Bulletin of the American Physical Society
40th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 54, Number 7
Tuesday–Saturday, May 19–23, 2009; Charlottesville, Virginia
Session M1: Poster Session II (4:00 - 6:00 pm) |
Hide Abstracts |
Room: Newcomb Hall Ballroom |
|
M1.00001: SPECTROSCOPY, LIFETIMES, OSCILLATOR STRENGTHS |
|
M1.00002: Strong infrared lines among the lowest three even configurations of Fe II Narayan C. Deb, Alan Hibbert Two recent observational studies [1-2] of the infrared [Fe II] $\lambda$12567/$\lambda$16435 line ratio suggest that the available theoretical A-values [3-4] for these transitions contains errors of up to 40\%, although the two observations also differ to a similar extent. The empirically derived A-values [1] generally agree much more closely with [3] than with [4]. We have carried out a large scale CI calculation of [Fe II] lines covering the near infrared to far infrared spectrum, with a total of 72,492 configuration state functions (CSFs) for the 100 fine-structure levels belonging to the $3d^64s$, $3d^7$ and $3d^54s^2$ configurations. Our results also tend to show much better agreement with [3] than with [4], and therefore with the empirical A-values of [1]. In particular, our calculated result for the ratio of the A-values of $\lambda$12567 and $\lambda$16435 is 1.04, in agreement with [3], while [1] obtain 1.13, only 9\% higher, whereas [4] obtain 0.79, similar to the result implied in [2]; it is argued in [1] that such a low value is inconsistent with their observations. We anticipate that our new results will have a significant effect on the interpretation of other astrophysical observations.\\ $[1]$ Smith N \& Hartigan P, ApJ {\bf{638}} (2006) 1045\\ $[2]$ Rodriguez-Ardila A {\it et al} A \& A {\bf{425}} (2004) 457\\ $[3]$ Nussbaumer H \& Storey P J, A \& A {\bf{193}} (1988) 327\\ $[4]$ Quinet P {\it et al} A \& AS {\bf{120}} (1996) 361\\ [Preview Abstract] |
|
M1.00003: Two-photon transitions in the He$^{+}$ ion embedded in strongly-coupled plasmas Yew Kam Ho, H.F. Lai, Y.C. Lin There have been considerable interests in atomic processes in weakly-coupled Debye plasmas [1]. Here, we report an investigation on two-photon transitions for the He$^{+}$ ion embedded in strongly-coupled plasmas. The 1$s$-2$s$, 1$s$-3$s$, 1$s$-4$s$, 1$s$-3$d$ and 1$s$-4$d$ two-photon transitions for the He$^{+}$ ion are studied. Using the ion-sphere (IS) model [2] for strongly-coupled plasmas, and employing B-spline basis to represent the wave functions, the absorption coefficients, resonant enhancement frequencies, and transparency frequencies for various ion-sphere radii are calculated using a pseudo-state method [3]. Detailed results will be presented at the meeting. [1] L. B. Zhao and Y. K. Ho, \textit{Phys. Plasmas} \textbf{11}, 1695 (2004); A. Yu and Y. K. Ho, \textit{Phys. Plasmas} \textbf{12}, 043302 (2005); S. Sahoo and Y. K. Ho, \textit{Phys. Plasmas} \textbf{13}, 063301 (2006); S. Kar and Y. K. Ho,\textit{ Phys. Plasmas} \textbf{15}, 013301 (2008); S. Paul and Y. K. Ho, \textit{Phys. Plasmas} \textbf{15}, 073301 (2008); \textit{Phys. Rev. A} \textbf{78}, 042711 (2008) [2] S. Ichimaru, \textit{Rev. Mod. Phys.} \textbf{54}, 1017 (1982). [3]. R. J. Drachman and A. K. Bhatia, and A. A. Shabazz, \textit{Phys. Rev.} A \textbf{42} 6333 (1990). [Preview Abstract] |
|
M1.00004: Radiative lifetime measurements of high-$n$ Rb Rydberg states Duncan Tate, Drew Branden, Tamas Juhasz, Tatenda Mahlokozera, Cristian Vesa, Roy Wilson, Mao Zheng, Andrew Kortyna We present results of radiative lifetime measurements of the $n\ell$ Rydberg states of rubidium in the range $30 \le n \le 50$ and $0 \le \ell \le 2$ ($s$, $p$ and $d$ states) using cold atoms in a MOT. Two experimental techniques have been adopted to reduce random and systematic errors. First, a frequency doubled, pulse amplified diode laser is used to excite the target $n\ell$ Rydberg state. The output from this laser has a Fourier-transform linewidth of $\approx 100$ MHz at 480 nm, and results in minimal shot-to-shot variation in the Rydberg state population when it is used to drive the $5p_{3/2}$ $\rightarrow$ $n\ell$ transition. Second, we monitor the target state population as a function of time delay from the 480 nm laser pulse using a short mm-wave pulse that is resonant with a one- or two-photon transition $n\ell$ $\rightarrow$ $n^\prime\ell^\prime$. We then selectively field ionize the $n^\prime\ell^\prime$ state, and detect the resulting electrons with a microchannel plate (MCP). We step the time delay between the laser pulse and the mm-wave pulse and acquire the MCP signal as a function of the delay. This signal is an accurate mirror of the $n\ell$ population, which we fit to an exponential decay to recover the $n\ell$ state lifetime. [Preview Abstract] |
|
M1.00005: Excitation energies, radiative and autoionization rates, dielectronic satellite lines, and dielectronic recombination rates for excited states of Mg-like W from Na-like W U.I. Safronova, A.S. Safronova, P. Beiersdorfer Energy levels, radiative transition probabilities, and autoionization rates for $2p^63l'nl$ ($n=3-13$) and $2p^64l'nl$ ($n=4-7$), and $2p^53l'3l''nl$ ($n=3-4$) states in Mg-like tungsten are calculated using the COWAN, HULLAC, and RMBPT codes. Autoionizing levels above the thresholds $2p^63l$ and $2p^64l$ are considered. Branching ratios relative to the first threshold and intensity factors are calculated for satellite lines, and dielectronic recombination (DR) rate coefficients are determined for the first excited states.Contributions to DR rate coefficients from the excited $2p^63l'nl$ states with $n \ge 14$ and $2p^64l'nl$ states with $n \ge 8$, and additionally from core-excited $2p^53l'3l''nl$ states with $n \ge 5$ are estimated by extrapolation of all atomic parameters. The total DR rate coefficient is derived. These data as well as theoretical satellite spectra are important for L-shell diagnostic of very high-temperature laboratory plasmas such as future ITER plasmas [Preview Abstract] |
|
M1.00006: Dielectronic recombination of Xe$^{8+}$ ion and satellite lines of Xe$^{7+}$ ion Rajan Bista, Ulyana Safronova, Reinhard Bruch, Yuri Ralchenko The Hartree-Fock-Relativistic method (Cowan code) and the relativistic many-body perturbation theory are used to perform a large-scale calculation of atomic parameters for dielectronic recombination (DR) of Pd- like Xe$^{8+}$. The energy levels, radiative transition probabilities, and autoionization rates are reported for $4d^94fnl$, $4d^95l'nl$, ($n$=5-8), and $4d^96lnl$ ($n$=6-7) states in Ag-like Xe$^{7+}$. The partial and total DR rate coefficients are calculated with account of high-$n$ states, and contribution of different atomic configurations to DR is discussed. The branching ratios and intensity factors are calculated for dielectronic satellite lines. The obtained results can be used for modeling of various Xe plasmas including those used in lithography applications. [Preview Abstract] |
|
M1.00007: Progress towards measurement of the electron electric dipole moment using the PbF molecule: Spectroscopic constants of the known electronic states of PbF Christopher McRaven, Poopalasingam Sivakumar, Milinda Rupasinghe, Greg Hall, Trevor Sears, Neil Shafer-Ray The lead monofluoride molecule provides for a 1000- to 10,000- fold improvement in sensitivity to an electron electric dipole moment (e-EDM) over atomic-based measurements. The density of the relavistic electronic wave function near the lead nucleus leads to this exaggerated sensivity. This density also leads to a mixing of the $^2\Pi$ ground state with $^2\Sigma$ excited states. For this reason, comparison of measurements of the electronic structure to calculation leads to a better understanding of the sensitivity of the molecule to an e-EDM. Here we present new spectroscopic constants for the $A$, $B$, $C$, $D$, $E$, and $F$ states. It was previously believed that the $A\ ^2\Sigma_{1/2}$ and the $X_1\ ^2\Pi_{1/2}$ state formed a simple mixed $^2\Pi - ^2\Sigma$ system. Our data suggest a more complicated system in which higher vibrational states of the $A^2\Sigma_{1/2}$ electronic state mix with the $X_1\ ^2\Pi_{1/2}$ state whereas the lower vibrational states mix with the $D^2\Pi_{1/2}$ electronic state. [Preview Abstract] |
|
M1.00008: Precision spectroscopy of cold Li atoms using an optical frequency comb Jason Stalnaker, Sean Bernfeld, Leanne Sherry, Zwoisaint Mears-Clarke The atomic structure of lithium (Li) has aroused a significant amount theoretical and experimental interest as a system in which precision atomic calculations and spectroscopic measurements can be united to yield scientifically significant results. While there have been many experimental investigations of Li spectroscopy, particularly isotope shifts and hyperfine structure on the $2\: ^2S_{1/2} \rightarrow 2\: ^2P_{1/2,3/2}$ ($D1$, $D2$) transitions, they suffer from significant disagreements and systematic effects. We are in the process of developing an experiment to resolve the current discrepancies and improve on the accuracy of the spectroscopic measurements in Li. By combining the mature techniques of atom cooling and trapping with the extraordinary spectroscopic accuracy provided by optical frequency combs we anticipate that we will be able to measure the optical frequencies of the $D1$ and $D2$ transitions to an absolute accuracy of 5 kHz. [Preview Abstract] |
|
M1.00009: Measuring atomic oscillator strengths by single atom spectroscopy Jianwei Lee, Syed Abdullah Aljunid, Meng Khoon Tey, Brenda Chng, Gleb Maslennikov, Christian Kurtsiefer We propose a method for obtaining the oscillator strengths of atomic transitions based on single atom spectroscopy. The method is based on a direct measurement of an AC Stark shift of atomic energy levels for a single atom trapped in an optical tweezer [1]. The method is independent of the knowledge of the trapping field at the atom. The results can be applied to obtain the previously unknown oscillator strengths for dipole transitions involving the first excited state of alkali metals. [1] M. K. Tey, Z. Chen, S. A. Aljunid, B. Chng, F. Huber, G. Maslennikov and C. Kurtsiefer, {\it Strong interaction between light and a single trapped atom without the need for a cavity,} Nature Physics {\bf 4}, 924(2008) [Preview Abstract] |
|
M1.00010: Hyperfine-quenched {\boldmath $2s2p\,{^3\!P_2} - 2s^2\,{^1\!S_0}$} M2 transition in Be-like ions K.T. Cheng, M.H. Chen, W.R. Johnson For isotopes with non-zero nuclear spins, the $2s2p\,{^3\!P_2} - 2s^2\,{^1\!S_0}$ M2 transition in Be-like ions is affected by hyperfine mixing with the much stronger $2s2p\,{^{1,3}\!P_1} - 2s^2\,{^1\!S_0}$ E1 transitions. In this work, these hyperfine-quenched M2 rates are calculated with a large-scale relativistic configuration-interaction method in a perturbative approach that includes coherent hyperfine mixing between the $^3\!P_1$ and $^1\!P_1$ states. It is found that the effect of hyperfine quenching is significant and that for some low-$Z$ Be-like ions with $I=1/2$, the ${^3\!P_2} - {^1\!S_0}$ transition will show up in measurements as a two-component decay comprising of a slower, unperturbed decay from the $F=J+I=5/2$ level and a much faster, hyperfine-quenched decay from the $F=J-I=3/2$ level. [Preview Abstract] |
|
M1.00011: PHOTON INTERACTIONS WITH ATOMS, IONS, AND MOLECULES |
|
M1.00012: Nondipole Effects in the Photodetachment of Cl$^{-}$ Jobin Jose, Gagan B. Pradhan, Vojislav Radojevic, Pranawa C. Deshmukh, Steven T. Manson Calculations of the quadrupole channels for Cl$^{-}$ photodetachment have been carried out using the relativistic-random-phase approximation (RRPA) over a broad energy range form threshold to several hundred eV. Unlike the dipole channels, shape resonances occur in both 2p and 3s quadrupole photoabsorption; consequently, both subshell cross sections are significantly modified owing to interchannel coupling. The nondipole photoelectron angular distribution parameters exhibit structure that is explained in terms of these shape resonances and Cooper minima in both dipole [1] and quadrupole channels. This work was supported by DST (India), DOE and NSF. [1] V. Radojevic, J. Jose, G. B. Pradhan, P. C. Deshmukh and S. T. Manson, Can. J. Phys. (in press). [Preview Abstract] |
|
M1.00013: Photoionization of Isonuclear Sequences Gagan B. Pradhan, Jobin Jose, Vojislav Radojevic, Pranawa C. Deshmukh, Steven T. Manson Calculations of the photoionization of the 2s subshell of Ar, Ar$^{+6}$ and Ar$^{+8}$, and Mg, Mg$_{+2}$ and Mg$^{+8}$ have been carried out using the relativistic-random-phase approximation with relaxation (RRPA-R). Based upon calculations omitting relaxation, it has been assumed that inner-shell cross sections are essentially unaltered, as a function of photon energy, by the removal of outer shell electrons [1,2]. The present results show that, when relaxation is considered, the removal of an outer shell electron can indeed affect an inner-shell main line (ionization without simultaneous excitation) cross section. This effect is particularly strong in the Ar isonuclear sequence where the relaxation of the 3p orbitals affects the Ar results compared to Ar$^{+6}$. This work was supported by DST (India), DOE and NASA. [1] R. F. Reilman and S. T. Manson, Ap. J. Supp. \textbf{40}, 815 (1979) and reference therein. [2] G. Nasreen, S. T. Manson and P. C. Deshmukh, Phys. Rev. A \textbf{40}, 6091 (1989). [Preview Abstract] |
|
M1.00014: ABSTRACT WITHDRAWN |
|
M1.00015: Femtosecond Dynamics and Multiphoton Ionization driven with an Intense High Order Harmonic Source Jeroen van Tilborg, Tom Allison, Travis Wright, Marc Hertlein, Roger Falcone, Yanwei Liu, Hamed Merdji, Ali Belkacem We have constructed a high intensity high order harmonic source at the Lawrence Berkeley National Lab delivering $\sim $10$^{9}$ extreme ultraviolet photons/shot on a gas target and used it to observe multiphoton ionization and conduct femtosecond EUV-pump IR-probe experiments. Following excitation by 20-25 eV photons, we observed that the excited ethylene cation (H$_{2}$C-CH$_{2})^{+}$ experienced isomerization to the ethylidene configuration (HC-CH$_{3})^{+}$ in 50$\pm $25 fs, followed by an H$_{2}$ stretch motion. Experimental data and analysis from several experiments as well as a future outlook of our efforts will be presented. [Preview Abstract] |
|
M1.00016: Effects of relative phase between coupled vibrational modes in CARS microscopy Vishesha Patel, Vladimir Malinovsky, Svetlana Malinovskaya Coherent anti-Stokes Raman scattering has emerged as a promising tool for noninvasive imaging of biological spices and many other biological applications. The rich spectrum obtained from CARS contains the vibrational signatures of the molecules, that can be used for molecular specific structure imaging. Main obstacles in this technique are the non-resonant background as well as the lack of selectivity. Here, using recently proposed the roof method, we demonstrate the possibility for suppression of the background and selective excitation among many {\em coupled} molecular vibrational modes. We consider a model of two coupled harmonic oscillators representing two molecular vibrational modes and analyze the effects of relative phase between initially populated states and the conditions for selective excitation and creation of a maximum coherence. Analysis of the dressed state picture shows the relative phase conditions for the adiabatic passage leading to the desired quantum yield. The numerical results demonstrate that coupling and initial relative phase between vibrational modes play an important role in achieving maximum CARS coherence and selectivity. [Preview Abstract] |
|
M1.00017: Photoionization of Fullerene Ions of Various Mass in the Energy Range of the Giant Plasmon Excitations David Esteves, Ron Phaneuf, Alex Aguilar, A.L. David Kilcoyne, Alfred Mueller, Stefan Schippers, Carmen Cisneros, Mustapha Habibi, Kiran Baral, Nagendra Aryal A systematic study of single photoionization of fullerene ions was conducted at ALS to examine the dependence of the cross sections on fullerene mass.~ Present single ionization measurements of C$_{40}^{+}$, C$_{50}^{+}$, C$_{60}^{+}$, and C$_{70}^{+}$ are combined with previous measurements for C$_{80}^{+}$ and C$_{84}^{+}$ to examine the mass-dependent behavior of the giant plasmon resonances in the 18 eV to 72 eV energy range.~ Both the surface plasmon and volume plasmon resonances are identified and compared to determine whether simple scaling relations may be used to predict the behavior of other fullerenes.~ Initial analysis indicates a correlation between fullerene ion mass and the location and strength of these plasmon resonances. [Preview Abstract] |
|
M1.00018: ATOMIC AND MOLECULAR STRUCTURE, INCLUDING IN STATIC FIELDS |
|
M1.00019: Ground state and resonant states of helium in exponential cosine screened Coulomb potential Arijit Ghoshal, Y.K. Ho We have investigated the ground state and a resonance state of normal helium atom in exponential cosine screened Coulomb potential (ECSCP) with screening parameter$\lambda $: $V(r)\,=\,-\,\frac{1}{r}\,e^{-\lambda r}\cos (\lambda r)$ (in a.u.), where $r$ denotes the inter-particle distance. Within the framework of Ritz's variational principle and making use of a highly correlated wave function, we have determined the ground state energies and wave functions of the helium atom for different values of the screening parameter$\lambda $. Furthermore, we have shown that the ground state energy of helium for a particular value of $\lambda $ does converge with increasing number of terms in the wave function. In addition, using the stabilization method, we have investigated the doubly excited $2s^{2} \quad ^{1}S^{e}$ resonance state in helium with ECSCP. Resonance energy and width for various $\lambda $ values are calculated. Our present work will play a useful role in the investigations of atomic structures in quantum plasmas [1]. [1]. P.K. Shukla and B. Eliasson, \textit{Phys. Lett. A} \textbf{372,} 2899 (2008). [Preview Abstract] |
|
M1.00020: Mass analyzed threshold ionization (MATI) with VUV radiation Oleg Kostko, Sang Kyu Kim, Kevin R. Wilson, Stephen R. Leone, Musahid Ahmed Mass analyzed threshold ionization is a combination of threshold ionization spectroscopy with mass spectrometry. Similar to zero electron kinetic energy (ZEKE), MATI spectroscopy takes advantage of the field ionization of long lived high Rydberg states to obtain an ionization threshold and perform spectroscopy on the resulting cation. MATI at the synchrotron utilizing tunable VUV light opens up a novel way to perform spectroscopy on ions and improve the resolution in ionization energy determination in comparison with conventional photoionization efficiency curve measurements. This method is implemented at the Advanced Light Source and vibrationally-resolved MATI spectra for simple di- and polyatomic molecules (O$_{2}$, N$_{2}$, H$_{2}$O, N$_{2}$O, C$_{2}$H$_{2}$, and C$_{6}$H$_{6})$ are measured. This preliminary work allows us to test the applicability of MATI at a synchrotron and prepare for investigation of more complex systems such as mixtures of molecules, isomers and clusters. [Preview Abstract] |
|
M1.00021: Koester-Kronig decay in endohedral atoms Miron Ya Amusia, Larissa V. Chernysheva Fullerene shell can in principle prominently affect the shape of the electron energy distribution in the Koester--Kronig decay of an atom A, caged inside the C60 shell, i.e. of an endohedral A@C60. For isolated atoms, the probability of decay and emitted electron spectrum depend strongly on details of the wave function of the vacancy and the emitted electron. It was demonstrated quite a while ago that taking into account electron correlations in the frame of Random Phase Approximation with Exchange alters considerably the Koester-Kronig decay probability. We have considered the decay of vacancy in 2s subshell in Ar@C60 - 2s$^{-1}$. The main channels of this decay are 2s$^{-1}$ -- 2p$^{-1}$3s$^{-1}$(3p$^{-1})$ep (es,d). We estimated the modification of the interelectron interaction due to fullerene shell presence and found it inessential. We found that due to its reflection by the static potential of the fullerenes shell the outgoing electron spectrum is modified by up to thirty percent. This effect may increase in other atoms due to variation of the outgoing electron energy. The probability of the transition 2s$^{-1}$ -- 2p$^{-1}$ via emission of the fullerenes shell electrons proofed to be negligible. Of some importance is the shake-off of fullerene shell electrons that accompany the atomic vacancy decay. [Preview Abstract] |
|
M1.00022: \textit{Ab Initio} Calculation of Double Photoexcitation of Rydberg Resonance States of Helium below the $N $=2 Threshold in a Strong DC Electric Field John Heslar, Shih-I Chu We present a complex-scaling (CS)-generalized pseudospectral (GPS) method in hyperspherical coordinates (HSC) for \textit{ab initio }accurate treatment of the electron structure and quantum dynamics of two-electron systems. The GPS method allows non-uniform and optimal spatial discretization of the two-electron Hamiltonian in HSC with the use of only very modest number of grid points. The procedure is applied for the precision calculation of the energies and widths of doubly-excited Rydberg resonance states as well as the ionization rates of the He atom in an external dc electric field of 84$.$4 \textit{kV/cm}. The effects of dc-field ionization rates on the 1S$^{e}$, 1P$^{o}$, and 1D$^{e}$ states for $n $= 10-20 have been identified and studied in detail. [Preview Abstract] |
|
M1.00023: Two effective potentials for spin-independent relativistic and QED corrections to the Rydberg energy levels of helium J. Babb The effective potentials for energy corrections arising from one and two transverse photon exchange in Rydberg states of helium are reanalyzed. The result, expressed as an integral over the virtual photon frequency, is compared to the Araki-Sucher effective potential and its applicability to actual calculations of energy shifts is assessed. [Preview Abstract] |
|
M1.00024: Atom interferometry measurements of the polarizability of Na, K, and Rb William Holmgren, Melissa Revelle, Vincent Lonij, Alexander Cronin We measured the static ground state polarizability of three different atomic species (Na, K, and Rb) using a Mach-Zehnder atom interferometer. We describe how we can achieve an uncertainty of 1\% for each of these measurements. The interferometer is produced by atom-wave diffraction from two nanogratings. An electric field gradient across the atom beam paths provides a polarizability dependent phase shift to the atom interference fringes. Since all three polarizability measurements are performed in the same apparatus, we anticipate reporting polarizability ratios with better than 1\% precision. We will also discuss the major sources of uncertainty that cannot be canceled by ratio measurements: the beam velocity and velocity spread. This work is supported by the NSF. [Preview Abstract] |
|
M1.00025: One and two-electron hydrogenic, helium and helium-hydrogenic molecular chains in a strong magnetic field Nicolais Guevara Leon, Alexander V. Turbiner, Juan C. Lopez Vieyra A classification for one and two-electron molecular hydrogenic, helium and helium-hydrogenic chains in a strong magnetic field $B \leq 10^{16}\,$G is given. At very large magnetic fields the longest hydrogenic chains contain at most five protons indicating the existence of the $\rm{H}_5^{4+}$ and $\rm{H}_5^ {3+}$ ions, respectively. It was also found that helium and helium-hydrogenic chains can exist at large magnetic fields with up to three and four nuclei for one and two-electrons, respectively. [Preview Abstract] |
|
M1.00026: ATOMIC PHOTOIONIZATION AND PHOTODETACHMENT PROCESSES |
|
M1.00027: Intra-doublet correlations in 4d subshell of Xe Miron Ya Amusia, Larissa V. Chernysheva We demonstrate here that an additional near threshold structure appear due to influence of four 4d3/2 electrons upon the six 4d5/2. This effect is a manifestation of interaction between levels that are initially degenerate after this degeneration is eliminated. Being a relativistic effect, this phenomenon can be treated non-relativistic as well. The energy splitting between spin-orbit components of the 4d level can be taken from experiment and the nature of the 4d5/2 and 4d3/2 splitting is inessential. The approach used is similar to that developed for consideration of intra-doublet correlations between 3d3/2 and 3d5/2 Xe levels. We treated Xe in the non-relativistic RPAE frame, considering the 3d10 as consisting of two groups of spin-up and spin-down electrons. The case of 4d is different from 3d since the spin-orbit splitting in 4d is much smaller --2 eV. We demonstrate that the account of intra-doublet correlations leads to a small maximum close to threshold in 4d5/2 and a prominent variation of the cross-section at 75-81 eV. The variation for 4d3/2 is smaller, but substantial. [Preview Abstract] |
|
M1.00028: Spin-mixed doubly excited resonances in Ca and Sr spectra Tu-nan Chang, T.K. Fang For heavier alkaline-earth atoms, with a smaller energy separation between higher excited autoionizing resonances and a more substantial spin-dependent interaction, one expects a stronger mixing between different spin states and thus more complicated spectra. However, the earlier observed spectra have shown that the resonance structures are, in fact, relatively smooth above the second ionization threshold compared with those between the first and second ionization threshold, where the resonance decays only into one dominating ionization channel. The lack of complex resonance structure results primarily from a much faster decay rate in the presence of multiple decay channels with a broader total resonance width and substantial overlaps between neighboring resonances. In this work, we present a detailed theoretical estimate the spin mixing, based on the BSCR approach [1], to demonstrate explicitly how the spin-dependent interaction affects the mixing of different spin states along various autoionization series for Ca and Sr as energy increases. [1] T. K. Fang and T. N. Chang, Phys. Rev. A76 012721 (2007). [Preview Abstract] |
|
M1.00029: Photoionization of Atomic Sc A.M. Sossah, H.-L. Zhou, S.T. Manson, A. Hibbert Photoionization cross sections are calculated for the ground ([Mg]$ 3p^{6}3d4s^{2}$ $^{2}$D$^{e})$ state of atomic Sc for photon energies from threshold to 40.0 eV. The discrete Sc$^{+}$ orbitals are generated using both the AUTOSTRUCTURE and CIV3 codes, and R-matrix is used to carry out the cross section calculations. The results are compared with each other, then with previous calculations and available experimental data for final-ionic states representing the $3d$ and $4s$ main lines and associated satellites (ionization with excitation) in the region of the 3\textit{p $\to $ 3d }giant resonances [1]. Reasonably good agreement between our non-relativistic results and experiment is obtained. This work is supported by US DOE and NSF \\[4pt] [1] S. B. Whitfield, K. Kehoe, R. Wehlitz, M. O. Krause, and C. D. Caldwell $\to $hys. Rev. A \textbf{64}, 022701 (2001). [Preview Abstract] |
|
M1.00030: Quantifying the Asymmetry of Giant Resonances in Sc$^{3+}$ Photorecombination and Sc$^{2+}$ Photoionization Tom Gorczyca, Dragan Nikolic, Nigel Badnell We report on strong interference effects for the asymmetric, broad, and highly-correlated $3p^5 3d^2({}^{2}\hspace*{-.5mm}F^{{\rm o}}_{J})$ resonances in the photorecombination of ${\rm Sc}^{3+}$. Using a perturbative multiconfiguration Breit-Pauli approach, we present theoretical photorecombination cross sections that compare favorably with the Test Storage Ring measurements of Schippers~{\em et al.}~[1]. In order to reproduce the observed asymmetric resonance profiles, it was necessary to include resonance-continuum and $3p^5 3d^2$-$3p^5 3d4s$ resonance-resonance interference to the next-highest order. By using the principle of detailed balance for the same resonance region, we also present ${\rm Sc}^{2+}$ photoionization cross sections that agree with the Advance Light Source measurements of Schippers~{\em et al.}~[2]. This higher-order perturbative method yields analytical expressions for the Fano asymmetry parameters $q$ in terms of computed radiative and autoionization transition amplitudes. \newline [1] S. Schippers, et al., Phys. Rev. A {\bf 65}, 042723 (2002). \newline [2] S. Schippers, et al., Phys. Rev. A {\bf 67}, 032702 (2003). [Preview Abstract] |
|
M1.00031: Photoionization Cross Section for Ce$^{4+}$ in the 4d Giant Resonance Energy Range: Experimental Measurements and Theoretical Interpretations Mustapha Habibi, Ronald A. Phaneuf, David E. Esteves, Ulyana I. Safronova, Arthur L.D. Kilcoyne, Alejandro Aguilar, Carmen Cisneros Absolute measurements of single and double photoionization cross sections for Ce$^{4+}$ ion were performed in the 4d excitation energy range using the ion-photon merged-beams endstation at undulator beamline 10.0.1 of the Advanced Light Source. Comparison of the results to multi-configuration Hartree-Fock calculations indicate a 25{\%} population of metastable states in the primary ion beam. The cross sections are dominated by 4d - 4f transitions. Resonances in the cross section arising from excitations of 4d electrons to 4f, 5f, 6p, and 7p were identified. Integrating the cross sections over the experimental energy range gives a total oscillator strength of 10.32, consistent with the sum-rule value of 10 for a filled 4d shell. [Preview Abstract] |
|
M1.00032: Valence-shell photoionization of the C$\ell$ like Ar$^+$ ion A.M. Covington, A. Aguilar, I.R. Covington, G. Hinjosa, C.A. Shirley, R.A. Phaneuf, I. Alvarez, C. Cisneros, I. Dominguez-Lopez, M.M. Sant'Anna, A.S. Schlachter, C.P. Ballance, B.M. McLaughlin The properties of Argon ions are of importance in atmospheric and astrophysical plasmas where abundances are required in the modeling of B-type stars in the Orion nebula, and the interstellar medium. Absolute cross-section measurements made at the Advanced Light Source in Berkeley California, for M-shell photoionization of Ar$^+$ are reported on for discrete photon energies ranging from 27.4 eV to 60.0 eV. The high-resolution spectroscopic absolute photoionization cross-section measurements indicate the target ion beam is a statistical admixture of the $^2$P$^o_{3/2}$ ground state and the $^2$P$^o_{1/2}$ metastable state of Ar$^+$. At all of the photon energies considered, the experimental photoionization cross sections are in excellent agreement with the predictions made from theoretical calculations performed using a parallel version of the R-matrix codes in intermediate coupling within the semi-relativistic Breit-Pauli approximation. Further details and a comprehensive set of results will be presented at the meeting. [Preview Abstract] |
|
M1.00033: Photoionization of positive and negative ions stuffed inside C60 fullerene Miron Ya. Amusia, Larissa V. Chernysheva We performed calculations of photoionization cross-section and other parameters characterizing this process for endohedrals consisting of C60 and located at the center inside noble gas atom and adjacent positive and negative ions. We have considered outer $p$- and $s$- subshells for the groups (F$^{-}$, Ne, Na$^{+})$, (Cl$^{-}$, Ar, K$^{+})$ and outer $p$- , $s$- and $d$- subshells for the groups (Br$^{-}$, Kr, Rb$^{+})$ and (I$^{-}$, Xe, Cs$^{+})$. The possibility that the outer electron from the negative ion goes to the fullerenes shell was neglected. The fullerenes shell was described by the zero-thickness ``orange-type'' potential that was taken into account non-perturbatively, in the RPAE frame. In all considered cases, as it should be, the inclusion of the fullerenes shell transformed the smooth atomic photoionization cross-section (and other photoionization parameters) curves into strongly oscillating curves. There appeared a systematic difference between negative ions on the one hand and neutral atoms and particularly positive ions on the other. Namely, the negative ions presented much richer near threshold structure than their isoelectronic neighbors. [Preview Abstract] |
|
M1.00034: Non-perturbative treatment of orange-type potential in endohedrals Miron Ya. Amusia, Larissa V. Chernysheva We developed a system of programs that permit to treat non-perturbatively the effect of the fullerene shell upon the stuffed atom photoelectrons in the frame of RPAE. We use the zero-thickness ``orange-skin'' potential. Usually this potential was applied to calculate a factor that permitted to obtain all photoionization characteristics of an endohedral directly from respective characteristics of isolated atoms. It appeared, however that even when the photoelectron energy is low enough, the fullerenes shell can affect not only the real states of the electron on the way of the atom. Surprisingly enough at the first glance, the fullerene shell, even being remote quite far from the central atom in the endohedral, can strongly affect the intermediate virtual states. Therefore, the factorization of the fullerenes shell effects become in general incorrect. To take the modification of the virtual states, one has to treat the considered process with participation of the endohedral atom within the frame of a given model. We developed simple programs that permit to take into account one zero-thickness fullerenes potential or two -- for ``onion-type'' endohedrals in the RPAE frame and performed concrete calculations for Ar@C60. [Preview Abstract] |
|
M1.00035: Photoionization of onion-type endohedrals Miron Amusia, Larissa Chernysheva, Evgeniy Liverts We developed a program that permits to treat endohedral atoms with two fullerenes shells and performed corresponding calculations for Ar atom stuffed inside two spherically symmetric shells that consists of sixty and two hundred forty carbon atoms. To describe the action of the C60 shell upon the photoionization of an atom located inside the fullerene, the zero-thickness (``orange skin'') potential model was extensively used. This simple model permits to present the results of C60 action as an oscillating factor that permits to present all characteristics of the endohedral photoionization as corresponding atomic characteristic multiplied by the above-mentioned factor. This model potential is valid only for slow photoelectrons, the wavelength of which is much bigger than the thickness of the C60 shell. It is necessary also that the radius of C60 exceeds considerably the thickness of C60. We derived analytic expressions for the factor that takes into account both shells of an onion-type fullerene. Concrete calculations are performed for Xe atom stuffed into the onion-type structure --Ar@C60C240. The induced oscillations of the photoionization cross-section became much more complex and stronger than in Ar@C60. [Preview Abstract] |
|
M1.00036: ELECTRON-MOLECULE COLLISIONS |
|
M1.00037: Polarized Fluorescence from H$_2$ and D$_2$ Excited by Polarized Electron Impact J.W. Maseberg, T.J. Gay We report relative Stokes parameters for the following rotationally isolated molecular Fulcher band transitions in H$_2$ and D$_2$ excited from singlet ground states by spin-polarized electrons: \begin{center} \vspace{-.2cm} H$_2$ $d\:^3\Pi_u^-(v'=0)$ $\rightarrow$ $a\:^3\Sigma_g^+(v''=0)$ $+$ $\gamma(601.83$ nm$)$ $Q(1)$ \\ H$_2$ $d\:^3\Pi_u^-(v'=2)$ $\rightarrow$ $a\:^3\Sigma_g^+(v''=2)$ $+$ $\gamma(622.48$ nm$)$ $Q(1)$ \\ H$_2$ $d\:^3\Pi_u^-(v'=2)$ $\rightarrow$ $a\:^3\Sigma_g^+(v''=2)$ $+$ $\gamma(623.84$ nm$)$ $Q(3)$ \\ H$_2$ $d\:^3\Pi_u^+(v'=2)$ $\rightarrow$ $a\:^3\Sigma_g^+(v''=2)$ $+$ $\gamma(618.30$ nm$)$ $R(1)$ \\ $\;$D$_2$ $d\:^3\Pi_u^-(v'=0)$ $\rightarrow$ $a\:^3\Sigma_g^+(v''=0)$ $+$ $\gamma(600.68$ nm$)$ $Q(3)$. \end{center} \vspace{-.2cm} Values of the circular polarization fraction normalized to the incident electron spin polarization, P$_3$/P$_e$, for the above $Q(1)$ transitions are found to be ${\sim}0.15$, and smaller values are measured for the $Q(3)$ lines. For the $R(1)$ case, somewhat larger values of ${\sim}0.20$ are obtained. [Preview Abstract] |
|
M1.00038: Ionization of Molecular Hydrogen by Low-Energy Electron Impact Alian Aquino, Louis Romero, J.G. Childers Doubly-differential cross sections for the ionization of H$_2$ by low-energy electron impact have been measured at incident energies ranging from 17.6~eV to 40~eV and scattering angles of $20^\circ$ to $120^\circ$. The calibration of the electron analyzer during these measurements employed the recent doubly- differential cross section measurements of helium.\footnote{E.\ Schow, K.\ Hazlett, J.\ G.\ Childers, C.\ Medina, G.\ Vitug, I.\ Bray, D.\ V.\ Fursa, and M.\ A.\ Khakoo, {\em Phys.\ Rev.\ A} {\bf 72}, 062717 (2005).} Comparisons will be made to recent theoretical calculations. [Preview Abstract] |
|
M1.00039: Vibrational Excitation of Water by Low-Energy Electrons Murtadha A. Khakoo, John H. Muse, Carl Winstead, Vincent McKoy Experimental and calculated differential and integral cross-sections for electron-impact excitation of the unresolved stretching modes (100+001) and the bending mode (010) of water will be presented. The experimental DCSs are taken over an extensive range of incident energies (1eV to 100eV) and scattering angles (10 to 130 degrees) and are normalized to the recently measured elastic DCSs.\footnote{Khakoo et al., Phys. Rev. A 78, 052710 (2008).} The calculations are carried out in the adiabatic approximation using the Schwinger multichannel method. The present results are compared to previous theoretical and experimental results in the literature. [Preview Abstract] |
|
M1.00040: Electron Impact Excitation of Molecular Nitrogen: Excitation of the $C~^{3}\Pi_{u}$, $E~^{3}\Sigma_{g}^{+}$, and $a^{\prime\prime}~^{1}\Sigma_{g}^{+}$ States and Vibrationally-Resolved Excitation of the $C~^{3}\Pi_{u}~(\nu^{\prime})$ State C.P. Malone, P.V. Johnson, J.A. Young, I. Kanik, S. Rahman, B. Ajdari, M.A. Khakoo Differential cross sections (DCSs) were investigated for electron impact excitation of the $C~^{3}\Pi_{u}$, $E~^{3} \Sigma_{g}^{+}$, and $a^{\prime\prime}~^{1}\Sigma_{g}^{+}$ states from the ground state in N$_{2}$. The DCSs were obtained from new measurements of energy-loss spectra in the region of 10.75eV to 12.75eV measured at incident energies between 13eV and 100eV and for scattering angles ranging from $5^{\circ}$ to $130^{\circ}$. Vibrationally-resolved DCSs are presented for electron impact excitation from the ground state to the $C~^{3}\Pi_{u}~(\nu^{\prime})$ state, where $\nu^{\prime} $=0, 1, 2, 3, and 4. Relative excitation probabilities for the vibrational levels of the $C~^{3}\Pi_{u}$ state are shown to demonstrate non-Franck-Condon behavior for excitation energies less than approximately 50eV. [Preview Abstract] |
|
M1.00041: Rate Coefficients of Singly Ionized Triatomic Hydrogen Using An RF Ion Trap Nick Pope, Sam Ronald, Emily Mount, Adrian Daw, Anthony Calamai In order to better understand the interactions and composition of the universe, it is essential to know reaction rates between ions, neutral species, electrons, and photons. A significant reaction of interest is H2 + H2+ $\rightarrow$ H3+ + H, a fundamental reaction that produces some of the most abundant ions in the interstellar medium and other areas of the universe. Due to its instrumental role in forming many different polyatomic molecules, rate coefficients for singly ionized triatomic hydrogen are needed in order to accurately model its interactions in the interstellar medium. Singly ionized triatomic hydrogen is studied using a quadrupole radio frequency ion trap coupled with a time of flight mass spectrometer. Singly ionized diatomic hydrogen is created by electron bombardment with diatomic hydrogen. H2+ and H3+ are then studied by ejecting the ions into an active-film electron multiplier. By variation of experimental parameters, systematic uncertainties are addressed and rate coefficients for the H2+ + H2 $\rightarrow$ H3+ + H at electron-volt energies are determined. [Preview Abstract] |
|
M1.00042: Ultra-cold electron collisions with the N$_2$H radical Brendan M. McLaughlin, Robert C. Forrey Ultra-cold electron collisions with the N$_2$H radical are presented. 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. Ultra-cold 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 from the eigenphase sums as a function of 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. Further details will be presented at the meeting. [Preview Abstract] |
|
M1.00043: MOLECULAR PHOTOIONIZATION, PHOTODETACHMENT, AND PHOTODISSOCIATION PROCESSES |
|
M1.00044: Time-resolved photoionization of superfluid He droplets Oleg Kornilov, Oliver Gessner, Chia Wang, Stephen Leone, Daniel Neumark Superfluid helium droplets are unique objects of active theoretical and experimental research. They serve as model few-body quantum systems representing a simplified structure of nuclei as well as ultracold nano-containers for investigation of embedded atoms and molecules. The methods applied to study He droplets range from mass spectrometry to elaborate laser spectroscopy techniques, which renedered many exciting results including demonstration of free rotations inside the droplets. One of the very inspiring questions in current research is the dynamics of ionization of Helium droplets. The available experimental approaches have not given a clear picture of an ionization event, and, most interestingly, on influence of superfluid, coherent nature of the droplet on the ionization dynamics. If present, such influence is expected at very short time-scale before droplet heats up and looses its undergoes transition to normal fluid. In this paper the novel method of femtosecond time-resolved photoelectron spectroscopy is applied to He droplets. High-order harmonic generation process is used to create femtosecond VUV pulses to trigger the photoionization event and IR pulses are used as a probe. Several transient channels are observed and possible mechanisms of energy exchange are discussed. [Preview Abstract] |
|
M1.00045: Subshell-resolved photoionization in the reciprocal space: Metal and noble gas atoms in a fullerene cage Matt McCune, Mohamed Madjet, Himadri Chakraborty Theory has predicted oscillations in the photoionization cross section of various atoms trapped in C$_{60}$. Most of the studies however modeled the confining shell by a simplistic one-active-electron potential. We recently established a method that treats the C$_{60}$ electrons in a sophisticated multi-electron frame based on the density functional theory [1]. Using this method, we perform calculations for noble gas atoms in C$_{60}$. In the past, the free C$_{60}$ photo cross section, which also shows oscillations, was analyzed by a Fourier-transform technique to determine the origin of the oscillation [2] and its dependence on the electron's rotational motion [3]. In the present work, we employ the Fourier analysis to unravel the interplay between specific ionization modes that induces oscillations in the cross section of a confined atom. The quality of oscillations is found to strongly differ from the outermost to an inner subshell. [1] Madjet et al., J. Phys. B \textbf{41}, 105101 (2008); [2] Ruedel et al., Phys. Rev. Letts. \textbf{89}, 125503 (2002); [3] McCune et al., J. Phys. B FTC \textbf{41}, 201003 (2008). [Preview Abstract] |
|
M1.00046: Time-independent and time-dependent calculations on one and two-photon ionization of diatomic molecules with a grid-based method in prolate spheroidal coordinates Liang Tao, C.W. McCurdy, T.N. Rescigno We show how to combine finite elements and the discrete variable representation in prolate spheroidal coordinates to develop a grid-based approach for quantum mechanical studies involving diatomic molecular targets. The use of exterior complex scaling in the present implementation allows for a transparently simple way of enforcing Coulomb boundary conditions and therefore straightforward application to electronic continuum problems. The time-independent and time-dependent calculations of photoionizaton cross sections for H$_2^+$, as well as time-independent results for the two-electron H$_2$ target, show that the efficiency and accuracy of the present approach offers distinct advantages over methods based on single-center expansions. [Preview Abstract] |
|
M1.00047: Break down of the two-step model in K-shell photoemission and subsequent decay in CO$_{2}$ Th. Weber, F. Sturm, M. Schoeffler, N. Neumann, T. Osipov, H.K. Kim, U. Lenz, A. Landers, L. Cocke, R. Doerner, A. Belkacem, S. Lee, K. Ueda Recently K. Ueda and coworkers measured at SPring8, Japan molecular-frame photoelectron angular distributions of the carbon 1s photoemission from CO$_{2}$. The electronic emission pattern displays a weak but definite asymmetry with respect to the central carbon atom around the shape resonance, suggesting a breakdown of the two-step model for the description of core-level photo-ionization and subsequent Auger decay. One possible explanation for this puzzling asymmetry is that the angular dependence of the outgoing photoelectron is modified by the instantaneous dipole moment of the vibrating CO$_{2}^{+}$ ion, registering information about its asymmetric vibrational motion at the time of photoejection. Prompt Auger decay may then initiate dynamics sensitive to the asymmetric geometry registered by the photoelectron. Using the COLTRIMS technique we tried to confirm the observation of the asymmetry and study its variation with photon energy, while measuring the Auger and photoelectrons in coincidence with the ionic fragments in order to pinpoint the origin of the breakdown in the expected symmetry of this process. We will show first results. [Preview Abstract] |
|
M1.00048: Observation of oscillations in the third dissociation continuum of molecular hydrogen Elizabeth F. McCormack, Deborah Farrington, Donald P. Fahey, Robert C. Ekey, Jr. Double resonance spectroscopy via the$EF{ }^1\Sigma _g^+ ,v'_{EF} =6,J'$ state has been used to probe the energy region of the H(n=1) + H(n=3) dissociation threshold. Above threshold the continuum is detected by ionizing H(n=3) to produce H+, which is then detected by using a time-of-flight mass spectrometer. A notable modulation is observed in the H+ production above threshold. This observed structure is thought to be due to an extension of the series of vibrational levels belonging to the inner and outer wells of the \textit{ungerade} double-well $B"\overline B $(3)${ }^1\Sigma _u^+ $state into the continuum above threshold. Comparisons with previously measured single photon absorption spectra and calculated photodissociation cross sections support this explanation. Just below threshold many transitions have been observed for the first time and assignments and term energies are reported. The new energy measurements presented here provide significant constraints on \textit{ab initio} calculations including nonadiabatic effects in the long-range $B"\overline B $(3)${ }^1\Sigma _u^+ $state of this fundamental system. [Preview Abstract] |
|
M1.00049: H$\alpha $ Fluorescence Intensity and Polarization from Photodissociated H$_{2}$, D$_{2}$ and HD J.R. Machacek, V.M. Andrianarijaona, J.E. Furst, T.J. Gay, A.L.D. Kilcoyne, A.L. Landers, K.W. McLaughlin We have measured the intensity and linear polarization of H$\alpha $ (n=3$\to $n=2) 656.3 nm fluorescence resulting from H and D atoms created by photodissociation of H$_{2}$, D$_{2}$ and HD using linearly-polarized photons with energies ranging from 16.5 to 17.6 eV. Between the threshold for atomic n=3 production at 16.6 eV and the n=4 production threshold at 17.3 eV, the relative cross section and polarization data are free from cascade contributions due to higher-lying atomic states. The photon beam energy width used for this work was 3 meV. Comparison of relative intensities to previous measurements [1] show marked differences. However, the polarization is in qualitative agreement. [1] H. Frohlich \textit{et al.}, Z. Phys. D \textbf{34}, 119 (1995). Support provided by the NSF (Grant PHY-0653379), DOE (LBNL/ALS) and ANSTO (Access to Major Research Facilities Programme). [Preview Abstract] |
|
M1.00050: Production of Excited Atomic Hydrogen from Methane J.R. Machacek, V.M. Andrianarijaona, J.E. Furst, T.J. Gay, A.L.D. Kilcoyne, A.L. Landers, K.W. McLaughlin We have measured the production of Ly$\alpha $ and H$\alpha $ fluorescence from atomic H for the photodissociation of CH$_{4}$ by linearly-polarized photons with energies between 20 and 65 eV. Comparison between our Ly$\alpha $ relative cross section and that previously reported [1] show different peak height ratios. This also occurs in the H$\alpha $ cross section when compared to previous data [2]. We do not observe as significant a drop in either cross section above 35 eV. Our measurements were taken with pressures two orders of magnitude lower than those used in ref. [1]. We present comparisons between data sets and a discussion of possible systematic effects. [1] H. Fukuzawa \textit{et al.}, J. Phys. B. \textbf{38}, 565 (2005). [2] M. Kato et al., J. Phys. B. \textbf{35}, 4383 (2002). Support provided by the NSF (Grant PHY-0653379), DOE (LBNL/ALS) and ANSTO (Access to Major Research Facilities Programme). [Preview Abstract] |
|
M1.00051: Progress towards measurement of the electron electric dipole moment using the PbF molecule: Continuous ionization of PbF Milinda Rupasinghe, Christopher McRaven, Poopalasingam Sivakumar, Neil Shafer-Ray The lead monofluoride molecule provides for a 1000- to 10,000- fold improvement in sensitivity to an electron electric dipole moment (e-EDM) over atomic-based measurements. In a pulsed laser detection scheme, the technique of resonance enhanced multi photon ionization (REMPI) is typically 100 to 10,000 times more sensitive than laser induced florescence (LIF). In a pseudo continuous detection scheme, much higher data collection rates can be achieved compared to a pulsed laser detection scheme. Here we present the recent data collected using a pseudo continuous ionization scheme. [Preview Abstract] |
|
M1.00052: Non-physical consequences of the Muffin-tin -- type intra-molecular potential Miron Ya. Amusia, Arkadiy Baltenkov We demonstrate that in the frame of muffin-tin -- like potential non-physical peculiarities appear in molecular photoionization cross-sections and other characteristics of this process that are a consequence of ``jumps'' in the potential and discontinuous of its derivative at some radius. The role of the size of this ``jumps'' is illustrated by choosing three values of the size of potential ``jumps''. The result obtained are tightly connected to the studied previously effect of the influence of non-analytical behavior of the potential acting upon a particle $U(r)$as a function of $r$on its photoionization cross-section. In reality, such potential has to be an analytic in magnitude and first derivative function of $r$. Introduction of non-analytic features in model $U(r)$leads to non-physical features in the corresponding cross-section -- oscillations, additional maxima etc. It is demonstrated here in the frame of a model of hydrogen atom surrounded by a barrier that for reasonable values of it leads to non-physical oscillations that are almost as strong as physical oscillations in the two-atomic molecule photoionization cross-section. [Preview Abstract] |
|
M1.00053: Orientation-dependent phenomena in photoelectron angular distributions due to strong-field ionization of laser-irradiated diatomic molecules Vladimir Usachenko, Pavel Pyak, Vyacheslav Kim, Shih-I Chu We report about orientation-dependent effects arising in molecular {\it photoelectron angular distributions} (PAD) due to well pronounced contribution from ionization of inner molecular valence shell(s) to strong-field above-threshold ionization of laser-irradiated homonuclear diatomic molecules ($N_{2}$, $O_{2}$ and $F_{2}$). In particular, our calculation results, obtained within the Density-Functional-Theory based Strong-Field-Approximation [V. I. Usachenko, P. E. Pyak and V. V. Kim {\em Phys. Rev.} A {\bf 79} 116901 (2009)], suggest that within the high-intensity field domain ($I \ge 3\cdot 10^{14}$ $W/cm^{2}$) the molecular ionization dynamics for internuclear axis orientation angles $\pi/3 \le \Theta \le 2\pi/3$ (with respect to the incident laser field polarization) does become very pronounced and manifested by the well predominant contribution rather from the $1\pi_{u}$ inner shell than from the {\it highest occupied molecular orbital} (HOMO) ($3\sigma_{g}$ in $N_{2}$ or $1\pi_{g}$ in $O_{2}$ and $F_{2}$, normally predominantly contributing under standard cases). [Preview Abstract] |
|
M1.00054: ATOM-ATOM AND ATOM-MOLECULE COLLISIONS |
|
M1.00055: Absolute atomic collision cross section measurements using Rb atoms confined in magneto-optic and magnetic traps David Fagnan, J. Wang, B.G. Klappauf, J.L. Booth, K.W. Madison We present an experimental study of a technique to measure absolute total collision cross sections using laser cooled $^{85}$Rb and $^{87}$Rb atoms confined in either a magneto-optic or a magnetic quadrupole trap. Atom loss from the trap is caused by collisions with room temperature atoms of either He or Ar introduced into the vacuum cell, and the total collision cross section is inferred from knowledge of the residual gas density. The loss rates from magneto-optic (MOT) and pure magnetic traps are compared and significant differences are found. In contrast to previous work by Matherson \emph{et.~al.}[Phys. Rev. A 78, 042712 (2008)], we find that the cross section for trap loss inducing collisions in a MOT depends on the trap laser detuning, casting doubt on the reliability of this technique for traps based on dissipative, radiation pressure forces. The loss inducing collisions in a pure magnetic trap are studied for different low-field seeking spin states, and, unlike for a MOT, we find that the collision rates appear to be independent of trap depth. We also find for He or Ar background gas that the collision cross sections depend on the particular isotope and atomic spin state of the magnetically trapped rubidium. [Preview Abstract] |
|
M1.00056: Measurement of the Fine Structure Mixing Cross-Section for Rubidium in the Presence of Helium Buffer Gas Brian Patterson, Gregory Jemo, Ryan Meeter, Jerry Sell, Randy Knize We report measurements of the cross-section for collisional excitation transfer between the $^{5}P_{1/2 }$and $^{5}P_{3/2 }$states of rubidium in the presence of a helium buffer gas for a range of helium pressures. The measurements were carried out using selected femtosecond pulses from a mode-locked Ti:Sapphire laser tuned to the D2 transition of rubidium. Fluorescence from both the D1 and D2 transitions was detected using time-correlated single photon counting. The $^{5}P_{3/2 }\to $ $^{5}P_{1/2 }$mixing cross section was determined by fitting the fluorescence data to the analytic solutions of the rate equations for a three-level system. The measurements were repeated using pump light tuned to the D1 transition of rubidium and for helium pressures of 1, 2, and 3 atm. [Preview Abstract] |
|
M1.00057: Nonlinear Pressure Shifts of Rubidium in Inert Gases Bart McGuyer, Yuan-Yu Jau, William Happer Vapor-cell atomic frequency standards are based on the hyperfine (microwave) magnetic-resonance frequencies of optically pumped alkali-metal atoms in inert buffer gas. Through the hyperfine-shift interaction, buffer gas induces pressure shift and broadening in these microwave resonances. Previous work uncovered nonlinear dependence in the pressure shifts of $^{87}$Rb and Cs atoms to the pressure of buffer gases Ar and Kr, but not He or N$_{2}$. The nonlinearity is thought to result from alteration to the hyperfine-shift interaction due to temporary van der Waals molecules formed between alkali-metal and buffer-gas atoms. We investigate nonlinear pressure shifts for both isotopes of Rb, $^{87}$Rb and $^{85}$Rb. This study will test the current model for nonlinear pressure shifts of alkali metals in inert gases. [Preview Abstract] |
|
M1.00058: Effects of Electric Fields on Heteronuclear Feshbach Resonances in Ultracold $^6\rm{Li}-^{87}\rm{Rb}$ Mixtures K.W. Madison, Z. Li Magnetic Feshbach resonances (FRs) provide a powerful tool to control microscopic interactions in ultracold atomic gases. Recent theoretical work has demonstrated the possibility of inducing FRs in heteronuclear atomic mixtures by applying a static electric field. The mechanism is based on the interaction of the instantaneous dipole moment of the collision complex with the external electric field. Recently, we have generated accurate singlet and triplet interaction potentials for ultracold collisions in $^6$Li--$^{87}$Rb mixtures based experimental measurements. We use these potentials to investigate the effects of external electric fields on elastic collisions in ultracold Li--Rb mixtures. We report on a number of fascinating phenomena including the observation that the electric field induces a coupling which breaks the degeneracy of states with non-zero angular momentum producing multiple FRs. Recently it was observed that magnetic dipole-dipole interactions can produce a similar effect, splitting a $p$-wave Feshbach resonance into a doublet corresponding to the magnitude of the projection of the orbital angular momentum onto the field axis. The major difference here is that the splitting is continuously tunable using an applied electric field and more than an order of magnitude larger. [Preview Abstract] |
|
M1.00059: Formation of heavy Rydberg ion-pair states in collisions of K($n$p) Rydberg atoms with attaching targets M. Cannon, C. Wang, F.B. Dunning The formation of heavy-Rydberg ion-pair states through electron transfer in collisions between K($n$p) Rydberg atoms and molecules that attach low-energy electrons is investigated. The measurements show that low-$n$ collisions with a wide variety of target species (SF$_{6}$, c-C$_{7}$F$_{14}$, C$_{6}$F$_{6}$, and CCl$_{4})$ can lead to formation of bound ion-pair states and that, under appropriate conditions, a small fraction of these can subsequently dissociate as free ions through conversion of internal energy in the negative ion into translational energy of the product ion pairs. The lifetimes of those ion pairs that do dissociate are typically $\sim $ 1-5 $\mu $s. The data are analyzed using a semi-classical Monte Carlo collision model which shows that many of the bound ion pairs pass relatively close to one another facilitating energy conversion (and charge transfer). Work is in hand to detect ion-pair states directly through electric-field-induced dissociation and examine their properties in more detail. [Preview Abstract] |
|
M1.00060: Complex scattering length trends for rotationally-excited molecules in ultracold collisions with He Benhui Yang, Jeff Nolte, P. Stancil, R. Forrey, N. Balakrishnan The study of atom-molecule collisions in the ultracold regime has attracted substantial attention in recent years with an interdisciplinary impact on physics, chemistry, and quantum computation. These two-body collisions are governed by $s$-wave scattering with inelastic quenching processes becoming important for high internal excitation. In this work, quantum close-coupling scattering calculations are performed for rotationally-excited linear molecules (H$_2$, HD, CO, O$_2$, and CO$_2$) and non-linear molecules (H$_2$O, NH$_3$, and CH$_4$) due to collisions with He. The results are given in terms of the ratio of the imaginary part of the scattering length $\beta$ to the real part $\alpha$ which give measures of inelastic and elastic probabilities, respectively. For linear molecules, the ratio $\beta / \alpha$ generally increases with decreasing rotational constant. Conversely, $\beta /\alpha \sim 0.1$ for all of the considered non-linear molecules, nearly independent of rotational excitation. Such a large ratio, indicating significant quenching, suggests that these non-linear molecules would not be good candidates for cooling and trapping experiments. [Preview Abstract] |
|
M1.00061: Polarization Spectroscopy and Collisions in NaK C.M. Wolfe, S. Ashman, J. Huennekens, B. Beser, J. Bai, A.M. Lyyra We report current work to study transfer of population and orientation in collisions of NaK molecules with argon and potassium atoms using polarization labeling (PL) and laser-induced fluorescence (LIF) spectroscopy. In the PL experiment, a circularly polarized pump laser excites a specific NaK $A^{1}\Sigma^{+}$($v$=16, $J$) $\leftarrow$ $X^{1}\Sigma^{+}$($v$=0, $J\pm1$) transition, creating an orientation (non-uniform $M_{J}$ level distribution) in both levels. The linear polarized probe laser is scanned over various $3^{1}\Pi$($v$=8, $J' \pm1) \leftarrow$ $A^{1}\Sigma^{+}$($v$=16, $J'$) transitions. The probe laser passes through a crossed linear polarizer before detection, and signal is recorded if the probe laser polarization has been modified by the vapor (which occurs when it comes into resonance with an oriented level). In addition to strong direct transitions ($J'$ = $J$), we also observe weak collisional satellite lines ($J'$ = $J\pm n$ with $n$ = 1, 2, 3, ...) indicating that orientation is transferred to adjacent rotational levels during a collision. An LIF experiment (with linear polarized pump and probe beams) gives information on the collisional transfer of population. From these data, cross sections for both processes can be determined. We experimentally distinguish collisions of NaK with argon atoms from collisions with alkali atoms. [Preview Abstract] |
|
M1.00062: Noble gas quenching of rovibrationally excited H$_2$ Bradley C. Hubartt, N. Balakrishnan, Luke Ohlinger, Robert C. Forrey Collisions between noble gas atoms and hydrogen molecules are investigated theoretically by solving the time-independent Schr\"odinger equation. Various initial states of the molecule are considered and the calculations are performed for each system over a large range of collision energies. Cross sections for quenching of rovibrationally excited states of H$_2$ are reported for Ar and Kr colliders and comparisons are made with previous calculations involving He. Trends in the energy dependence for the heavier systems are very similar, including resonance behavior, which suggests that the dynamics involving heavy noble gas atoms are less sensitive to the fine details of the potential. [Preview Abstract] |
|
M1.00063: Ytterbium atom-ion Collisions Peng Zhang, Alexander Dalgarno, Robin Cote Studies of the charge transfer process in collisions of ytterbium atoms (Yb) with ytterbium ions (Yb$^{+})$ at cold and ultracold temperatures are reported. The molecular potential energy curves, $^{2}\Sigma _{g}^{+}$ and $^{2}\Sigma _{u}^{+}$, of Yb$_{2}^{+}$ are determined at the multi-reference averaged quadratic coupled cluster level of theory with the long range polarization potential described by the accurate dipole polarizability of 142 a.u.. The calculated cross sections are large in the limit of low temperature and show considerable structures that arise from a combination of shape resonances modulated by glory oscillations and Regge oscillations. The thermally averaged charge transfer rate coefficients are in good agreement with the results from a recent experiment and with the Langevin formula at temperatures below 100 K. The scattering lengths for various isotopes computed both from semi-classical theory and from fitting to the effective range expansion are reported and agree well with each other. For higher temperatures, we compare quantal and semiclassical results, and investigate the range of applicability of the Langevin formula. [Preview Abstract] |
|
M1.00064: COLLISIONS INVOLVING CLUSTERS |
|
M1.00065: Complexity in the ionization dynamic of Helium dimers M.S. Sch\"{o}ffler, J. Titze, H.-K. Kim, R.E. Grisenti, N. Neumann, L. Ph. H. Schmidt, O. Jagutzki, H. Schmidt-B\"{o}cking, R. D\"{o}rner Helium dimers (He$_2$) are a Van-der-Waals bound system and the most extreme quantum matter in AMO physics with a binding energy below 0.1 $\mu$eV (1.1 mK). Its internuclear distance varies from 2 to several hundreds Angstrom (larger than a C60 fullerene). Their existence was predicted theoretically by Slater in 1928 and the experimental prove followed 1994 by Sch\"{o}llkopf in a diffraction experiment. Single and double charged projectiles with energies of 25 - 150 keV/u were used to fragment the Helium dimer into two He$^+$-ions. Using the COLTRIMS (COLd Target Recoil Ion Momentum Spectroscopy) imaging technique we measured the three dimensional momentum vector of all fragments (He$^+$-ions and emitted electrons). We found different fragmentation/decay mechanisms, one involving the inter atomic coulombic decay (ICD). [Preview Abstract] |
|
M1.00066: DFT Optimization of Symmetric Be$_{2}$Si Cage Clusters Robert Binning, Daniel Bacelo Density functional theory calculations have been performed on several beryllium silicide cage clusters in which the atoms occupy the vertices of classic Archimedean solids. The BPW91 functionals with numerical basis sets were employed in the optimizations. The calculations were carried out to confirm the hypothesis that stable Be$_{2}$Si clusters may be obtained by substituting Si for Be atoms in stable pure beryllium clusters. Stable beryllium clusters are obtained from symmetrical Be$_{n}$ polyhedra in which sides are triangular or capped pentagonal, and the Archimedean clusters composed of these elements with Si substitutions are indeed found to produce stable beryllium silicides. [Preview Abstract] |
|
M1.00067: COHERENT CONTROL |
|
M1.00068: Hamiltonian Monodromy: Unexpected behavior of atoms in traps J.B. Delos, G. Dhont, D. Sadovskii, B. Zhilinskii A system exhibits monodromy if we take the system around a closed loop in its parameter space, and we find that the system does not come back to its original state. Many systems have this property, including hydrogen in crossed fields, cylindrically symmetric barrier systems, such as the ``mexican hat'' potential, the spherical pendulum, dipolar molecules in fields, and near-linear molecules. Atoms in a trap can display a newly discovered dynamical manifestation of monodromy. We show the behavior in computations, and provide a theoretical explanation. [Preview Abstract] |
|
M1.00069: An Experimental Scheme for Observing Dynamical Monodromy with Ultra-Cold Atoms M.K. Ivory, J.B. Delos, S. Aubin We propose an experimental scheme based on trapped ultra-cold atoms for observing the recently predicted phenomenon of dynamical monodromy. It occurs when an ensemble of trajectories forming a loop of initial conditions evolves continuously in time into a topologically different loop with the same total energy and angular momentum as the original ensemble. Unlike classical particles, using ultra-cold atoms allows one to quantum mechanically freeze out internal properties of the particles. Atom-atom interactions can be suppressed using K39 and a Feshbach resonance. The atoms can be contained using an optical dipole trap formed from blue- and red-detuned lasers creating a donut-shaped potential. The energy of the center peak can be changed by increasing or decreasing the power of the blue-detuned laser. The angular momentum of the particle can be controlled by a rotating magnetic field. By controlling these external potentials, one can manipulate the energy and angular momentum of the atoms to generate the closed path in energy-angular momentum space that is necessary for producing dynamical monodromy. [Preview Abstract] |
|
M1.00070: Experimental demonstration of painting arbitrary and dynamic potentials for Bose-Einstein condensates Kevin Henderson, Changhyun Ryu, Calum MacCormick, Malcolm Boshier There is a pressing need for robust and straightforward methods to create potentials for trapping Bose-Einstein condensates which are simultaneously dynamic, fully arbitrary, and sufficiently stable to not heat the ultracold gas. We show here how to accomplish these goals, using a rapidly-moving laser beam that ``paints'' a time-averaged optical dipole potential in which we create BECs in a variety of geometries, including toroids, ring lattices, and square lattices. Matter wave interference patterns confirm that the trapped gas is a condensate. As a simple illustration of dynamics, we show that the technique can transform a toroidal condensate into a ring lattice and back into a toroid. The technique is general and should work with any sufficiently polarizable low-energy particles. [Preview Abstract] |
|
M1.00071: VIBRATIONAL AND ROTATIONAL MOLECULAR COHERENCE |
|
M1.00072: Orientation-Dependent Multiphoton Ionization of Diatomic Molecules: Many-Electron Time-Dependent Density Functional Approach Dmitry Telnov, Shih-I Chu We present time-dependent density functional calculations of multiphoton ionization (MPI) of diatomic molecules N$_{2}$, O$_{2}$, and F$_{2}$ with arbitrary orientation of the molecular axis by intense linearly-polarized laser pulses with the wavelength 800~nm. For the peak intensity $1\times 10^{14}$~W/cm$^{2}$, the inner shells contributions to the MPI probability are quite significant for N$_{2}$ molecule, particularly at intermediate angles, while for O$_{2}$ the highest-occupied molecular orbital contribution is still dominant. Our calculations performed on F$_{2}$ molecule at the peak intensities $2\times 10^{14}$~W/cm$^{2}$ and $1\times 10^{15}$~W/cm$^{2}$ show that the effect of the inner shell electrons on MPI becomes more important with increasing intensity of the laser field, and orbital switching may occur: the contributions of spin orbitals with larger ionization potentials exceed those of spin orbitals with smaller ionization potentials. The orientation dependence of the total MPI probability becomes more isotropic for stronger laser field. [Preview Abstract] |
|
M1.00073: Role of multiple orbital dynamics in multiphoton ionization of CO$_2$ in strong laser fields: The time-dependent Voronoi-cell finite difference method Sang-Kil Son, Shih-I Chu We theoretically investigate multiphoton ionization (MPI) of carbon dioxide in strong linearly-polarized laser pulses as a function of the angle between the molecular orientation and the field polarization. For a multicenter singularity problem in polyatomic molecules, we develop a new time-dependent Voronoi-cell finite difference (TDVFD) method with highly adaptive molecular grids. Many-electron time-dependent density functional calculations are performed by TDVFD, taking into account the detailed electronic structure and responses in multiple orbital dynamics. Our results show that the angular dependence of MPI is reflected by the perturbed orbital symmetry of multiple orbitals. The maximum peak of MPI is calculated at 40 degree in fair agreement with the recent experiment, which is significantly deviated from previous theories based on the single active electron approximation. [Preview Abstract] |
|
M1.00074: Ultrafast plasma dynamics in rare gas clusters Jan Michael Rost, Ionut Georgesc, Alexey Mikaberidze, Ulf Saalmann We study two cases of ultrafast electron plasmas in rare gas clusters. In the first one a pump-probe scenario with two 250 attosecond pulses (40 eV photon energy) is used [1] to generate and probe a plasma of a few electrons in a small Ar$_13$ cluster. We discuss the properties of this minimal plasma. In the second case we subject a rare gas cluster to a regular strong laser pulse (800 nm wavelength). A plasma of cigar shape is ignited in the cluster by some seed atoms with lower ionization potential than those of the cluster. Linear or elliptic polarization of the laser can be applied, only changing the shape of the plasma, which is non-spherical in both cases. This is important to ignite the plasma in the first place, which is an ultrafast process since it does not require nuclear motion [2]. \\[4pt] [1] Ulf Saalmann, Ionut Georgescu and Jan M. Rost, New J. Phys. 10, 025014 (2008).\\[0pt] [2] Alexey Mikaberidze, Ulf Saalmann, Jan M. Rost, submitted (2009). [Preview Abstract] |
|
M1.00075: Determining the absolute phase and intensity of a two-color laser field D. Ray, W. Cao, Z. Chen, S. De, H. Mashiko, P. Ranitovic, C.D. Lin, I.V. Litvinyuk, C.L. Cocke, M.F. Kling, G.G. Paulus The left-right asymmetry of electron emission from single atoms by intense few-cycle 800 nm pulses is well known and forms the basis of the stereo-phasemeter method$^{1}$ of measuring the carrier-envelope phase of short pulses. Here we report experiments which demonstrate a similar asymmetry caused by the superposition of two colors (800 and 400nm) forming many-cycle pulses. We obtain Xe spectra as a function of the phase between the two colors. The spectra exhibit a pronounced left-right asymmetry as a function of phase in both the ``direct'' and the ``plateau'' regions of electron energy. Recently established quantitative rescattering theory (QRS) allows us to analyze momentum images of the rescattering (plateau) high-energy electrons. Using QRS theory we can determine accurately the laser peak intensity and the absolute phase of the two-color electric field. Our results also agree with semi-classical calculations. $^{1}$G. G. Paulus et al., PRL \textbf{91}, 253004 (2003). [Preview Abstract] |
|
M1.00076: A multi-electrode velocity-map imaging apparatus to study laser induced molecular dynamics S. De, D. Ray, N.G. Johnson, I. Bocharova, M. Magrakvelidze, C.L. Cocke, I.V. Litvinyuk, I. Znakovskaya, A. Wirth, M.F. Kling We have designed and built a multi-electrode VMI spectrometer capable of detecting up to 300 eV electrons with good momentum resolution. The spectrometer is based on an original design which utilizes a multiple electrostatic lens system to contain the high energy electrons, while maintaining good volume focusing. The spectrometer is used together with super-sonic atomic and molecular jet gas targets in the J. R. Macdonald Laboratory. We measured 3D momentum distributions of ATI electrons produced by intense femtosecond laser pulses to determine the resolution of the spectrometer experimentally and compare the result to Simion calculations. We will present first results on using this device to record phase dependent control of electron localization in the dissociative ionization of simple molecules in two-color intense laser fields and the dynamic alignment and orientation of carbon monoxide after excitation by a two-color laser field. [Preview Abstract] |
|
M1.00077: Adiabatic Floquet representation of atomic systems J.V. Hern\'andez, Yujun Wang, B.D. Esry The adiabatic Floquet method has been successfully used to study simple molecular systems such as H$_2^+$ for several years now. This poster presents an adiabatic Floquet picture for atomic systems. Adiabatic potential curves are thus generated for both atomic hydrogen and helium that incorporate the laser field nonperturbatively. As for H$_2^+$, these potentials can be used to develop an intuitive picture of atomic multiphoton processes. We also show how the potentials can be produced for two-color pulses. Numerical solutions of the time-dependent Schr\"odinger equation are interpreted using the adiabatic Floquet potentials to gauge the utility of this new representation. [Preview Abstract] |
|
M1.00078: Genetic-algorithm implementation of atomic potential reconstruction from differential electron scattering cross sections Junliang Xu, Zhangjin Chen, Hsiao-Ling Zhou, Chii-Dong Lin We demonstrate the successful implementation of genetic algorithm for the retrieval of atomic potentials using elastic differential cross sections (DCS) between free electrons and atomic ions for electron energies from a few to several tens of electrons volts. Since the DCS over this energy region can be extracted from laser-generated high-energy photoelectron momentum spectra, the results suggest that infrared lasers can be used to image the target structure. Extending to molecular targets, in particular, to transient molecules created by an earlier pump pulse, our results suggest that few-cycle infrared probe lasers can be used for dynamic chemical imaging with temporal resolution of a few femtoseconds. [Preview Abstract] |
|
M1.00079: Charge Transfer Molecular Rotor DCVJ Investigated by Coherent Anti-Stokes Raman Spectroscopy Laszlo Ujj, Scott Miller, Jonathan Welch, Charles Amos, Chandra Prayaga Coherent anti-Stokes Raman Spectroscopy (CARS) has been shown to be one of the most powerful experimental methodologies for obtaining vibrational information from both stable and transient molecular species$^{1}$. The electronically enhanced polarization sensitive version of CARS is even more effective for measuring molecular vibrational information not easily reachable by spontaneous Raman spectroscopy. Theoretical and experimental principles associated with CARS with an emphasis on points relevant to the interpretation of experimental spectra will be presented. The method is applied to measure the vibrational manifold of DCVJ for the first time. DCVJ is a charge transfer molecular rotor showing a viscosity dependent fluorescence quantum yield. Based upon the measured CARS spectra, the effect of inhibition of the internal rotation on the vibrational motion of the molecule will be discussed. The design and operation of an all solid-state broadband nanosecond CARS system will be also presented. An overview of applications of molecular rotors in biology and information technology will be outlined. Ref.: \textbf{1}. L. Ujj and G. H. Atkinson, ``Coherent Anti-Stokes Raman Spectroscopy'', in Handbook of Vibr. Spect., Wiley {\&} Sons, Ltd., (2002). [Preview Abstract] |
|
M1.00080: Spontaneous vs. Coherent Raman Scattering: A Comparison Under Biologically Relevant Conditions Sarah R. Nichols, Brandon R. Bachler, Meng Cui, Jennifer P. Ogilvie Coherent anti-Stokes Raman scattering (CARS) microscopy has become an active field of research due to the intrinsic molecular contrast it provides. Coherent signals such as CARS have been shown to be orders of magnitude larger than those obtained with spontaneous Raman scattering under certain conditions. However, under conditions appropriate for biological imaging, there has been a lack of systematic comparison between spontaneous and coherent Raman scattering signals. We perform such a comparison imaging study on polystyrene beads and find comparable signal levels for coherent Stokes Raman scattering (CSRS) and spontaneous Stokes scattering, contrary to many reports in the CARS microscopy literature. We present calculations to support the measurements, and discuss the implications for biological imaging. The advantages provided by coherent methods are mitigated in biological samples by the low incident power ($\sim $1mW), short interaction lengths, and low concentrations. The nature of the sample and the necessary imaging conditions must be considered when choosing between coherent and spontaneous Raman methods. [Preview Abstract] |
|
M1.00081: Electromagnetic Enhancement Factor of Surface-enhanced Raman Scattering of Rh6G Molecules on Au Nanoparticles JaeTae Seo, Wanjoong Kim, Sungsoo Jung Surface-enhanced Raman spectroscopy (SERS) of molecules on nanometals has been intensively studied for technical application of bio-chemical sensing. Among physical origins of SERS enhancement, the electromagnetic effect is the most fundamental contribution of SERS enhancement. Relevant REF of C-C stretching mode of Rh6G near 1511 cm$^{-1}$ was shown two-order enhancement with 5-nm Au colloidal nanoparticles. The REF was greatly enhanced up to $\sim $six orders with $\sim $35 nm Au particles, and was enhanced $\sim $five orders with 40-nm Au nanoparticles. The reduction of REF with smaller sizes is possibly due to the scattering of conduction electrons on particles surfaces; that with larger sizes is probably due to tips or complex structures. This work at Hampton University was supported by the National Science Foundation (HRD-0734635, HRD-0630372, and ESI-0426328/002) and the U.S. Army Research Office (W911NF-07-1-0608). [Preview Abstract] |
|
M1.00082: COLD ATOMS, MOLECULES, AND PLASMAS |
|
M1.00083: Towards production of Bosonic $^{41}$K$^{87}$Rb molecule in a 3-dimensional optical lattice Jun Kobayashi, Tetsuo Kishimoto, Kai Noda, Yousuke Fujikake, Yoshiyuki Yamariku, Masahito Ueda, Shin Inouye One of the major goals in the field of ultracold gases is the production of ultracold polar molecules. Due to anisotropic, long range interaction, a polar molecular gas is expected to show us a rich variety of new phenomena, including anisotropic collapse and a super-solid phase. Last year, JILA group have successfully created a high-phase space density gas of Fermionic polar molecules $^{40}$K$^{87}$Rb in the absolute ground state[1] Our goal is to explore a degenerate gas of Bosonic polar molecules. We prepare ultracold atomic gas mixture of $^{41}$K and $^{87}$Rb, and combine those atoms adiabatically to form molecules. Previously, we explored the basic properties of a gas of $^{41}$K, producing a $^{41}$K BEC of 3x10$^{5}$ atoms with a direct evaporation[2]. Here we report production of a quantum degenerate mixture of $^{87}$Rb and $^{41}$K atoms. This quantum degenerate mixture of atoms should be converted into Bosonic polar molecules in the absolute ground state via combination of Feshbach association and STIRAP performed in a 3D optical lattice. [1] K.-K. Ni et al., Science 322, 231 - 235 (2008) [2]T. Kishimoto et al., arXiv:0812.4335 (2008) [Preview Abstract] |
|
M1.00084: Trap lifetime study of ultracold ground-state KRb molecules D. Wang, S. Ospelkaus, K.-K. Ni, M.H.G. de Miranda, B. Neyenhuis, D.S. Jin, J. Ye We have produced near quantum degenerate $^{40}$K$^{87}$Rb polar molecules in their rovibrational ground state using magneto-association followed by STIRAP transfer. Preliminary measurements show that trap lifetime of these fermion molecules is limited to $\sim$ 100 ms. We are investigating the KRb loss in the presence of either K or Rb atoms to look for evidence of chemical reactions at ultracold temperatures. This work is supported by the NSF and NIST. [Preview Abstract] |
|
M1.00085: Preliminary results on a new method for producing ultracold molecular ions Wade Rellergert, Kuang Chen, Scott Sullivan, Eric Hudson We describe a new method for the production of ultracold molecular ions. This method utilizes sympathetic cooling due to the strong collisions between appropriately chosen molecular ions and laser-cooled neutral atoms to realize ultracold, internal ground-state molecular ions. In contrast to other experiments producing cold molecular ions, our proposed method efficiently cools both the internal and external molecular ion degrees of freedom. Preliminary results from experiments aimed at cooling trapped molecular ions using an Yb MOT are presented. [Preview Abstract] |
|
M1.00086: Toward Trapped Ultracold Molecules in the Absolute Ground State Nathan Gilfoy, Stephan Falke, Colin Bruzewicz, Eric Hudson, David DeMille We report on experimental efforts toward the coherent transfer of optically trapped RbCs molecules to their absolute, singlet ground state. Beginning with spin-polarized Rb and Cs atoms, heteronuclear molecules are formed by photoassociation and decay into high vibrational levels of the triplet ground state. The molecules can be transferred to the absolute ground state, which possesses a large electric dipole moment, via an electronically excited level of mixed singlet and triplet character. A two-photon-transfer process was previously demonstrated in our lab with pulsed lasers. We have implemented a high power cw diode laser system in order to resolve and control the rotational and hyperfine structure. Further, the transfer can be made coherent by applying a StiRAP scheme. We report on the results of high resolution spectroscopy for level selection of the coherent transfer of optically trapped molecules. [Preview Abstract] |
|
M1.00087: Ultracold molecules based on two-electron atoms Gael Reinaudi, Klejda Bega, Tanya Zelevinsky Ultracold diatomic molecules offer exciting possibilities for studies of novel states of matter, quantum information, and precision measurements. Two-electron-atom based molecules are particularly promising for precision measurements, such as variations of the proton-electron mass ratio. They are expected to be efficiently produced via photoassociation on singlet-triplet transitions. Heteronuclear molecules based on the two-electron alkaline-earth-like atoms are likely to have a reasonably large dipole moment, and are interesting for quantum information and studies of long-range interactions in ultracold quantum gases. We present the construction of an experimental apparatus to cool, trap, and manipulate either single or mixed species of two-electron atoms (Sr, Yb) in an optical lattice, as well as the most efficient pathways to ultracold molecule formation with these species. [Preview Abstract] |
|
M1.00088: Prospects for aligning ultra-cold molecules via magnetic sublevel dependent ac Stark effect Jianbing Qi We study the population dynamics of a three-level molecular system coupled by two lasers using density matrix equations. In a molecular transition, the coupling laser induced ac Stark effect influences the magnetic sublevel differently and the transition line strength depends on the angular momentum of the molecular states as well as the photon's polarization. The individual magnetic sublevel population can be controlled by the amplitude and detuning of the coupling laser. This provides a spectroscopic means of isolating individual magnetic sublevel and thereby of producing aligned or even oriented molecules. We propose an experimental scheme to observe this effect in an ultra-cold molecule system. [Preview Abstract] |
|
M1.00089: Generation and Spectroscopy of LiRb Molecules: towards coherent optical control with multi-photon photo-association John Lorenz, Adeel Altaf, Sourav Dutta, Ping Wang, Daniel Elliott, Yong Chen We report on our progress in studying the formation and manipulation of polar LiRb molecules photo-associated in a dual species Rb-85/Li-7 magneto-optical trap (MOT). Spectroscopic techniques will allow determination of the rovibronic structure of these molecules. The internal states of the resulting LiRb molecules will be manipulated using coherent optical interactions. We aim to achieve optically-based local control of the density and the rotational superposition states of these molecules, thereby controlling the dipole-dipole interaction between adjacent LiRb molecules. Ultimately, we are interested in using these techniques to establish grounds for quantum logic gates based on such polar molecules. [Preview Abstract] |
|
M1.00090: Achieving Ground Polar Molecular Condensates by a Chainwise Atom-Molecule Adiabatic Passage Jing Qian, Weiping Zhang, Hong Y. Ling A chainwise stimulated Raman adiabatic passage (STIRAP), characterized with a single STIRAP between the initial and final lasers, is generalized from a pure multistate molecular to a coupled multi-level heteronuclear atom-molecule system where the role of the initial transition is played by photoassociation. Special attention is given to the relative strength between different intermediate lasers, a control knob inaccessible to the usual three-level systems. Discussions have been focused on how this control, when combined with the stability inherent of the atom-molecule STIRAP, may serve as a new tool in fighting against the weakness of photoassociation, making the proposed scheme attractive to experimental endeavors for creating ground polar molecule condensates. [Preview Abstract] |
|
M1.00091: Towards Ultracold Mixtures and Molecules of Lithium and Ytterbium Atoms Subhadeep Gupta, Anders Hansen, Alexander Khramov, Jana Smith Exquisite control of interactions between ultracold atoms is possible using scattering resonances. Ultracold diatomic molecules can also be formed using Feshbach and photoassociation resonances. Applying these methods between two different atomic species can lead to novel quantum phases of matter. These include Fermi superfluids with mass imbalance and strongly dipolar molecular superfluids. Further, stable ultracold dipolar molecular samples are promising systems for precise tests of fundamental symmetries and time variations of fundamental constants. We will report on progress towards building a system of ultracold lithium and ytterbium atoms to achieve these goals. [Preview Abstract] |
|
M1.00092: ULTRACOLD COLLISIONS AND PHOTOASSOCIATION |
|
M1.00093: Inelastic collisions in cold dipolar gases Catherine Newell, Michael Cavagnero Two elementary models of molecular structure are used to investigate inelastic collisions in cold trapped dipolar gases--first a two-state model of a polar molecule and then a three-state model consisting of a rotor molecule in an electric field. Cross sections and rate constants, calculated semiclassically, yield dramatically different results for the two types of dipoles. In particular, the two state model predicts collision rates proportional to $d^2$ where $d$ is the intrinsic dipole moment, while the rotor model gives collision rates proportional to $\mu^2$ where $\mu$ is the field-dependent induced dipole moment. Both elastic and inelastic scattering of the two-state dipoles peaks for low-values of the applied field, while the cross sections vanish at low fields for rotor dipoles. [Preview Abstract] |
|
M1.00094: Resonant Coupling in the Heteronulcear Alkali Dimers for Direct Photoassociative Formation of X $^1\Sigma^+$ v$''$= 0 Ultracold Molecules Jayita RayMajumder, Michael Bellos, Ryan Carollo, Matthew Recore, Michael Mastroianni, William Stwalley, Edward Eyler, Phillip Gould We have studied the resonant coupling between rovibronic levels of different electronic states for the ten heteronuclear alkali dimers formed from combinations of Li, Na, K, Rb, and Cs. We focus on the energy range $<$ 100 cm$^{-1}$ below the lowest two excited asymptotes, which is relevant for photoassociative molecule formation. Within this range, we concentrate on coupled levels that have good Franck-Condon overlap with the absolute rovibronic ground state, X(v=0, J=0). We will present promising schemes for directly forming ultracold X(0,0) dimers by single-photon photoassociation followed by spontaneous emission, as recently demonstrated for LiCs\footnote{Deiglmayr, et al., Phys. Rev. Lett. 101, 133004 (2008)}. [Preview Abstract] |
|
M1.00095: Forming ultracold LiK molecules from Li-K mixtures Sandipan Banerjee, Marko Gacesa, Robin C\^ot\'e We present a theoretical study of scattering properties of ultracold Li + K in an external magnetic field. Based on the isotopes involved, Li-K mixtures can have a fermi-fermi, fermi-bose or bose-bose symmetry. We use the best available molecular potentials adjusted to reproduce recent measurements of Feshbach resonances in a $^6$Li-$^{40}$K mixture\footnote{E.Wille et.al. PRL 100, 053201 (2008)} to accurately predict the positions of Feshbach resonances and other scattering properties in remaining isotopic mixtures. The effect of higher partial waves in those cases is discussed. We suggest a scheme for photoassociative formation of ultracold LiK molecules in their lowest ro-vibrational levels in the molecular ground state. [Preview Abstract] |
|
M1.00096: Coherent Control of Ultracold Collisions with Nonlinear Frequency Chirps: Experiment and Simulations J.A. Pechkis, J.L. Carini, C.E. Rogers III, P.L. Gould We report on measurements and simulations of ultracold collisions between Rb atoms induced by frequency-chirped laser light. Either positive or negative chirps, centered at a variable detuning below the atomic resonance, sweep over 1 GHz in 100 ns. If the light is resonant with an attractive atom-pair potential at some point during the 40 ns chirped pulse, the pair is excited, potentially resulting in trap loss. In previous work with linear chirps,$^{1}$ the negative chirp yielded a lower collisional loss rate $\beta$ than the positive chirp at certain center detunings. We attribute this to the fact that the negative chirp follows the excited-state wavepacket trajectory and, thus, can de-excite the wavepacket, coherently blocking the collision. In the present work, we use nonlinear chirps, either concave-down or concave-up. For the negative chirp, we find a dependence on the details of the nonlinearity under conditions where coherent collision blocking occurs. In particular, the concave-down chirp yields a higher $\beta$ than the linear and concave-up chirps, a trend supported by quantum mechanical simulations of the collision process. Our results indicate the importance of the shape of the frequency chirp on the excited-state wavepacket dynamics. This work is supported by DOE. \\*$^{1}$ M.J. Wright \emph{et al.}, Phys. Rev. A \textbf{75} 051401(R) (2007) [Preview Abstract] |
|
M1.00097: Collision dynamics of magnetically trapped Na and Rb MATTHEW GIBBS, TETSUYA ISHIKAWA, GUSTAVO TELLES, CHANDRA RAMAN We present a study of the collision dynamics of a dual species sample of magnetically trapped $^{23}$Na and $^{87}$Rb atoms.~ Careful control of loading dynamics and internal state preparation was necessary to minimize inter-species trap losses.~ Simultaneous magnetic trapping of the two species in the $\vert $1,-1$>$ state was achieved with lifetimes of several seconds, which suggests an absence of strong interactions in the ultracold regime, as well as the possibility of sympathetic cooling.~ The observation and probing of spin exchange collisions and Feshbach resonances in this mixture are our immediate major interests, and the future goal is to synthesize and manipulate NaRb ultracold polar molecules. [Preview Abstract] |
|
M1.00098: Analytic models of ultracold atomic collisions for application to confinement-induced resonances Satyan Bhongale, Ivan Deutsch, Servaas Kokkelmans We construct simple analytic models of the S matrix, accounting for both scattering resonances and smooth background contributions for collisions that occur below the s-wave threshold. Such models are important for studying confinement-induced resonances such as those occurring in cold collisions of 133Cs atoms in separated sites of a polarization-gradient optical lattice. Because these resonances occur at negative energy with respect to the s-wave threshold, they cannot be studied easily using direct numerical solutions of the Schr\"odinger equation. Using our analytic model, we extend previous studies of negative-energy scattering to the multichannel case, accounting for the interplay of Feshbach resonances, large background scattering lengths, and inelastic processes. [Preview Abstract] |
|
M1.00099: Photoassociative Spectroscopy of Ultracold, Metastable Argon M.K. Shaffer, G. Ranjit, C.I. Sukenik We will present results from our study of photoassociative spectroscopy of metastable argon atoms confined in a magneto-optical trap. Spectra have been obtained, as a function of probe intensity, in a region up to 10 GHz red detuned from the trapping transition. Preliminary analysis of the spectra has been done using the near-dissociation LeRoy-Bernstein method. We will also discuss extension of the work to other metastable, noble gas atoms. [Preview Abstract] |
|
M1.00100: Feshbach resonances in $^{52}$Cr-$^{53}$Cr and $^{53}$Cr-$^{53}$Cr gas Z. Pavlovi\'c, R. C\^ot\'e, H.R. Sadeghpour We present calculations of Feshbach resonances in the ultra-cold boson-fermion and fermion-fermion mixtures in a chromium gas. In the bosonic chromium-chromium collision, the Feshbach resonances are determined by magnetic dipolar interaction of atoms in the ground state with a large magnetic moment, $6\mu_B$, while the presence of a fermionic, $^{53}$Cr, component leads to resonances due to hyperfine interaction term, whose constant is $A=-80.6$ MHz. Apart from mapping the position and width of resonances, we also follow the behavior of the vibrational levels in the magnetic field. The results are obtained through coupled-channel quantum calculations that utilize exact solutions of the Schr\"odinger equation for the $1/r^6$ potential and frame transformation to hyperfine states. [Preview Abstract] |
|
M1.00101: Observation of Exchange Reactions in Ultracold Atom-Molecule Collisions J.P. D'Incao, B.D. Esry, S. Knoop, F. Ferlaino, M. Berninger, M. Mark, H.-C. N{\"{a}}gerl, R. Grimm We study exchange reactions in an ultracold gas mixture of Cs atoms and Cs$_2$ Feshbach molecules. Our theoretical and experimental studies were able to demonstrate the important role of the large scattering lengths in the collision dynamics. We have found large rates for the conversion between two different molecular states through the $A_{2}$+$B$$\rightarrow$$AB$+$B$ reactive scattering process, where the final products can still remain trapped. Both theoretical and experimental results are in an excellent agreement, demonstrating that this reaction process is tunable --- therefore providing a striking example of ultracold controlled chemistry. [Preview Abstract] |
|
M1.00102: Four-body Efimov effect predicted in a two-component ultracold gas Yujun Wang, W. Blake Laing, B.D. Esry Contrary to decades-old predictions that the Efimov effect does not generalize to four-body systems, we have identified a four-body Efimov effect in essentially exact numerical solutions of the four-body problem. We build upon existing results for three-body Efimov physics by applying a Born-Oppenheimer approximation to a system of three (identical) heavy atoms $H$ interacting with a light atom $L$. We have found that as the first $HHL$ three-body bound state forms, four-body bound states with energies bearing the Efimov scaling signature start accumulating. When the three-body states are weakly bound Efimov states, we observe embedded three-body and four-body Efimov features in $HL+H+H$ recombination rates and also in $HHL+H$ relaxation rates. We will discuss the significance of four-body Efimov physics for both few-body theory and for experiments with two-component ultracold gasses. [Preview Abstract] |
|
M1.00103: Prediction of Feshbach resonances from three input parameters Thomas M. Hanna, Eite Tiesinga, Paul S. Julienne We have developed a model of Feshbach resonances in gases of ultracold alkali metal atoms using the ideas of multichannel quantum defect theory. Our model requires just three parameters describing the interactions - the singlet and triplet scattering lengths, and the long range van der Waals coefficient - in addition to known atomic properties. Without using any further details of the interactions, our approach can accurately predict the locations of resonances. It can also be used to find the singlet and triplet scattering lengths from measured resonance data. We apply our technique to $^{6}$Li--$^{40}$K and $^{40}$K--$^{87}$Rb scattering, obtaining good agreement with experimental results, and with the more computationally intensive coupled channels technique. [Preview Abstract] |
|
M1.00104: EXOTIC STATES IN RYDBERG ATOMS |
|
M1.00105: Observation of quantum revivals in very-high-$n$ atoms Brendan Wyker, J.J. Mestayer, F.B. Dunning, C.O. Reinhold, S. Yoshida, J. Burgd\"orfer We demonstrate long-term quantum coherence extending over several hundred orbital periods in very-high-$n$ near-circular wave packets. These are created from strongly-polarized quasi-one-dimensional $n\sim $306 Rydberg states by applying a short pulsed transverse electric field. The resulting wave packet undergoes strong transient localization forming a ``Bohr-like'' atom. This localization is rapidly lost due to dephasing. At late times, however, repeated quantum revivals are observed indicating that quantum coherence can be maintained over microsecond time scales and that even large mesoscopic systems can display quantum behavior. The experimental observations are well reproduced by quantized classical Monte Carlo simulations. Research supported by the NSF, the Robert A. Welch Foundation, the OBES, U.S. DoE to ORNL, and by the FWF (Austria). [Preview Abstract] |
|
M1.00106: Creation of non-dispersive Bohr-like wave packets Jeff Mestayer, B. Wyker, F.B. Dunning, C.O. Reinhold, S. Yoshida, J. Burgd\"orfer We demonstrate the use of a periodic train of half-cycle pulses to create strongly-localized non-dispersive wave packets in very-high-$n$ ($n \quad \sim $ 300) Rydberg atoms that travel in near-circular orbits about the nucleus. This motion can be maintained for hundreds of orbital periods mimicking the original Bohr model of the hydrogen atom which envisioned an electron in circular classical orbit about the nucleus. The conditions for formation of non-dispersive Bohr-like wave packets are discussed with the aid of Classical Trajectory Monte Carlo (CTMC) simulations and demonstrated through experiment. Research supported by the NSF, the Robert A. Welch Foundation, the OBES, U.S. DoE to ORNL, and by the FWF (Austria). [Preview Abstract] |
|
M1.00107: Nondispersing Bohr wave packets using circularly polarized microwave fields Haruka Maeda, Joshua Gurian, Thomas Gallagher It is possible to make nondispersing Bohr wave packets in a straightforward way starting from Li Rydberg atoms in an np eigenstate. These atoms are first exposed to a linearly polarized microwave field at the orbital frequency, 17.6 GHz at n=72. The linearly polarized field phase locks the electron wave packet to the microwave phase, making a nondispersing wave packet in which the electron oscillates in a highly eccentric, approximately linear orbit. We detect the phase locked motion of the electron with a 1/2 ps half-cycle pulse synchronized with the microwave field. Slowly changing the microwave polarization from linear to circular polarization creates a nondispersing Bohr wave packet that survives for thousands of orbits. This work is supported by the National Science Foundation. [Preview Abstract] |
|
M1.00108: Long-range interaction between ground and excited state hydrogen atoms Daniel Vrinceanu, Alex Dalgarno The asymptotic expansion at large distances is obtained for the interaction between a ground state hydrogen atom and an excited hydrogen atom with principal quantum number $n=2,\ldots, 10$. A degenerate perturbation theory up to the second order is employed to obtain accurate results. The asymptotic representation for several special cases is found in the limit of large quantum number $n$. [Preview Abstract] |
|
M1.00109: QUANTUM INFORMATION |
|
M1.00110: Logic Operations Using the Zeno Effect Bryan Jacobs, James Franson The quantum Zeno effect can be used to implement quantum logic operations using single photons as the qubits. In this context the Zeno effect is used to inhibit failure events that would otherwise occur in a linear optics system. In practice, no actual measurements are required and equivalent results can be obtained using strong two-photon absorption to inhibit the growth of undesired probability amplitudes. It is shown here that similar effects can be used to implement classical logic and memory devices. In these devices nonlinear dissipation is used to prevent the buildup of an electromagnetic field in a resonator. Aside from their potential practical applications, these results show that the Zeno effect is a possibility in any system characterized by a wave equation. [Preview Abstract] |
|
M1.00111: Fidelity of quantum teleportation based on temporally resolved photodetection of collective spontaneous emission Richard Wagner, James Clemens We employ quantum trajectory theory to model temporally resolved photodetection of collective emission from a pair of atoms to investigate the performance of a conditional quantum teleportation protocol. One atom is entangled with another qubit in a Bell state and the other is in an arbitrary state. We find that the fidelity, minimized over the state to be teleported, exceeds the classical limit of 2/3 provided that the combined photon collection and detection efficiency exceeds 3/4. [Preview Abstract] |
|
M1.00112: Experimental investigation of the connection between weak measurements and violation of the Leggett-Garg Inequality Michael Goggin, Marcelo Almeida, Marco Barbieri, Benjamin Lanyon, Jeremy O'Brien, Andrew White, Geoff Pryde By weakly measuring the polarization of a photon between two strong polarization measurements, we experimentally demonstrate that there is a one-to-one correlation between achieving strange weak values and violating the Leggett-Garg inequality (LGI) as was recently predicted by Williams and Jordan [N. S. Williams, and A. N. Jordan {\bf 100}, 026804 (2008)]. Furthermore, we investigate the effect of measurement strength on the magnitude of the anomalous weak values and the extent of the LGI violation. [Preview Abstract] |
|
M1.00113: Realizing Collective Strong Coupling with Ion Coulomb Crystals in an Optical Cavity J.P. Marler, A. Dantan, M. Albert, P.F. Herskind, M. Drewsen Clouds of cold ions are an interesting alternative system to a single atom/ion for studying CQED effects. When trapped and cooled below a critical temperature, ions form a spatially ordered state, referred to as an ion Coulomb crystal. In our setup, we trap and cool $^{40}\mathrm{Ca}^+$ ions in sufficient number to access the so-called strong collective coupling regime, where the collective coupling, $g\sqrt{N}$, exceeds both the dipole decay rate, $\gamma$, and the cavity decay rate, $\kappa$. We will present the first signals of collective strong coupling, in this system - most dramatically manifested via the vacuum Rabi splitting. Finally, we measure the temporal coherence of collective Zeeman sub-states in the $3\mathrm{d}^3\mathrm{D}_{3/2}$-level by induced Larmor precession. The measured coherence times are of the order of the best reported values for single ions in equivalent magnetic field sensitive states. Our results make the system a promising candidate for the realization of various quantum information devices, including quantum repeaters and quantum memories. [Preview Abstract] |
|
M1.00114: Cavity QED with trapped neutral atoms Michael Gibbons, Chung-Yu Shih, Soo Kim, 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 loading and storage of individual atoms delivered from a magneto-optic trap to the resonator using two parallel atom conveyors. We will discuss the current progress towards implementing atom-atom entanglement within the cavity, as well as future applications. [Preview Abstract] |
|
M1.00115: RF atomic magnetometer with spin squeezing Georgios Vasilakis, Vishal Shah, Michael Romalis Atom projection noise sets a fundamental limit on the sensitivity of atomic magnetometry. Spin squeezing can overcome this limit, but for time scales shorter than the transverse spin relaxation time. In traditional high density alkali atom magnetometers the transverse relaxation time is mainly limited by spin exchange collisions between alkali atoms; however in the limit of high polarization spin exchange collisions do not contribute to the relaxation mechanism (light narrowing effect). We are exploring experimentally the possibility of utilizing spin squeezing in combination with the light narrowing effect to increase the sensitivity of a $^{39}$K RF magnetometer. The Faraday rotation of a linearly polarized probe pulsed at twice the Larmor frequency is used as a quantum non demolition probe for the spin squeezing. Preliminary results demonstrate the reduction of the probe back-action on the spin projection. A high power pump laser polarizes the medium to nearly 100{\%}, and is switched off during the data acquisition. A well suited application for this magnetometer is the detection of NQR signals, which last for timescales comparable to the relaxation time. [Preview Abstract] |
|
M1.00116: MATTER WAVE INTERFEROMETRY |
|
M1.00117: Atom interferometry using Kapitza-Dirac scattering David Anderson, Rachel Sapiro, Rui Zhang, Georg Raithel We demonstrate two atom interferometric schemes based on Kapitza-Dirac scattering in a magnetic trap. In the first method, two Kapitza-Dirac scattering pulses are applied with a small time delay between them. High contrast interference is observed both using a thermal cloud and a Bose-Einstein condensate (BEC). In the second method, two Kapitza-Dirac scattering pulses are applied to a BEC with a time separation sufficiently large that the interfering orders complete half an oscillation in the magnetic trap; this enables interferometry between spatially separated paths. We also review related lattice experiments performed using the same setup. [Preview Abstract] |
|
M1.00118: Nano-gratings and the atom-surface Van der Waals interaction Vincent Lonij, Will Holmgren, Ben McMorran, Alex Cronin Nano-gratings are used in several atom- and electron-interferometers as coherent beamsplitters. Diffraction from these nano-gratings can be studied to observe the effect of the Van der Waals atom-surface interaction. In addition, these gratings have recently been used in atom-interferometers to detect a velocity dependent VdW induced phase shift. Determination of the VdW potential strength C3 from these studies, is limited by a lack of knowledge of the geometric parameters of the grating. Measurements of these parameters by conventional methods are plagued with several systematic errors. By studying diffraction of a beam of Na atoms at different angles of incidence, we are able to determine the geometric parameters with a precision that is competitive with conventional imaging methods. The precision is great enough to be able to notice the effect of atoms deposited on the gratings by the atom-beam. [Preview Abstract] |
|
M1.00119: Towards a Rb-Li Ring Interferometer G. Edward Marti, Enrico Vogt, Anton Oetti, Ryan Olf, Dan Stamper-Kurn Our novel setup is a second-generation magnetic ring trap where we will employ specialized, micro-fabricated magnetic coils with 3D integration housed in a low magnetic field noise environment. These coils will generate very precise, smooth and tightly confining trapping fields. The diameter of the magnetic ring trap can be controlled and adjusted over a wide range from tens of microns to several millimeters. When employing the ring trap as a Sagnac-type atom interferometer with a pulsed source of thermal atoms, a large enclosed area is advantages to increase the resolution of the gyroscope. However, we will decrease the radius to fill the ring with degenerate quantum gases and study the effects of a non-trivial topology on coherence and dynamics of Bose-Einstein condensates. We will load the ring trap with both rubidium and lithium atoms, which will allow us to explore diverse regimes of matterwave interferometry with bosonic and fermionic atoms of differing interaction strengths, including attractive and repulsive condensates. [Preview Abstract] |
|
M1.00120: Mateucci-Pozzi force, Aharonov-Bohm phase and the Ponderomotive AB-effect Herman Batelaan, Shawn Hilbert, Adam Caprez, Brett Barwick The presence of force for the Mateucci-Pozzi effect, which was once thought to be an Aharanov-Bohm type effect, is demonstrated experimentally. This is contrasted to the absence of force for the Aharonov-Bohm effect as we showed earlier$^{1}$. In this context, it is perhaps interesting to point out that our theoretical prediction of the Ponderomotive Aharonov-Bohm$^{2}$ effect can not be explained in a time-averaged picture by a force, but in the time dependent picture is due to a force. To complicate this line of reasoning even more we point out some relativistic issues for the ``Feynman paradox'' that have not been related before to the Aharonov-Bohm effect$^{3}$. 1. A. Caprez, B. Barwick, and H. Batelaan, \textit{''Macroscopic Test of the Aharonov-Bohm Effect,''} Phys. Rev. Lett. \textbf{99}, 210401 (2007). 2. B. Barwick, H. Batelaan, Aharonov--Bohm phase shifts induced by laser pulses, New. J. Phys. \textbf{10, }083036, (2008). 3. A. Caprez, H, Batelaan, Found. Phys. Accepted for publication (2009). [Preview Abstract] |
|
M1.00121: Experiment on Matter wave self-Imaging in pulsed optical standing wave field Ke Li, Lu Deng, M.G. Payne, M.S. Zhan In this Paper we report a non-Raman-Nath regime diffraction of a condensate by an optical standing wave. We demonstrate atomic CM motion-based bidirectional, high-order matter-wave self-imaging and condensate momentum oscillation. We emphasize that this phenomenon exists in the non-Raman-Nath regime that is also far away from typical Bragg regime, where the atomic CM motion plays a key role. We further note that the matter-wave self-imaging effect reported here is very different from the temporal matter-wave Talbot effect reported previously. To the best of our knowledge, such a full matter-wave self-imaging due to CM motion has never been demonstrated before. We consider a system of two electronic states and n momentum states, and take numerical simulation of the diffraction probabilities for the first few significant diffraction orders. It shows that at $\tau _P \approx 23\mu {\kern 1pt}s$ the zeroth-order diffraction probability is near 100{\%} whereas all high orders are very small. This approximately agrees with the observed time of $\tau _P =25\mu {\kern 1pt}s$ when all n $\ge $ 1 orders are very small. [Preview Abstract] |
|
M1.00122: Slow Ion Interferometry Christopher Erickson, Dallin Durfee We will discuss an ion interferometer which is under construction. The device will utilize a laser-cooled source of $^{87}$Sr$^+$ ions which will be split and recombined using stimulated Raman transitions inside of a conducting cylinder. The interferometer will be able to measure electric and magnetic fields with unprecedented precision. Potential uses of the device include practical applications such as the precision measurement of the evolution of fields near solids to reveal their electronic structure. It will also be used for fundamental tests of the basic laws of electromagnetism and the search for a non-zero photon rest mass. The device should enable the detection of a possible photon rest mass more than 100 times smaller than previous laboratory experiments. We will discuss both the details of the device and the theory connecting deviations from Coulomb's inverse-square law to a theory of massive photons. [Preview Abstract] |
|
M1.00123: Mean Field Theory of Resonant Matter Wave Amplification Yuping Huang, Michael Moore Previous studies of matter wave amplification (MWA) in Bose- Einstein condensates have focused on the off-resonance regime, where the excited electronic state is only virtually occupied, resulting in a relatively slow amplification rate. In order to determine the maximum obtainable MWA rate, we investigate Raman MWA in the resonant regime, using intense nanosecond pulses to complete the amplification process on a time scale where spontaneous emission can be neglected. We find that phase-coherent MWA is still possible even when the transition is fully saturated. The MWA rate initially increases linearly with the laser intensity and then saturates when the Rabi frequency of the driving pulse becomes comparable to the superradiance-broadened linewidth of the excited state. We compare two theoretical approaches: 1) a master-equation treatment of a coupled-mode model with no spatial dynamics, and 2) a full multi-mode solution of the Maxwell-Schr\"odinger dynamics. We find that spatial effects become significant only when the sample size of seed wave surpasses that of gain medium, after which the MWA process is slowed by at least an order of magnitude. [Preview Abstract] |
|
M1.00124: Talbot Interferometer for Free Electrons Ben McMorran, Alex Cronin We report the first demonstration of a Talbot interferometer for electrons, similar to ones that have been demonstrated for atoms. The interferometer was used to image the Talbot carpet formed by 2 keV-energy electrons behind a nano-fabricated material grating. The Talbot interferometer design uses two identical gratings, and is particularly sensitive to distortions of the incident wavefronts. To illustrate this we used our interferometer to measure a 2-meter radius of curvature for the wavefronts in a weakly focused electron beam. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700