (2001). [2] S. Kar and Y. K. Ho, Phys. Rev. A \textbf{76}, 032711(2007); Phys. Lett.$ A$\textbf{370}, 306 (2007) ; to be published. [3] J. P. D'Incao\textit{ et al.}, \textit{Phys. Rev. A} \textbf{75}, 032503 (2007). [4] Y. K. Ho, \textit{Phys. Reports} \textbf{99}, 1 (1983). [Preview Abstract] |
|
L2.00106: Bragg Spectroscopy of a Strongly Interacting $^{85}$Rb Bose-Einstein Condensate Robert Wild, Scott Papp, Juan Pino, Shai Ronen, John Bohn, Deborah Jin, Carl Wieman, Eric Cornell We report on measurements of the large-momentum excitation spectrum of a strongly interacting Bose-Einstein condensate (BEC). Using a magnetic-field Feshbach resonance to tune atom-atom interactions in the condensate, we reach a regime where quantum depletion of the ground state and beyond mean-field corrections to the condensate chemical potential are significant. The Bragg resonance line shift due to strong interactions was found to be significantly less than that predicted by a mean-field theory, and demonstrates the onset of beyond mean-field effects in a gaseous BEC as Ref[1]. \newline \newline [1] E.~K. Irish, Phys. Rev. Lett. {\bf 99}, 173601 (2007). [Preview Abstract] |
|
L2.00107: Excitation Spectrum a Strongly Interacting Rb85 Bose-Einstein Condensate Shai Ronen, John Bohn, Scott Papp, Juan Pino, Robert Wild, Deborah Jin, Carl Wieman, Eric Cornell The excitation spectrum of a Bose-Einstein condensate is ordinarily described by the Bogoliubov theory. However, near a Feshbach resonance, when the interactions get strong, one expects deviations from this theory, which may be calculated within the higher order Beliaev theory (Sov. Phys. JETP 34,299 (1958)). It has been well known that at low momenta Beliaev theory predicts an increase in the excitation energy. Here we highlight the fact that at large momenta in fact the opposite is true, and we map the transition between the two limits. We also study the effect of the effective range correction to the two-body scattering at large momentum transfer, and compare the theory with a Bragg scattering experiment in Rb85. [Preview Abstract] |
|
L2.00108: Proliferation of phase defects in a 3D array of Bose-Einstein condensates Shihkuang Tung, Giacomo Lamporesi, Volker Schweikhard, Eric Cornell Bose-Einstein condensates are loaded into a 3D optical lattice. A large lattice spacing of 4-5 $\mu$m allows us to have a 3D BEC array with hundreds of atoms in each site. By controlling the optical power of the lattice, we are able to fine tune the tunneling of the atoms between lattice sites. The critical temperature and the proliferation of phase defects in the 3D array of BECs are studied. [Preview Abstract] |
|
L2.00109: Vortex Lattices in a Crossed-Beam Optical Dipole Trap Michael Goldman, Elizabeth Petrik, Daniel Guest, David Hall We report on experimental studies of rotating ${}^{87}$Rb Bose-Einstein condensates confined in a crossed-beam optical dipole trap. We observe vortex lattice lifetimes that are comparable to condensate lifetimes --- on the order of seconds --- despite the absence of strict cylindrical symmetry in the trap. The purely optical confinement permits experiments that explore the behavior of rotating multicomponent (spinor) condensates. Recent progress and future prospects will be discussed. [Preview Abstract] |
|
L2.00110: Appearance of modulated spatial pattern in a dual-species BEC during condensate growth. Shai Ronen, John Bohn, Laura Halmo, Mark Edwards It has been long known that a dual-species BEC with a sufficiently large repulsive intra-species interaction becomes immiscible. In a recent experiment with Rb85 and Rb87 by the Wieman group at JILA, a complicated pattern of multiple interleaved ``bubbles'' of the the two species has been observed upon the end of evaporative cooling. This observation defies expectations that the ground state should only have a single boundary between the two species. We purpose a model wherein this spatial pattern is formed during condensate growth through a modulation instability mechanism. We model the growth of the condensates with a linear gain term added to the Gross Pitaevskii equation, and obtain qualitatively similar patterns to the experiment. We also predict the conditions which would maximize the number of bubbles. [Preview Abstract] |
|
L2.00111: Modeling evaporative cooling of a dual-species Bose-Einstein L. Halmo, M. Edwards, S. Ronen, J.L. Bohn, C.W. Clark A recent experiment performed on a Bose-Einstein condensate mixture of Rb85 and Rb87 by the Wieman group at JILA observed a complicated pattern of multiple interleaved ``bubbles'' of the two species at the end of evaporative cooling. In this experiment, the condensate mixture was formed by first cooling the thermal- gas mixture in a magnetic trap and then transferring the sample into an optical trap where final cooling was achieved by decreasing the depth of the optical trap until condensate formation occurred. We have studied the evaporative cooling of the condensate mixture in the optical trap under conditions similar to those in the JILA experiment by evolving a ``thermally excited'' initial state with the Gross-Pitaevskii equation [R.J.\ Marshall, et al., Phys.\ Rev.\ A, {\bf 59}, 2089 (1999)]. Our studies of the results of evaporative cooling have included both linear and exponential ramping of the cooling and include the effect of gravity. We also compare our results with experiment. [Preview Abstract] |
|
L2.00112: Towards Dual BEC: Zeeman slower approach. Matthew Gibbs, Andrew Seltzman, Edward Thiemann, Tetsuya Ishikawa, Gustavo Telles, Chandra Raman We present the features of an experimental apparatus, specially built to produce and investigate dual species atomic Bose-Einstein condensates of $^{23}$Na and $^{87}$Rb. The system has many interesting capabilities including a dual oven with a distillation chamber for safe handling, the ability to generate kilogauss magnetic fields, and high optical access. Our approach incorporates a Zeeman slower, capable of delivering a large flux of both Na and Rb atoms to be captured in a dual species magneto-optical trap. Later, $^{87}$Rb atoms are sympathetically cooled by large numbers of $^{23}$Na atoms, evaporativelly cooled down to the quantum degeneracy. We are interested in observing quantum statistical effects, interaction tuning, and production of heteronuclear ultracold dimer molecules. Future experiments and ideas may be presented. [Preview Abstract] |
|
L2.00113: BEC of Potassium-41: towards creation of ultracold polar molecules Jun Kobayashi, Tetsuo Kishimoto, Kai Noda, Kiyotaka Aikawa, Masahito Ueda, Shin Inouye One of the major goals in the field of ultracold gases is the production of ultracold polar molecules. Due to anisotropic, long-range interaction, a polar molecular gas is expected to show us a rich variety of new phenomena, including anisotropic collapse and a super-solid phase. We work with a two-species ultracold atomic gas of $^{41}$K and $^{87}$Rb. We successfully produced a BEC of $2\times10^5$ $^{41}$K atoms. A BEC of $^{41}$K was first realized by the LENS group[1]. However, since that experiment was based on sympathetic cooling with $^{87}$Rb, the characteristics of $^{41}$K under evaporative cooling were unknown. Furthermore, producing a high phase-space density $^{41}$K cloud by laser cooling alone was expected to be difficult because of the small hyperfine splitting of the excited states (13MHz). We show that compressed-MOT and Doppler cooling stages are essential for achieving a 100uK cloud with a number density of $5\times10^{10} $cm$^{-3}$. Typically, $9\times10^8$ atoms are loaded in a magnetic trap. We see a difference in efficiency of evaporative cooling using an rf-transition between magnetic sublevels and between hyperfine states. The underlying physical mechanism is discussed. [1] G. Modugno et al., Science 294, 1320 (2001). [Preview Abstract] |
|
L2.00114: A lattice of permanent magnetic microtraps for ultracold atoms Mandip Singh, Alexander Akulshin, Andrei Sidorov, Russell McLean, Peter Hannaford We report on the loading and trapping of ultracold $^{87}$Rb atoms in a one dimensional permanent magnetic lattice [1] of period 10 $\mu $m produced on an atom chip. The grooved structure which generates the magnetic lattice potential is fabricated on a silicon substrate and coated with a perpendicularly magnetized multilayered TbGdFeCo/Cr film of effective thickness 960 nm. Under our experimental conditions up to 2$\times $10$^{6 }$atoms are trapped at a distance of less than 5 $\mu $m from the surface with a measured lifetime of about 450 ms and at trap frequencies up to 90 kHz. These results are important in the context of studies of quantum coherence of neutral atoms in periodic magnetic potentials on an atom chip. In addition, we report on experimental results demonstrating the reflection dynamics of a Bose Einstein condensate and ultracold atoms in the lattice potential. \textbf{References: } [1] M. Singh, \textit{et al.,} arXiv: 0801.0624 [physics-atom-ph]. [Preview Abstract] |
|
L2.00115: Progress towards quantum-gas experiments in optical lattices Daniel Pertot, Daniel Greif, Rebekah Schiller, Dominik Schneble We present our progress towards quantum simulation experiments with ultracold bosonic atoms in an optical lattice. We have achieved Bose-Einstein condensation of rubidium-87 in a transporter apparatus featuring a moving-coil TOP trap (McTOP). Quasi-pure condensates containing up to one million atoms are routinely produced with high stability. As atomic micro-motion in TOP traps precludes the direct loading of condensates into a single quasimomentum state of an optical lattice, we are in the process of implementing a loading scheme involving evaporation of nearly-condensed thermal clouds in a crossed optical dipole trap. We will discuss our recent experimental results. [Preview Abstract] |
|
L2.00116: Quantum Phases with Bose-Condensed Cesium Atoms in an Optical Lattice Xibo Zhang, Chen-Lung Hung, Nathan Gemelke, Cheng Chin The realization of the Mott-insulator to superfluid phase transition with neutral atoms in an optical lattice provides a tantalizing opportunity to test many-body physics with a high degree of accuracy. We report progress on an experimental and quantitative comparison of the superfluid to Mott-insulator quantum phase boundary with results from the Bose-Hubbard model, using Bose-condensed cesium atoms confined to a thin layer of an optical lattice potential. Feshbach resonances with cesium atoms enable us to scan the on-site interaction over a wide range without modifying the tunneling rate and the overall trapping potential; chemical potential can be adjusted by loading a varied mean atomic density into the lattice. We describe the physical apparatus constructed for this investigation, including novel construction designed to achieve precise and agile control of the magnetic field used in tuning interactions, adiabatic loading and manipulation of the lattice potential, and tight two-dimensional confinement applied to negate the effect of gravity without sacrifice in system homogeneity. [Preview Abstract] |
|
L2.00117: Spinor BECs in optical lattices and ultralow magnetic fields. Chad Fertig, Joshua Hughes, Wesam El Qadi Bose-Einstein condensates (BECs) of spinor atomic gases have already proven to be powerful system in which to explore quantum magnetism over a range of parameters impossible to access in the solid-state. However, many exciting quantum magnetic phenomena predicted to occur for spinor BECs have remained unobserved, for two fundamental reasons: (1) Small spin interaction energies can imply impracticably long time scales for relaxation dynamics; (2) the phenomena may be strongly suppressed by the presence of typical background magnetic fields. At the University of Georgia we are currently constructing an all-optical 87-Rb BEC apparatus which incorporates extensive passive and active magnetic shielding expected to reduce background magnetic fields to below 1-microGauss, realizing the zero-field limit for our condensates. We will report on our progress, focusing on several novel features of the apparatus, including the design of the multi-layer mu-metal shield and a new method of direct offset locking two or more lasers. [Preview Abstract] |
|
L2.00118: Continuous Observation of Spinor Dynamics in a Sodium Bose-Einstein Condensate Stephen Maxwell, Yingmei Liu, Sebastian Jung, Lincoln Turner, Paul Lett Optically trapped BEC is almost ten years old, but the rich physics of ultracold spin- changing collisions is only now being studied in detail. While collisions in a thermal gas are often thought of as random, incoherent events, in a Bose-Einstein condensate (BEC) the coherent nature of collisions becomes clear. We make use of an optically trapped sodium condensate in the F=1 hyperfine state to explore equilibria and dynamics in a system allowing spin-changing collisions. This system is antiferromagnetic and stably forms a single domain across the full dimensions of the condensate (in contrast to ferromagnetic F=1 Rb). Previously at NIST, we studied the nonlinear dynamics of Zeeman population oscillations in this system. In a new series of experiments, we continuously monitor the evolution of our BEC using a Faraday polarimeter. We observe the collective Larmor precession of the BEC in real time, limited by the scattering rate of the probe beam. Spin-collision dynamics are manifest as modulation of the Larmor carrier. [Preview Abstract] |
|
L2.00119: Quantum Magnetism with Ultracold Atoms Jennie Guzman, Sabrina Leslie, Mukund Vengalattore, Christopher Smallwood, Dan Stamper-Kurn We report on a number of recent experimental studies of F=1 $^{87}$Rb spinor Bose Einstein condensates. Utilizing in-situ magnetization sensitive imaging, we are able to spatially and temporally resolve the vector magnetization profile of the spinor condensate. We probe the evolution of spin textures in an inhomogeneous magnetic field and explore the thermal equilibrium properties of the ferromagnetic spinor condensate. In addition, we study the amplification of quantum fluctuations in a spinor condensate that is rapidly quenched from its paramagnetic phase to its ferromagnetic phase. We characterize the amplification of these quantum fluctuations, as well as the initial quantum fluctuations from which they evolve. [Preview Abstract] |
|
L2.00120: DYNAMIC AND OUT-OF-EQUILIBRIUM PHENOMENA IN COLD ATOMS |
|
L2.00121: Dynamics of a trapped 1D Bose gas for finite interaction strength Dominik Muth, Alexander Mering, Michael Fleischhauer We investigate the dynamics of a 1D Bose gas in a harmonic trap with point like interactions, recently studied experimentally in [1]. Starting from a discretisation of this model we calculate the groundstate properties and time evolution in the resulting Bose-Hubbard model using the time-evolving block decimation algorithm, TEBD. Both the case of vanishing interaction strength corresponding to the trivial case of free bosons, and the quasi integrable hard core case are well understood [2]. Furthermore recently exact solutions have been found in the absence of a trap potential and few particles [3]. We are focusing on the dynamics in the region with finite repulsive interaction and in a trap. Forall cases, using TEBD, we are able to calculate the propagation in both momentum and real space. \newline \newline [1] T. Kinoshita, T. Wenger, D. Weiss, Nature 440, 900 (2006) \newline [2] M. Rigol, V. Dunjko, V. Yurovsky, M. Olshanii, Phys. Rev. Lett. 98, 050405 (2007) \newline [3] H. Buljan, R. Pezer and T. Gasenzer, arXiv:0709.1444 (2007) [Preview Abstract] |
|
L2.00122: Loschmidt's Cooling Vijayashankar Ramareddy, Ishan Talukdar, Gil Summy A quantum $\delta$-kicked rotor can be understood theoretically using a kick to kick Floquet operator which has both kicking and free evolution terms. If time reversal is performed after $t$ kicks, (by changing the pulse period and phase of the potential) the evolution of the system returns to the initial distribution in the next $t$ kicks and results in a narrowing of the distribution which is equivalent to cooling [1]. The temperature has been predicted to go down by several orders of magnitude. We explore the experimental implementation of this cooling with a Bose-Einstein condensate kicked by a standing light wave. [1] J. Martin et. al. arXiv:0710.4860 (2007). [Preview Abstract] |
|
L2.00123: RYDBERG ATOMS AND MOLECULES |
|
L2.00124: Ionization of Xe(nf) Rydberg Atoms at Surfaces: Effect of Stray Fields Dennis Neufeld, Hardin Dunham, Stephan Wethekam, James Lancaster, F.B. Dunning The ionization of xenon Rydberg atoms excited to the lowest-lying state in the $n$~=~20 Stark manifold at Si(100) surfaces possessing a robust ($\sim $ 10{\AA}) native oxide layer and at Au(111) surfaces is investigated as a function of the angle of incidence. Analysis of the data in both cases points to the presence of localized stray fields at the surface associated with surface inhomogeneities which modify the atom-surface separation at which ionization occurs and the ion collection efficiencies. A simple model is presented to justify this assertion and its implications are discussed. Measurements are being extended to surfaces with lithographically-patterned electrode arrays to better test the model and explore the use of Rydberg atoms to investigate local electric fields at nanostructured surfaces. [Preview Abstract] |
|
L2.00125: Diode Laser Excitation of Rydberg Lithium Atoms for Collision Studies. Paul Oxley, James Daly We give experimental details of diode laser excitation of 7Li atoms to the 10p atomic state. The excitation uses three narrow bandwidth grating-stabilized diode lasers to reach the 10p state, via the 2p and 3s states. Simultaneous locking of all three lasers produces a continuous source of 10p atoms. Locking of the 3s-10p transition is achieved by detecting the 10p-2s fluorescence at 238 nm using a photomultiplier tube. In the future these atoms will be used as a target in very slow charge transfer collisions with singly charged ions. These experiments will test for the presence of quantum effects in these collisions which have thus far been treated classically. [Preview Abstract] |
|
L2.00126: Rydberg excitation blockade effects in strongly magnetized atom clouds E. Paradis, C. Hempel, B. Knuffman, R. Mhaskar, M. Shah, G. Raithel We present progress on work towards characterizing the Rydberg blockade mechanism within a strong magnetic field (B = 3T). Either permanent quadrupole moments or induced dipole moments could provide a strong interaction between neighboring Rydberg atoms, leading to a blockade. These interactions cause deviations of the spatial Rydberg atom distribution from random ordering that can be detected in a spatially-resolved read-out of Rydberg excitations. The high magnetic field setup offers several key advantages in realizing such a measurement: Diamagnetic Rydberg states are well suited for this research because they are non-degenerate and have large oscillator strengths for photo-excitation. Further, electron imaging in strong magnetic fields lends itself to straightforward realization of imaging with considerable magnification. In this poster, we will present experimental and theoretical progress on this project. [Preview Abstract] |
|
L2.00127: Computational Studies of Many-Body Interactions in Ultra-cold Rydberg Atom Samples of Various Geometries Thomas J. Carroll, Michael W. Noel, Christopher Daniel, Timothy Sidie Ultra-cold highly-excited atoms in a magneto-optical trap (MOT) are strongly coupled by the dipole-dipole interaction. The effect of the spatial arrangement of a sample of Rydberg atoms on their interactions is a complex experimental question. We have developed a computational model of these systems in order to explore the importance of many-body effects, geometry, and energy level structure on the time evolution of the sample. The model simulates the time evolution of groups of Rydberg atoms in different geometric arrangements of atoms including amorphous, thin cylinder of excitation vs. thick, two closely spaced cylinders, and a crossed cylinder arrangement. Simulation results are presented for the time-dependence, peak widths, and interaction strengths for the different geometries while also varying the density of the atomic sample. Where possible, results are compared to experiment. [Preview Abstract] |
|
L2.00128: Electron-Rydberg collisions at ultra-low temperatures Daniel Vrinceanu, Thomas Pohl, Hossein Sadeghpour Precise knowledge of collisional transition rates between excited atomic states is essential for understanding the dynamics of various terrestrial and astrophysical plasmas. Here we present extensive Monte-Carlo calculations of electron-impact induced transitions between highly excited Rydberg states, and provide accurate rate coefficients. For moderate energy changes, our calculations confirm widely applied, previously obtained expressions, but reveal strong deviations at small energy transfer, which become increasingly important for highly excited Rydberg states, as formed in ultracold neutral plasmas or dilute astrophysical plasmas. Our plasma simulations demonstrate that these corrections have significant impact on the short-time dynamics of Rydberg atom formation, and yield good agreement with recent ultracold plasma experiments. [Preview Abstract] |
|
L2.00129: Dynamics of Low-Density Rydberg Gases Erik Brekke, Jason Day, Thad Walker A state dependent stimulated emission probe was used to investigate the coherent and dynamic properties of cold Rydberg atoms. $^{87}$Rb atoms were excited to various nl Rydberg states from a MOT via continuous two-photon excitation. A stimulated emission probe laser was then used to bring the Rydberg atoms down to the 6P$_{3/2}$ state, allowing detection of decay photons as a Rydberg atom detection method. Phase-matched four-wave mixing was also achieved and the angular dependence investigated. This coherent process is optimized when detuned from the Rydberg state, giving as much as 40{\%} phase-matched light. In addition, the stimulated emission probe technique shows that radiative processes dominate the Rydberg population dynamics on a time scale much faster than the natural radiative lifetime. Modeling suggests superradiant emission may be the dominant factor [T. Wang \textit{et al., }Phys. Rev. A \textbf{75}, 033802 (2007)]. [Preview Abstract] |
|
L2.00130: Microwave Spectroscopy of a Frozen Rydberg Gas Edward Shuman, Paul Tanner, Tom Gallagher In cold Rydberg atom samples the dipole-dipole interaction can lead to many interesting dynamic processes. In particular it can lead to atomic motion, spontaneous ionization, and even plasma formation. Here we present microwave spectroscopy of the dipole-dipole interaction in a frozen Rydberg gas. In particular we create a dense gas of 300 $\mu $K of n$\sim $40 $^{85}$Rb atoms. We then use microwave spectroscopy to probe the dynamics of the Rydberg atoms. [Preview Abstract] |
|
L2.00131: Homoclinic Tangle Approach to Ionization of Highly Excited Rydberg Atoms Korana Burke, Kevin Mitchell A highly excited Rydberg atom exposed to periodic external electric field impulses exhibits chaotic behavior. We study the system where an atom is exposed to alternating positive and negative impulses. We show that ionization of this system is organized by a homoclinic tangle attached to a fixed point at infinity. We present theoretical calculations for predicting the homoclinic tangle signature in a proposed experimental setup. Using the geometric and topological structure of the homoclinic tangle we show how survival probability for the starting wave-packet changes as a function of impulse timing, strength and duration. [Preview Abstract] |
|
L2.00132: NONLINEAR DYNAMICS |
|
L2.00133: The Topology of Chaotic Transport and Escape Jaison Novick, Kevin Mitchell, John Delos Chaotic transport and escape appears in many different systems such as the escape of an asteroid from a planet's gravitational field to the escape of ionizing electrons from hydrogen in parallel electric and magnetic fields. Numerical simulations have shown that the times to escape some region without return possess a complicated fractal structure. These fractals result from the intersection of a line of initial conditions and a homoclinic tangle, which is formed from the intersections of infinitely long stable and unstable manifolds emanating from an unstable fixed point. Our group has developed Homotopic Lobe Dynamics, a topological theory that allows one to predict subsets of the fractals seen in numerical simulations. We first show how to apply homotopy to a homoclinic tangle to obtain a set of symbols and a dynamical mapping on the symbols. A symbol and its mappings encode the evolution of an entire family of trajectories. Given a symbol and its mappings, we show how to construct a theoretical fractal. Finally, we compare a predicted fractal to one obtained from a numerical simulation of trajectories propagating in an open chaotic vase-shaped billiard. [Preview Abstract] |
|
L2.00134: Study of critical behavior of periodically driven cold atomic system Myoung-Sun Heo, Yonghee Kim, Wonho Jhe It is well known that the parametrically driven magneto-optically trapped atoms are occupied in the symmetric period-2 states. When the atom number increased, recently observed spontaneous symmetry breaking(SSB) of atomic population which inherently possesses the light-induced attractive interaction. In particular, this dependence seems to show a sort of critical behavior. And another interesting behavior of this system is response to the additional oscillating bias fields. This responses show the hysteresis which is very similar to magnetic system. We measure the dependence of hysteresis loop area on the rate of change of the additional bias fields. The amplitude and frequency dependence are measured and system size, or atom number dependence also measured. The results show some scaling relations. Here we have elucidated the criticality existing in the strongly driven interacting many-particle system consisted up of cold atoms from static and dynamic perspectives. [Preview Abstract] |
|
L2.00135: Quantum chaos using the delta kicked accelerator Vijayashankar Ramareddy, I. Talukdar, Gil Summy, G. Bahenaein, P. Ahmadi The quantum delta kicked accelerator (QAM) can be realized by subjecting a particle to a periodic $\delta$-potential and a linear potential such as gravity. The quantum $\delta$-kicked accelerator exhibits a phenomenon of resonance which happens whenever the period of kicking is a rational fraction of the half-Talbot time. A theory of QAM occurring at integer multiples of the half-Talbot time was developed by [1] which treats the closeness of the time period to one of the primary resonance as Planck's constant and a classical mapping can be used to study the resonances. Here we extend the $\epsilon$-classical theory to the resonances occurring at high order resonances and use the classical mapping to study these resonances. [1] S. Fishman et. al., Phys. Rev. Lett. 89, 084101 (2002); J. Stat. Phys. 110, 911 (2003). [Preview Abstract] |
|
L2.00136: Toward a Curriculum Innovation Kevin F.W. Thoronka This paper proposes an innovation on HIV prevention, in response to the United Nations Millennium Development Goal to combat HIV/AIDS. The curriculum innovation is through a participatory research design of life skills based education course, involving both healthy faculty tutors and young community leaders at the centre. The innovation builds onto the strengths of previous IIV prevention interventions and argues that effective life skills based education targets the individual, peers and the wider community since the same levels are crucial in HIV transmission. The innovation also recommends a rethinking of the content used to teach and learn life skill based education to prevent HIV and recommends that such content is to be co-conducted by the young community involvement. The content is to be delivered in a participatory way in order for the young community leaders to engage in critical action to prevent HIV. Because of the novelty of such an intervention, the innovation recognizes that such an approach to the design and implementation of the curriculum initiative is complex and involves careful planning, monitoring and evaluation to yield desired outcomes. In conclusion, the innovation recommends that HIV prevention can be possible even in a country such as Sierra Leone, with increasing HIV prevalence in the world. [Preview Abstract] |
|
L2.00137: Slowing Supersonic Beams via Elastic Reflection from Moving Crystals: An Atomic Paddle Adam Libson, Ed Narevicius, Christoph Schaeff, Isaac Chavez, Max Riedel, Christian Parthey, Uzi Even, Mark Raizen We report the slowing of a supersonic beam of helium using specular reflection from a receding crystal. We use an Even-Lavie pulsed supersonic nozzle to generate a 511 m/s beam of helium at 250 mK. The beam is reflected from a Si(111)-H(1x1) crystal prepared \textit{ex-situ }via wet etching and mounted on the tip of a spinning rotor. By controlling the rotor velocity we can continuously tune the velocity of the slowed beam. We have slowed the beam to as low as 246 m/s without affecting its temperature. Applications to slowing of molecular hydrogen and deuterium will be discussed. [Preview Abstract] |
|
L2.00138: Single-Proton Self-Excited Oscillator Nicholas Guise, Gerald Gabrielse A new apparatus and experiment adapts the techniques from the recent electron g-2 measurement to a single proton suspended within a Penning trap. The smaller proton charge/mass presents significant experimental challenges, but if we can overcome the substantially weaker signal/noise, the payoffs are considerable. Our primary goal is a direct observation of the single-proton spin-flip transition, which would open the way to a novel measurement of the proton magnetic moment, and allow a comparison of the proton and antiproton g-factors at precision likely to be a million times higher than achieved to date. As an initial milestone, we have achieved the first single-proton self-excited oscillator. This technique allows for a large-amplitude oscillation despite the inherent anharmonicity of our Penning trap, and promises stability approaching the level required for spin-flip detection. [Preview Abstract] |
|
L2.00139: ABSTRACT WITHDRAWN |
|
L2.00140: Controlled Formation of Ultracold Diatoms via Laser Catalysis: $^6$Li$^6$Li+$^7$Li Xuan Li, Gregory Parker, Paul Brumer, Ioannis Thanopulos, Moshe Shapiro Laser catalysis techniques are applied to the quantum control of
an ultracold $^6$Li$^6$Li$^7$Li collinear collision on the
$1^4A'$ electronic potential energy surface via a fermion-boson
light-induced exchange reaction,
$^7{\rm Li}^6\textrm{Li}
(^3\Sigma^+)$$+^6{\rm Li}(^2S)
\stackrel{\hbar\omega_0}{\longleftrightarrow}(^7{\rm Li}^6{\rm
Li}^6{\rm Li})^*
\stackrel{\hbar\omega_0}{\longleftrightarrow}$
$^6\textrm{Li}_2(^3\Sigma_u^+)$ $+^7\textrm{Li}(^2S)$. We show
that the cold ($T_r\approx 1.75$ K) reactant $^6$Li+$^6$Li$^7$Li,
when optically coupled to the intermediate bound states on the
$1^4A''$ electronic potential energy surface, can be transferred
to the ultracold ($0.01$ mK $ |
|
L2.00141: Generalized Ionization scaling law for high energy ion-aligned elliptic Rydberg hydrogen collisions Kevin Cornelius, Marc Ward, Thomas Cooper The classical trajectory Monte Carlo method was used to calculate electron ionization cross sections involving fully stripped ions of He, C, Ar and Kr colliding with aligned elliptic Rydberg hydrogen for various excited n states. Cross sections from target eccentricities of -0.9 to 0.9 over the energy range 1.21 keV/u and 64 keV/u were used to develop a high energy ionization scaling law as a function of reduced collision speed , initial n state, projectile charge , and eccentricity. Our scaling law accurately predicts all theoretical CTMC cross section values for reduced collisions speeds larger than 2.5q. [Preview Abstract] |
|
L2.00142: Characteristics of Bose-Einstein condensation in an optical lattice Guin-Dar Lin, Wei Zhang, Luming Duan We discuss several possible experimental signatures of the Bose-Einstein condensation (BEC) transition for an ultracold Bose gas in an inhomogeneous optical lattice. Based on the commonly used time-of-flight imaging technique, we show that the momentum-space density profile in the first Brillouin zone, supplemented by the visibility of interference patterns, provides valuable information about the system. In particular, by crossing the BEC transition temperature, the appearance of a clear bimodal structure sets a qualitative and universal signature of this phase transition. Furthermore, the momentum distribution can also be applied to extract the condensate fraction, which may serve as a promising thermometer in such a system. [Preview Abstract] |
|
L2.00143: Numerical study of two-body correlation in a 1D lattice with perfect blockade Bo Sun, Francis Robicheaux We investigate the correlation properties in frozen Rydberg gases driven by an external laser. Due to the well-known dipole blockade, pair excitation within the so-called blockade radius is greatly suppressed. This gives us the motivation to partition the whole gas into smaller pieces which we term ``pseudoatoms". Each pseudoatom can then be treated as a two-level system, initially in the ground state. By adopting a simplified model where pair excitation within a finite range is perfectly blocked, we compute the dynamics of excitation and two-body correlation in a 1D lattice. We find that two-body quantum correlation drops very fast with the distance between pseudoatoms. However, the total correlation does not show such fast drop with distance. This implies that there is no long range order in such systems. [Preview Abstract] |
|
L2.00144: Experimental test of non-local realism using a fiber-based source of polarization-entangled photon pairs Matthew Eisaman, Elizabeth Goldschmidt, Jingyun Fan, Alan Migdall We describe a bright, wavelength-tunable source of polarization-entangled photon pairs that uses a single-mode microstructure fiber in a Sagnac interferometer at room temperature [1]. We create all four Bell states with a two-photon coincidence rate of 7 kHz/nm over wavelengths spanning more than 20 nm, and measure the fidelity of each Bell state to be greater than 95{\%} using quantum-state tomography [2]. We compare our measurements of two-photon polarization correlations to the predictions of quantum mechanics, and to the predictions of local realistic and non-local realistic theories. Our measurements are consistent with quantum-mechanical predictions, violating Bell's inequality in the CHSH form by 15 standard deviations (excluding local hidden-variable theories) and violating a Leggett-type non-local hidden-variable inequality by 3 standard deviations (excluding a certain class of non-local hidden-variable theories) [3]. Refs. [1] J. Fan, M. D. Eisaman, and A. Migdall, PRA 76, 043836 (2007). [2] J. Fan, M. D. Eisaman, and A. Migdall, Opt. Express 15, 18339 (2007). [3] M. D. Eisaman, E. A. Goldschmidt, J. Chen, J. Fan, and A. Migdall, ``Experimental test of non-local realism using a fiber-based source of polarization-entangled photon pairs,'' PRA (in press). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700