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 E1: Poster Session I: 4:00 pm - 6:00 pm |
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Room: HUB-Robeson Center Alumni Hall |
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E1.00001: FUNDAMENTAL SYMMETRIES AND PRECISION MEASUREMENTS (Co-Sponsored by GFC) |
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E1.00002: A $^{87}$Sr Optical Lattice Clock Sebastian Blatt, Gretchen K. Campbell, Andrew D. Ludlow, Martin M. Boyd, Jan W. Thomsen, Michael J. Martin, Jun Ye We report on our recent progress on a optical atomic clock with high accuracy and stability based on ultracold fermionic lattice-confined $^{87}$Sr atoms. We have evaluated the systematic effects at $1\times 10^{-16}$, enabling an improved measurement of the absolute clock transition frequency. The frequency of the $^1S_0$-$^3P_0$ transition was measured as $429\,228\,004\,229\,873.83 \pm 0.37$~Hz, where the final fractional uncertainty represents one of the most accurate measurements of an optical atomic frequency to date. In combination with data from the Paris and Tokyo groups, this measurement is used to limit Local Position Invariance by limiting coupling of fundamental constants to the gravitational potential. [Preview Abstract] |
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E1.00003: Femtosecond laser frequency comb for precision astrophysical spectroscopy Chih-Hao Li, Andrew J. Benedick, Peter Fendel, Alex Glenday, Franz X. Kaertner, David F. Phillips, Dimitar Sasselov, Andrew Szentgyorgyi, Ronald L. Walsworth Spectroscopy is a crucial tool for cosmology and the search for extrasolar planets. Broadband frequency combs have revolutionized precision spectroscopy in the laboratory with absolute frequencies determined to better than one part in $10^{15}$. Good long-term stability and reproducibility are also major advantages of the frequency comb. However, their application to any astrophysical spectrograph requires increasing the comb-line spacing by at least 10-fold from today's high repetition rate sources operating at about 1 GHz. We report the successful test of a 40-GHz comb generated from a 1-GHz source, without compromise on long-term stability, reproducibility and resolution. The application of this novel technique to astrophysics should allow more than a 10-fold improvement in Doppler-shift sensitivity, with significant impact to many fields, including the search for extrasolar Earths, the direct measurement of the universe expansion and the detection of the temporal variation of physical constants. [Preview Abstract] |
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E1.00004: Current status and future directions for the PbO electron EDM experiment David DeMille, Paul Hamilton, Sarah Bickman, Yong Jiang, Hunter Smith, Amar Vutha The results from the first data in our search for a permanent electric dipole moment (EDM) of the electron using a lead oxide (PbO) vapor cell will be presented. We will discuss the current statistical sensitivity of the experiment and methods we've used to increase it. We will also discuss near term improvements using a second laser to move our fluorescence detection to the blue as well as the long term prospects of a higher sensitivity experiment utilizing a long microwave absorption cell. [Preview Abstract] |
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E1.00005: Laser trapping of radium for an electric dipole moment measurement P. Mueller, I.A. Sulai, W. Trimble, I. Ahmad, K. Bailey, M. Bishof, J.P. Greene, J.R. Guest, R.J. Holt, Z.-T. Lu, T.P. O'Connor, H.A. Gould The best limits on time-reversal violation in the nuclear sector are currently set through electric dipole moment (EDM) searches on the neutron and Hg-199. Recent theoretical calculations predict that atomic EDM measurements of certain octupole-deformed nuclei, e.g., in the radium isotopic chain, are two to three orders of magnitude more sensitive to the underlying time-reversal violation than the one in Hg-199. Ra-225, with nuclear spin 1/2 and a radioactive half-life of 15 days, is a particularly attractive candidate for a tabletop EDM measurement based on a laser-cooling and trapping approach. Towards this end, we have successfully cooled and trapped atoms of Ra-225 and Ra-226 in a magneto-optical trap -- a first for this rare element -- and have identified black-body radiation as a beneficial source of optical repumping. We will present our laser cooling scheme and ongoing measurements of atomic level energies, lifetimes, isotope shifts and hyperfine structure in radium and discuss our progress towards an EDM measurement of Ra-225 based on an optical dipole trap. This work is supported by DOE, Office of Nuclear Physics, under contract No. DE-AC02-06CH11357. [Preview Abstract] |
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E1.00006: Electron EDM Search with Trapped Molecular Ions Russell Stutz, Huanqian Loh, Laura Sinclair, Eric Cornell A sample of trapped molecular ions offers unique possibilities to search for a permanent electron electric dipole moment (EDM). Specifically, we plan to perform this search using the unpaired electron spins in the $^3\Delta_1$ state of trapped HfF$^+$ molecular ions. The ions will be confined in a linear RF Paul trap, allowing for long electron spin coherence times for increased sensitivity to an electron EDM. Effective internal fields of the molecular ions should exceed $10^{10}$~V/cm, and the molecules are easily polarized in $\sim$ 1V/cm electric fields due to a small $\Omega$ doubling splitting in the $^3\Delta_1$ state. HfF$^+$ molecular ions are created via laser ablation of a Hafnium target in the presence of a He + 1\%SF$_6$ supersonic expansion. The expansion cools the ions rovibrational and translational temperatures to a few Kelvin. We will report current experimental progress. [Preview Abstract] |
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E1.00007: Cryogenic molecular beam source of ThO for a measurement of the electric dipole moment of the electron Yulia V. Gurevich, O. Keith Baker, Wesley C. Campbell, David DeMille, John M. Doyle, Gerald Gabrielse, Maarten A.H.M. Jansen, Amar C. Vutha A cryogenic beam of thorium monoxide (ThO) molecules in the metastable H state has been proposed as a system for measuring the electric dipole moment of the electron. We report our progress towards realizing a cold, high-flux molecular beam source of ThO, including production and buffer-gas cooling of ThO molecules and an experimental lower limit on the lifetime of the H state. [Preview Abstract] |
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E1.00008: Progress towards a Nuclear Anapole Moment Measurement in $^{137}$BaF. Sidney Cahn, Dennis Murphree, David Rahmlow, David DeMille, Edward Deveney, Richard Paolino, Mikhail Kozlov We report progress in our experiment to measure nuclear spin- dependent parity violating effects. Our first goal is to measure the nuclear anapole moment of $^{137}$BaF. We have developed an intense, cold beam of BaF molecules by laser ablation and supersonic expansion. This beam is injected into a homogeneous 0.5 T magnetic field. The field is measured and shimmed with an array of custom broadband NMR probes and commercial room-temperature shim array. We have observed Stark-induced transfer between two Zeeman-rotational sublevels of $^{138}$BaF as a function of magnetic field, indicative of the Zeeman-tuned level crossing of these two states. A similar level-crossing in $^{137}$BaF will be used to amplify the effect of the nuclear anapole moment to an observable level. [Preview Abstract] |
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E1.00009: A Compact, Rotating Co-Magnetometer for Tests of Fundamental Symmetries Justin M. Brown, Sylvia J. Smullin, Thomas W. Kornack, Michael V. Romalis We describe a compact K--$^3$He co-magnetometer on a rotating platform for tests of CPT and Lorentz invariance. Optical pumping polarizes electrons in a high-density K vapor. Spin-exchange collisions between alkali and noble gas atoms polarize the $^3$He nuclei. An appropriately applied magnetic field cancels the $^3$He magnetization allowing for magnetometer operation in the highly sensitive spin-exchange relaxation free (SERF) regime. The resulting co-magnetometer is insensitive to magnetic fields, but sensitive to electron and neutron couplings to anomalous fields. The co-magnetometer also behaves as a sensitive gyroscope. By reversing the direction of the experiment every $\approx 1$ min, we can test for CPT and Lorentz violation on faster timescales than on a frame fixed to the Earth. This reduces many systematic long term drifts. We will discuss implementation of the rotating experiment and accounting for the gyroscopic signal from Earth's rotation in the CPT and Lorentz violation searches. [Preview Abstract] |
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E1.00010: Calculation of parity-nonconserving amplitude in Ra$^+$ Rupsi Pal, Dansha Jiang, Marianna Safronova, Ulyana Safronova We have calculated parity-nonconserving $7s-6d$ amplitude $E1_{PNC}$ in Ra$^+$ using relativistic high-precision all-order method where all single and double excitations of the Dirac-Hartree-Fock wave function are included to all orders of perturbation theory. Detailed study of the uncertainty of the PNC amplitude is carried out; additional calculations are performed to evaluate the effect of the triple excitations and to estimate some of the missing correlation corrections. A systematic study of the parity-conserving atomic properties, including the calculation of the transition matrix elements, lifetimes, hyperfine constants, as well as dipole and quadrupole ground state polarizabilities, is carried out. The comparisons are made between the size of the correlation corrections in Ba$^{+}$ and Ra$^{+}$. The results are compared with other theoretical calculations and available experimental values. [Preview Abstract] |
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E1.00011: Hyperfine resonances in metastable $^{129}$Xe discharge cells Steven W. Morgan, Tian Xia, Yuan-Yu Jau, William Happer We have measured the hyperfine resonance linewidths of metastable $^{129}$Xe in electrodeless rf discharge cells. The linewidths on the order of 10 kHz for Xe pressures of a few millitorr are dominated by collisions with other Xe atoms and no buffer gases are present. Additional contributions come from collisions with the walls as well as with impurities which may be drawn off the cell walls due to the harsh plasma environment. If used for small atomic clocks, metastable noble gases could require less power and would be relatively insensitive to temperature variations when compared with alkali metal atoms. [Preview Abstract] |
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E1.00012: Prism-based Cr:forsterite laser frequency comb stabilization and carrier-envelope offset frequency linewidth narrowing. Rajesh Thapa, Karl Tillman, Kevin Knabe, Andrew Jones, Brian Washburn, Kristan Corwin Infrared frequency combs in the near IR, based on lasers such as Cr:forsterite, are important for frequency measurements in the telecommunications band. We have actively stabilized a self-referenced prism-based Cr:forsterite frequency comb using both prism and power control inside the cavity. We also report dramatic reduction in the linewidth of the carrier envelope offset frequency ($f_{0})$ by at least two orders of magnitude simply by inserting a knife edge into the laser cavity after the prisms. We have stabilized the laser when the $f_{0}$ beat width was both wide ($\sim $1.5 MHz) and narrow ($\sim $10 kHz) although the locking was less robust with the narrower beat note. We measured the fractional stability of the comb by counting the repetition frequency ($f_{r})$ and $f_{0}$. The fractional stability of the comb at 10 s was limited by the frequency counter resolution to $<$10$^{-12}$. An optical characterization of the stability is in progress. Furthermore, we will use this comb to characterize optical frequency references based on acetylene-filled hollow photonic band gap optical fibers. [Preview Abstract] |
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E1.00013: Ramsey fringe width compared to the spectral width of the driving pulse pair James Supplee, Varun (Mac) Makhija In a population inversion versus detuning curve, fringes due to a Ramsey pulse-pair are vastly narrower than a peak due to just one of the pulses would be. For subtler reasons, the Ramsey fringe width is also less than the inversion peak that would be obtained using one long pulse with duration as long as the entire Ramsey pair including the time between pulses. This narrowing is by a factor of about 0.6 in many typical circumstances, but that factor can vary (sometimes significantly) depending on parameters such as pulse duration, pulse area, and time between pulses. We are doing calculations using an idealized semiclassical model with a two-level quantum system to address the following question: In which parameter regimes is the Ramsey fringe width well explained just by the spectral width of the driving pulse pair? [Preview Abstract] |
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E1.00014: Separated Oscillatory Field Microwave Measurement of the n=2 Triplet P Fine-Structure of Helium J.S. Borbely, M.C. George, M. Weel, L.D. Hessels, E.A. Hessels The Ramsey method of separated oscillatory fields is being used to make a very precise microwave measurement of the n=2 triplet P J=1-to-J=2 interval in helium. The excellent signal-to-noise obtained in these measurements allows for extensive studies of possible systematic effects. Comparison between precise measurements of the n=2 triplet P fine structure and theoretical predictions will allow for a precise determination of the fine-structure constant when the current large discrepancy between experiment (PRL \underline {95} 203001; PRL \underline {87} 173002; PRL \underline {84} 4321; Can J Phys \underline {83} 301) and theory (PRL \underline {97} 013002; Can J Phys \underline {80} 1195) is resolved. [Preview Abstract] |
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E1.00015: MOLECULAR SPECTROSCOPY AND STRUCTURE |
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E1.00016: Photoassociation of a spin-1 BEC to molecular states with hyperfine structure Eva Bookjans, Christopher D. Hamley, Ghazal Behinaein, Peyman Ahmadi, Michael S. Chapman We report on the high resolution (5 MHz) photoassociation spectroscopy of $^{87}$Rb spin-1 BEC to the 1g (P$_{3/2}) \quad v$=152 excited molecular state manifold. Using a combination of dipole selection rules, collision channel analysis and rotational progression of the spectrum we identify total molecular angular momentum, F, and total molecular nuclear spin, I, for the observed states. These identifications are compared to a hyperfine-rotational Hamiltonian [1] for Hund's case (c). We find a good agreement to the predicted lines. The eigenvalues of this Hamiltonian was used to predict further weak lines which their existence are confirmed experimentally. In conclusion, we demonstrate the use of spin dependent photoassociation to experimentally identify hyperfine-rotational structure of the molecular states with sufficiently high resolution. These studies will improve current understanding of the hyperfine-rotation molecular potentials in Hund's case (c). [1] X.T. Wang, et al., Phys. Rev. A. 57, 4600 (1998). [Preview Abstract] |
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E1.00017: Analysis of hyperfine structure in photoassociation spectra T. Bergeman The low Doppler width in photoassociation spectra from cold atoms makes hyperfine structure clearly visible, especially with heavier alkali atoms. Recently the focus has been on photoassociation to weakly bound dimers [1,2]. However there are also useful data on somewhat more deeply bound levels [2] for which a different coupling scheme is appropriate. Following [3], we use a $\vec{F} = \vec{J} + \vec{I}$ representation, and develop a transformation between this and the usual case $e$ representation which applies at asymptotically large internuclear distance. We hope to model and assign hyperfine structure in $\Omega$ = 1 states, using appropriate ground and excited state wavefunctions. To obtain eigenvalues from very large DVR matrices, we use a ``stepwise diagonalization'' procedure, which appears to be more efficient than standard sparse matrix methods. \newline [1] E. Tiesinga {\it et al}. PRA {\bf 71}, 052703 (2005); K. M. Jones {\it et al}, RMP {\bf 78}, 483 (2006). \newline [2] Data on Rb$_{2}$ from J. Qi, D. Wang, Y. Huang, H. Pechkis, E. Eyler, P. Gould, W. C. Stwalley, C. C. Tsai and D.J. Heinzen; Data on RbCs from A. J. Kerman, J. M. Sage, S. Sainis and D. DeMille. \newline [3] B. Gao, PRA {\bf 54}, 2022 (1996). [Preview Abstract] |
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E1.00018: New Data and Analysis of Available Data on the $A^{1}\Sigma_{u}^{+}$ and $b^{3}\Pi_{0u+}$ States of Rb$_{2}$ T. Bergeman, H. Salami, A.J. Ross, P. Crozet, A. Allouche, M. Aubert-Fr\'{e}con, B. Beser, J. Bai, A.M. Lyyra, S. Kotochigova, C. Lisdat, O. Dulieu The lowest excited states of alkali dimers are of interest as intermediaries in the excitation of higher levels and in the production of ultracold ground state molecules. With help of new data, particularly on low vibrational levels of the $A$ state, and improved {\it ab initio} estimates of potentials and spin-orbit functions, we have produced an improved fit to available data on the $A$ and $b$ states of Rb$_{2}$. Currently, the rms residual of our fit is 0.22 cm$^{-1}$, as compared with experimental uncertainties of 0.003 to 0.008 cm$^{-1}$. This suggests that the primary structures are reproduced in the model, but there remains some deficiency, perhaps in the form of the spin-orbit coupling function, or associated with insufficient data on the $b ^{3}\Pi_{0u+}$ state. [Preview Abstract] |
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E1.00019: New Data and Analysis of Available Data on the $A^{1}\Sigma_{u}^{+}$ and $b ^{3}\Pi_{u0}$ States of Cs$_{2}$ T. Bergeman, H. Salami, O. Dulieu, D. Li, F. Xie, L. Li The lowest excited states of alkali dimers are of interest as intermediaries in the excitation of higher levels and in the production of ultracold ground state molecules. For the heavier alkali dimers, there are large spin-orbit interactions that complicate the analysis. For Cs$_{2}$, recently medium-resolution spectroscopy at Tsinghua U. has provided information on levels of the $b^{3}\Pi_{0u\pm}$ states below the $v$=0 level of the $A$ state. These data yield the $b$ state vibrational numbering and a value for $T_{e}$ accurate to $\pm$ 1.5 cm$^{-1}$, and have permitted us to analyze and fit previously obtained data [1,2] on the $A$ state. Our model includes spin-orbit coupling for which we use a Morse-type function with an $R$-dependent correction factor. Currently, the rms residual of our fit to the new data is 1.65 cm$^{-1}$, and 0.14 cm$^{-1}$ for the older Fourier transform spectroscopy data, which has experimental uncertainties of 0.003 cm$^{-1}$. Additional data on regions with few observed $b$ state levels would undoubtedly improve the fit results. \\ 1. J. Verg\'{e}s and C. Amiot, J. Mol. Spectrosc. {\bf 126}, 393 (1987). \\ 2. C. Amiot and O. Dulieu, J. Chem. Phys. {\bf 117}, 5155 (2002). [Preview Abstract] |
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E1.00020: Measurement of NaK $3^1\Pi \to X^1\Sigma ^+,A^1\Sigma ^+$ Absolute Transition Dipole Moment Functions using Autler-Townes Spectroscopy and Calibrated Fluorescence S.J. Sweeney, E. Ahmed, P. Qi, A.M. Lyyra, J. Huennekens We describe a two-laser experiment using OODR and Autler-Townes splittings to determine NaK $3^1\Pi \to X^1\Sigma ^+,A^1\Sigma ^+$ absolute transition dipole moment functions. Resolved $3^1\Pi \to A^1\Sigma ^+$ and $3^1\Pi \to X^1\Sigma ^+$ fluorescence is recorded with the frequencies of a Ti:Sapphire laser (L1) and a ring dye laser (L2) fixed to excite particular $3^1\Pi \left( {19,11,f} \right)\leftarrow 2\left( A \right)^1\Sigma ^+\left( {{v}',11,e} \right)\leftarrow 1\left( X \right)^1\Sigma ^+\left( {{v}'',J\pm 1,e} \right)$ transitions. The coefficients of a trial transition dipole moment function $\mu \left( R \right)=a_0 +a_1 R^{-2}+a_2 R^{-4}+...$ are adjusted to match the relative intensities of resolved spectral lines terminating on $A^1\Sigma ^+\left( {{v}',11,e} \right)$ and $X^1\Sigma ^+\left( {{v}'',11,e} \right)$ levels. These data provide a \textit{relative} measure of the function $\mu \left( R \right)$ over a broad range of $R$. Next L2 is tuned to the specific $3^1\Pi \left( {19,11,f} \right)\leftarrow A^1\Sigma ^+\left( {10,11,e} \right)$ transition and focused to an intensity large enough to split the levels via the Autler-Townes effect. L1 is scanned over the $A^1\Sigma ^+\left( {10,11,e} \right)\leftarrow X^1\Sigma ^+\left( {1,J\pm 1,e} \right)$ transition to probe the AT lineshape, which is fit using density matrix equations to yield an \textit{absolute} value for $\left| {\left\langle {3^1\Pi \left( {19,11,f} \right)\left| {\mu \left( R \right)} \right|A^1\Sigma ^+\left( {10,11,e} \right)} \right\rangle } \right|$. This value is used to place the relative $\mu \left( R \right)$ obtained with resolved fluorescence onto an absolute scale. We compare with recent theoretical results. [Preview Abstract] |
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E1.00021: Bound-free Emission in the NaK Molecule B.M. McGeehan, S. Ashman, S.J. Sweeney, C.M. Wolfe, J.P. Huennekens, A.P. Hickman We are extending the analysis of the bound-free emission from the $4\,^3\Sigma^+$ electronic state to the $a(1)\,^3\Sigma^+$ repulsive state of the NaK molecule. In previous work, Burns {\it et al.} [J. Chem.~Phys. {\bfseries 119} 4743--4754 (2003)] measured spectra from initial vibrational levels up to $v = 8$, determined a refined potential for the $4\,^3\Sigma^+$ state, and obtained relative values of the transition dipole moment function $M(R)$ in the range $R \sim 3.8$~\AA\ to 4.6~\AA. Recent measurements include data for many additional vibrational levels up to $v = 34$ of the $4\,^3\Sigma^+$ state. The new data provide information about $M(R)$ for larger values of $R$, including a region where theoretical calculations have predicted sharp structure due to an avoided crossing. Using a version of R. J. Le~Roy's code BCONT that we modified, we will obtain values $M(R)$ for a larger range of $R$, and we will refine the inner repulsive wall of the potential for the $a(1)\,^3\Sigma^+$ state. [Preview Abstract] |
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E1.00022: Energy structure and dynamics of the $B"\overline B { }^1\Sigma _u^+ $ and D${ }^1\Pi _u^+ $state of molecular hydrogen near the third dissociations limit Elizabeth McCormack, Robert Ekey, Joe Croman, Aaron Marks Two-color, resonantly-enhanced, multiphoton ionization spectroscopy is used to probe highly excited vibrational levels of the $B"\overline B { }^1\Sigma _u^+ $ and D${ }^1\Pi _u^+ $states of molecular hydrogen near the n=3 dissociation limit. Transitions are observed via two-photon excitation of the $E,F{ }^1\Sigma _g^+ ,v'=6,J'$ state from the ground state. Both molecular and atomic ion production are detected as a function of wavelength by using a time-of-flight mass spectrometer. Term energies of multiple rovibrational levels the $B"\overline B { }^1\Sigma _u^+ $ and D${ }^1\Pi _u^+ $ states and lifetimes of the J = 1-4, $v $= 12, 13 and 14 levels of the D${ }^1\Pi _u^+ $state are reported. The trend of lifetime with vibration is strongly suggestive of a new dissociation channel opening up for the high vibrational levels. Recent theoretical calculations of the rotational interaction of the D${ }^1\Pi _u^+ $ state with the 6 lowest ${ }^1\Sigma _u^+ $ states of H$_{2}$ are invoked to explain the dynamics of these highly excited vibrational levels. [Preview Abstract] |
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E1.00023: Fine structure measurements of high-L Rydberg states of H$_{2}$. Eteri Svanidze, Spencer Johnson, Erica Snow Measurement of the fine structure pattern of high-angular momentum Rydberg states provides information about the basic properties of the ion core, such as the polarizability. Recently a \underline {r}esonant \underline {e}xcitation \underline {S}tark \underline {i}onization \underline {s}pectroscopy (RESIS) apparatus has been constructed at the SUNY Fredonia campus. A Doppler-tuned CO$_{2}$ laser resonantly excites transitions in a fast molecular beam, which are detected by Stark ionization. We report here our experimental progress in the fine structure measurements of high-L Rydberg states of the ground vibrational state of molecular hydrogen. [Preview Abstract] |
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E1.00024: Long-range multipole potential model study for Rydberg states of triatomic hydrogen molecule Jia Wang, V. Kokoouline, C.H. Greene The long-range multipole potential model has proven to be useful in studying Rydberg states of the hydrogen molecule ($\rm{H_2}$). In this model, the Rydberg electron interacts with the ion core through polarizability and quadrupole interactions. In conjunction with multichannel quantum defect theory (MQDT), we apply this model to the study of the energy levels of Rydberg states in the triatomic hydrogen molecule ($\rm{H_3}$). [Preview Abstract] |
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E1.00025: Retrieval of internuclear separations of molecules from intense laser-induced high-order harmonic spectra. Cheng Jin, Van-Hoang Le, Ngoc-Ty Nguyen, Anh-Thu Le, Chii-Dong Lin Using high-order harmonics generated by intense infrared laser pulses, an iterative method for retrieving the internuclear separations of N$_{2}$, O$_{2}$, and CO$_{2}$ molecules is presented. It is shown that accurate results can be retrieved with a small set of harmonics and with one or few alignment angles of the molecules. The internuclear separations of linear molecules can be retrieved from harmonics generated by isotropically distributed molecules. It is further demonstrated that the internuclear separations can also be retrieved by fitting the extracted transition dipole moment from harmonic spectra. It is concluded that time-resolved chemical imaging of molecules in terms of infrared laser pulses with femtosecond temporal resolution is possible. [Preview Abstract] |
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E1.00026: Aluminum anions and water: nucleophilic reactivity and free-electron metal clusters Patrick Roach, Arthur Reber, W. Hunter Woodward, Shiv Khanna, A. Welford Castleman, Jr. When coupled with appropriate theoretical considerations, the presence or absence of a reaction under strictly controlled conditions can be used to gain insight into electronic structure, bond strength, overall stability, and the general nature of a cluster of atoms. It will be shown that aluminum cluster anions react selectively with water molecules based on cluster size. Additionally, it will be suggested using first principles density functional theory that for certain cluster sizes reactivity events can be attributed mainly to the geometric, rather than electronic structure of a cluster. These findings provide a representative example of a hitherto unsubstantiated variable capable of governing and tuning reactivity, namely the energetics of a dissociative transition state at the cluster surface . [Preview Abstract] |
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E1.00027: ATOMIC PHOTOIONIZATION AND PHOTODETACHMENT PROCESSES |
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E1.00028: Coherent one- and two-photon ionization of excited barium John R. Tolsma, Chris H. Greene We calculate the photoionization cross sections of the 6s6p 1Po state of barium by either one or two photons. In both cases the final state energies reach the vicinity of the 5d ionization thresholds. The effects of hyperfine interactions due to isotope mixing in naturally occuring barium are also examined. This study uses variational R-matrix and quantum defect techniques to calculate the rich array of autoionizing resonances in this energy range. The two-photon cross section calculation utilizes a small set of intermediate levels that arise in the second-order time-dependent perturbation expansion. Using the channel dependent scattering parameters we attempt to calculate photoelectron angular distributions, phase coherence effects, and branching ratios of the autoionized electrons. Experimental data[1] have shown that these physical observables can be controlled by varying the relative phase of the single and double photon excitation paths. Future applications in coherent control are discussed. [1] Rekishu Yamazaki and D.S. Elliott, Phys. Rev. Lett. 98, 053001 (2007) [Preview Abstract] |
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E1.00029: Photoionization of Heavy Atomic Ions Connor P. Ballance, Patrick H. Norrington, Brendan M. McLaughlin Photoionization cross sections of heavy atomic elements, in low stages of ionization, are currently of interest both experimentally and in astrophysics. The data from such processes have many applications in planetary nebulae, where they are of use in identifying weak emission lines of $n$-capture elements. Furthermore, photoionization experiments on heavy atomic ions, at the Advanced Light Source (ALS) in Berkeley, has highlighted the need to have high quality calculations in order to fully interpret experimental data. A recently developed relativistic R-matrix code (DARC), for parallel architectures, has been modified now to include photoionization processes. We have performed calculations for photoionization cross sections, on a number of different atomic ion species (Se, Kr, Ar and Xe) in their low stages of ionization, using both the Breit-Pauli and the relativistic Dirac-R-matrix method. Where possible, we compare our theoretical results with ongoing experiments being performed at the ALS. Such comparisons indicate suitable agreement and serve as the ultimate benchmark for our work. Further details will be presented at the meeting. [Preview Abstract] |
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E1.00030: Photoionization of Xe confined in C$_{60}$ Zhifan Chen, Alfred Z. Msezane The photoionization cross section for the endohedral
Xe@C$_{60}$ atom is investigated by modeling the C$_{60}$ as an
attractive short range spherical shell with potential $V(r)$,
given by $V(r)=-V_0$ for $r_i |
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E1.00031: Infrared Photodetachment Spectroscopy of As$^{- }$ N.D. Gibson, C.W. Walter, A.P. Snedden, R.L. Field III, J.Z. Shapiro, C.M. Janczak, D. Hanstorp The binding energy and fine structure splittings of the arsenic negative ion (As$^{-})$ have been measured using tunable laser photodetachment threshold spectroscopy. The relative cross section for neutral atom production was measured with a crossed laser-ion beam apparatus over selected photon energy ranges between 0.63 -- 0.81 eV. An $s$-wave threshold was observed near 0.8048 eV due to the opening of the As$^{-}$ (4$p^{4} \quad ^{3}P_{2})$ to As (4$p^{3} \quad ^{4}S_{3/2})$ ground state to ground state transition, which defines the electron affinity of As. Thresholds were also observed for detachment from the J = 0 and 1 levels of As$^{-}$, permitting accurate determination of the fine structure splittings. The values measured in the present work are consistent with previous measurements [1,2], and substantially reduce the uncertainties. [1] T.P. Lippa \textit{et al}., J. Chem. Phys. \textbf{109}, 10727 (1998); [2] G. Haeffler \textit{et al.}, Z. Phys. D \textbf{42}, 263 (1997). [Preview Abstract] |
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E1.00032: Column density effect in photoionization and photoabsorption spectra T.N. Chang, J.L. Luo, T.S. Yih, Yuxiang Luo In our effort to measure both the absorption and ionization spectra in a single experimental set-up, we have demonstrated that the column density not only affects strongly the structure profiles of an atomic resonance but also alternates significantly the back ground cross sections in the ionization measurement. Together with the peak cross sections estimated from the convoluted theoretical spectra for the lowest resonance of the He (1,0)$^{-}_{0}$ series, we present a procedure that could be applied effectively to determine the energy resolution and the detailed characteristics of the monochromater (i.e., slit) function of a given light source. [Preview Abstract] |
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E1.00033: Cross sections for non-sequential two-photon double ionization of helium Johannes Feist, Stefan Nagele, Renate Pazourek, Emil Persson, Joachim Burgd\"orfer, Barry Schneider, Lee Collins The generalized cross sections for non-sequential two-photon double ionization of helium at photon energies from 39.5\,eV to 54.4\,eV have been the subject of several recent theoretical studies. Quantitative agreement between the different approaches has not yet been reached. In this contribution, we present converged results for the total integrated and triply differential cross sections for the above process, which are based on the direct integration of the time-dependent Schr\"odinger equation. We compare our data with calculations from other authors and investigate to what extent electronic correlation in the representation of the double continuum affects the cross sections. We also study the influence of the pulse shape on the value of the cross sections extracted from time-dependent approaches. [Preview Abstract] |
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E1.00034: Calculation of Electron Affinity and Partial Cross Sections of Hf$^-$ Lin Pan, Donald Beck We have calculated for the first time the electron affinity (EA) of Hf$^-$, using the relativistic configuration interaction method. Our calculations show Hf$^-$ has only one bound state 5d$^2$6s$^2$6p $J$=5/2, which is a 6p attachment to the ground state of Hf I. By combining our valence stage result with the separate estimate for the modest core-valence contribution, the EA of Hf$^-$ is about 0.114 eV. So far there have been only two experimental results [1,2] for the EA of Hf$^-$, but both gave only the limits. Our result falls within both of the limits. We also calculate the partial cross sections for photodetachment to the lower lying neutral thresholds. [1] M-J. Nadeau {\em et al}, Nucl. Instr. and Meth. B {\bf 123}, 521 (1997) [2] Vernon T. Davis {\em et al}, Nucl. Instr. and Meth. B {\bf 241}, 118 (2005) [Preview Abstract] |
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E1.00035: Photoionization of $Sc^{+2}$ Ayao Sossah, Hsiao-Ling Zhou, Steven Manson Photoionization cross section calculations are performed on the ground ($[Ne]3s^23p^63d{ }^2D_{3/2}^e )$ and the first two excited ($[Ne]3s^23p^63d{ }^2D_{5/2}^e $ and $[Ne]3s^23p^64s \quad { }^2S_{1/2}^e )$ states of $Sc^{+2}$ for photon energies from threshold to 68.0 eV. The discrete $Sc^{+3}$ orbitals are generated using the computer program AUTOSTRUCTURE; 24 configurations are included in the configuration-interaction (CI) calculation for $Sc^{+3}$. In addition to the non-relativistic (LS-coupling) R-matrix method, we have used the relativistic (Breit-Pauli) R-matrix method to carry out the calculations to focus on relativistic effects. The results are compared with previous theoretical results and existing experimental data, and rather good agreement with experimental data is obtained. The most prominent ($3p\to 3d)$ giant resonances are analyzed and identified, and our calculated positions and widths are compared with experimental results. This work is supported by US DOE and NASA. [Preview Abstract] |
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E1.00036: Double-electron photoionization of outer electrons in complex atoms. M. Ya. Amusia The aim of this talk is to demonstrate that$^{ }$double-electron photoionization of outer electrons in complex atoms proceeds via virtual creation of the nearest in energy $s$-vacancy instead of direct elimination of two outer electrons. As a result, the elimination of outer electrons by a single photon takes place not because solely of the interaction between ionized electrons, but due to a more complex mechanism, namely that with active participation of the closest $s- $electron. The suggested mechanism becomes particularly important at high photon energies$\omega $. It is known that there the one-electron photoionization cross-section $\sigma _s^+ (\omega )$ for an $s- $electron decreases as $\sigma _s^+ (\omega )\sim 1/\omega ^{7/2}$with $\omega $ growth. In the most studied case of helium double-electron ionization its cross-section $\sigma _s^{++} (\omega )$ decreases also as $\sigma _s^{++} (\omega )\sim 1/\omega ^{7/2}$ thus leading to a known fact that the ratio $R_{ss/s} =\sigma _s^{++} (\omega )/\sigma _s^+ (\omega )$ is $\omega $ independent at$\omega \to \infty $. The suggested mechanism changes the situation dramatically leading for two outer $p$-electrons photoionization to the ratio $R_{pp/p} \sim \omega \to \infty $ at$\omega \to \infty $, because $\sigma _{pp}^{++} (\omega )\sim 1/\omega ^{7/2}$while $\sigma _p^+ (\omega )\sim 1/\omega ^{9/2}$. This feature could be observed experimentally if to study two outgoing electrons in coincidence. [Preview Abstract] |
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E1.00037: Fano Parameters for Li Inner-Shell Resonances in the 70--74.5 eV Region Dragan Lukic, Scott B. Whitfield, Ralf Wehlitz We have measured the relative ion-yield of lithium between 70 and 74.5 eV in the region of 1s3$\ell n\ell'$ ($n>=3$) inner-shell excitations using highly monochromatized photons. We employed the PGM undulator beamline at the Synchrotron Radiation Center with a resolving power of 13,000 and have tracked the autoionizing resonances to higher energies than in previous experiments\footnote{G.\ Mehlman, J.W.Cooper, and E.\ B.\ Saloman, Phys.\ Rev.\ A {\bf 25}, 2113 (1982)}$^,$\footnote{L.\ M.\ Kiernan {\it et al.}, J.\ Phys.\ B {\bf 29}, L181 (1996)}. Using Fano profiles to fit our data we have analyzed the resonances in our ion yield spectra and obtained resonance parameters that we compare to previously published experimental and theoretical values. We find good agreement with the theoretical calculations of Chung and Chang\footnote{K.T.\ Chung and J.C.\ Chang, Phys.Rev.\ A {\bf 61}, 030701(R) (2000)}. [Preview Abstract] |
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E1.00038: Photodetachment Cross Sections in External Magnetic Fields Christian Bracher, Arnulfo Gonzalez, Yigal Weinstein Near-threshold photodetachment of negative atomic ions provides an almost monochromatic, nearly pointlike source of electrons that can be used to probe the quantum dynamics of electrons in externally applied electromagnetic fields. These fields cause modulations both in the observed photocurrent spectrum, and the spatial distribution of the emitted photoelectrons. In the case of a uniform electric field, the changes in the photocurrent are well understood, and have been used to establish photodetachment microscopy as a tool in precision spectroscopy. Considerably more intricate patterns arise when the photodetachment is performed in a magnetic field environment. In our contribution, we examine the total photocurrent as well as the photoelectron density profile for electrons emitted in the presence of either a homogeneous magnetic field, or a magnetic monopole field. Employing Green function methods and semiclassical techniques as complementary approaches, we identify and explain some distinctive features in the detachment cross sections. [Preview Abstract] |
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E1.00039: Photoionization of Be-like Ions: $R$-matrix Calculations W.-C. Chu, H.-L. Zhou, S.T. Manson The photoionization of the beryllium-like iso-electronic series has been studied. The wave functions of target ions were built with CIV3 program. The Breit-Pauli $R$-matrix method was used to calculate the cross sections in the photon-energy range between the ionization threshold and 1$s^{2}$3$d_{5/2}$ threshold for each ion. For the total cross sections of C$^{2+}$, N$^{3+}$, and O$^{4+}$, our results match the experiments well. For the ground state photoionization, we identified and characterized the resonances converging to 1$s^{2}$2$l_{j}$ and 1$s^{2}$3$l_{j}$ thresholds with their quantum defects, energies and widths using the eigen-phase sum methodology, and compared the present work with other researchers. We discuss the interactions among resonances which explain the seemingly erratic behavior of the resonances and summarize the general appearance of resonances, in both energies and widths, along a resonance series and along the iso-electronic series. This work was supported by DOE. All calculations were performed on the NERSC system. [Preview Abstract] |
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E1.00040: Relativistic effects in inner-shell photoionization of excited sodium H.-L. Zhou, A.M. Sossah, S.T. Manson, A. Hibbert Using a semi-relativistic Breit-Pauli (BP) R-matrix method we calculated the inner-shell photoionization of the Na $2p^63p \quad { }^2P1/2$ and $^2P3/2$ excited states. Extensive correlation is included in initial and final state wave functions to approximate complete sets. The calculated energies of initial states of Na are within 1{\%} of the NIST value. The J-dependent branching ratios of the Na$^{+} \quad 2p^53p \quad { }^{1,3}Lj$ agree quite well with experimental results.\footnote{D. Cubaynes, et al., Phys. Rev. Lett. \textbf{92}, 233002 (2004).} These branching ratios are nearly photon energy independent except in resonance regions. We predict strong $2s2p^63p^2$ resonances around 68.2 eV photon energy, but there is no experiment to compare with. We also used fully relativistic Dirac R-matrix code to calculate the photoionization of excited Na. The results are compared with the BP results. This work was supported by DOE and NSF. The work was performed using the NERSC computer system. [Preview Abstract] |
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E1.00041: Photoionization accompanied by excitation at intermediate photon energies Evgenii Drukarev, Evgeny Liverts, Miron Amusia, Rajmund Krivec, Victor Mandelzweig We calculate the photoionization with excitation- to photoionization ratios $% R_{n\ell}$ and $R_n=\Sigma_\ell R_{n\ell}$ for atomic helium and positive heliumlike ions at intermediate values of the photon energies. The final state interactions between the electrons are included in the lowest order of their Sommerfeld parameter. This enables us, in contrast to purely numerical calculations, to investigate the roles of various mechanisms contributing beyond the high-energy limit. The system of the two bound electron is described by the functions obtained by the Correlation Function Hyperspherical Harmonic Method. For the case of heliumlike ions we present the high energy limits as power expansion in inverse charge of the nucleus. We analyze the contribution of excitation of states with nonzero orbital momenta to the ratios $R_n$. In the case of helium our results for $R_n$ are in good agreement with those of experiments and of previous calculations. [Preview Abstract] |
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E1.00042: Spin-Orbit Activated Interchannel Coupling Effect in Dipole and Quadrupole Photoionization S. Sunil Kumar, P.C. Deschmukh, T. Banerjee, S.T. Manson Spin-orbit activated interchannel coupling has been found to affect photoelectron parameters in both the dipole and quadrupole manifolds [1-3]. This effect has been reported in the dipole photoionization parameters of 3d subshells of Xe [1], Ba [1, 3] and Cs [1, 3] and quadrupole spin-polarization parameters of Xe 3d [2]. In the present work, dipole and quadrupole photoionization from 4d and 4p subshells of Xe and 5d and 5p subshells of Rn have been investigated. The effect is significant in dipole photoionization of Xe 4d and Rn 5d, and in quadrupole photoionization of Xe 4p and of Rn 5p states. [1] M. Ya. Amusia, L. V. Chernysheva, S. T. Manson, A. M. Msezane, and V. Radojevic, Phys. Rev. Lett. \textbf{88} 093002 (2002). [2] M. Ya. Amusia, N. A. Cherepkov, L. V. Chernysheva, Z. Felfli and A. Z. Msezane, J. Phys. B \textbf{38} 1133 (2005). [3] T. Richter, E. Heinecke, P. Zimmermann, K. Godehusen, M. Yal\c{c}inkaya, D. Cubaynes, and M. Meyer, Phys. Rev. Lett. \textbf{98} 143002 (2007). [Preview Abstract] |
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E1.00043: Photoionization of Ions of the Cerium Isonuclear Sequence in the Energy Range of 4d Excitations M. Habibi, D.A. Esteves, R.A. Phaneuf, A. Aguilar, A.L.D. Kilcoyne, C. Cisneros Absolute measurements of photoionization cross sections for Ce$^{q+}$ ions (1 $\le $ q $\le $ 9) were performed in the photon energy range 105 -- 150 eV by merging beams of ions and monochromatized synchrotron radiation at the Advanced Light Source. Cross sections were measured for both single and double photoionization of Ce$^{+}$, Ce$^{2+}$ and Ce$^{3+}$. The photon energy resolution was 0.1 eV. The cross sections for initial charge states (1 $\le $ q $\le $ 9) are dominated by extremely broad resonance features due to 4d excitation-autoionization in this energy range, while that for Fe$^{9+}$ is characterized by narrow resonances. The reactant ion beams comprised unknown admixtures of ions in their ground state and in long-lived metastable states, complicating their detailed interpretation. Research supported by the Division of Chemical Sciences, Geosciences and Biosciences of the U.S. Department of Energy. [Preview Abstract] |
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E1.00044: Photoionization of Fe$^{7+}$ in the $3p-3d$ resonance energy region M.F. Gharaibeh, U.I. Safronova, R.A. Phaneuf, E.D. Emmons, A.L.D. Kilcoyne, A.S. Schlachter, A. Mueller, I.M. Savukov Photoionization of Fe$^{7+}$ in the energy range of $3s$ and $3p$ inner-shell excitations were studied using photoion spectroscopy with monochromatized synchrotron radiation. The resonance structure in the range 150 -- 180~eV is attributed to [$3s^23p^63d, 3s^23p^64s$] -- [$3s^23p^54s5s$, $3s^23p^53d5s, 3s^23p^53d6s$, $3s^23p^53d4d, 3s^23p^53d5d$, $3s3p^63d4p$] transitions. Relativistic many-body perturbation theory was used to evaluate multipole (M1 and E2) matrix elements to obtain lifetimes of the $3s^23p^63d^3D_{5/2}$ and $3s^23p^64s\ ^2S_{1/2}$ metastable levels. These calculations started from an argonlike closed-shell Dirac-Fock potential. Matrix elements were calculated using both relativistic many-body perturbation theory, complete through second and third orders, and the relativistic all-order method restricted to single and double excitations. To reproduce resonance structure in the photoionization cross section, a large-scale COWAN calculation including about 30 configurations was used. [Preview Abstract] |
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E1.00045: Photoionization cross sections for Ce$^{8+}$ and Ce$^{3+}$; Experiment and theory M. Habibi, D.A. Esteves, R.A. Phaneuf, U.I. Safronova, A. Aguilar, A.L.D. Kilcoyne, C. Cisneros, I.M. Savukov Cross sections for single photoionization of Ce$^{8+}$ and single and double photionization of Ce$^{3+}$ in the energy range of $4d$ inner- shell excitations were studied using photoion spectroscopy with monochromatized synchrotron radiation. Resonance structure observed in the range 120 -- 140~eV is attributed to $4d^{10}5s^25p^{k}4f^{n}$ - $4d^{9}5s^25p^{k}4f^{n+1}$ transitions. Metastable $4d^{10}5s^25p4f$ states of Ce$^{8+}$ were found to be important in interpreting the measurements. Relativistic many-body perturbation theory was used to evaluate multipole (M1, E2, and M3) matrix elements to obtain lifetimes of metastable levels. Extremely fast autoionizing decay is responsible for the broad spectra. Large-scale calculations using the COWAN code confirm that the natural widths of some levels of the $4d^{9}5s^{2}5p^{k}4f$ configurations are in the range 1--2~eV. [Preview Abstract] |
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E1.00046: Photo-Double Ionization: Threshold Law and Low-Energy Behavior A. Temkin, A.K. Bhatia The threshold law for photoejection of two electrons from atoms (PDI) is derived from a modification of the Coulomb-dipole (C-D) theory. The C-D theory applies to two-electron ejection from negative ions (photo-double detachment:PDD).The modification consists of correctly accounting for the fact that in PDI that the two escaping electrons see a Coulomb field, asymptotically no matter what their relative distances from the residual ion are. We find the analytic threshold law $\mathcal{Q}$$(E)$ i.e. the yield of residual ions to be $\mathcal{Q}$$_f(E) \propto E+C_WE^{\gamma_W}+CE^{5/4}\sin[\frac{1}{2}{\rm ln}E+\phi]/{\rm ln}(E)$. The first and third terms are beyond the Wannier law. The Wannier exponent for neutral targets is $\gamma_{W}$=1.056. The first and third terms are beyond the Wannier law. Our threshold law can only be rigorously justified for residual energies $\le 10^{-3}$eV. Nevertheless in the present experimental range (0.1 - 4 eV), our form, without the second (Wannier) term, can be well fit to the experimental results for He, Li, and Be, as compared to the Wannier law alone, which has a larger error for Li and Be, and for both of which the data also show indications of modulation. which are also well fit by our formula. [Preview Abstract] |
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E1.00047: Double-to-single photoionization ratio of plasma-embedded helium atom at X-ray energies Sabyasachi Kar, Yew Kam Ho The double photoionization of helium by absorption of a high-frequency photon have gained considerable interest in theoretical [1-2] and experimental [3] studies during the last decades. In this work, we have investigated the asymptotic ratios of double-to-single photoionization of plasmas-embedded helium atom at very high photon but non-relativistic energies in the framework of the Debye model for weakly coupled plasmas [4]. The ratio of double-to-single photoionization for free atom is determined as 1.644{\%}, in good agreement with the synchrotron measurements [3] and other theoretical predictions [1, 2]. The asymptotic ratio of double-to-single photoionization cross-sections for different screening parameters along with the single, the double, and the total photoionization asymptotic cross sections will be presented at the meeting. [1] R. C. Forrey, et al., Phys. Rev. A \textbf{51}, 2112 (1995). [2] R. Krivec, M. Ya. Amusia, and V. B. Mandelzweig, Phys. Rev. A \textbf{62}, 064701 (2000). [3] J. C. Levin \textit{et al.}, Phys. Rev. Lett. \textbf{67}, 968 (1991); \textbf{76}, 1220 (1996). [4] S. Kar and Y. K. Ho, Phys. Rev. A, to be published (2008). [Preview Abstract] |
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E1.00048: Cancellation of correlations in the nonrelativistic high energy limit of photoeffct E.G. Drukarev, R.H. Pratt We investigate the total effect of correlations on photoionization of atomic states with a nonzero value of orbital momentum in the nonrelativistic high energy asymptotic limit. The tendency for cancellation among such effects was reported in a particular situation of the angular distributions [1], and then more generally in [2], where it was found that the cancellations manifest themselves at the amplitude level, for both p and d states. We find that these cancellations can partially be viewed as a consequence of the closure properties satisfied by the eigenfunctions of the Hamiltonian. In the limit of a system with all the discrete and continuum states occupied, closure would give total cancellation. There is also total cancellation between the contributions of all such bound states and of the low energy continuum states, i.e. there are identities among these amplitudes. For real atoms results can be obtained from the closure results by subtracting contributions of the unoccupied bound states and of continuum states, using the quantum defect theory combined with the Fermi-Segre theorem. The corrections to the cancellation required by closure are small, and they tend to increase the cancellation. [1] V. K. Dolmatov, A. S. Baltenkov, and S. T. Manson, Phys. Rev. A \textbf{ 64}, 042718 (2002); [2] E. G. Drukarev and R. H. Pratt, Phys. Rev. A \textbf{72}, 06270 (2005). [Preview Abstract] |
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E1.00049: ATOMIC, MOLECULAR, AND CHARGED PARTICLE COLLISIONS |
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E1.00050: Ion induced dissociation dynamics of acetylene: Signature of vibrational flopping Sankar De, I.V. Litvinyuk, Jyoti Rajput, A. Roy, C.P. Safvan, P.N. Ghosh We report the results of dissociation dynamics of multiple charged acetylene molecules formed in collision with 1.2 MeV Ar$^{8+}$ projectiles. Using the coincidence map, we found the evidence for molecular deformation due to a vibrationally active transition state of multiply charged C$_{2}$H$_{2}$ under the impact of low energy projectiles. `Butterfly-like' structures are observed in the coincidence spectra [1] between hydrogen and carbon ionic fragments. Such structures can be generated by numerical simulations and are found to originate from the bending motion of the dissociating molecule. From the measured slopes of the coincidence islands for carbon atomic fragments and theoretical values determined from the charge and momentum distribution of the correlated particles, we observe a diatom-like behaviour of the C--C charged complex during dissociation of multiply charged acetylene [2]. This is a signature of sequentiality in the breakup dynamics of this multiply charged molecular species. The results will be compared with those obtained in pump-probe experiments using intense few cycle laser pulses. Ref: [1] S. De et al. JCP, 127, 051101 (2007); [2] S. De et. al. PRA (accepted) [Preview Abstract] |
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E1.00051: Storage Modes in a Passive Electrostatic \underline {E}lectron \underline {R}ecycling \underline {S}pectrometer (\textit{ERS}). D.R. Tessier, T.J. Reddish, F.H. Read, A.J. Alderman, P. Hammond A new type of electron spectrometer based around the storage of low energy ($\sim $30 eV) electrons in electrostatically defined orbits has been recently reported [Phys Rev Lett \textbf{99}, 253201 (2007)]. The \textit{ERS} consists of two hemispherical deflection analysers (HDAs) whose exits and entrances are connected by a series of electrostatic lenses to form a race-track structure of ``desk-top'' size. Electrons are injected into the ring in a pulse of length $\sim $ 50 ns through one of the HDA's onto the optical axis of the ERS and stored with lifetimes of $\sim $50$\mu $s (corresponding to $\sim $150 orbits of the $\sim $65cm circumference). We outline the theoretical description of the charged particle optics design leading to long term storage of electrons in the ring. Preliminary experimental results exploring storage as a function of different mean pass energies in the two HDA's will also be presented. Complex orbital behavior is observed under certain operating conditions, indicating the likelihood of the storage of electrons of well-defined kinetic energy. [Preview Abstract] |
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E1.00052: Ro-vibrational Charge Exchange Cross Sections in C $^{4+}$ and H$_{2}$ Scattering at Low Energies Dwayne C. Joseph, Bidhan C. Saha, Robert J. Buenker We report the calculation for electron capture during C $^{4+}$ collisions with molecular hydrogen at low incident energies. Using the multi reference single- and double-excitation (MRD-CI) method [1] we calculate all adiabatic potential energy curves and the non-adiabatic coupling matrix elements. We use quantum close coupling method [2] to evaluate various excitation cross sections. Details will be presented at the meeting. [1] R. J. Buenker and S. D. Peyerimhoff, Thoer. Chim. Acta 35, 33 (1974). [2] B. C. Saha, in Electron-Molecule Scattering and Photoionization, edt P. G. Burke and J. B. West, p 221 (1988). [Preview Abstract] |
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E1.00053: Simulation of cometary x rays in collisions of keV C$^{5+}$, C$^{6+}$, Ne$^{8+}$ with CO, H$_{2}$, and He Kenneth Miller, Quentin Kessel, Winthrop Smith, Juri Simcic, Ara Chutjian About 10 years ago, 50-1000 eV x rays were found to be emitted from comets in the inner solar system [1]. The x-rays result from charge exchange interactions between highly-charged heavy ions of the solar wind and gases emanating from the warming comet nucleus [2]. JPL's Highly Charged Ion Facility [3] and a UConn XUV spectrometer were used to measure relative line emission cross sections from ion-gas collisions of solar wind constituents with gas targets of cometary interest. Different target gases are found to affect the projectile (n,l) states following capture. We also report some preliminary data on the projectile velocity dependence of the cross sections, to compare with observations from space and with theoretical models [4]. 1. C. M. Lisse, et al., Science, \textbf{274}, 205 (1996). 2. T. E. Cravens, Science, \textbf{296}, 1042, (2002). 3. J. B. Greenwood, A. Chutjian, S. Smith, Astrophysical J. \textbf{259}, 605, (2000). 4. V. Kharchenko, A. Dalgarno, Astrophysical J. \textbf{554}, L99, (2001). This research is supported by NASA NCC5-601 and at JPL by arrangement with NASA. [Preview Abstract] |
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E1.00054: ATOM-ATOM AND ATOM-MOLECULE COLLISIONS |
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E1.00055: Velocity-Dependent Cross Sections of Rovibrationally Inelastic Processes from Doppler Lineshapes Paula Matei, Steven Coppage, Brian Stewart Spectroscopic techniques are employed in the studies of rovibrationally inelastic processes in the Li$_{2}$* (A)~--~noble gas system. We present new results of Velocity Selected by Doppler Shift (VSDS) experiments. Our goals are to look for experimental evidence of a novel vibrational transfer mechanism that involves impacts with the side of the molecule, and to investigate and compare different combinations of rotational and vibrational energy transfer. The experimental results will be compared with cross sections calculated from \textit{ab initio} potential surfaces. [Preview Abstract] |
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E1.00056: Formation of Heavy Rydberg K$^{+}-\mbox{SF}_6^- $ Ion-Pair States in K($n$p)-SF$_{6}$ Collisions M. Cannon, Y. Liu, F.B. Dunning At low $n$ ($n\approx $10 -- 15), electron transfer in collisions between K($n$p) Rydberg atoms and SF$_{6}$ can lead to formation of bound K$^{+}-\mbox{SF}_6^- $ ion pairs that orbit at relatively large separations, frequently referred to as heavy-Rydberg ion-pair states because of their similarities to atomic Rydberg states. The production of such ion pairs is examined through measurements at different values of $n$ and with different Rydberg atom velocities. The lifetimes of the ion pairs are measured by observing the time development of the $\mbox{SF}_6^- $ signal, part of which results from dissociation of bound ion pairs through the transfer of internal energy from the $\mbox{SF}_6^- $ ions into translational energy of the ion pair. The data point to bound ion-pair lifetimes of $\sim $1 -- 2$\mu $s, which are many times larger than their orbital periods of $\sim $30 -- 150ps. This work is being extended to other attaching molecules to further examine the properties of heavy Rydberg systems. [Preview Abstract] |
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E1.00057: Laser Ablation and Buffer-Gas Cooling of Alkali and Rare Earth Metals Wesley Campbell, Maxwell Parsons, Rupak Chakraborty, John Doyle We present studies of cold atomic vapors of Li, K, Cs, and Yb produced through pulsed laser ablation into 4 K helium buffer gas. The atomic ground state density of ablated species is monitored by laser absorption spectroscopy. We observe rapid thermlization of the atomic vapor to the temperature of the buffer gas and find that for Yb, the lifetime of the vapor matches a simple diffusion model. This is also true for Li up to a specific threshold in buffer-gas density. For K, Rb, and Cs, we see a short timescale loss that is inconsistent with diffusion to the cell walls. The diffusion cross section of Li is measured, allowing for the use of lithium as a ``standard'' gauge of buffer-gas density. [Preview Abstract] |
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E1.00058: Hyperfine State-Changing Collisions of Cs(6\textit{P}$_{1/2}$) Atoms with Argon Perturbers Laurie Morgus, Tyler Morgus, Tyler Drake, John Huennekens A two-step excitation experiment has been employed to measure the collisional rate coefficients and to study the velocity distribution of Cs(6$P_{1/2})$ atoms that have undergone a single hyperfine state-changing collision with Ar. Argon pressure broadening rates and shifts of the Cs 6$P_{1/2}(F') \quad \to $ 8$S_{1/2}(F'')$ transitions have been determined. In the experiment, a narrowband Ti:Sapphire laser is tuned to line center of the 6$S_{1/2}(F$ = 4) $\to $ 6$P_{1/2}(F'$ = 3 or 4) transition. Then, the frequency of a narrowband cw dye laser is scanned over the 6$P_{1/2} \quad \to $ 8$S_{1/2}$ manifold to probe the populations of the 6$P_{1/2}$ hyperfine levels. Absorption of probe laser photons is monitored by detecting 8$S_{1/2 }\to $ 6$P_{3/2 }$fluorescence. The experiment is conducted at room temperature, where the Cs density is low. The Ar pressure is varied from 0 -- 1.52 Torr, leading to Cs-Ar collisions that transfer population from the directly excited 6$P_{1/2}(F')$ level to the other 6$P_{1/2}$ hyperfine level. The data are analyzed using a density matrix formalism to yield the rate coefficients for Cs(6$P_{1/2})$-Ar hyperfine state changing collisions. In addition, the one-dimensional velocity changing collision kernel for Cs(6$P_{1/2})$ atoms prepared with $v_{z }$= 0 that undergo $F'$ = 3 $\leftrightarrow \quad F'$ = 4 hyperfine state-changing collisions with argon is reported. [Preview Abstract] |
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E1.00059: Rotational energy transfer in CH$_4$ collisions with He atoms Benhui Yang, Phillip Stancil Methane is an active constituent in the Earth's atmosphere, is one of the important greenhouse gases, is an important species in the atmospheres of T dwarfs, and is likely present in the carbon-rich atmospheres of circumstellar shells. Quantitative determinations of state-to-state cross sections and rate coefficients for the CH$_4$-He scattering system are therefore of interest for numerical models of atmospheric and astrophysical environments. In this work, quantum close-coupling and coupled-state approximation scattering calculations for quenching of rotationally excited CH$_4$ due to collisions with He are performed for collision energies between 10$^{-7}$ and 3000 cm$^{-1}$ using the MP4 potential of Calderoni {\it et al.} [J. Chem. Phys. {\bf 121}, 8261 (2004)]. State-to-state cross sections and rate coefficients from selected initial rotational states of CH$_4$ in symmetries $A$, $E$ and $F$ are presented. Comparison of cross section with available theoretical results and experimental data are also presented. [Preview Abstract] |
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E1.00060: Isotope effects for complex scattering lengths of He-H$_2$ Jeff Nolte, Benhui Yang, Phillip Stancil, Teck-Ghee Lee, N. Balakrishnan, Robert Forrey, Alexander Dalgarno In this study we examine the effects of varying the molecular mass on the complex scattering lengths in collisions of molecular hydrogen and He. The variation in the diatomic mass is effected by holding the mass of one atom constant while varying the mass of the other. Specifically, we examine the three cases where the fixed atom is one of the three isotopes of hydrogen; H, D, and T. For each species HX, DX, and TX, where X denotes the atoms of varying mass, we consider collisions with both $^{3}$He and $^{4}$He. By performing close-coupling calculations using the scattering program MOLSCAT and a three-dimensional He-H$_{2}$ Born-Oppenheimer potential energy surface, we obtain cross sections from which we can calculate the real and imaginary parts of the scattering length. In examining the scattering lengths withing this ``reduced mass space," we observe zero-energy resonances for HX and DX where the mass of X is less than 1 amu. This reveals the presence of bound states below the dissociation limit of the He-H$_{2}$ complex which were previously predicted. We also examine the behavior of cross sections for individual state-to-state transitions. [Preview Abstract] |
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E1.00061: Ultracold collisions of spin-polarized metastable hydrogen atoms Robert C. Forrey The status of {\em ab initio} calculations of very low temperature cross sections for collisions between two spin-polarized metastable hydrogen atoms is discussed. Degeneracy between the 2s and 2p states produces long-range coupling that is non-vanishing at first order in perturbation theory. The degeneracy is lifted by the Lamb shift and fine structure splittings. Multiple adiabatic potential curves yield a set of coupled equations that must be solved at low energies. The electrostatic dipole-quadrupole interaction produces non-adiabatic radial coupling between (2s,2p) and (2p,2p) states. The Coriolis interaction yields non-adiabatic angular coupling that must be accounted for when working in a body-fixed frame. All of these contributions may be handled in a space-fixed atomic gauge that is particularly convenient for a spin-polarized system. The latest theoretical results are compared with an existing experiment. [Preview Abstract] |
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E1.00062: The mutual influence of reactive and non-reactive scattering channels in atom--molecule collisions. I. Simbotin, R. C\^{o}t\'{e}, A. Dalgarno In this work, we study D+H$_2$ collisions for the main purpose of understanding the influence of the reactive scattering channels on the non-reactive scattering channels. We will present a detailed quantitative comparison between the results of full calculations (including rearrangement) and non-reactive calculations. We perform this comparison by artificially eliminating the possibility of rearrangement and by allowing only for inelastic scattering. [Preview Abstract] |
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E1.00063: Cold collisions of OH with He Edmund Meyer, Manuel Lara, John Bohn Cooling polar molecules is the next big step in achieving control of the microscopic world. The rich structure of diatomic molecules, as compared to atoms, presents a new level of difficulty in attaining such a feat. Possibilities for state-changing collisions can be fairly high due to small nuances in the structure of the molecule. Most studies up till now focus on cold collisions (mK range) between He and molecules in $\Sigma$ symmetries, meaning zero electronic orbital angular momentum about the internuclear axis. The interest in He is due to the advancement and success of buffer gas cooling. Our understanding of energy transfer in cold collisions will be broadened by considering molecules in other symmetries. To this end, we consider cold collisions of a molecule in $\Pi$ symmetry, meaning one unit of electronic orbital angular momentum. The way in which energy is shuffled in this type of molecule is funadamentally different than previous studies due to the change in Hund's case from (b) to (a). We present the first calculations of cold collisions of He with diatomic molecules in $\Pi$ symmetries including the effects of hyperfine structure. We focus primarily on the collisions between He and OH, which is a molecule of much interest to both the experimental and theoretical groups working in the field of cold collisions of molecules. [Preview Abstract] |
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E1.00064: REACTIVE SCATTERING AND RECOMBINATION PROCESSES |
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E1.00065: Theoretical Studies of Dissociative Recombination D.O. Kashinski, R.F. Malenda, A.P. Hickman, D. Talbi We are currently investigating the dissociative recombination (DR) of electrons with molecular ions such as $\mathrm{N}_2\mathrm{H}^+$ and $\mathrm{C}_3\mathrm{H}_3^+$. Both these ions exist in the interstellar medium, and accurate DR rate constants are needed for astrophysical models. Elaborate electronic structure calculations of potential surfaces for $e^- + \mathrm{N}_2\mathrm{H}^+ \rightarrow \mathrm{N}_2 + \mathrm{H}$ have been carried out in the linear geometry [D. Talbi, Chem.~Phys. {\bfseries 332} 289--303 (2007)]. Additional work is necessary to determine the autoionization width $\Gamma$, which is essential for a dynamics calculation. We are using the block diagonalization method to determine both diabatic potential curves and $\Gamma$; the status of the calculations will be presented at the conference. In addition, preliminary work on the $\mathrm{C_3H_3^+}$ molecular ion has investigated the normal modes of the motion. We expect that energy flow into and out of the vibration of a single CH bond may influence the overall DR dynamics, and we account for this effect using an appropriate quantum mechanical wave function for the initial state. [Preview Abstract] |
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E1.00066: ELECTRON-MOLECULE COLLISIONS |
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E1.00067: Fluorescence Polarization of Hydrogen and Deuterium Molecules Excited by Polarized Electron Impact J.W. Maseberg, T.J. Gay We report relative Stokes parameters for molecular and atomic transitions in H$_2$ and D$_2$ excited by spin-polarized electrons. Specifically, rotationally isolated transitions in the $d$ $^3\Pi_u$$1s\sigma3p\pi$ $\rightarrow$ $a$ $^3\Sigma_g^+$$1s\sigma2s\sigma$ band have been studied as well as Balmer-$\alpha$ excited fragments for both H and D. Values of the circular polarization fraction normalized to the incident electron spin polarization, P$_3$/P$_e$, for atomic emission (656 nm) from H and D are nearly equivalent ($\sim$0.08 near threshold), and higher values are found for the case of molecular fluorescence ($\sim$0.14 for H$_2$). [Preview Abstract] |
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E1.00068: The Nuclear Configuration Effects on Electron Impact Ionization Cross Sections of He and H2 Measured in the Perpendicular Plane Ola Al-Hagan, Don Madison, Christian Kaiser, Andrew Murray The effect of nuclear configuration on the differential cross sections for ionization of atomic He and molecular H2 will be reported. In these investigations, ionization into the perpendicular plane is investigated since this geometry is highly sensitive to nuclear scattering. Consequently, the perpendicular plane provides an ideal test-case to investigate the influence of different nuclear configurations on the ionization process. Experimental cross sections for He and H2 (same number of protons differently configured) show remarkable similarities and differences which can be explained in terms of elastic scattering for the respective nuclei. [Preview Abstract] |
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E1.00069: Electron scattering from the N$_2$H radical Brendan M. McLaughlin, Robert C. Forrey Electron collisions with the N$_2$H radical are an essential constituent of understanding electron detachment in low energy H$^-$ + N$_2$ collisions. Potential energy curves for both the neutral N$_2$H and anion N$_2$H$^-$ molecules are calculated as a function of the N$_2$ - H bond length in the C$_s$ symmetry point group, for perpendicular, colinear and bent geometry using a CAS-CI approximation. Low energy electron scattering from the N$_2$H molecule are performed with the R-matrix method using a multi-state close-coupling approach to determine the scattering cross-sections as a function of the colliding electron energy. The autoionization linewidth ($\Gamma$) and resonance energies found near threshold in the elastic scattering cross sections are determined as a function of the stretching of the N$_2$ - H bond length, where the N$_2$ molecule is fixed at its equilibrium geometry. A complex potential is then constructed from the resonance parameters and used in the heavy particle dynamical calculations to determine the low energy electron detachment cross sections and rates. Results for isotopic replacement of H$^-$ by D$^-$ have also been obtained for this cold molecular complex. Further details will be presented at the meeting. [Preview Abstract] |
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E1.00070: Excitation Probabilities and Pathways in e-N$_{2}$O Collisions J. William McConkey, Charles P. Malone, Paul V. Johnson, Joseph M. Ajello, Isik Kanik Vacuum ultraviolet emissions following electron impact dissociative excitation of N$_{2}$O have been studied over the wavelength range 80--180 nm and for electron energies from threshold up to 300 eV. Calibrated spectral data are presented at 100 eV incident energy. The dominant N \textsc{i} (2$p^{3} \quad ^{4}$S\r{ } -- 3$s ^{4}$P) multiplet at 120.0 nm has a measured maximum cross section of (2.2 $\pm $ 0.3) $\times $ 10$^{-18}$ cm$^{2}$ at 100 eV, which in turn was used to normalize 100 eV cross sections for all observed spectral features. In addition, excitation functions corresponding to the dominant emission features have been analyzed in detail with particular emphasis on the near-threshold region. Possible dissociation channels are discussed. Acknowledgement: This work was carried out at JPL, Caltech, under contracts with NASA. This research was performed while CPM and JWMcC held NASA Fellowships at JPL. [Preview Abstract] |
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E1.00071: Momentum Imaging in Dissociative Ionization of Small Molecules by Low Energy Electron Impact J.D. Daughhetee, J.B. Williams, M. Sch\"offler, J. Stewart, E.J. Clothiaux, A.L. Landers Our experimental apparatus enables observation of electron collisions with either molecular or atomic targets. A pulsed electron gun is used to create collision events within a diffuse target. The resulting positive fragment ions are then guided toward a position sensitive multi-hit detector by means of a pulsed electric field. Collision information such as momentum, fragment charge state, and flight time is subsequently analyzed in coincidence. A coaxial magnetic field allows for electron energies ranging from a few eV up to 2 keV. Preliminary measurements of dissociative ionization of small molecules will be presented. [Preview Abstract] |
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E1.00072: QUANTUM OPTICS, MATTER OPTICS, AND COHERENT CONTROL |
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E1.00073: Electromagnetically induced transparency in a Cs 6S-8S two-photon transition Chin-Chun Tsai, Hsiang-Chen Chui, Yi-Chih Lee, Ray-Yuan Chang, Ying-Yu Chen, Yi-Hsiu Chang We report the investigation of V-type electromagnetically induced transparency (EIT) in a Cs 6S-8S two-photon transition. This EIT occurs only under a very high coupling intensity due to the weak coupling of two-photon transition. In our experiment, an external cavity diode laser frequency stabilized on the Cs hyperfine transition $|6 ^2S_{1/2}, F=4 \rangle\rightarrow|6 ^2P_{3/2}, F=5\rangle$ is served as a pumping field. The coupling field is a high power tunable Ti:sapphire laser which scanned through the two-photon transitions of Cs $|6 ^2S_{1/2}, F=4\rangle\rightarrow|8 ^2S_{1/2}, F=4\rangle$ at 822 nm. The coupling laser was retro- reflected through a confocal lens system and overlapped with the pump laser at the center of a temperature stabilized Cs cell. The cascade fluorescence from $|7 ^2P_{3/2} \rangle\rightarrow|6 ^2S_{1/2}\rangle$ and the power of transmitted pump laser were monitored simultaneously. An EIT signal of the pump field has been observed while the coupling laser frequency is resonant to the two-photon transition. [Preview Abstract] |
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E1.00074: Electromagnetically induced transparency in rubidium: An advanced undergraduate laboratory Shannon Mayer, Abraham Olson Electromagnetically induced transparency (EIT) is a quantum interference effect used to modify the optical response of an atomic medium to a resonant laser field. In EIT, a non-resonant pump laser beam can result in the reduction of absorption of a weak, resonant probe laser beam, provided the fields are coherently coupled by a common state. EIT provides a unique means of coherently controlling photons and has potential applications in fields ranging from quantum computing to telecommunications. In this advanced laboratory we describe the theory and experiment for investigating ladder-type EIT in rubidium gas. The theoretical absorption profile of a weak probe laser beam tuned across the 5S 1/2 to 5P 3/2 transition (780.2 nm) is modeled in the presence of a strong coupling laser beam tuned to the 5P 3/2 to 5D 5/2 transition (776.0 nm) and the absorption transparency window is characterized. Using grating-feedback diode lasers, we observe EIT experimentally in rubidium gas and compare the results to the theoretical model. Applications of EIT to high-resolution two-photon spectroscopy are also discussed. This laboratory uses much of the same equipment as the saturated absorption experiment commonly performed on the D2 line in rubidium, so it is easily implemented in laboratories with the equipment to conduct that experiment. [Preview Abstract] |
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E1.00075: Effect of optical pumping in V and $\Lambda $ type pump probe systems Shrabana Chakrabarti, Biswajit Ray, Pradip N. Ghosh We have investigated the effect of a strong pump laser copropagating with a probe laser for both $\Lambda $ and V type level schemes of the pump and probe fields inside a room temperature Rb vapour cell. With the $\Lambda $ type scheme certain absorption enhanced peaks are observed across the Doppler broadened probe absorption profile. In addition to these peaks an Electromagnetically Induced Transparency dip is also observed at the centre of one of these peaks. For V type scheme pump probe spectroscopy with co and counter propagating pump probe beams are studied. In both cases we observe velocity selective resonances (VSR) which are strongly modified by optical pumping effects to another hyperfine component of the ground state. A repumping laser, from the dark ground level is used to transfer atoms from the dark state to the pump probe cycle to reduce the optical pumping effect. The effect of a control laser on the Lamb dip spectrum of the probe laser has also been investigated. [Preview Abstract] |
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E1.00076: Quantum coherence effects in a six-level atomic system driven by three lasers Jianbing Qi We study the fluorescence spectrum and the absorption of the probe laser in a six-level atomic system coupled by three lasers. A variety of interesting fluorescence spectral features can be attained by controlling the amplitude and detuning of the lasers. Quantum interference, such as the extremely narrow spectral lineshape, and fluorescence quenching, is observed. The absorption spectrum of the probe laser shows electromagnetically induced transparency (EIT), which can be controlled by two coupling lasers. The EIT can be manipulated from a single transparent window to double transparent windows at different probe frequencies. [Preview Abstract] |
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E1.00077: WAVEPACKET DYNAMICS AND COHERENT CONTROL |
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E1.00078: Realization of Bohr-like circular wavepackets Jeff Mestayer, B. Wyker, F.B. Dunning, C. Reinhold, S. Yoshida, J. Burgd\"orfer We demonstrate a protocol to create localized wavepackets in very-high n Rydberg states that travel in near-circular orbits around the nucleus. Although these wavepackets slowly dephase and eventually lose their localization, their motion can be followed for several orbital periods. These wavepackets represent the closest analog yet achieved to the original Bohr model of the atom, i.e., an electron in circular classical orbit around the nucleus. The time evolution of the momentum and position of the wavepackets is monitored using, respectively, short half-cycle pulses and sudden field steps, which are applied after a variable time delay and along different directions. The present technique is explained with the aid of CTMC simulations, and possible extension to creation of elusive ``planetary atoms'' in highly correlated stable multiply-excited states is discussed. Research supported by the NSF, the Robert A. Welch Foundation, the OBES, U.S. DoE to ORNL, and by the FWF (Austria). [Preview Abstract] |
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E1.00079: Extracting irreversible dephasing rates from the echoes of Rydberg Stark wavepackets. Jeff Mestayer, B. Wyker, F.B. Dunning, C. Reinhold, S. Yoshida, J. Burgd\"orfer The precession of an electric dipole moment in an external electric field can be reversed by a reversal of the field direction. This time reversal operation allows the study of reversible and irreversible dephasing of Rydberg wavepackets through measurements of the electric dipole echoes generated by the time reversal. The effects of different sources of dephasing are discussed in detail. Stochastic interactions with the environment are analyzed in a controlled manner using artificially synthesized ``colored'' noise. The rate of irreversible dephasing is obtained from the reduction in the size of echoes when multiple field reversals are applied. Research supported by the NSF, the Robert A. Welch Foundation, the OBES, U.S. DoE to ORNL, and by the FWF (Austria). [Preview Abstract] |
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E1.00080: Transferring Rydberg wavepackets between islands across the chaotic sea. Shuhei Yoshida, C. Reinhold, J. Burgdorfer, J. Mestayer, B. Wyker, F.B. Dunning The classical phase space of periodically driven Rydberg atoms is characterized by a series of stable islands embedded in a chaotic sea. While phase flow between islands that are separated by the chaotic sea is classically forbidden, quantum dynamics allows such transfer by means of ``dynamical tunneling''. In this work we describe a classical protocol by which a Rydberg wavepacket trapped in a stable period-1 island, whose evolution is synchronized with a periodic sequence of the driving pulses, can be efficiently transferred to a period-2 island such that it evolves with twice the period. This period doubling protocol is analyzed theoretically and demonstrated experimentally. The transfer from a period-1 to a period-2 island is realized using two superposed trains of half-cycle pulses whose relative time delay is varied adiabatically. It is shown that the present protocol provides a tool to manipulate the angle variable of a Rydberg wavepacket while its conjugate principal action is maintained constant. Research supported by the NSF, the Robert A. Welch Foundation, the OBES, U.S. DoE to ORNL, and by the FWF (Austria). [Preview Abstract] |
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E1.00081: Coulomb Explosion Imaging with Shaped Pulses Z. Wang, G.Y. Chen, G. Minker, S. Iacangelo, W.T. Hill, III Pulse shaping has wide application from coherent control of chemical reactions to quantum computing. We have built a system capable of creating and characterizing optimized pulse shapes with large bandwidths -- $>$ 25 nm. Phase and amplitude shaping are controlled with a liquid crystal spatial light modulator (SLM) while a combination of spectral interferometry techniques -- FROG, SPIDER, and SEA TADPOLE -- are exploited to reconstruct the temporal and spectral phase along with the amplitude of the electric field. Optimized shapes are generated via closed-loop feedback, enabled by a Genetic Algorithm (GA). This poster outlines the application of the GA in combination with Coulomb explosion imaging of small molecular systems. [Preview Abstract] |
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E1.00082: Theoretical study of impulsive orientation of asymmetric top water molecules Chitra Rangan, Andrew Senchuk We theoretically study the orientation of a polar, asymmetric top molecule by a terahertz half-cycle pulse. This study is motivated by recent experimental results by C. Herne and P.H. Bucksbaum on the orientation of water molecule using terahertz half-cycle pulses. The half-cycle pulse is modelled as an impulse. The degree of orientation is calculated. Our aim is to characterize the calculated orientation curves in terms of rotational spectroscopy constants. [Preview Abstract] |
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E1.00083: Longitudinal optical phonon induced exciton dephasing in artificial atoms Yiming Mi, Shuichi Iwata Due to the interactions among longitudinal optical (LO) phonons and artificial atoms (AAs), a new mechanism of LO phonon induced exciton dephasing and spectral broadening has been found. Provided that the full excitonic spectra are considered, this mechanism plays an important role in exciton dephasing and spectral broadening. With the help of an exactly solvable quadratic coupling model and generalizing the exact solution of the model to an arbitrary number of excitonic states, such considerable exciton dephasing in different kinds of AAs is demonstrated in this paper. [Preview Abstract] |
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E1.00084: CAVITY QED |
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E1.00085: Cavity QED of optical lattice clocks Dominic Meiser, Brandon Peden, Murray Holland Optical lattice clocks are fast approaching a regime where experimental limitations will be fundamental rather than technical. One approach to addressing these issues is to generate the optical lattice in a cavity, where the experimenter can take advantage of information imprinted on the lattice fields. Here, we present a theoretical framework for studying optical lattice clocks in cavities. In both linear and ring geometries, we use this cavity QED formalism to investigate fundamental phenomena such as cavity-assisted cooling, Bloch oscillations, and spin-squeezing. [Preview Abstract] |
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E1.00086: A High Flux Cold Atomic Beam for Experiments in Strongly Coupled Cavity QED Basudev Roy, Michael Scholten, Luis Orozco, Saijun Wu We present a high flux continuous source of cold atoms for cavity QED experiments in the regime of strong coupling.~ A 2D+ MOT, loaded by rubidium dispensers in a dry film coated vapor cell, loads a secondary moving-molasses MOT (MM-MOT) at a rate of 1.5*10$^{10}$ atoms/s.~ The MM-MOT provides a velocity tunable (3 to 10 m/s) high flux continuous beam.~ We direct the beam through the 64 $\mu $m waist of a high finesse optical cavity with 246 $\mu $m mirror spacing. The atom-cavity coupling rate g, cavity dissipation rate $\kappa $, and atomic decay rate $\gamma $ are (g, $\kappa $, $\gamma )$/2$\pi $ = (8, 2, 3) MHz, placing the system in the strong regime.~We are currently characterizing the source using the cavity QED system and will report its performance as a function of MOT parameters. [Preview Abstract] |
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E1.00087: Steps Towards Cavity QED experiments with cold ion Coulomb Crystals J.P. Marler, P. Herskind, A. Dantan, M. Albert, M. Drewsen Clouds of ions present an interesting alternative to traditional single neutral atom based experiments to study CQED. Ions can be easily trapped and cooled for long times and in sufficient number to potentially access the strong coupling regime even with a physically realizable finesse (mode volume) of the cavity. In the present experiment thousands of $^{40}$Ca$^+$ ions are trapped in a linear Paul trap incorporating a high finesse (F$\sim$3200) optical cavity. We will show results which indicate that the number of ions inside the cavity mode is in principle high enough to achieve strong collective coupling. Near term plans include fundamental studies of cavity QED, and exploring the possibility of using cavity interactions to aid in cooling of neutral molecular species. Briefly discussed will be a planned experiment which will employ an optical field to further investigate and control the nature of the ion Coulomb crystal structures formed. [Preview Abstract] |
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E1.00088: Single-Atom Single-Photon Quantum Interface David Moehring, Joerg Bochmann, Martin Muecke, Holger Specht, Bernhard Weber, Tatjana Wilk, Gerhard Rempe By combining atom trapping techniques and cavity cooling schemes we are able to trap a single neutral atom inside a high-finesse cavity for several tens of seconds. We show that our coupled atom-cavity system can be used to generate single photons in a controlled way. With our long trapping times and high single-photon production efficiency, the non-classical properties of the emitted light can be shown in the photon correlations of a single atom. In a similar atom-cavity setup, we investigate the interface between atoms and photons by entangling a single atom with a single photon emitted into the cavity and by further mapping the quantum state of the atom onto a second single photon. These schemes are intrinsically deterministic and establish the basic element required to realize a distributed quantum network with individual atoms at rest as quantum memories and single flying photons as quantum messengers. This work was supported by the Deutsche Forschungsgemeinschaft, and the European Union SCALA and CONQUEST programs. D. L. M. acknowledges support from the Alexander von Humboldt Foundation. [Preview Abstract] |
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E1.00089: Microfabrication and assembly of an integrated cavity QED and atom chip experiment Daniel Brooks, Tom Purdy, Dan Stamper-Kurn We have combined high-finesse optical resonators with an atom chip to study quantum atom optical systems. Fabry-Perot cavities in the single-atom strong coupling regime are aligned through micromachined holes in thinned silicon substrates that also house the microfabricated circuitry for magnetic trapping and transport of cold atoms. These high current capacity wires will allow for atoms to be confined well within a single anti-node of the cavity mode. A reproducible etch process of selectively removing some of the dieletric layers of the cavity mirrors' coatings was found to enhance transmission without adding scattering losses. The combined chip and cavities are actively temperature stabilized at the end of a two stage vibration-isolation mount inside an UHV chamber. [Preview Abstract] |
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E1.00090: Cavity QED with trapped neutral atoms Soo Kim, Michael Gibbons, Chung-Yu Shih, Peyman Ahmadi, Michael Chapman Cavity QED systems consisting of neutral atoms coupled to high-finesse optical micro-cavities have important applications to quantum information processing. We have developed an experiment with trapped atoms in a high finesse cavity in the strong coupling regime. We have demonstrated deterministic loading and storage of individual atoms delivered from a magneto-optic trap to the resonator using an atom conveyor [1]. We will also discuss future applications. [1] K.M. Fortier et al., \textit{Phys. Rev. Lett. }\textbf{98}, 233601 (2007). [Preview Abstract] |
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E1.00091: Numerical vs. Semiclassical Evaluation of Casimir Forces in Piston Geometries Martin Schaden, Liviu Mateescu Using a modified wordline approach[1] for a massless scalar field satisfying Dirichlet boundary conditions, we numerically obtain the Casimir force on a piston in a cylindrical cavity with a cylinder head of different radius. There are no contributions from arbitrarily short paths and the Casimir \textit{force} on the piston is finite for all systems considered. Our algorithm for Casimir forces in closed concave geometries is numerically stable, fast and accurate. For a hemispherical cylinder head, we analytically and numerically obtain an attractive contribution to the Casimir force that is inversely proportional to the elevation of the piston and does not depend on the radius of the cylinder. This attractive contribution to the Casimir energy cannot be distinguished from one due to the presence of a charge. It is of higher semiclassical order and was not observed in the leading description by periodic orbits [2]. By changing the radius of the cylinder head compared to that of the cylinder, we numerically verify the semiclassical estimate [2] that the Casimir force on the piston is drastically reduced by a hemispherical cylinder head. We also present preliminary numerical studies for a massless scalar field satisfying Neumann boundary conditions. [1] H. Gies, K. Langfeld and L. Moyaerts, JHEP 0306, 018 (2003); H. Gies and K. Klingmuller, Phys. Rev. D74, 045002 (2006). [2] L Mateescu and M. Schaden, [quant-ph/0705.3435]. [Preview Abstract] |
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E1.00092: DEGENERATE FERMI GASES |
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E1.00093: Atom-Molecule Coherence in a Bose-Fermi Mixture J.D. Perreault, T.D. Cumby, M.L. Olsen, D.S. Jin Feshbach resonances have become a powerful tool for controlling the interaction between atoms in an ultracold gas. Experiments have shown that it is possible to create a coherent superposition of atoms and molecules when starting from a BEC. This presentation will show evidence indicating that it is also possible to create an atom-molecule superposition from a thermal Bose-Fermi mixture of Rb-87 and K-40 atoms. In particular, preliminary investigations into which experimental parameters influence the contrast and coherence time of the atom-molecule oscillations will be discussed. This could provide new insight into what the leading decoherence or dephasing mechanisms are for this novel quantum superposition state. [Preview Abstract] |
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E1.00094: BCS Pairing Detection by Electromagnetically Induced Transparency Lei Jiang, Han Pu, Weiping Zhang, Hong Ling We seek a new application of electromagnetically induced transparency (EIT), a well-known phenomena in quantum optics; to detect the onset of the BCS transition to superfluidity in a degenerate atomic fermi gas involving a pump and a copropagating probe laser field. We show that when a BCS pairing emerges, the EIT spectrum makes a qualitative change, which can be traced to the two-photon resonance condition being momentum-independent for a normal gas but momentum-dependent for a BCS paring phase. We will calculate and discuss the EIT spectrum under different situations including when the pseudo gap cannot be ignored. [Preview Abstract] |
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E1.00095: Measurements of Binding Energies of p-wave Feshbach Molecules in a gas of $^6$Li Christopher Ticknor, Jurgen Fuchs, Paul Dyke, Gopi Veeravalli, Eva Kuhnle, Wayne Rowlands, Peter Hannaford, Chris Vale We present measurements of the binding energies of $^6$Li p-wave Feshbach molecules in the three resonances of the two lowest hyperfine states. We find the binding energy scales linearly with magnetic field detuning across all resonances. The gradients of the binding energies have been determined to be 113 +-7, 111+-6, and 119+-8 for the 11, 12, and 22 Feshbach resonances, respectively, in good agreement with theoretical predictions. Further properties of these Feshbach molecules are also investigated. [Preview Abstract] |
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E1.00096: Loss-induced heating in a cold atom BCS superfluid Ryan M. Kalas, Eddy Timmermans Loss-induced heating in a cold atom BCS superfluid The loss of fermion particles caused by the background scattering, spin relaxation, or three-body recombination processes that generally limit cold atom trap lifetimes gives rise to a heating mechanism that can be particularly significant in the weakly-interacting quantum degenerate regime. For weakly attractive fermions in multiple spin states, this heating was shown to compete significantly with the formation of the BCS superfluid state. The heat capacity and the excitation dispersions play an essential role in this calculation. In this poster, we calculate the loss-induced heating rate of a low temperature, homogeneous cold atom system that has reached the BCS state, thereby altering the heat capacity and quasiparticle dispersion from their analogues in the normal state. We find that the high momentum region of the quasiparticle distribution contributes significantly. As a consequence, the heating rate becomes sensitive to the high momentum dependence of the superfluid order parameter. [Preview Abstract] |
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E1.00097: Tools and Techniques for Strongly Interacting Fermions A.B. Bardon, L.J. LeBlanc, M.H.T. Extavour, D.M. Jervis, J. McKeever, A. Stummer, J.H. Thywissen Previously in the Toronto Ultra-Cold Atoms Lab we have cooled $^{87}$Rb and $^{40}$K to quantum degeneracy in a chip trap. Over the past year we have expanded the capabilities of this experiment. We have added a crossed optical dipole trap, and used it to evaporatively cool $^{87}$Rb to a Bose-Einstein condensate of $10^4$ atoms. Unlike magnetic traps, the dipole trap allows us to freely choose our magnetic field and quantum states. Varying the magnetic field, we observed the $^{40}$K Feshbach resonance between the $|F=9/2, m_F=-9/2\rangle$ and $|F=9/2, m_F=-7/2\rangle$ states at 202G. The hyperfine state preparation was made possible by a homemade microwave source. A second generation chip will allow better coupling of the microwaves to the atoms, as well as polarization control of rf, and higher magnetic field gradients. Using these new tools, we are making progress towards observing itinerant ferromagnetism in fermions. [Preview Abstract] |
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E1.00098: ABSTRACT WITHDRAWN |
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E1.00099: ULTRACOLD DIPOLAR GASES |
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E1.00100: Manifestations of the roton mode in dipolar Bose-Einstein condensates Ryan Wilson, Shai Ronen, Han Pu, John Bohn We investigate the structure of harmonically trapped Bose-Einstein condensates (BECs) with long-range anisotropic dipolar interactions. We find that even a small perturbation in the trapping potential can lead to dramatic changes in the condensate's density profile for sufficiently large dipolar interaction strengths and trap aspect ratios. By employing a generalized perturbation theory, we relate these oscillations to a previously-identified ``roton-like'' mode that is believed to exist in dipolar BECs~\footnotemark[1]. The same physics is responsible for radial density oscillations in vortex states of dipolar BECs that have been reported previously~\footnotemark[2]. \footnotetext[1]{\hspace{1pt} S. Ronen, D. C. E. Bortolotti, and J. L. Bohn, Phys. Rev. A {\bf 74}, 013623 (2006).} \footnotetext[2]{\hspace{2pt} S. Yi and H. Pu, Phys. Rev. A {\bf 73}, 061602(R) (2006).} [Preview Abstract] |
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E1.00101: Pseudopotential treatment of two interacting dipoles in an anisotropic harmonic trap K. Kanjilal, D. Blume Recently, there has been a lot of interest in ultra cold dipolar gases. In addition to the short-range spherically symmetric contact interaction, these systems interact through the long-range anisotropic dipole-dipole potential. The ratio between the strengths of the short- and long-range potentials can be tuned experimentally. We consider two aligned dipoles in an elongated harmonic trap. Although the dipolar potential is long-ranged, it can be replaced by a zero-range pseudopotential if the length scale of the dipole-dipole interaction is much smaller than the trap length. Generalizing previous work for spherically symmetric confinement, we determine the eigenequation for two interacting dipoles under cylindrically symmetric confinement analytically. The resulting eigenergies agree well with those obtained numerically for a shape dependent model potential. The agreement improves further if the energy dependence of the generalized scattering lengths is accounted for. Implications for the many-body system will be discussed. [Preview Abstract] |
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E1.00102: Toward Creation of an Ultracold Dense Gas of Polar Molecules Kang-Kuen Ni, Silke Ospelkaus, A. Pe'er, M. Miranda, B. Neyenhuis, J. Zirbel, S. Kotochigova, P. Julienne, J. Ye, D. Jin We present experimental efforts toward the creation of ultracold gas of KRb polar molecules. We start by creating extremely weakly bound molecules using a magnetic-field Feshbach resonance. This ultracold dense sample of Feshbach molecules provides a starting point for coherent optical transfer schemes aimed at creating tightly bound, polar molecules. Starting with Feshbach molecules, we have performed two-photon and one-photon spectroscopy. We have also demonstrated coherent optical transfer of Feshbach molecules to a more deeply bound state in the electronic ground state. We will discuss suitable routes to extend this work to even more deeply bound vibrational levels where the molecules can have a significant electric dipole moment. [Preview Abstract] |
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E1.00103: Trapped Ground State Ultracold Polar Molecules Nathan B. Gilfoy, Eric R. Hudson, Stephan Falke, C.D. Bruzewicz, David DeMille Recently we have optically trapped ultra-cold, polar RbCs molecules in high-lying vibrational levels of the triplet ground electronic state. Inelastic collision rates of these molecules with Rb and Cs atoms have been measured for individual vibrational levels over an order of magnitude of binding energies. A simple model of the collisional process is shown to accurately reproduce the observed scattering rates. We are currently implementing a state transfer process, previously demonstrated in our lab, to populate the absolute ground state. We will discuss our recent measurements of ultra-cold inelastic molecular collisions as well as progress towards trapping molecules in the absolute ground state. [Preview Abstract] |
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E1.00104: Simultaneous K and Cs trapping and prospect for ultracold polar molecules Daniel Barker, Mattie Whitmore, Marin Pichler We report on progress towards simultaneous cooling and trapping of K and Cs atoms. The main objective is to produce sufficient densities in overlapping trapped species to perform photoassociation of ultracold KCs molecules. We rely on separate diode lasers systems for cooling and repumping transitions for both Cs and K. A tapered laser amplifier for K cooling is currently being built. The photoassociation, ground-state molecule production and resonant multi-photon detection schemes will be presented and possible applications will be discussed. [Preview Abstract] |
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E1.00105: ATOMS IN OPTICAL LATTICES |
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E1.00106: Design and construction of a Site-resolved Optical Lattice for Ultracold Fermions Dylan Jervis, Josefine Metzkes, Lindsay LeBlanc, Alma Bardon, Jason McKeever, Marcius Extavour, Alan Stummer, Joseph Thywissen Ultra-cold atoms in optical lattices allow for the study of lattice models, including the single-band and multi-band Hubbard models. The preparation and evolution of ultra-cold atoms in optical lattices is typically measured destructively through time-of-flight (TOF) imaging. At low temperatures, interesting many-body phases occur, including the Neel transition to anti-ferromagnetic ordering. However, when atoms are cooled below the interaction energy $\emph{U}$ the temperature becomes difficult to diagnose using TOF methods. We discuss a proposal to image a single plane of ultra-cold atoms in an optical lattice in-situ. Single-site imaging will permit an entropy, and thus temperature, measurement of the system. Spin-sensitive in-situ imaging will allow for local measurements of spin ordering and domain structure. The central feature of the proposed imaging system is a UHV cell in which $^{40}$K fermions are trapped close (~200$\mu$m) to a thin vacuum window, on the other side of which lies a microscope. We discuss the proposed design and recent progress. [Preview Abstract] |
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E1.00107: Evidence for Metallic Behavior in the Bose-Hubbard Model David McKay, Matt White, Matt Pasienski, Brian DeMarco We report measurements on transport of a $^{87}$Rb Bose-Einstein Condensate loaded into a 3D optical lattice well-characterized by the Bose-Hubbard model. We have measured temperature-dependent dissipation of center-of-mass oscillations in the low-velocity limit. The observed damping rate levels out as the system is cooled, which is the signature of a metallic phase. This behavior is consistent with the cross-over between quantum tunneling and thermal activation of phase slips. We find excellent agreement with this model and our measurements of the damping rate as a function of the Bose-Hubbard parameters. We have also observed vortices nucleated by center-of-mass motion, providing further evidence for quantum phase slips. [Preview Abstract] |
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E1.00108: Ultracold bosons in optical superlattices with disorder: tunnelling induced Mott insulators Dominik Muth, Alexander Mering, Michael Fleischhauer Using the infinite size time evolving block decimation (iTEBD) algorithm, which is capable to calculate the ground state for translationally invariant Hamiltonians directly in the thermodynamic limit, we determine the superfluid to Mott-insulator phase transition for a Bose-Hubbard model with superlattice. The results agree well with a DMRG approach and, for small hopping J, with the cell strong-coupling perturbative approach found in [1], showing the existence of loophole insulators, i.e. incompressible phases which vanish for J=0. Adding uniformly distributed disorder to the system, we show both analytically and numerically that the loophole domains detach from the J=0 axis, creating Mott insulating islands surrounded by a Bose-glass phase. [1] P. Buonsante, A. Vezzani - Phys. Rev. A 72, 013614 (2005) [Preview Abstract] |
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E1.00109: The Bose-Fermi Hubbard model in the light and heavy fermion limits Alexander Mering, Dominik Muth, Michael Fleischhauer We discuss mixtures of bosons and spin-polarized fermions in optical lattices in the limits of heavy and light fermions. The first case is mapped to a Bose-Hubbard system with binary disorder or a superlattice potential. Boundaries between Mott- insulating and compressible phases are determined analytically within an extended strong-coupling expansion. DMRG calculations reveal furthermore a novel phase with Bose-glass character. In the opposite limit of ultra-light fermions an effective boson Hamiltonian is derived with oscillatory long-range interactions leading to additional phases such as compressible density-waves. Analytic predictions for the CDW amplitude are made and compared to DMRG data. The numerical studies show furthermore that the CDW is always associated with exponential decay of bosonic correlations. Moreover, the CDW phase has a very slow crossover into a Luttinger liquid phase. [Preview Abstract] |
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E1.00110: Characteristics of condensed bosons in the vicinity of Mott insulating states Kuei Sun, Smitha Vishveshwara, Courtney Lannert We study the inhomogeneous system of strongly-interacting bosons in optical lattices. We focus on the weak tunneling region wherein a condensate is predicted to exist between two Mott insulating phases. We use a pseudo-spin approximation to the Bose-Hubbard system to model the effective potential which confines the condensate order parameter and to analyze collective excitations of the system. We also consider the effect of applying a radio- frequency (RF) magnetic field in this region. We find that the RF spectrum for driving transitions from one hyperfine species of bosons to another is markedly different between the Mott insulating phase and the condensed phase. In particular, the former has one resonant peak, while the latter has two peaks which show shifts of the order of the tunneling strength between lattice sites. Our results and analyses provide a means of verifying the existence of the condensate. [Preview Abstract] |
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E1.00111: Superfluid and supersolid phases of dipolar Bose gases in an optical lattice Ippei Danshita, Carlos A.R. Sa de Melo We study a superfluid (SF) phase and supersolid (SS) phases of a dipolar Bose gas at zero temperature in a two-dimensional (2D) optical lattice. We consider the situation in which the dipoles are polarized by an additional external field and the anisotropy of the long-range dipolar interaction is tunable by varying the direction of the polarization. In this situation, two types of supersolid ordering can occur: not only checkerboard ordering but also stripe one. We apply a mean-field approximation to the extended Bose-Hubbard model and determine the phase boundaries between a SF, a checkerboard SS, a striped SS, and collapse. We find a direct phase transition between a checkerboard SS and a striped SS. We also find that this transition is a first-order one and is characterized by a hysteretic behavior. [Preview Abstract] |
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E1.00112: Noise Correlation Measurements on the 3D Disordered Bose-Hubbard Model Matthew Pasienski, Matthew White, David McKay, Brian DeMarco Atomic shot noise correlations can be used to study hidden order---or lack thereof---in atomic Bose-Hubbard (BH) systems and may be a promising tool for exploring the properties of the disordered BH model. To approach this model, an optical speckle field is used to add fine-grained disorder to a 3D optical lattice. The correlation length of the speckle field is less than twice the lattice period along all three lattice directions. We will discuss atomic shot noise correlation measurements on ultra-cold atom clouds released from this disordered 3D optical lattice. [Preview Abstract] |
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E1.00113: Interaction-induced dephasing of Bloch oscillations - experiments and simulations Mattias Gustavsson, Elmar Haller, Manfred Mark, Johann Danzl, Russell Hart, Hanns-Christoph N\"agerl A BEC in an optical lattice undergoes Bloch oscillations when subject to an external force. However, interactions lead to dephasing, limiting the number of oscillations one can observe. We quantitatively characterize this dephasing by tuning the interaction strength using a Feshbach resonance. If the external force is strong enough that tunneling between lattice sites is negligible, the dephasing process leads to a regular structure in momentum space on momentum scales much smaller than the Brillouin zone. We can reproduce this structure through simulations of discrete 1D Gross-Pitaevskii equations and with a simple model of interfering Wannier-Stark states. The zero crossing of the scattering length can be determined precisely by minimizing the dephasing and we demonstrate control of the scattering length over four orders of magnitude. In the weakly interacting limit, we can follow more than 20000 oscillations over 12 s. By adding an additional harmonic potential, collapse and revival of the oscillations can be observed. [Preview Abstract] |
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E1.00114: Dissipation Fermionizes a One-Dimensional Gas of Bosonic Molecules Dominik M. Bauer, Niels Syassen, Matthias Lettner, Thomas Volz, Daniel Dietze, Juan J. Garcia-Ripoll, Ignacio Cirac, Gerhard Rempe, Stephan D\"urr Here we report on our latest results about ultracold molecules in optical lattices. First, we show how dissipation creates a Tonks gas of molecules. If a gas of bosons is confined to 1D, the interaction between particles can become so important that the strongly correlated regime is reached. This is called a Tonks-Girardeau gas. In the limit of infinite interaction strength, one cannot find two bosons at the same position. Previous studies of the Tonks gas relied on elastic interactions. Second, we observe large-amplitude Rabi oscillations between an atomic and a molecular state near a Feshbach resonance (1). The frequency and amplitude of the oscillations are well described by a two-level model. The observed density dependence of the oscillation frequency agrees well with the theoretical prediction. We confirm that the state produced after a half-cycle contains exactly one molecule at each lattice site. In addition, we show that for energies in a gap of the lattice band structure, the molecules cannot dissociate. \newline (1) Phys. Rev. Lett. 99, 033201 (2007) [Preview Abstract] |
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E1.00115: Anyonic Interferometry and Protected Memories in Atomic Spin Lattices Liang Jiang, Gavin Brennen, Alexey Gorshkov, Klemens Hammerer, Mohammad Hafezi, Eugene Demler, Mikhail Lukin, Peter Zoller Systems with topological order can exhibit remarkable phenomena such as quasi-particles with anyonic statistics and might be used for naturally error-free quantum computation. Here we describe how to unambiguously detect and characterize such states in recently proposed spin lattice realizations using ultra-cold atoms or molecules trapped in an optical lattice. We propose an experimentally feasible technique to access non-local degrees of freedom by performing global operations on trapped spins mediated by an optical cavity mode. We show how to reliably read and write topologically protected quantum memory using an atomic or photonic qubit. Furthermore, our technique can be used to probe statistics and dynamics of anyonic excitations. [Preview Abstract] |
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E1.00116: Progress Towards a Quantum Gas Microscope Amy Peng, Waseem Bakr, Jonathon Gillen, Simon Foelling, Markus Greiner We will present the latest progress towards a quantum gas microscope to experimentally realize and study complex many-body systems realized with a BEC of rubidium in an optical lattice. The experiment should allow us to achieve sub-micron optical resolution. Such imaging enables single atom sensitivity and optical resolutions on the order of the lattice spacing. The high resolution optics also enables flexible preparation of quantum states as well as the generation of arbitrarily shaped potentials. [Preview Abstract] |
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E1.00117: Investigation of the polarization dependence of optical dipole traps for quantum computing Bert David Copsey, Katharina Gillen-Christandl In an effort to find ways to create scalable arrays of neutral atoms that allow bringing atoms together and apart for 2-qubit gate operations, we are exploring the dependence of different dipole trap and optical lattice geometries on the trap light polarization. Several dark spot optical lattice and dipole trap geometries that have sufficiently low scattering rates for laser detunings comparable to the (ground state) hyperfine splitting have been proposed [1, 2]. To fully explore the polarization dependence of these traps, we explicitly calculate the full expression for the optical dipole potential for this case, based on the expression given in [3]. We will present our progress towards identifying trap geometries with different light polarizations that might be used to bring atoms together and apart for two-qubit gates. 1. Phys. Rev. A 70 032302 (2004), 2. Phys. Rev. A 73 013409 (2006), 3. Phys. Rev. A 57(3) 1972 (1998). [Preview Abstract] |
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E1.00118: Constructing Diodes and Transistors for Ultracold Atoms Ronald Pepino, John Cooper, Dana Anderson, Murray Holland The ultracold atom-optical analogy to electronic systems is presented, along with the master equation formalism that is applied to this novel physical context of system-reservoir interactions. The proposed formalism lends itself quite readily to not only the study of atomtronic systems, but also transport properties of ultracold atoms in optical lattices. We demonstrate how these systems can be configured so that they emulate the behavior of the electronic diode, field effect transistor (FET), and bipolar junction transistor (BJT). The behavior of simple logic gates: namely, the AND and OR gates are follow as direct consequences of the atomtronic BJTs. [Preview Abstract] |
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E1.00119: Two ultracold atoms in an optical lattices: comparison of an exact numerical treatment and the Bose-Hubbard model Alejandro Saenz, Philipp Schneider, Sergey Grishkevich A widely used method for describing a system of interacting bosonic particles in an optical lattice is the Bose-Hubbard model. It represents the wave functions in the basis of Wannier functions of the first Bloch band of the lattice, which are well localized at each lattice site. The Bose-Hubbard Hamiltonian takes only on-site interaction by a delta-type pseudopotential and hopping of particles to the next neighboring lattice sites into account. Despite its simplicity, the model can describe important characteristics of the physical system such as the phase transitions between the Mott insulator and superfluid phase. We compare the solutions of the Bose-Hubbard model to our solutions for different multi-well lattices and interaction strengths, to investigate in which regimes the model is applicable. An interesting system in itself, which we investigate, is the double-well potential filled with two particles. It already shows all important features of hopping and interaction of particles, which may lead to an implementation of a set of two qubit quantum gates. For this it is crucial to examine how the center-of-mass motion affects the decoherence of the system. [Preview Abstract] |
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E1.00120: VORTICES AND SOLITONS |
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E1.00121: Studies of spontaneous vortex formation during Bose-Einstein condensation. Tyler Neely, Chad Weiler, Ashton Bradley, Matthew Davis, Brian P. Anderson We experimentally observe the spontaneous creation of quantized vortices in Bose-Einstein condensates during the BEC phase transition. Numerical simulations based on the Stochastic Gross-Pitaevskii equation formalism show excellent quantitative agreement with experimental results. We will present results of ongoing experiments characterizing spontaneous vortex formation in BECs created in various trap geometries, including multiply connected and nearly two-dimensional potential wells. [Preview Abstract] |
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E1.00122: Quantum shock and soliton dynamics in the splitting and merging of BECs JiaJia Chang, Peter Engels We experimentally study the quantum shock dynamics resulting from the splitting and merging of two Bose-Einstein condensates in an elongated Ioffe-Pritchard type trap. Our experiments are carried out in the high-density, non-adiabatic regime and we find the dynamics to be dependent on atom number and dipole potential strengths. For example, a uniform soliton train is observed within a merged condensate for low atom numbers whereas the formation of a pronounced density bulge and a non-uniform soliton train are observed for higher atom numbers. We will describe recent and ongoing experimental results. [Preview Abstract] |
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E1.00123: Nonlinear phenomena in Bose-Einstein condensates Lincoln D. Carr We present a medley of results from the last three years on nonlinear phenomena in BECs [1]. These include exact dynamics of multi-component condensates in optical lattices [2], vortices and ring solitons [3], macroscopic quantum tunneling [4], nonlinear band theory [5], and a pulsed atomic soliton laser [6]. 1. {\it Emergent Nonlinear Phenomena in Bose-Einstein Condensates: Theory and Experiment}, ed. P. G. Kevrekidis, D. J. Frantzeskakis, and R. Carretero-Gonzalez (Springer-Verlag, 2008). 2. R. Mark Bradley, James E. Bernard, and L. D. Carr, e-print arXiv:0711.1896 (2007). 3. G. Herring, L. D. Carr, R. Carretero-Gonzalez, P. G. Kevrekidis, D. J. Frantzeskakis, Phys. Rev. A in press, e-print arXiv:0709.2193 (2007); L. D. Carr and C. W. Clark, Phys. Rev. A v. 74, p.043613 (2006); L. D. Carr and C. W. Clark, Phys. Rev. Lett. v. 97, p.010403 (2006). 4. L. D. Carr, M. J. Holland, and B. A. Malomed, J. Phys. B: At. Mol. Opt. Phys., v.38, p.3217 (2005) 5. B. T. Seaman, L. D. Carr, and M. J. Holland, Phys. Rev. A, v. 71, p.033622 (2005). 6. L. D. Carr and J. Brand, Phys. Rev. A, v.70, p.033607 (2004); L. D. Carr and J. Brand, Phys. Rev. Lett., v.92, p.040401 (2004). [Preview Abstract] |
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E1.00124: Simulating charged particles in a magnetic field with ultra-cold atoms using light-induced effective gauge fields Yu-Ju Lin We experimentally study light-induced gauge potentials in a $^{87}$Rb Bose-Einstein condensate. Instead of rotating the trap, we prepare the atoms in a spatially-varying optically dressed state. The atomic spin state is dressed by a spatially varying two-photon Raman coupling between the three $F=1$ hyperfine ground states. The resulting effective magnetic field is equivalent to rotating the condensate (and transforming to the rotating frame), and thus generates vortices. The inter-vortex distance is given by $\sqrt{2\pi} l_B$. Using the technique, the minimum possible $l_B \approx\sqrt{R_{\rm TF} \lambda/8 \pi}$ is the magnetic length for a uniform field, $R_{\rm TF}$ is the condensate diameter, and $\lambda\approx805\ {\rm nm}$ is the optical wavelength. We investigated adiabatic loading of the condensate into the ground-band of Raman dressed state, which also remains in the many-body ground state. Its projection onto the internal states of various state-dependent Bragg momenta are well understood. [Preview Abstract] |
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E1.00125: NEW EXPERIMENTAL TECHNIQUES |
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E1.00126: Construction of an inexpensive heat pipe oven. Timothy Grove, Mark Masters We present a new, low cost method of building an all copper heat-pipe oven. Copper heat pipe ovens have several advantages over more traditional stainless steel ovens. They heat up/cool down more rapidly (particularly useful in advanced undergraduate teaching laboratories), ideal for experiments involving magnetic fields, and less expensive. For our design, the most of the construction parts are available at local hardware and plumbing supply stores, and the assembly requires no machining. [Preview Abstract] |
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E1.00127: A air-bearing based, random orbital drive system for a longitudinally pumped solid state dye laser Fredrik De Armond, Robert Dill, Joseph Suelzer, Mark Masters We present our results of an investigation of organic dye doped plastics as a lasing medium. The host materials we have examined are poly(methyl methacrylate) [acrylic], epoxy, polyester and polyurethane. Various solvents have been used to improve dye dispersion within the material. We produce plastic doped disks which are contained in a Littman configuration cavity. Longitudinal pumping with a frequency doubled pulsed Nd:YAG laser is used. To improve the lifetime of the doped disks we have incorporated the disk into an air-bearing assembly. By introducing translational motion with a solenoid, the disk undergoes random orbital motion with respect to the pump laser beam. Lifetime of the disk, lasing quality parameters (bandwidth, tunability, power) are examined. [Preview Abstract] |
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E1.00128: Line Narrowing of a Broad Area Laser Diode Jerry Sell, Wooddy Miller, Dallas Wright, Boris Zhdanov, Randy Knize An external cavity for a broad area laser diode will be presented which significantly narrows the spectral bandwidth. Broad area laser (BAL) diodes are relatively low cost while achieving high output powers with a compact and efficient design. However, they generally have poor spatial characteristics and a typical linewidth of several nanometers. In order to make BAL diodes useful for such applications as spin-exchange optical pumping, laser spectroscopy, and nonlinear optics, a narrow linewidth is crucial. Previously we reported on a narrowband external cavity laser diode array\footnote{B.V. Zhdanov, T. Ehrenreich, and R.J. Knize, Elec. Lett. \textbf{43} (4), 221 (2007).}, which achieved a linewidth of 11 GHz and an operating power of approximately 10 W at 852 nm, making it very useful for cesium vapor laser pumping. We will present our most recent results of further line narrowing (MHz's) using a high power (30 W) single emitter broad area laser diode. [Preview Abstract] |
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E1.00129: High Power Diode Pumped Cesium Lasers Jerry Sell, Boris Zhdanov, Randy Knize We will discuss high power cesium vapor lasers pumped by multiple laser diode arrays. Previously a single laser diode array (LDA) has been shown to efficiently optically pump (63\% overall optical efficiency) a cesium vapor laser.\footnote{B. Zhdanov and R.J. Knize, Opt. Lett. \textbf{32} (15), 2167 (2007).} The LDA operates at 852 nm which pumps the Cs $D_2$ line, with a buffer gas present (ethane) at 500 torr which quenches the 6$P_{3/2}$ state to the 6$P_{1/2}$ state. Lasing then occurs back to the ground state at 894 nm. This setup succeeded in achieving a continuous wave output power of 10 W. Two similar laser diode arrays were used to pump a rubidium cell, where the output power was measured to be 17 W with a total optical efficiency of 46\%. Our progress using multiple LDA's to pump a Cs cell will be given, for both continuous wave and pulsed operation. [Preview Abstract] |
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E1.00130: Instrumental Asymmetry Reduction in Polarized Electron Beams M.I. Fabrikant, K.W. Trantham, T.J. Gay We report progress in the reduction of instrumental asymmetries (IAs) related to the photoemission of polarized electrons from GaAs caused by circularly-polarized diode laser beams [1]. Such asymmetries can mask true helicity-dependent interactions between the emitted electrons and chiral targets. Minimization of laser intensity IAs is achieved by chopping two spatially separated light beams with orthogonal polarizations which are recombined and passed through a quarter-wave plate to yield a single beam with rapidly flipping helicity. We have demonstrated the ability to reduce intensity IAs of the laser beam itself to less than 2 x 10$^{-6}$ [2]. We have also investigated the IAs of the photemission current from the GaAs. At present, we are able to reduce the photoemission asymmetry to values that are comparable to the laser intensity asymmetry. Implications for experiments measuring effects due to electron circular dichroism [3] will be discussed. [1]Trantham K.W. \textit{et al} J. Phys. B. \textbf{28} L543 (1995) [2] Fabrikant M.I.\textit{ et al} submitted to Appl. Opt. [3] Mayer S., Kessler J. Phys. Rev. Lett. \textbf{74}, 4803 (1995) Funding for this project was provided by Undergraduate Creative Activities and Research Experiences (UCARE) and the National Science Foundation (PHY-0653379). [Preview Abstract] |
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E1.00131: Comment on Elimination of Polarization Dependence from Optical Excitation Functions J.W. Maseberg The measurement of optical excitation functions excited by electron impact is typically accomplished by recording fluorescence emitted into a small solid angle perpendicular to the incident electron beam. This measured intensity is not proportional to the emission cross section due to target alignment, and a linear polarizer is typically oriented at the ``magic angle'' ($54.7^\circ$) with respect to the incident electron beam in order to eliminate this polarization dependence [1]. Existing literature for the derivation of the value for the magic angle assumes the polarizing element is ideal. A simple expression for this angle that accounts for the use of a partial polarizer is presented. [1] P.N. Clout and D.W.O. Heddle, J. Opt. Soc. Am. \textbf{59}, 715 (1969). [Preview Abstract] |
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E1.00132: NEW THEORETICAL METHODS |
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E1.00133: Fermion condensation: a strange idea successfully explaining behavior of numerous objects in Nature M. Ya. Amusia, Vasily Shaginyan Strongly correlated Fermi systems are fundamental systems, lacking theoretical understanding. Ideas of quantum and thermal fluctuations at a quantum critical point (QCP) have been put forward and the non-Fermi liquid (NFL) behavior of these systems was attributed to fluctuations. But these ideas failed to describe other properties. Facts about heavy-fermion (HF) metals and two dimensional (2D) $^{3}$He demonstrate very high values of the quasiparticle effective mass$m^\ast $. Fermion condensation quantum phase transition preserving quasiparticles and related with unlimited growth of $m^\ast $is capable to describe strongly correlated systems. In that case$m^\ast $ becomes temperature, density, magnetic field etc. depended but the very concept of Landau quasiparticles remains untouched. We found that despite different microscopic nature of 2D $^{3}$He and HF metals, both exhibits the same NFL behavior at QCP. NFL behavior is universal and independent of the peculiarities of Fermi-system. [Preview Abstract] |
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E1.00134: Resonances in dipositronium. Joseph DiRienzi, Richard Drachman Previously we studied the possible resonances in PsH.[1], assuming Ps$^{-}$ interacting with H$^{+}$ as the principal configuration. Now we look at the resonances in Ps$_{2}$ in a similar manner with Ps$^{-}$ and e$^{+}$. In this situation we use a variational method to determine the radial function of the bound state. We first look at the system without any exchange of electrons and positrons. Then we examine the system by including electron exchange but no positron exchange. In these two cases the solution of the variational equation involves a local effective potential. The predicted energy levels are fairly close in both these cases. The full problem also includes antisymmetrization of the two positrons giving rise to a non-local potential and increasing the mathematical difficulty of determining the resonant states. [1] J. DiRienzi and R.J. Drachman, Physical Review A, \textbf{76}, 032705 (2007) [Preview Abstract] |
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E1.00135: Electronic structure calculation of atoms and molecules through a DFT approach in the Amlan K. Roy In this follow-up of the recently proposed work \footnote{A. K. Roy, Int. J. Quant. Chem. \textbf{108} 837 (2008).} on the pseudopotential calculation of atoms and molecules using cartesian coordinate grids (CCG) detailed results are presented to demonstrate the usefulness and applicability of the same. About 50 molecules and 10 atoms are studied systematically, for both local and non-local exchange-correlation combinations, utilizing the Hay-Wadt type effective core potentials. The localized gaussian basis set, the electron density as well the various two-body potentials are constructed directly on the grid. Thorough comparison on the total energy, individual energy components, eigenvalues, atomization energies and the potential energy curves with the widely used quantum chemistry programs reveals that these two results are virtually identical for all practical purposes. Additionally the highest occupied molecular orbital energies for a series of molecules show significant improvements by using the LB (van Leeuwen-Baerends) exchange potential, compared to both LDA or the BLYP results. [Preview Abstract] |
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E1.00136: Computation of the Time-Translation Operator Using Time-Spectral-Elements Charles Weatherford The time-translation operator [U(t)] is usually applied directly to an initial quantum mechanical state in order to translate the state in time. Many traditional techniques are available for this computation, all of which are essentially sequential and do not parallelize well for modern high performance computing platforms. The need for a more scalable method, especially in coming era of many-core computers, is great. I propose to use an algorithm which employs spectral elements in time and spectral or spectral elements in space to compute, not the time-translated initial state, but rather the time-translation operator itself. The operator U(t) is first expanded in shifted Chebyshev polynomials with an argument given by the scaled time-independent part [H0(t)] of the generally time-dependent Hamilton H(t). The coefficients of the expansion are the same shifted Chebyshev polynomials with time argument. These operators are then projected onto a manifold of initial states which are all propagated at once by forming a set of simultaneous equations with the initial condition of U(t=0)=1. The width of the time elements is determined by h-p optimation. The algorithm is used to solve several model problems. [Preview Abstract] |
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E1.00137: First-principles Time-dependent Density Functional Theoretical Approach for Quantum Transport of Molecular Electronic Devices Zhongyuan Zhou, Shih-I Chu We present a first-principles time-dependent density functional theoretical approach that is computationally feasible for quantitative treatment of quantum transport of molecular devices. In this approach, the bias is equivalent to an external field and the effect of the bias is depicted by an interaction of electrons with the field. The quantum transport properties are determined by a set of occupied electron orbitals obtained by solving the time-dependent Kohn-Sham equation in Markovian process. The approach is applied to the calculation of conductance of carbon and gold wires connected to aluminum electrodes. The results are compared with available experimental and theoretical results. The current-voltage characteristic or resistance change with bias and wire sizes are also explored. [Preview Abstract] |
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E1.00138: Low Energy Elastic Electron Scattering from Molecular Targets Murtadha A. Khakoo, John Muse, Helen Silva, Cristina Lopes, B. Vincent McKoy, Carl Winstead, Marco A.P. Lima, Marcio Bettega An overview of recent activity between Cal State and Juiz de Fora (Expt) and CalTech and Campinas and U. F. Parana (Theory) regarding elastic electron scattering from Methanol, Ethanol, Butanol and Propanol and Water, Molecular Hydrogen and Molecular Nitrogen will be presented. The experimental data (using an aperture source of gas) were taken at energies of 1eV up to 100eV and the theory is the Multichannel Schwinger with Polarization effects included. In most cases agreement between theory and experiment is very good, considering these are large calculations. [Preview Abstract] |
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E1.00139: Positronium -- Helium Scattering at Low Energies. Jason Engbrecht Recently we have completed a long term effort to utilize a Doppler broadening technique to observe positronium thermalization in a Helium gas, and extract information on the momentum-transfer cross section for this interaction. Simultaneous acquisition of lifetime and Doppler broadening data allowed for dramatic improvements to statistical and systematic source of error. These improvements allowed the precision of the experiment to be improved by a factor of 5 over previous Doppler experiments and extended the observable energy range down to thermal energies. Our results also demonstrate the first experimental evidence of an energy dependent cross section. Finally, we will discuss future directions for study of positronium-atom interactions. [Preview Abstract] |
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E1.00140: Initial Findings and Proposal for a Pulsed Positronium Beam Dan Endean, Jason Engbrecht To date, work with positronium (Ps) has required either indirect statistical measurements or analysis done with high ($>$10 eV) energy beams. Here we propose a low energy Ps beam that will allow for investigation of fundamental questions concerning Ps, such as gas scattering cross-sections and condensed matter surface interactions. These results may also improve material science analysis techniques by providing a better theoretical basis for pore analysis of materials. Our research has shown that a nanotube material should be capable of producing a directional Ps source with a room temperature velocity distribution. Analysis of this material has demonstrated that up to 10{\%} of incident positrons form Ps and will likely diffuse through these nanotubes in a collimated beam. We outline the steps we have taken toward creating this Ps beam as well as offer insight into the nature and relevance of the measurements that could be made with such a beam. [Preview Abstract] |
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E1.00141: Saturation of three-body recombination fluorescence in ultracold neutral plasmas Scott Bergeson, Francis Robicheaux Three-body recombination (TBR) in ultracold neutral plasmas is a sensitive function the electron temperature. In strongly coupled plasmas, the traditional description of TBR should break down. We measurement fluorescence from recombination events and observe that the fluorescence rate begins to saturate as the low-temperature limit is approached. We also present evidence suggesting that the pathway to fluorescence from low-lying energy states may be different than what is traditionally thought. [Preview Abstract] |
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E1.00142: Early time dynamics of ultracold neutral plasmas Adam Denning, Scott Bergeson On the earliest time scales, disorder induced heating changes the ion velocity distribution. This is a response to the ion's local electric microfield. It has been shown that ion motion is ballistic on the potential landscape. We measure disorder induced heating rate at various densities and electron temperatures to probe to average microfield in these systems. Early results show greater accelerations than expected and also electron screening effects. [Preview Abstract] |
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E1.00143: Towards a Beta Asymmetry Measurement of Polarized Radioactive Atoms in an Optical Dipole Trap Fang Fang, Haiyan Wang, David Feldbaum, Andrew Hime, David Vieira, Xinxin Zhao Laser cooled and trapped radioactive atoms provide an ideal sample for studying parity violation in beta decay. We present recent progress in undertaking a high precision beta-recoil measurement of radioactive $^{82}$Rb atoms in an optical tweezer. We have demonstrated the loading of $^{82}$Rb atoms from a magneto-optical trap (MOT) to a far off resonance dipole trap formed by a YAG laser and observed the evidence of spontaneous spin polarization of atoms in optical dipole trap loading [1]. We'll present the latest progress in polarizing the sample with optical pumping and precision measurement of the sample polarization. In our proposed beta asymmetry measurement, we plan to load $^{82}$Rb atoms from a MOT into an optical tweezer and then beam the atoms down to a science chamber where the atoms will be polarized and their beta decay will be measured. \newline [1] Trapping radioactive $^{82}$Rb in an optical dipole trap and evidence of spontaneous spin polarization. D. Feldbaum, H. Wang, D. Vieira and X. Zhao. Physical Review A 76, 051402(R) (2007). [Preview Abstract] |
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