Bulletin of the American Physical Society
38th Annual Meeting of the Division of Atomic, Molecular, and Optical Physics
Volume 52, Number 7
Tuesday–Saturday, June 5–9, 2007; Calgary, Alberta, Canada
Session R1: Poster Session III |
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Room: TELUS Convention Centre Exhibition Hall B, 4:00pm - 6:00pm |
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R1.00001: WAVEPACKET DYNAMICS AND COHERENT CONTROL |
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R1.00002: Controlled vibrational quenching of nuclear wave packets in $D_2^+$ Thomas Niederhausen, Uwe Thumm The sudden ionization of neutral $D_2$ molecules by a short and intense pump laser pulse may create a wave packet as a coherent superposition of vibrational states on the lowest ($1s\sigma_g^+$) adiabatic potential curve of the $D_2^+$ molecular ion. We investigate the possibility of manipulating the bound motion, dissociation, and vibrational-state composition of such nuclear wave packets with one (or several) ultra-short (6 fs) intense (1 x 10$^{14}$ W/cm$^2$) near infrared (800 nm) control laser pulses. We show numerically that a single control pulse with an appropriately tuned time delay can significantly quench the vibrational state distribution of the nuclear wave packet by increasing the contribution of a selected stationary vibrational state of the molecular ion to more than 50\%. We also show that a second control pulse with a carefully adjusted delay can further squeeze the vibrational state distribution and suggest a scheme for a multi control pulse ``Raman shaping''. Since the resulting nuclear wave function is almost stationary, fragmentation of the molecular ion with a final intense probe pulse can be used to project its nodal structure onto the measurable kinetic energy release, thereby suggesting a tool for assessing the degree at which the nuclear motion in a small molecule can be controlled. [Preview Abstract] |
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R1.00003: Engineering Rydberg Wavepackets Using a Chirped Half-Cycle Pulse Train Jeffrey Mestayer, Wei Zhao, Jim Lancaster, F. Barry Dunning, Shuhei Yoshida, Carlos Reinhold, Joachim Burgdorfer A protocol for driving Rydberg atoms to a narrow band of targeted final n states with the aid of a chirped train of half-cycle pulses (HCPs) is described. A localized wavepacket can be generated and maintained by a periodic driving force. The dynamics of such a wavepacket can be manipulated almost as easily and as freely as the dynamics of a single classical particle. This is demonstrated experimentally by exciting potassium atoms to the lowest-lying quasi-one-dimensional (quasi 1-D) states in the n = 350 Stark manifold and transporting them to a narrow range ($\Delta $n$\sim \pm $20) of higher-n states centered on values of n of up to n $\sim $ 670. The protocol is remarkably efficient, with over 90{\%} of the parent atoms surviving the HCP sequence in strongly-polarized quasi-1D states. [Preview Abstract] |
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R1.00004: Rovibrational wave packet manipulation using shaped mid infrared femtosecond pulses toward quantum computing Masaaki Tsubouchi, Takamasa Momose Laser pulse shaping which was developed in near infrared (NIR) has been recently extended into mid infrared (MIR: 3 -- 10 $\mu $m). In the presented study, the signal output (NIR: 1.1 -- 1.5 $\mu $m) of an optical parametric amplifier was shaped with a Dazzler, and mixed in a AgGaS$_{2}$ crystal with the idler pulse to generate MIR pulses. Although the relation between the shapes of NIR and MIR light is complicated due to DFG process in the crystal with finite (2 mm) thickness, the shape of MIR light can be completely characterized by comparing with calculated profiles. The shaped MIR light which is well characterized can be used to manipulate rovibrational wave packet on the electronic ground state. We simulated the wave packet motion and its observable by solving the time-dependent Schr\"odinger equation, and discussed how the shape of MIR pulse is transferred into the wave packet. Application of rovibrational wave packet manipulation to quantum computation will be discussed. [Preview Abstract] |
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R1.00005: Population transfer in Na s-p Rydberg ladder by chirped microwave pulse H. Maeda, J.H. Gurian, T.F. Gallagher Quantum defects of $ns$ and $np$ Rydberg states of Na are quite large, $\delta_s = 1.35$ and $\delta_p=0.85$, respectively, while for $n\ell$ states with $\ell \geq 2$ values of $\delta_ {\ell}$ are nearly zero. Therefore Na $ns$ and $np$ states are energetically isolated from the higher angular-momentum states in the same $n$ manifold. Together with the fact that energy spacing between $ns$ and $np$ states and $ns$ and $(n-1)p$ states are almost equal, i.e., $\Delta E_{ns-np} \approx \Delta E_{(n-1)p-ns}\approx 1/2n^3$ in a.u., we can think of Na $ns$ and $np$ Rydberg states as a specific example of simple ladder system consisted with only $s$ and $p$ angular momentum states. Here we demonstrate that population transfer in the Na $s$-$p$ Rydberg ladder can be effectively achieved using a frequency chirped microwave pulse, which dominantly couples only $s$ and $p$ states under a suitable condition. This work has been supported by the NSF. [Preview Abstract] |
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R1.00006: Quantum Control of Atomic Hydrogen Using Laser Fields Xingjun Zhang, Eddie Red, Albert Wynn III, Charles Weatherford A method for the ab initio simulation of STIRAP (stimulated Raman adiabatic passage) [1,2] laser quantum control of the energy level poulations of atomic ions will be described. The method employs a new algorithm for the solution of the time- dependent Schr\"odinger equation which avoids the time-propagator and uses spectral elements in time with a spectral spatial basis.[3] This results in a set of coupled simultaneous equations and is thus an implicit stable procedure. In order to treat the continuum problem (ionization), a complex absorbing potential is used. The spectral spatial basis used is the Coulomb Sturmians.[4] As an initial application, the control of the levels of atomic hydrogen will be presented. [1] S.A. Rice and M. Zhao, Optical Control of Molecular Dynamics, Wiley, New York, 2000. [2] M. Shapiro and P. Brumer, Principles of the Quantum Control of Molecular Processes, Wiley, New York, 2003. [3] C.A. Weatherford, E. Red, and A. Wynn III, J. Mol. Structure (Theochem) 592, 47 (2002). [4] J. Avery, Hyperspherical Harmonics and Generalized Sturmians, Kluwer, Dordrecht, 2000. [Preview Abstract] |
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R1.00007: QUANTUM OPTICS |
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R1.00008: ABSTRACT WITHDRAWN |
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R1.00009: ABSTRACT WITHDRAWN |
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R1.00010: Composite pulse manipulation of atomic qubits Thomas Henage, Marie Delaney, Erich Urban, Todd Johnson, Larry Isenhower, Deniz Yavuz, Thad Walker, Mark Saffman We present recent progress on the use of composite pulse techniques for fast, high fidelity manipulation of neutral atom qubits in optical dipole traps. We electronically control the amplitude and phase of a 3.4 GHz microwave signal in under 200 ns. The time modulated microwave signal is applied to a laser diode which generates sidebands with controllable amplitude and phase that drive two-photon stimulated Raman transitions between Rb hyperfine states. The Raman fields allow qubit rotations at rates greater than 1 MHz. Using this system we demonstrate the use of composite pulses for manipulation of trapped atomic qubits. [Preview Abstract] |
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R1.00011: Coherence in a strongly driven four-level molecular system Jianbing Qi We will present a detailed discussion of the coherence effect of a four-level molecular system driven by three lasers. A weak probe laser is used to probe a ground state to the first excited state. The response of the probe laser depends on the relative coupling strength of the two coupling lasers. The population spectra of the excited states display complex structures which are strongly affected by the driving lasers and detuning of the lasers. We used density matrix equations to derive analytical solutions for the probe absorption and the population spectra. We will also discuss the control of the population of the excited states by the coupling lasers. [Preview Abstract] |
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R1.00012: Effects of coupling between the vibrational modes on CARS signal Vishesha Patel, Svetlana Malinovskaya CARS is well suited spectroscopy method for imaging specific molecules, e.g., proteins and live cells, diagnosis of cancerous cells, imaging dueterated compounds, etc. CARS imaging techniques avoid problems associated with photo bleaching and photo induced toxicity. The CARS signal is accompanied by a strong non resonant background which may overshadow the weak signal of interest. Two methods, using femtosecond chriped laser pulses and providing the Rabi oscillation and the adiabatic passage type of control [1], allow one to achieve sensitivity with high resolution and are known to efficiently suppress background. It has been previously shown that coupling between vibrational modes affects the sensitivity of the Raman signal and selective excitation of vibrational modes [2]. In this paper we will discuss simulation results on vibrational coupling between modes and its impact into control mechanisms of the CARS signal. \newline \newline [1] S.A.Malinovskaya, Physical.Rev.A 73, 033416(2006) \newline [2] S.A. Malinovskaya,P.H. Bucksbaum, and P.R. Berman, J. Chem. Phys. 121, 3434 (2004). [Preview Abstract] |
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R1.00013: Generation of High-Power Laser Light with GHz Splitting Nick Proite, Brett Unks, Deniz Yavuz We demonstrate the generation of two high-power laser beams whose frequencies are separated by the hyperfine transition frequency in Rb-85. The system uses a single master diode laser appropriately shifted by a high frequency acousto-optic modulator and amplified by tapered amplifiers. This system produces two 1 Watt laser beams with a frequency spacing of 3.035 GHz. We discuss possible applications of this system including Electromagnetically Induced Transparency-like effects in both hot vapor cells and ultracold atomic clouds. [Preview Abstract] |
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R1.00014: The N+CPT resonance Michael Crescimanno, Michael Hohensee, Cindy Hancox, David Phillips, Ron Walsworth Of relevance to compact atomic frequency standards, we investigate a model of the N+CPT joint optical resonance.~ We compare analytical solutions of a 4-state theory, as well as numerical solutions of the optical Bloch equations, to experimental investigations of N+CPT resonances in 87Rb.~ Our results inform the optimization of N+CPT based frequency standards. [Preview Abstract] |
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R1.00015: ABSTRACT WITHDRAWN |
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R1.00016: CAVITY QED |
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R1.00017: Studies of many atoms strongly coupled to a high finesse optical cavity. Kater Murch, Kevin Moore, Subhadeep Gupta, Dan Stamper-Kurn We utilize a hybrid magnetic trap -- cavity QED apparatus to conduct studies of ultracold atoms strongly coupled to a high finesse optical cavity. Up to 5 x 10$^{4} \quad ^{87}$Rb atoms are trapped at the antinodes of an in-cavity far-off resonance optical standing wave. Atoms can be either probed directly using absorption imaging, or indirectly from the shift of the cavity resonance. Using a combination of these probes, we conduct measurements of the heating in the system. For strongly coupled cavities, quantum-optical properties of the cavity system strongly influence the heating of the atomic sample. Cavity-induced heating becomes dominant for atomic systems with large single-atom cooperativity, and may limit cavity-based quantum non-demolition measurements such as those being pursued experimentally by our group and others. [Preview Abstract] |
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R1.00018: Barium ion trap cavity QED Adam Steele, Layne Churchill, Paul Griffin, Michael Chapman We have constructed a barium ion trap cavity QED system that is designed to reach the strong coupling regime. Strong coupling between a single atom and an optical cavity is an important paradigm for quantum optics and an important element for quantum information processing. We have confined laser cooled chains of barium ions in a linear Paul trap. These ions will be coupled to a mode in a high finesse optical cavity resonant with the $ S_{1/2} \rightarrow P_{1/2}$ transition at 493 nm. We present our progress towards this integration of ion trap and cavity QED technologies. [Preview Abstract] |
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R1.00019: Steady state of two-mode cavity QED beyond the low intensity Rebecca Olson Knell, David Norris, Jietai Jing, Luis A. Orozco Cavity QED with two orthogonal polarization modes with multilevel atoms permits the identification of spontaneous emission through the light escaping in the undriven mode. We present our experimental investigations of the steady state behavior of this system when the resonant drive of one of the cavity modes is strong. This driving regime also has entanglement that does not suffer from the intrinsic problem of a large vacuum component for the low intensity cavity QED. Our apparatus includes laser cooled Rb atoms that traverse a high finesse optical cavity. The coupling rate of the cavity mode to the atom $g$, the cavity decay rate $\kappa $, and the atomic fluorescence rate $\gamma $ are all similar and much larger than the inverse of the single atom transit time across the mode, so that multiple interactions between the light and the atom are possible. The parameters of the experiment place it in the intermediate regime of cavity QED. We look at the transmitted light out of the cavity in the two orthogonal modes. We compare our results to a model that includes three levels, two ground states and one excited state as a function of number of atoms and drive intensity. [Preview Abstract] |
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R1.00020: Evaporative Cooling of a Photon Fluid Brian Seaman, Douglas Mason, Murray Holland The field of ultracold atomic physics has made large advances using the insight gained from the manipulation of optical fields. We explore the opposite, recreating in optical systems effects usually seen only in atomic systems. The possibility of evaporatively cooling a ``photon fluid'' in a Fabry-Perot cavity is considered. This would allow for the creation a superfluid coherent beam of light from an incoherent source without inversion. [Preview Abstract] |
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R1.00021: ULTRACOLD MATTER III |
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R1.00022: Optical bottle beams for trapping neutral atoms Larry Isenhower, Mark Saffman We describe a novel interferometric approach to implementing a bottle beam which can be used for trapping of atomic species in regions of low intensity. Using a Mach-Zehnder interferometer with unequal magnification in the two arms we demonstrate an optical field which has low intensity surrounded by bright regions in all directions. The bottle beam provides a quartic trapping potential transverse to the symmetry axis of the trap, and is a possible route to tight confinement of single atoms in three spatial dimensions using optical access from a single side of the experiment. We discuss the decoherence properties of this type of trap for holding neutral atom qubits, and show that it in principle can be used to create an attractive potential simultaneously for both ground state and Rydberg atoms. [Preview Abstract] |
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R1.00023: Portable Atom Chip Vacuum Cell for Rapid BEC Production Matthew B. Squires, Evan A. Salim, William F. Holmgren, Dana Z. Anderson, Sterling E. McBride, Steven A. Lipp, Jeffery F. DeNatale, Robert E. Mihailovich We have developed a portable BEC system capable of fast loading of atoms onto an atom chip using a double MOT arrangement to spatially separate a high vapor pressure atom source region from an UHV atom cooling and chip region. The atom chip serves as one wall of the vacuum cell and has through-silicon UHV compatible electrical vias, which simplifies connection to on-chip conductors. The cell is constructed using an epoxy-less technique, which permits high bake-out temperature. We have observed that high bake out temperatures leads to excellent vacuum properties, but eliminates the effectiveness of light-assisted atom desorption as a means to modulate rubidium vapor pressure. Instead, fast loading in a 6 beam MOT is obtained by loading from a 2D MOT in a separate high vapor pressure region isolated from the UHV section with a 1 mm aperture. Captured atom flux is as high as 10$^{9}$ atoms/sec in the 6-beam MOT. [Preview Abstract] |
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R1.00024: Cost-effective magneto-optical trap of ytterbium atoms Chang Yong Park, Won-Kyu Lee, Dai-Hyuk Yu, Ho Suhng Suh, Sang Eon Park, Eok Bong Kim We report on a cost-effective magneto-optical trap (MOT) of ytterbium atoms by using diode lasers as a previous step for an optical lattice clock. For the purpose of MOT, we have specially designed GaN external cavity laser diodes (ECLD), which outputs 10 mW at a wavelength of 399 nm. One of the ECLD is used to trap the ytterbium atoms along x-axis, while additional F-P diode lasers, which is injection locked to the previous ECLD, is used for the trapping along y and z axes. These trapping lasers are frequency stabilized to Doppler free $^{1}$S$_{0}-^{1}$P$_{1}$ transition. We have trapped 5$\times $10$^{6}$ atoms for $^{174}$Yb and 2$\times $10$^{6}$ atoms for $^{171}$Yb respectably at a trapping temperature of 1 mK, which is still too high for settling the atoms inside the optical lattice. In order to further decrease the trapping temperature an additional cooling laser is necessary corresponding to $^{1}$S$_{0}-^{3}$P$_{1}$ transition with which ytterbium atoms can be cooled to 4 $\mu $K. To obtain the desired laser, 1112 nm ECLD with 200 mW output is frequency doubled through MgO doped PPLN waveguide. [Preview Abstract] |
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R1.00025: Rotating-radio-frequency ion traps. T. Hasegawa, J.J. Bollinger We discuss a new ion trap, the rotating-radio-frequency (rotating-rf) trap, in which the motion of a charged particle is described by trigonometric functions rather than the usual Mathieu functions of a normal rf trap.\footnote{R.I. Thompson, et al., Can. J. Phys. {\bf 80}, 1433 (2002).}$^,$\footnote{T. Hasegawa et al., Phys. Rev. A {\bf 72}, 043403 (2005).} In the rotating-rf trap, a rotating quadrupole electric field confines charged particles, whereas in a normal rf trap, an oscillating quadrupole electric field does. Ion motion in a rotating-rf trap is a superposition of two non-degenerate circular secular motions and two corresponding circular micromotions. The cases of applying a uniform dc magnetic field and a quadrupole dc electric field in addition to the rotating rf field are also discussed. Confinement in a rotating-rf trap can be tighter than in a normal linear rf trap with the same experimental parameter values. [Preview Abstract] |
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R1.00026: Measurement of the KRb ground-state dissociation energy using cw depletion of ultracold molecules Dajun Wang, Jin-Tae Kim, Edward E. Eyler, Phillip L. Gould, William C. Stwalley We have combined previous spectroscopic data [1] on the $X~^{1}\Sigma^{+}$ state of KRb with our recent binding energy measurements of high vibrational levels to obtain an improved value of the dissociation energy. Our measurement is carried out with ultracold KRb molecules formed by spontaneous emission following photoassociation of ultracold atoms. Pulsed laser ionization detection with vibrational selectivity and cw laser ion depletion with rotational resolution are used to measure the binding energies of high-$v''$ molecules directly. Using a common vibrational level, the term energy given in [1] is combined with our binding energy measurement to yield the dissociation energy of the $X~^{1}\Sigma^{+}$ state: $D_{e}$ = 4217.822 $\pm$ 0.003 cm$^{-1}$. We acknowledge support from NSF.\newline [1] C. Amiot et al., J. Chem. Phys., \textbf{112}, 7068(2002). [Preview Abstract] |
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R1.00027: Exploring Ultracold Atoms in Non-Abelian Gauge Potentials J.Y. Vaishnav, I.I. Satija, C.W. Clark The motion of ultracold, multilevel atoms in spatially varying laser fields can generate non-Abelian gauge potentials, if two or more of the dressed states are degenerate. We examine the spectral and other exotic characteristics of ultracold atoms moving in such non-Abelian gauge potentials, with a view to understanding phenomena like symmetry breaking and non-Abelian Berry phase. Our work is motivated by numerous proposals to create non-Abelian gauge fields in cold atom experiments. [Preview Abstract] |
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R1.00028: Polarization-dependent neutral atom trapping potentials of 2D optical lattices on a chip Bert David Copsey, Katharina Gillen-Christandl, Rajani Ayachitula We present the results of our computational investigation of atom trapping potentials in different two-dimensional (2D) optical lattice geometries for neutral atoms in magnetic substates other than m$_{F }$= 0. The geometries we tested include the basic 2D optical lattice presented in [1], as well as variations of these lattices involving a counterpropagating beam pair along one dimension, and a lattice with variable trap spacing along one dimension. The 2D optical lattices are created by interference of the evanescent waves of two or more different modes in a slab waveguide. The main focus of our study is on identifying waveguide and trap light parameters that may allow for the implementation of 2-qubit gates using 2D optical lattices. 1. Phys. Rev. A 70 032302 (2004). [Preview Abstract] |
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R1.00029: Adiabatic cooling of atoms trapped in a transformable optical trap Seung Koo Lee, Hui Dong Kim, Sin Hyuk Yim, D. Cho We demonstrate adiabatic cooling of rubidium atoms in an optical trap by gradually transforming the trap from a corrugated form of a standing wave to a flattened form of a traveling wave. We trap atoms in an optical trap formed by a Fabry-Perot interferometer, which is used as a power build up cavity (PBC). We phase modulate the trapping beam using an electro-optic modulator (EOM). When the modulation frequency is the same as a free spectral range of the PBC, both carrier and sidebands can couple to the cavity simultaneously. When the modulation index is 1.2, the carrier and the sidebands have the same power and the potential well near the center of the PBC becomes flat. By controlling the modulation index we can change time-averaged intensity distribution of the intra cavity trap beam from a standing wave to a flattened form of a traveling wave. Accompanying reduction in the oscillation frequency of the trapped atoms leads to adiabatic cooling for the longitudinal degree of freedom. [Preview Abstract] |
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R1.00030: Observation of stationary and non-stationary flow past an obstacle in a Bose-Einstein condensate Peter Engels, Collin Atherton We experimentally study the fluid flow past an obstacle moving through an elongated Bose-Einstein condensate with repulsive interactions. Depending on the speed and strength of the obstacle, both stationary and non-stationary regimes are accessed. At slow speeds as well as at very fast speeds, stationary fluid flow is obtained. However, at intermediate speeds, a non-stationary regime is observed in which the condensate gets filled with a stack of dark solitons. Both attractive and repulsive obstacles are studied, and a significant difference in the critical velocities for nonstationary flow is found for the two cases. [Preview Abstract] |
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R1.00031: Analytic Beyond-Mean-Field BEC Density Profiles at Next-Order in Dimensional Perturbation Theory Martin Dunn, W. Blake Laing, Deborah Watson The density profile of a BEC offers an experimentally accessible window into beyond-mean-field effects in a macroscopic quantum object. These effects include a greater spatial extent resulting from hard collisions within the system as well as fermionization and crystallization in quasi-one and two dimensional systems. Even at lowest order, dimensional perturbation theory (DPT) yields wave functions of large-N systems which include correlation effects, and which have previously been used to derive the lowest-order density profile. DPT has now been extended beyond the lowest order to the next-order wave function. In this work we show how to derive the next-order density profile (a function of one degree of freedom) from this next-order DPT wave function (a function of a very considerable number of degrees of freedom). The functional form of the higher-order density profile includes the possibility of fermionization/crystallization. [Preview Abstract] |
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R1.00032: Interactions of low-energy ions and electrons with Bose-Einstein condensates Rachel Sapiro, Rui Zhang, Georg Raithel We will present plans for experiments intended to explore interactions between low-energy ions and electrons and Bose-Einstein condensates (BECs). The BEC apparatus, which will be described in the presentation, is a double-trap system that employs miniature U-trap and Z-trap configurations for the final stages of atom trapping and cooling. Currently, we create BECs with $\sim 3 \times 10^5$ rubidium atoms. Planned modifications of the apparatus will allow us generate, control and image ions in present inside the BEC. In our presentation, we will describe the complete setup, discuss experimental progress, and outline the planned experiments. These include studies of changes in the effective mass of the ions due to clusters of atoms forming around them [1], and of perturbations of the BEC due to the presence of embedded ions [2]. \newline [1] R. C\^{o}t\'{e}, V. Kharchenko, M. D. Lukin, Phys. Rev. Lett. {\bf 89}, 093001 (2002). \newline [2] P. Massignan, C. J. Pethick, H. Smith, Phys. Rev. A {\bf 71}, 023606 (2005). [Preview Abstract] |
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R1.00033: Bose-Condensed $^7$Li in a Random Potential James Hitchcock, Y.P. Chen, M. Junker, D. Dries, C. Welford, R.G. Hulet Imposing a random potential on a Bose-Einstein condensate (BEC) of $^7$Li creates a unique system for studying superfluid behavior in the presence of disorder. We generate a random optical potential by passing a 1 $\mu$m laser though a ground glass diffuser. The resulting laser speckle pattern is then overlapped with the probe beam and projected onto the atoms. This setup allows for almost simultaneous imaging of the atomic cloud and the random potential. Parameters such as the disorder strength and disorder correlation length can be precisely characterized. We can control the disorder strength by varying the laser intensity and the atomic interaction (scattering length) via a Feshbach resonance. We have investigated the effects of disorder on dipole oscillation in a harmonic trap, and time of flight expansion of the BEC. This system has allowed us to study such phenomena as quantum phase fluctuations, localization and interplay between interaction and disorder. [Preview Abstract] |
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R1.00034: First branch of liquid states of a many-atom Bose system Bo Gao We present more detailed properties of the first branch of the liquid states as suggested and studied recently, including the equilibrium density and the equilibrium energy-per-particle of the liquid, speed of phonons, and pair correlation functions. Results are presented both for liquid branches corresponding to negative scattering lengths\footnote{B. Gao, J. Phys. B \textbf{37}, L227 (2004).} and for those corresponding to positive scattering lengths\footnote{B. Gao, Phys. Rev. Lett. \textbf{95}, 240403 (2005).}. [Preview Abstract] |
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R1.00035: Dilute Bose gases interacting via power-law potentials Ryan Kalas, Doerte Blume Neutral atoms interact through van der Waals potentials, which asymptotically fall off as $r^{-6}$. The behaviors of dilute Boses gases can to a good approximation be described by the atom-atom scattering length $a_s$. However, as the system becomes more dense, corrections arise that depend on the characteristic length of the van der Waals potential. Making use of both essentially exact numerical calculations and semi-analytical solutions, we parameterize these corrections by analyzing the energetics of two- and few-atom systems under external harmonic confinement. We generalize these results to particles interacting through a longer-ranged potential, which asymptotically falls off as $r^{-4}$. Finally, we consider homogeneous systems interacting through different power-law potentials. [Preview Abstract] |
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R1.00036: Effects of perturbations in photoassociation spectra of ultracold Cs$_2$ Marin Pichler, William C. Stwalley, Olivier Dulieu Perturbations in photoassociation spectra of ultracold cesium are presented. High precision photoassociation spectra up to 54 cm$^{-1}$ below the Cs ($6S_{1/2}$)+Cs($6P_{1/2}$) asymptote revealed perturbations related to resonant coupling between electronic states of the same symmetry but belonging to different asymptotes. The perturbations, which are manifested as irregularities in vibrational level spacings, are most pronounced for the $0_{u}^{+}$ state, but to some extent present in the $1_{g}$ and $0_{g}^{-}$ states, which are also affected by predissociation. Theoretical calculations of perturbations for all three states and found qualitative agreement with the experimental results. Additionally, we present perturbations involving pure long range $0_{g}^{-}$ state and the dark $2_u$ state below the Cs($6S_{1/2}$)+Cs($6P_{3/2}$) asymptote. Level shifts and additional spectral features are found in this case. [Preview Abstract] |
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R1.00037: Ultracold three-boson systems near a Feshbach resonance: the role of large effective ranges Yujun Wang, J.P. D'incao, B.D. Esry We have studied the behavior of ultracold three-boson systems as the effective range is varied from being much smaller than the scattering length to being much larger. Such variations in the effective range allow us to more realistically model the behavior near a Feshbach resonance [Petrov,Jonsell]. We use model two-body interactions and the adiabatic hyperspherical representation to produce effective three-body potentials from which we try to extract universal behavior. The degree to which these three-body systems behave universally will be discussed. To facilitate this, comparisons will be made with the predictions from zero range potential models. Preliminary numerical calculations suggest that such models may be insufficient, but a more complete analysis will be presented. [Preview Abstract] |
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R1.00038: Evaporative cooling of potassium atoms Shin Inouye, Tetsuo Kishimoto, Jun Kobayashi, Kiyotaka Aikawa, Kai Noda, Takuto Arae, Masahito Ueda Recent advances in manipulating interactions between ultracold atoms opened up various new possibilities. One of the major goal of the field is to produce ultracold polar molecules. By utilizing a magnetic field induced Feshbach resonance, it is possible to produce heteronuclear molecules from a degenerate gas mixture. We are setting up an experiment to produce a degenerate gas mixture of fermionic alkali atoms, lithium-6 and potassium-40. Fermionic atoms are good candidate for minimizing the expected inelastic loss at the Feshbach resonance. For keeping the system as simple as possible, we decided to use bosonic potassium (potassium-41) as a coolant, and sympathetically cool the fermionic species. We will present our experimental setup and initial results for evaporatively cooling bosonic potassium atoms. [Preview Abstract] |
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R1.00039: Cold collisions of oriented molecules E. Abrahamsson, T.V. Tscherbul, R.V. Krems Orienting molecules with dc electric fields is a versatile technique for studying the mechanisms of inelastic collisions and chemical reactions. Here, we use rigorous quantum theory of collisions in electromagnetic fields [1,2] to study the electron spin relaxation of magnetically trapped $^2\Sigma$ and $^3\Sigma$ molecules oriented by electric fields. We demonstrate that inelastic collisions of CaD($^2\Sigma$) and ND ($^3\Sigma$) molecules can be manipulated by varying the strength of the dc electric field as well as the relative orientation between the electric and magnetic fields. The increase of the energy gap between the ground $N=0$ and the first excited $N=1$ rotational levels results in suppression of the spin relaxation at a collision energy of 1 K [1,2]. We also demonstrate that electric fields inhibit rotational relaxation of $^2\Sigma$ molecules [2]. Our results show that (1) sympathetic and evaporative cooling of $^2\Sigma$-molecules in a magnetic trap may be facilitated by applying electric fields and (2) electric fields may induce nonadiabatic transitions in collisions of $^2\Sigma$ molecules with open-shell atoms [2]. The latter result indicates that chemical reactions between atoms and molecules in a magnetic trap can be effectively manipulated by dc electric fields. [1] R.V. Krems and A. Dalgarno, J. Chem. Phys. 120, 2296 (2004); [2] T.V. Tscherbul and R.V. Krems, Phys. Rev. Lett. 97, 083201 (2006); J. Chem. Phys. 125, 194311 (2006). [Preview Abstract] |
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R1.00040: Electric-Field-Induced Feshbach Resonances in Ultracold Alkali Metal Mixtures Zhiying Li, Roman Krems It is shown that the scattering length of alkali metal atoms in ultracold binary mixtures can be effectively modified by dc electric fields of $\sim$ 30 - 100 kV/cm. The mechanism of electric-field-control of ultracold collisions is based on the interaction of the instantaneous dipole moment of the collision complex with external electric fields. This interaction is dramatically enhanced near p-wave scattering resonances. We present a detailed analysis of Feshbach resonances in ultracold collisions of Li and Cs atoms in the presence of superimposed electric and magnetic fields. We show that the electric-field couplings between s- and p-wave collision channels may not only induce electric-field resonances, but also shift the positions of s-wave magnetic resonances, thereby making the electric field control of ultracold atoms possible even far away from p-wave resonances. In addition, we demonstrate that electric fields may rotate and spin up the collision complex of ultracold atoms at substantial rates leading to anisotropic ultracold scattering. Finally, we explore the effect of the relative orientation of magnetic and electric fields on collision dynamics near Feshbach resonances. References: R. V. Krems, Phys. Rev. Lett. 96, 123202 (2006); Z. Li and R. V. Krems, Phys. Rev. A (2007) (in press). [Preview Abstract] |
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R1.00041: Temperature and Velocity Measurements Through Fluorescence and Absorption Imaging in Ultracold Neutral Plasmas Jose Castro, Hong Gao, Priya Gupta, Sampad Laha, Clayton Simien, Thomas Killian Imaging probes are used to characterize Ultracold Neutral Plasmas and determine quantities such as velocity and temperature of both ion and electron species. Absorption imaging studies demonstrate that electron temperature evolution varies depending on the initial electron temperature and plasma density. Absorption imaging shows Doppler broadening due to the combined effects of the radially directed expansion velocity and the random thermal motion of the ions. To distinguish these two quantities, fluorescence imaging of Ultracold Neutral Plasmas is used to produce a spatially-resolved spectrum that is Doppler-broadened due to thermal ion velocity and shifted due to ion expansion velocity. Using these two distinct imaging probes, Ultracold Neutral Plasmas were studied under different initial conditions. [Preview Abstract] |
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R1.00042: p-wave Feshbach Molecules John Gaebler, John Stewart, John Bohn, Deborah Jin We present evidence for the production and detection of molecules using a p-wave Feshbach resonance between $^{40}$K atoms. We have measured the binding energies and lifetimes for these molecules. We find that the binding energies scale linearly with magnetic field near the resonance. At magnetic fields above the resonance we detect quasi-bound molecules with lifetimes set by the tunneling rate through the centrifugal barrier. We discuss the possibility of using a p-wave Feshbach resonance to study BCS-BEC crossover physics with finite angular momentum pairing. [Preview Abstract] |
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R1.00043: Density profiles of trapped ultracold fermion-boson mixtures and mediated interaction effects D.H. Santamore, Eddy Timmermans Quantum degenerate gas mixtures of fermionic and bosonic atoms are trapped fairly routinely. A Bose-Einstein condensate (BEC) is often used as a coolant to decrease the temperature of fermions (sympathetic cooling). On the other hand, the introduction of distinguishable atoms into the degenerate fermion gas generally induces fermion hole heating. We show that the fermion (boson)-mediated boson-boson (fermion-fermion) interactions can significantly alter both the fermion and boson density profiles, which conversely can be used to detect mediated interactions. We also present a low order linked-cluster calculation of the equation of state of a dilute homogeneous mixture of a normal single component fermion gas, mixed with a BEC. We also derive an improved Thomas-Fermi description of the trapped density profiles. Our results suggest that (a) boson-mediated fermion-fermion interactions can be repulsive, (b) the polaron shift can largely determine the fermion density profile, and (c) shrinking of the BEC-size can be the precursor of the fermion-boson phase separation transition as well as the mean-field collapse. [Preview Abstract] |
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R1.00044: PRECISION MEASUREMENTS & ATOMIC/MOLECULAR STRUCTURE IN FIELDS |
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R1.00045: High-accuracy calculation of black-body radiation shift in $^{133}$Cs primary frequency standard Kyle Beloy, Ulyana Safronova, Andrei Derevianko Black-body radiation (BBR) shift is an important systematic correction for the atomic frequency standards realizing the SI unit of time. In recent years there has been a controversy over the value of the BBR shift for the primary $^{133}$Cs standard. At room temperatures, reported values from various groups have differed at the $3 \times 10^{-15}$ level, while modern clocks are aiming at $10^{-16}$ accuracies. We have carried out high-precision relativistic many-body calculations of the BBR shift. For the BBR coefficient $\beta$ at $T=300K$ we have obtained $\beta=-(1.708\pm0.006) \times 10^{-14}$, implying $6 \times 10^{-17}$ fractional uncertainty. While in accord with the most accurate measurement, our 0.35\%-accurate value is in a substantial, 10\%, disagreement with recent semi-empirical calculations. We have identified an oversight in those calculations, largely resolving the controversy. These results were presented in PRL 97, 040801 (2006). [Preview Abstract] |
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R1.00046: Some Consequences of a Time Dependent Speed of Light Felix T. Smith For reasons connected with both cosmology (the flatness and horizon problems) and atomic physics (n-body Dirac equation, etc.), various proposals have been made to modify general or special relativity(SR) to accommodate a cosmologically decreasing light speed [J. Magueijo, Rep. Prog. Phys. \textbf{66}, 2025 (2003)]. Two such theories, projective SR [S.N. Manida, gr-qc/9905046; S. S. Stepanov, physics/9909009 and Phys. Rev. D, \textbf{62}, 023507 (2000)] and symmetric SR [F.T. Smith, Ann. Fond. L. de Broglie, \textbf{30}, 179 (2005)] adapt special relativity to in different ways to an expanding, hyperbolically curved position space and predict time-dependences of $c$ within reach of measurement but differing by a factor of two. Both theories bring in a new constant $\lambda ^{-1}=\sigma =c^2H_0 ^{-1}$. As Magueijo points, out the role of $c$ in physics and cosmology is so profound that many deep changes must follow if is not absolutely invariant in space and time. In particular, symmetric SR brings a new light to the Dirac large-number relationship between the constants of gravitation and atomic physics. [Preview Abstract] |
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R1.00047: N-resonance characterization for compact atomic clocks Cindy Hancox, Irina Novikova, Yanhong Xiao, David Phillips, Ronald Walsworth There is great current interest in developing small atomic clocks with low power consumption and fractional frequency stability of $10^{-12}/\sqrt{\tau/s}$ or better. N-resonances, all-optical three-photon-absorption resonances, offer a promising alternative to CPT-based clocks due to their high resonance contrast and the potential to cancel first-order light shifts. We present measurements of the N-resonance contrast, width and light-shift for $^{87}$Rb in a compact (1 mm long) buffer gas vapor cell and a 1 cm long paraffin-coated cell. [Preview Abstract] |
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R1.00048: Ultra-high resolution spectroscopy with a $^{87}$Sr lattice clock Gretchen K. Campbell, Sebastian Blatt, Martin M. Boyd, Andrew D. Ludlow, Tanya Zelevinsky, Seth M. Foreman, Thomas Zanon, Jun Ye We have performed ultra-high resolution spectroscopy using a $^{87}$Sr optical lattice clock. With the addition of a small magnetic bias field, the high line Q of the $^1S_0$-$^3P_0$ clock transition has allowed us to resolve the nuclear-spin sublevels, and make a precision measurement of the differential Land\'{e} g-factor between the $^1S_0$ and $^3P_0$ states arising from hyperfine mixing of the $^3P_0$ with the $^3P_1$ and $^1P_1$ states. Breaking the nuclear-spin degeneracy allows for a better characterization of systematic errors, and we have made measurements of these nuclear-spin related effects including the linear Zeeman shift and tensor polarizability. The ability to directly manipulate individual nuclear-spin levels also makes this an attractive system for quantum information. Recent progress towards an all optical comparison of atomic clocks, including the construction of a new strontium three-dimensional optical lattice will also be presented. [Preview Abstract] |
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R1.00049: Precision Measurements with Matter-wave Interferometry Christopher Erickson, Dan Christensen, Matthew Washburn, James Archibald, Marshall Van Zjill, Jeremiah Birrell, Adam Burdett, Dallin Durfee We will discuss progress on a neutral-calcium beam interferometer which is nearing completion. We will also present a proposal to measure electric and magnetic fields with extreme precision using a slow ion interferometer. The calcium interferometer utilizes a thermal beam for simplicity and high atom flux. Doppler shifts will be reduced using a novel alignment scheme for the Ramsey beams using precision prisms. The ion interferometer will utilize a slow beam of strontium-87 ions created by photon-ionizing a slow atomic beam. The ions will interact with three sets of laser beams which will drive stimulated Raman transitions. The proposed device will be used to search for variations from Coulomb's inverse-square law and a possible photon rest mass with a precision which is several orders of magnitude better than previous laboratory experiments. [Preview Abstract] |
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R1.00050: Measurement of a forbidden magnetic dipole matrix element in Rb T. Takekoshi, R.J. Knize For non-relativistic wavefunctions, the Rb 5S to 6S transition is E1 and M1 forbidden. For relativistic wavefunctions, the leading term is M1. The value of this lowest nS to (n+1)S matrix element has been calculated for all of the alkali atoms using relativistic many-body perturbation theory by Savukov, Derevianko, Berry, and Johnson [PRL \textbf{83} 2914 (1999)]. Their predicted value of the Cs 6S to 7S matrix element is within 16{\%} of the high-precision ($<$1{\%}) value measured by Bennett and Wieman [PRL \textbf{82} 2484 (1999)]. The Rb 5S to 6S M1 matrix element is predicted to be especially sensitive to contributions from negative-energy states. Including negative-energy states changes the calculated value by 60{\%}. We attempt a measurement of this matrix element at the 10{\%} precision level to investigate this effect. [Preview Abstract] |
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R1.00051: Current status of the measurement of the anapole moment in francium. Adrian Perez Galvan, Dong Sheng, Yanting Zhao, Luis Orozco We present the new generation experimental setup of the FrTRAP collaboration to measure the anapole moment in a chain of francium isotopes. The experiment will interface with the ISAC radioactive beam facility at TRIUMF. Our experimental design combines a double chamber currently under test with stable rubidium. The design permits both microwave and optical parity non-conservation measurement techniques. The nuclear anapole moment is a parity violating moment that arises from the nuclear weak interaction and can be probed with an electromagnetic interaction between an electron and the nucleus. Its measurement is a unique probe for neutral weak interactions inside the nucleus. Measurements in a chain of francium isotopes offer the unique opportunity of probing the electroweak interaction as a function of nuclear distribution. [Preview Abstract] |
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R1.00052: Time Dependence of the Speed of Light: A Measurement Needed Felix T. Smith Constancy of the speed of light has been unquestioned in physics and cosmology for 100 years, and it underlies applications such as GPS. Pauli stressed that Einstein's derivation of Lorentz invariance in mechanics and electromagnetism required the postulate that the measured speed of light is independent of the velocity of the light source, but not the wider condition of constancy of $c$ throughout in space and time. Limits on the variation of $\alpha =e^2/4\pi \varepsilon_{\mbox{o}} c\hbar $ cannot constrain $c$, because either $e$ or $\varepsilon_{\mbox{o}}$ may also vary. Cosmologists have pointed to important consequences if the light speed has declined systematically since the Big Bang. Two predictions [S. S. Stepanov, (2000); F. T. Smith, (2005)], differing by a factor of 2, connect $c^{-1}dc/dt$ with the reciprocal Hubble time. Modern optical techniques make possible a direct measurement of limits to the rate of change of $c$ (or equivalently, to the rate of change of the measured length of a standard test object) to the needed precision. To avoid microcrystalline changes in length, the test object may need to be maintained at liquid nitrogen temperature or below both during and between measurements. [Preview Abstract] |
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R1.00053: Towards a Beta Asymmetry Measurement of Polarized Radioactive Atoms in an Optical Dipole Trap Haiyan Wang, David Feldbaum, Andrew Hime, David Vieira, Xinxin Zhao Laser cooled and trapped radioactive atoms provide an ideal sample for studying parity violation in beta decay. We present recent progress in undertaking a high precision beta-recoil measurement of radioactive $^{82}$Rb atoms in an optical tweezer. We have demonstrated the loading of $^{82}$Rb atoms from a magneto-optical trap (MOT) to a far off resonance dipole trap formed by a YAG laser. A preliminary study of the trap loading efficiency and optical pumping into a stretched state will be presented. In our improved beta asymmetry measurement, we plan to load $^{82}$Rb atoms from a MOT into an optical dipole tweezer and then beam the atoms down to a science chamber where the atoms will be polarized and their beta decay measured. [Preview Abstract] |
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R1.00054: Resonator-enhanced optical guiding and trapping of Cs atoms Fang Fang, David Weiss We demonstrate a 90 cm launch of Cs atoms guided by a one-dimensional (1D) optical lattice. The 1064 nm wavelength optical lattice is made in a 2 m long build-up cavity of light. It provides a transverse guide depth of 150 $\mu $K. Near the top of their trajectory, the atoms are stopped and cooled by optical molasses, becoming trapped in the 1D lattice, which can then be loaded with multiple launches. With atoms stretched out over 5 cm, the effective volume of this extended atom trap is $\sim $50 mm$^{3}$. The trap is far from all magnetic sources, and will be used for a precision measurement of the electron electric dipole moment.~ [Preview Abstract] |
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R1.00055: Electric dipole $f$ values for Fe II $J=9/2\rightarrow 11/2^o$ transitions Donald R. Beck Relativistic configuration-interaction $f$ values have been obtained for all transitions between the lowest 17 $J=9/2$ and the lowest 27 $J=11/2^o$ levels. The 35 $f$ values $>$0.01 have an average gauge agreement of 3.6\% and generally agree well with the semi-empirical results of Raassen \footnote{A. J. J. Raassen, {\sf ftp://ftp.wins.uva.nl/pub/orth/iron/FeII.E1} (1999).}. The near degeneracy of many of the odd levels requires the introduction of small semi-empirical energy shifts \footnote{D. R. Beck, Phys. Scr. {\bf 71}, 447 (2005).}. A systematic way of estimating radial convergence is discussed. [Preview Abstract] |
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R1.00056: Properties of Magnetic Sublevel Coherences for Precision Measurements I. Chan, S. Beattie, A. Kumarakrishnan We have solved the density matrix rate equations for atoms interacting with laser fields that create coherences between adjacent magnetic sublevels of the F=3 ground state in $^{85}$Rb. The rate equations are solved in an irreducible tensor basis and allow us to calculate the polarization of the atoms as a function of time after interaction with the laser fields. We include all the states in the excited hyperfine manifold, assume that the magnetic sublevels are degenerate and compare the results with experiments using laser cooled atoms. We also describe the effect of a magnetic field on this system as a time dependent rotation about the quantization axis. The rotation matrix is written in terms of the Euler angles and the results are useful in modeling the signals used to measure the atomic g factor ratio using $^{85}$Rb and $^{87}$Rb isotopes. We also compare the results obtained for the magnetic field dependence using Rb vapour at room temperature. [Preview Abstract] |
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R1.00057: On the possibility of considering the fullerene shell C60 as a conducting sphere Miron Amusia, Arkadiy Baltenkov It has been shown that the fullerene shell in the static electric field behaves as a set of separate carbon atoms, rather than a conducting sphere [1]. We calculate the effective electric field ${\rm {\bf E}}_{eff} (\omega )$ at the fullerene center when the external ${\rm {\bf E}}(\omega )$ with frequency $\omega $ is applied to C$_{60}$. The modification of the external field comes from the effect of the dynamic dipole polarizability $\alpha _d (\omega )$ of the fullerene C$_{60}$ expressed via its total photoionization cross-section $\sigma (\omega )$[2]. We calculate the ratio $\eta (\omega )\equiv {\rm {\bf E}}_{eff} (\omega )/{\rm {\bf E}}(\omega )$ and then investigate whether $\eta (0)$ is equal to zero. The equality of the ratio $\eta (\omega )$ to zero in the static limit $\omega \to 0$ is the critical condition being general for a conducting body with any form. For C$_{60}$ this ratio is$\eta (0)\approx 2$, i.e. C$_{60}$ is not a hollow metallic sphere. It is shown that at any $\omega $ the frequency dependence of the ratio of the fields $\eta (\omega )$ at the center of the C$_{60}$ molecule and outside it has nothing to do with $\eta (\omega )$for the conducting sphere [1], which is additional evidence that the C$_{60}$ shell is strongly non-metallic. [1] J.-P. Connerade and A. V. Solov'yov, J. Phys. B 38, 807 (2005) [2] J. Berkowitz, J. Chem. Phys. 111, 1446 (1999). [Preview Abstract] |
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R1.00058: Long-range interactions between three P-state atoms in a magnetic field Sergey Alyabyshev, Roman Krems Using the spherical tensor expansion of the interaction potential between two open-shell atoms [1], we analyze adiabatic potential energy surfaces for three atoms in the 3P2 state in the presence of an external magnetic field. It is shown that anisotropic quadrupole-quadrupole interactions between three open-shell atoms may result in long-range repulsions due to avoided crossings between adiabatic surfaces correlating with different atomic states. The strength of the long-range repulsion depends on the magnitude of the applied magnetic field. [1] J.R. V. Krems, G. C. Groenenboom, and A. Dalgarno, Phys. Chem. A 108, 8941 (2004) [Preview Abstract] |
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R1.00059: Complete Single$-$Center Basis Sets in Atomic Calculations Scott I. Young, Kyle Rollin, Michael W.J. Bromley, Jim Mitroy, Kurunathan Ratnavelu Single particle orbitals centered on the nucleus are the most commonly used basis in large-scale calculations of atomic structure. The convergence towards a complete basis set, with respect to both the number and angular momenta of the orbitals included in a configuration interaction (CI) expansion, has been investigated using the ground and excited states of the helium atom [1,2,3]. This enabled energies to be determined to within $10^{-8}$ Hartree, whilst the convergence of the electron-electron $\delta$-function and other relativistic corrections have been examined in detail. Unusual convergence patterns in the CI-Kohn variational scattering method have been observed and, however, high-precision calculations of elastic positron scattering from atoms are achievable [4].\\ $[1]$ J.Mitroy, M.W.J.Bromley, K.Ratnavelu Int.J.Quant.Chem. \textbf{107} 907 (2007). \\ $[2]$ M.W.J.Bromley and J.Mitroy Int.J.Quant.Chem. \textbf{107} 1150 (2007). \\ $[3]$ K.Rollin, M.W.J.Bromley and J.Mitroy (in preparation). \\ $[4]$ S.I.Young, M.W.J.Bromley and J.Mitroy (in preparation). [Preview Abstract] |
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R1.00060: Precision Hyperfine Structure of $2\;^3$P State of $^3$He with External Magnetic QiXue Wu, G.W.F. Drake The theory of the Zeeman effect can be used to extrapolate precise measurements for the fine structure or the hyperfine structure to zero-field strength. In the present work, the hyperfine structure of $2\;^3$P state of $^3$He with external magnetic fields is precisely calculated. The values of the fields for 32 crossings and five anticrossings of the magnetic sublevels are theoretically predicted for magnetic field strengths up to 1 Tesla. The results are compared with experimental work. We include the linear terms, diamagnetic terms, and the $\alpha^2$ relativistic correction terms in the Zeeman Hamiltonian. All related matrix elements are calculated with high accuracy by the use of double basis set Hylleraas type variational wave functions[1,2].\newline [1] Z. -C. Yan and G.W.F. Drake, Phys.\ Rev.\ A {\bf 50}, R1980 (1994).\newline [2] Q. Wu and G.W.F. Drake, J.\ Phys.\ B {\bf 40}, 393 (2007). [Preview Abstract] |
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R1.00061: Experimental nonlinear studies of atoms and molecules with an intense VUV-photon source. Jeroen van Tilborg, Tom Allison, Marcus Hertlein, Thorsten Weber, Andrew Aquila, Sasa Bajt, Roger Falcone, Ali Belkacem Photons of energy in the 30-100 eV range can interact with core electronic states in atoms and small molecules. Through high-harmonic generation (HHG) by a terawatt near-infrared laser, such photons can now be delivered as energetic and ultra-short pulses ($>$10 nJ in $<$50 fs). After focusing of such VUV pulses, peak intensities can reach 10$^{13}$-10$^{14}$ W/cm$^{2}$, enabling nonlinear processes such as two-photon absorption to become detectable. In addition, intrinsic synchronization between laser and VUV photons allows for ultra-fast pump-probe experiments. The challenge in realizing these high harmonic pulses lays in phase matching, source optimization, separation of laser- and VUV-pulse, and their spectral and spatial characterization. Detailed information about these issues and their solution at LBNL will be presented On the application side, the latest results as well as planned experiments will be discussed. Such experiments include two-photon absorption of core electrons in Xenon, where a quadrupole giant resonance is expected, and two-photon double-ionization experiments on atoms and molecules. [Preview Abstract] |
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R1.00062: PHOTON INTERACTIONS WITH ATOMS, IONS, AND MOLECULES |
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R1.00063: Photoionization spectroscopy of even-parity autoionizing Rydberg states of argon atoms J.D. Wright, T.J. Morgan, Q. Gu, L. Li, J.L. Knee We use the J=0 and J=2 metastable states of argon created in a plasma discharge to perform photoionization spectroscopy of even-parity autoionizing Rydberg states of the argon atom between the first and second ionization limits. Fitting the data to a linear combination of Fano-type peaks allows us to extract the widths and q-parameters of the resonances. Finally, we compare the experimental profile of p-type multiplets to the results of recent theoretical calculations [1]. Agreement is good. \newline [1] I. D. Petrov, V. L. Sukhorukov, T. Peters, O. Zehnder, H. J. Worner, F. Merkt, H. Hotop, JPB 39 p. 3159 (2006) [Preview Abstract] |
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R1.00064: Space and Time Resolved Continuum Correlation in the Post-Collision Interaction of Core-Photoionized Neon A. Bhandary, A.L. Landers, F. Robicheaux, T. Osipov, M. Hertlein, M.H. Prior, A. Belkacem, P. Ranitovic, I. Bocharova, C.L. Cocke, T. Jahnke, M. Schoffler, J. Titze, R. Dorner We have used the COLTRIMS$^*$ technique to measure the momentum distribution of the photoelectron and the recoil ion produced by the core-photoionization of neon. Conservation of momentum allows us to determine the subsequent auger electron's momentum that is emitted when the Ne$^+$ relaxes to the Ne$^{2+}$ state. Momentum space plots of the electrons and the recoil ion are then used to resolve the three-body correlated post-collision interactions in space and time. Finally, classical calculations have been performed which corroborate our interpretation of the experimental results. \newline \newline $^*$R. Dorner, V. Mergel, O. Jagutzki, L. Spielberger, J. Ull- rich, R. Moshammer, and H. Schmidt-B\"aocking. Physics Reports, 330:96-192, 2000. [Preview Abstract] |
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R1.00065: Photoionization of Se+ and Se2+ Ions: Experiment and Theory D.A. Esteves, N.C. Sterling, Ghassan Alna'Washi, A. Aguilar, A.L.D. Kilcoyne, C.P. Balance, P.H. Norrington, B.M. McLaughlin The determination of elemental abundances in astrophysical nebulae are highly dependent on the accuracy of the available atomic data. Numerical simulations show that derived Se abundances in ionized nebulae can be uncertain by factors of two or more from atomic data uncertainties alone. Of these uncertainties, photoionization cross section data are the most important, particularly in the near threshold region of the valence shell. Absolute photoionization cross sections for Se$^+$ and Se$^{2+}$ ions near their thresholds have been measured at the Advanced Light Source in Berkeley, using the merged beams photo-ion technique. Theoretical photoionization cross sections calculations were performed for both of these Se ions using the state-of-the-art fully relativistic Dirac R-matrix code (DARC). The calculations show encouraging agreement with the experimental measurements. A more comprehensive set of results will be presented at the meeting. [Preview Abstract] |
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R1.00066: Experimental Identification of Specific Spin-Orbit Coupling Mechanisms During Photoionization J.R. Machacek, T.J. Gay, D.H. Jaecks, K.W. McLaughlin, O. Yenen Recent fluorescence polarimetry experiments have shown that even with a relatively light target like Ar, large relativistic effects are surprisingly common in photoionization. We show how dynamic magnetic effects during photoionization can be specifically identified as target spin-orbit coupling, target spin-continuum orbit coupling, or continuum spin-orbit coupling, the latter being the Fano effect. Our analysis involves the extraction of partial-wave cross sections from experimental polarization measurements for excited residual ion fluorescence. We demonstrate the application of this technique for fluorescence from the fine-structure resolved states of $Ar^+\,3p^4\,\left[ {{ }^3P} \right]\;4p\,{ }^2D_{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2} ,\,{ }^4P_{5 \mathord{\left/ {\vphantom {5 2}} \right. \kern-\nulldelimiterspace} 2} ,\,{ }^4D_{5 \mathord{\left/ {\vphantom {5 2}} \right. \kern-\nulldelimiterspace} 2} $. Support provided by the NSF (Grants PHY-0354946 and PHY-0098545) and the DOE (LBNL/ALS) [Preview Abstract] |
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R1.00067: Single and double photoionization of the laser-excited 6s6p 1Po state of Barium John R. Tolsma, Chris H. Greene We calculate the photoionization cross sections of the 6s6p 1Po state of barium by either one or two photons. In both cases the final state energies reach the vicinity of the 5d ionization thresholds.~This study uses variational R-matrix and quantum defect techniques to calculate the rich array of autoionizing resonances in this energy range. ~The two-photon cross section calculation utilizes Siegert pseudostates to describe the intermediate levels that arise in the second-order perturbation expansion. [Preview Abstract] |
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R1.00068: Photoelectron angular distribution measurements from $p$-electron photodetachment of Lu$^-$ A.M. Covington, S.S. Duvvuri, E.D. Emmons, R.G. Kraus, J.S. Thompson, V.T. Davis The spectral dependence of the angular distributions of photoelectrons produced by the single-photon photodetachment process h$\nu $+ Lu$^-$ ([Xe]$4f^{14}6s^25d 6p~^1D_2)$ $\rightarrow $ Lu ([Xe]$4f^{14}6s^25d~^2D_{3/2})$ + e$^-$, have been measured at discrete photon wavelengths ranging from 457.9 to 532 nm (2.71- 2.33 eV) using a crossed laser-ion beam apparatus. An intense 10 keV Lu$^-$ beam was crossed at 90$^\circ$ with a linearly polarized, continuous photon beam in order to produce photoelectrons. Photoelectron yields were measured as a function of the orientation of the laser polarization vector with respect to the momentum vector of the collected photoelectrons. The photoelectron angular distributions were used to determine asymmetry parameters. The spectral variation of the asymmetry parameter is shown to be consistent with the photodetachment of a $p$-electron using the model of Hanstorp $et al$ [Phys. Rev. A $\bf{40}$, 670 (1989)], and acts to verify the Lu$^-$ ground state configuration predicted by Elliav $et al$ [Phys. Rev. A, $\bf{52}$, 291 (1995)]. [Preview Abstract] |
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R1.00069: Tunable Laser Photodetachment Spectroscopy of Ce$^{-}$ N.D. Gibson, C.W. Walter, C.M. Janczak, K.A. Starr, A.P. Snedden, R.L. Field, P. Andersson The relative cross section for photodetachment from Ce$^{-}$ was measured over the photon energy range 0.5 -- 2.6 eV. Neutral atom production was measured as a function of photon energy for both long range survey scans and high resolution scans over interesting spectral features. The spectra reveal several continuum features likely associated with thresholds for opening detachment channels near 0.7 eV, 0.9 eV, and 1.3 eV. Five sharp peaks were observed over the range 0.61 -- 0.71 eV and their energies and widths were determined by fitting with Fano profiles. The results are compared to recent experimental [1] and theoretical [2] results for the electron affinity of Ce and the photodetachment spectrum of Ce$^{-}$. [1] V.T. Davis and J.S. Thompson, \textit{Phys. Rev. Lett.} \textbf{88}, 073003 (2002). [2] S.M. O'Malley and D.R. Beck, \textit{Phys. Rev. A} \textbf{74}, 042509 (2006); X. Cao and M. Dolg, \textit{Phys. Rev. A} \textbf{69}, 042508 (2004). [Preview Abstract] |
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R1.00070: Dynamical and relativistic effects in experimental and theoretical studies for inner-shell photoionization of sodium D. Cubaynes, J.-M Bizau, S. Diehl, F.J. Wuilleumier, H.-L. Zhou, S.T. Manson, A. Hibbert, N. Berrah, S. Canton, J.D. Bozek, E.T. Kennedy, L. Voky, X.-Y. Han High-resolution measurements for inner-shell photoionization of Na ground state over a 40-120 eV photon energy are presented along with the results of a semi-relativistic Breit-Pauli R-matrix calculation. The comparisons show excellent agreement generally, that gives a demonstration that the calculation includes the important relativistic and correlation effects. Relativistic effects are significant primarily in the neighborhood of narrow resonances. The importance of ``balancing'' the correlation included in initial and final state wave functions is emphasized. [Preview Abstract] |
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R1.00071: Calculation of inner-shell photoionization of ground state Na: relativistic vs. nonrelativistic calculation H.-L. Zhou, S.T. Manson, A. Hibbert Calculations of inner-shell photoionization of ground state Na over the photon energy range 40-100 eV have been performed using nonrelativistic LS coupling and relativistic Breit-Pauli (BP) R-matrix approximations. The BP R-matrix calculation adds the spin-orbit, mass-correction and Darwin terms to the non-relativistic Hamiltonian in order to include relativistic effects, giving 111 J-dependent states of Na$^{+ }$ from 61 LS states; the same target orbitals are used for both calculations. The calculated energy of ground state of Na is 5.1606 eV in LS coupling and 5.1756 eV in BP approximation ( NIST value is 5.14 eV). We find that in the neighborhood of the broad 2s$\to $np resonances, the results of LS and BP calculations are almost same, but in the neighborhood of narrow doubly-excited $2p^{5}$\textit{nln'l' }resonances, the BP calculations show spin-orbit splittings and differ significantly from the LS coupling results. [Preview Abstract] |
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R1.00072: Photo double detachment of CN$^{-}$: Electronic decay from an inner-valence hole in molecular anions R.C. Bilodeau, C.W. Walter, I. Dumitriu, N.D. Gibson, G.D. Ackerman, J.D. Bozek, B.S. Rude, R. Santra, L.S. Cederbaum, N. Berrah The first measurements of inner-valence photodetachment from CN$^{-}$ as well as theoretical calculations around the 2-electron threshold (25--90 eV) will be presented. Measured absolute cross sections for CN$^{+}$ production by photo double detachment of CN$^{-}$, and for C$^{+}$ and N$^{+}$ fragments produced from the dissociation of the excited molecule will be reported. The measurements also reveal the signature of inner-valence autoionization, similar to the interatomic Coulombic decay (ICD) phenomenon. This work confirms the predicted effect, which should in general be present for molecular anions, even in very small molecules. [Preview Abstract] |
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R1.00073: Inner Shell Studies in Transition Metal Negative Ions: d-shell Photoexcitation and Detachment R.C. Bilodeau, I. Dumitriu, N.D. Gibson, C.W. Walter, J.D. Bozek, Z.D. Pesic, D. Rolles, N. Berrah Results of the first inner-shell photoexcitation and detachment studies conducted on the transition metal negative ions will be presented. The experiments were conducted on Ru$^{-}$, Ni$^{-}$, Pd$^{-}$, and Pt$^{-}$ near the ns, np shells (n=3 for Ni, 4 for Ru and Pd, 5 for Pt) , and 4f shell (in Pt). All ions show significant probabilities for multi-electron ejection in the detachment and decay mechanisms, with a total of up to 4 electrons removed. Excitation of a p-electron into the nearly-filled d-shell (in Ru$^{-}$, Ni$^{-}$, and Pt$^{-})$ results in strong shape resonances, and excitation of a 4f-electron gives rise to conspicuous Feshbach resonances in Pt$^{-}$. In contrast, no resonances are observed in Pd$^{-}$, owing to its completely filled valence 4d shell, in spite of being in the same group as Ni and Pt. [Preview Abstract] |
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R1.00074: Time-dependent localized Hartree-Fock density-functional theory for photoionization processes of excited states of atomic systems Zhongyuan Zhou, Shih-I. Chu We propose a time-dependent localized Hartree-Fock density-functional approach for the treatment of photoionization processes of excited states of atomic systems. In this approach, Kohn-Sham (KS) equation with a spin-dependent localized Hartree-Fock (SLHF) potential being used as its exchange potential is solved to obtain electron spin-orbitals and orbital energies from which linear response function induced by an external radiation field is calculated and photoionization process is studied. The SLHF potential has good long-range behavior and thus allows one to treat the high-lying Rydberg states accurately. For demonstration, we apply this approach to calculate photoionization cross sections, linewidths, and resonance parameters of Ne. The results are in good agreement with experimental data and other theoretical calculations. We also present for the first time the photoionization cross sections of highly excited and inner-shell excited states of Ne. [Preview Abstract] |
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R1.00075: Electron affinity and photodetachment calculations of Nd$^-$ Steven M. O'Malley, Donald R. Beck Our recent relativistic configuration-interaction (RCI) calculations for the bound states of Ce$^-$\footnote{S. M. O'Malley and D. R. Beck, Phys. Rev. A {\bf 74}, 042509 (2006).} have shown the usefulness of analysis which combines calculated photodetachment cross sections with experimental measurements \footnote{V. T. Davis and J. S. Thompson, Phys. Rev. Lett. {\bf 88}, 073003 (2002).}. Here we present RCI results for 8 weakly bound ($\leq$ 0.2 eV) states of Nd$^-$ ($6p$ attachments to $4f^46s^2$). Photodetachment cross sections involving excited states of Nd {\sc i} are expected to resolve the discrepancy with the available experimental electron affinity of 1.916 eV \footnote{V. Davis and J. Thompson, Bull. Am. Phys. Soc. {\bf 48}, 98 (2003).}. Additional improvements of our methodology are also discussed. [Preview Abstract] |
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R1.00076: Non-dipole angular anisotropy parameters of photoelectrons from semi-filled shell atoms Miron Ya Amusia, Larissa V. Chernysheva We present the results of calculations of outer and next to the outer shell non-dipole angular anisotropy parameters of photoelectrons for semi-filled shell atoms in the Hartree-Fock one-electron approximation and in the frame of the Spin Polarized Random Phase Approximation with Exchange, which takes into account inter-electron correlations. We demonstrate for the first time that this characteristic of photoionization is essentially sensitive to the fact whether the photoelectron has the same or opposite spin orientation to that of the semi-filled shell. This can be detected experimentally since the term-dependence shows up in prominent corrections that are within the already achieved experimental accuracy. Note, that in spite of the fact that the non-dipole anisotropy parameter is usually for low enough photon energies much smaller than the dipole one (equal to 2 for s-subshells), it is quite measurable experimentally almost from the threshold even for He. For details see http://arxiv.org/phys/abs/physics/0606093 [Preview Abstract] |
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R1.00077: Dipole angular distribution and spin polarization of photoelectrons from semi-filled shell atoms Miron Amusia, Larissa Chernysheva We calculated photoelectrons' dipole angular anisotropy and spin-polarization parameters for a number of semi-filled shell atoms in the frame of the Spin Polarized Random Phase Approximation with Exchange. We consider photoelectrons from semi-filled and closed shells that are neighbours. We studied also photoelectrons from Cr$^{\ast}$ and Mo$^{\ast}$ that are formed by spin-flip of the outer $s - $electrons. To see the role of the nuclear charge variation, we have treated the case of 3$p$ - electrons in K, Ar and K$^{+}$. The following subshell were considered: N (2$p)$, P (3$p)$, Ar (3$p)$, K$^{+}$(3$p)$, K(3$p)$, Cr(3$p$, 3$d)$, Cr$^{\ast}$(3$d)$, Mn(3$p$, 3$d)$, As(3$d$, 4$p)$, Mo(4$p$, 4$d)$, Mo$^{\ast}$(4$d)$, Tc(4$p$, 4$d$, ), Sb(4$d$, 5$p)$, Eu(4$f)$. The detailed information can be found in [1].The peculiarities of obtained parameters as functions of photon frequency are quite prominent and deserve experimental investigation. \newline [1] M. Ya. Amusia and L. V. Chernysheva, http://arxiv.org/abs/physics/0701040 [Preview Abstract] |
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R1.00078: Photodetachment of Lanthanide Oxide Anions A.M. Covington, E.D. Emmons, R.G. Kraus, J.S. Thompson, D. Calabrese, V.T. Davis Laser photodetached electron spectroscopy (LPES) has been used to study the structure and collision properties of lanthanide oxide anions including LaO$_n^-$ and CeO$_n^-$. Preliminary photoelectron spectra from these anions will be presented along with ion beam production data from these and other lanthanide oxide anions. [Preview Abstract] |
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R1.00079: Ionization and Dissociation of $N_2 $ from 17.5 to 36.5 eV by Linearly and Circularly Polarized Light J.E. Furst, T.J. Gay, H. Gould, A.L.D. Kilcoyne, J.R. Machacek, K.W. McLaughlin We have measured the linear $\left( {P_1 } \right)$ and circular $\left( {P_3 } \right)$ polarization of the fluorescence emitted in the $\,B{ }^2\Sigma _u^+ \to \,X{ }^2\Sigma _g^+ \;\left( {{\nu }'=0,{\nu }''=0} \right)$ transition (391.4 nm) of $N_2^+ $ after photoionization of $N_2 $ by both linearly and circularly polarized VUV radiation. The value of $P_1 $ for linearly polarized excitation is in qualitative agreement with previous results [1]. Results for circularly-polarized excitation show significantly different energy dependence. In this energy range, photofragmentation into neutral atoms caused by the predissociation of doubly-excited Rydberg states via non-Rydberg doubly-excited resonances competes with photoionization [2]. We have measured the intensity and a distinct non-zero $P_3 $ of the fluorescence from the $NI\,\,3p\,{ }^4P^o\to 3s\,{ }^4P\,$ transition (818 nm) between 22.5 and 25 eV which corresponds to the initial excitation of the $N_2 $ Rydberg R(C) states. [1] J. A. Guest \textit{et al.}, Phys. Rev. A \textbf{28}, 2217 (1983) [2] P. Erman \textit{et al.}, Phys. Rev. A \textbf{60}, 426 (1999) Support provided by the NSF (Grant PHY-0354946), the DOE (LBNL/ALS) and the ANSTO (Access to Major Research Facilities Programme). [Preview Abstract] |
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R1.00080: Photoionization of Xe 3\textit{d} electrons in molecule Xe@C$_{60}$: interplay of intra-doublet and confinement resonances Miron Ya Amusia, Arkadiy S. Baltenkov, Larissa V. Chernysheva We demonstrate rather interesting manifestations of co-existence of resonance features in characteristics of the photoionization of 3$d$-electrons in Xe@C$_{60}$. It is shown that the reflection of photoelectrons produced by the 3$d$ Xe photoionization affects greatly partial photoionization cross-sections of $3d_{5/2} $ and $3d_{3/2} $ levels and respective angular anisotropy parameters, both dipole and non-dipole adding to all of them additional maximums and minimums. The calculations are performed treating the 3/2 and 5/2 electrons as electrons of different kinds with their spins ``up'' and ``down''. The effect of C$_{60}$ shell is accounted for in the frame of the ``orange'' skin potential model. It is essential that in the considered photon frequency region presented resonance features are not affected by the C$_{60}$ polarization. For details see http://arxiv.org/abs/physics/0609121. [Preview Abstract] |
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R1.00081: NEW THEORETICAL AND EXPERIMENTAL TECHNIQUES; APPLICATIONS OF AMO SCIENCE; NONLINEAR DYNAMICS |
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R1.00082: Exact Quantum Treatment of Continuum Electrons Teck-Ghee Lee, S. Yu Ovchinnikov, James Sternberg, V. Chupryna, D.R. Schultz, J.H. Macek An exact three-dimensional (3D) quantum mechanical treatment is presented for the evolution of continuum electrons in the fields of moving ions. The novel method introduced here allows one to propagate the continuum electrons to asymptotically large internuclear distances and obtain stable ejected electron momentum spectra. As a result, our computations resolve long standing controversies concerning top-of-barrier, superpromotion and cusp electron momentum distributions. While the method is employed for protons impact ionization of atomic hydrogen, it is general and readily applied to any problems involving electron motion in the presence of time-dependent external fields. [Preview Abstract] |
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R1.00083: Hyperangular Green's functions and the three body problem Seth T. Rittenhouse, Nirav P. Mehta, J.P. D'Incao, Chris H. Greene A Green's function approach is formulated and used to determine adiabatic hyperspherical potential curves. ~The Green's function is found for the hyperangular part of the non-interacting Schroedinger equation with any number of particles in any number of dimensions. This Green's function is then applied to the three-body problem with regularized, zero-range, pair-wise, s-wave interactions, which determine a quantization condition whose solution yields the adiabatic potential curves for any given total angular momentum and exchange symmetry. ~This method appears to generalize readily to handle multichannel, regularized, zero-range, pair-wise interactions. [Preview Abstract] |
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R1.00084: Thermalization of Suprathermal N($^{4}$S) atoms in He and Ar gases. Peng Zhang, Alexander Dalgarno The thermalization of hot nitrogen atoms in the He and Ar buffer gases is investigated. We calculate the rates of energy relaxation of fast nitrogen atoms and provide simple interpolative formulas for the N($^{4}$S) thermalization rates. The method of determination of the energy relaxation rate is based on the numerical solution of the Boltzmann kinetic equation, describing the evolution of the time- dependent distribution functions of fast nitrogen atoms. The rates of energy transfer in N($^{4}$S) + He and Ar collisions are determined using quantally computed differential cross sections of elastic collisions. Theoretical data on the energy relaxation of hot N($^{4}$S) atoms are compared with the results of recent experiments on the thermalization of fast N($^{4}$S) atoms in He and Ar buffer gases. The laboratory measurements of the Doppler shifts of the laser induced fluorescence of hot N($^{4}$S) atoms provide detailed information on the time-evolution of energy distribution functions of N($^{4}$S) atoms, and we employ these data for testing the theoretical predictions. Results of our ab initio calculations are in good agreement with experimental data. We report also the parameters of the simplified hard sphere model, which describes effective energy relaxation rates of hot N($^{4}$S) atoms, thermalizing with initial energies between 0.05 and 5 eV in different gases. [Preview Abstract] |
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R1.00085: Anti-relaxation Surface Coatings for High-Density Alkali-Metal Magnetometers Scott Seltzer, Michael Romalis, David Rampulla, Steven Bernasek, Sandrine Rivillon, Yves Chabal Anti-relaxation surface coatings eliminate the need for buffer gas in alkali-metal vapor cells, giving larger signals due to narrower optical linewidths as well as reduced sensitivity to magnetic field gradients. Paraffin and other coatings presently used to reduce surface relaxation typically cannot operate at the high temperatures (T$>100^{\circ}$C for cesium and T$>150^{\circ}$C for potassium) required to obtain alkali-metal density suitable for spin-exchange relaxation free (SERF) magnetometers. We have found that octadecyltrichlorosilane (OTS) coating can allow approximately 2000 collisions of a potassium atom with the cell walls before depolarization. OTS can operate at temperatures of at least 150$^{\circ}$C in the presence of potassium, and we have demonstrated a SERF magnetometer using an OTS-coated cell. We have also developed a reusable alkali vapor cell for simultaneous testing of multiple coated surfaces, and we are presently investigating several other coatings for chemical resistance to alkali metals, antirelaxation properties, and high-temperature operation. Development of a robust, high-temperature anti-relaxation surface coating would allow many experiments using very optically thick alkali vapor with a long spin relaxation time. [Preview Abstract] |
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R1.00086: Radio-frequency tunable atomic magnetometer for detection of solid-state NQR S.-K. Lee, K.L. Sauer, S.J. Seltzer, O. Alem, M.V. Romalis We constructed a potassium atomic magnetometer which resonantly detects rf magnetic fields with subfemtotesla sensitivity. The resonance frequency is set by the Zeeman resonance of the potassium atoms in a static magnetic field applied to the magnetometer cell. Strong optical pumping of the potassium atoms into a stretched state reduces spin-exchange broadening of the Zeeman resonance, resulting in relatively small linewidth of about 200 Hz (half-width at half-maximum). The magnetometer was used to detect $^{14}$N NQR signal from powdered ammonium nitrate at 423 kHz, with sensitivity an order of magnitude higher than with a conventional room temperature pickup coil with comparable geometry. The demonstrated sensitivity of 0.24 fT/Hz$^{1/2}$ can be improved by several means, including use of higher power lasers for pumping and probing. Our technique can potentially be used to develop a mobile, open-access NQR spectrometer for detection of nitrogen-containing solids of interest in security applications. [Preview Abstract] |
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R1.00087: An open-access, low-field MRI system for human lung imaging with hyperpolarized 3He Leo Tsai, Matthew Rosen, Chih-Hao Li, Ana Batrachenko, Ross Mair, Ronald Walsworth The human lung is exquisitely sensitive to gravity and posture. However, conventional high-field magnets used for hyperpolarized noble gas MRI of the human lung restrict subjects to lying horizontally. We have built an open-access, low-magnetic-field ($<$5 mT) MRI instrument which allows freedom of body positioning while providing high-resolution lung images. We have performed 3He lung MRI of human subjects in both the supine and upright positions; and used these images to make the first-ever maps of the heterogeneous distribution of oxygen in the human lung in an upright position. [Preview Abstract] |
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R1.00088: Phase noise compensation in optical fiber delivery of narrow-linewidth optical frequency standard Won-Kyu Lee, Chang Yong Park, Ho Suhng Suh, Dai-Hyuk Yu, Sang Eon Park We have transferred a narrow-linewidth 1550 nm laser through a 525 m fiber network with excellent transfer stability. The fiber-induce optical phase noise during the fiber transmission broadens the laser linewidth to several kHz. We have compensated this fiber-induced phase noise by configuring a noise-canceling servo. The compensated optical phase noise has the standard deviation of 0.21 rad. There was no cycle-slip in phase noise compensation. The transfer instability was 2x10$^{-17}$ at 1 s of averaging time. This is quite sufficient for the delivery of highly stable optical frequency standards currently available without fiber-induced noise. We have a plan to utilize this technique in building an ytterbium lattice clock. [Preview Abstract] |
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R1.00089: A dual-stage laser ablation source for cold atoms? William Farmer, Michael Amonson, Scott Bergeson A recent publication reports a low velocity, low divergence atomic beam generated by laser ablation [RSI 76, 113302 (2005)]. The reported velocities of 40 m/s and divergences of 20 mrad seem physically impossible for ablation sources. They were determined indirectly by measuring the index of refraction using a far-off-resonance laser. We report our efforts to reproduce this experiment and to measure the atomic density and velocity directly using laser induced fluorescence in an ablated calcium beam. [Preview Abstract] |
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R1.00090: Phase-locked scanning interferometer for frequency stabilization of multiple lasers Alexey Tonyushkin, Michael Di Rosa We report a simple scheme for stabilizing and tuning the length of a conventional piezo-driven optical cavity against the resonant transmission of a master laser. Different from the other schemes, we drive the piezo at its mechanical resonance of 5~kHz over an amplitude equivalent to one free spectral range and use a feedback circuit that incorporates a phase- sensitive detection of the master-laser transmission. The bandwidth of our cavity-lock circuit is 1.4~kHz, as limited by the resonance frequency of the cavity piezo. The mean cavity length is stabilized to a minimum Allan variance of $\sim$10~kHz (a length stability of 20 parts per trillion) equaling that of the polarization-stabilized He-Ne we use as our master laser. Here, we investigate the mechanical characteristics of the cavity, describe the lock circuit and its measured performance, and present calculations relating the phase-sensitive signal to cavity displacement. We believe our setup economizes the cost and amount of equipment necessary for stabilizing multiple cw lasers operating at different wavelengths. [Preview Abstract] |
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R1.00091: Simple scheme for temperature insensitive laser frequency stabilization Lucas Willis, Michael Lim We demonstrate two methods to combat differential intensity drifts in modulation-free laser frequency stabilization.~ The locking signal is derived from~the difference between~two frequency shifted Doppler-broadened absorption signals from a vapor cell.~ In one method, a single AOM is used in conjunction with analog divider IC's to normalize the absorption signal amplitudes before generating the dispersion-like signal.~ The other method uses two AOMs for active intensity correction.~ A sample of each beam is taken before the vapor cell and a feedback loop stabilizes the intensity by~actively attenuating~the RF sent to the AOM.~ We report on frequency stability of both setups. [Preview Abstract] |
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R1.00092: ABSTRACT HAS BEEN MOVED TO D1 |
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R1.00093: Study of Spontaneous Symmetry Breaking in Parametrically Driven Magneto-Optical Trap Yonghee Kim, Myoung-Sun Heo, Wonho Jhe, Heung-Ryoul Noh, Mark Dykman Recently, there were a lot of results related to many interesting nonlinear phenomena in parametrically driven Magneto-optical trap(MOT) system. Among them spontaneous symmetry breaking(SSB) is most interesting phenomenon. The SSB has been observed experimentally but it is not fully understood in microscopic view. We study the SSB theoretically by changing of variable in rotating frame and modeling the interaction between the atoms. We simulate the system with changing the interaction strength and diffusion constant, then compare with the experimental results. [Preview Abstract] |
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R1.00094: Prametric Excitation in a Magneto-optical Trap with Modulating the Magnetic Field Gradient Dahyun Yum, Myoung-Sun Heo, Younghee Kim, Heung-Ryoul Noh, Wonho Jhe Parametric resonance is a very interesting and important mechanism in divergent systems. There were a lot of researches relating to the parametric excitation in the magneto-optical trap system. However, the previous works were executed by modulating the cooling laser intensity only. While the intensity modulation shows limit cycle, Hopf-bifurcation and Ising like phase transition, due to its driven amplitude, magnetic field gradient modulation could reveal more interesting phenomena such as period doubling, chaos and so on. We have studied the transition problems between two attractors in period doubling area which are much far from equilibrium. The magnetic field modulation methods could give quantitative comprehensions of transition problems in the nonequilibrium system. [Preview Abstract] |
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R1.00095: Classical chaos in a novel inhomogeneous photonic billiard S. Saidi, G. Painchaud-April, J. Poirier, P.-Y. St-Louis, J. L{\'e}pine, L. J. Dub{\'e} Dielectric microcavities / microlasers are becoming key components for novel opto-electronic devices. They represent a realization of a wave chaotic system (see companion contribution in Category 4.4) where for instance the lack of symmetry in the resonator shape leads to non-integrable ray dynamics in the short-wavelength limit ({\em photonic billiard}). Contrary to usual procedure where a transition from a regular to a chaotic regime is induced by a geometric deformation of a circular cavity, we propose a scenario inducing rotational symmetry breaking by choosing an inhomogeneous dielectric material inside a circular cavity, i.e {\em chaos in an integrable billiard geometry} . We study the consequences of this choice, isolate the conditions for integrability in such systems, describe the transition to chaos and classify the effects of the symmetry of the inhomogeneous dielectric on the trajectories. [Preview Abstract] |
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R1.00096: Wave chaos in a new class of optical microcavity G. Painchaud-April, J. Poirier, P.-Y. St-Louis, J. L{\'e}pine, S. Saidi, L. J. Dub{\'e} We introduce a new class of open optical microcavity whose confinement and directional emission properties can be engineered through modification of a space-dependent refractive index. Numerical results are provided for a microdisc with Gaussian deformation of the refractive index. This leads to a new way of breaking integrability and inducing chaos in the classically equivalent system ({\em photonic billiard}, see companion contribution in Category 7.3) and to the potential fabrication of reconfigurable microlasers. [Preview Abstract] |
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R1.00097: ELECTRON-ATOM AND ELECTRON-MOLECULE COLLISIONS |
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R1.00098: Differential Cross Sections for the Electron Impact Excitation of Molecular Nitrogen Murtadha A. Khakoo, S. Wang, Paul V. Johnson, Charles P. Malone, I. Kanik New measurements of differential cross-sections (DCS) for electron impact excitation of the a''$^{1}\Sigma_{g}^{+}$, b,c,o $^{1}\Pi_{u}$ and b',c'$^{1}\Sigma_{u}^{+}$. are presented. The measurements were taken at incident electron energies of 17.5eV,20eV, 30eV, 50eV and 100eV and for scattering angles of 3$^{o}$ to 130$^{o}$ in closely spaced intervals. From the data we observe a cusp-like behavior in the DCS of the a''$^{1}\Sigma _{g}^{+ }$excitation at small scattering angles, hitherto undetected by past measurements and were able to get estimated optical oscillator strengths for the b,c,o,b' and c' excitations. Comparison of the present results with those available in the literature will also be presented. [Preview Abstract] |
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R1.00099: An Accurate, but Novel Application of the Relative Flow Technique, Using a Moveable Aperture Source of Gas Atoms to Measure Elastic Electron Scattering Differential Cross Sections Murtadha A. Khakoo, Kyle Keane, Colin Campbell, Shayne Cairns The implementation of a powerful, accurate and novel method to measure elastic differential scattering cross sections (DCS) from gaseous targets, without having to know the molecular diameters of the gases used, will be presented. This is possible by taking advantage of the cosine angular distribution of gas produced by a thin aperture source. Preliminary tests with N$_{2}$ and C$_{2}$H$_{4}$ and other polyatomics will be presented at the meeting. [Preview Abstract] |
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R1.00100: Temperature Dependent Studies of Negative Ion Lifetimes M. Cannon, Y. Liu, L. Suess, F.B. Dunning, J. Steill, R.N. Compton The lifetimes of $SF_6^- $ ions produced in K(\textit{np})/SF$_{6}$ collisions at high $n$ are being investigated as a function of target temperature over the range 300K to 600K. At room temperature, collisions are found to lead predominantly to the formation of long-lived $SF_6^- $ ions with lifetimes $\tau >$1ms. As the target temperature is raised long-lived ($\tau >$0.5ms) ions are still observed but their mean lifetime is reduced. In addition, the growth of a short-lived ion signal ($\tau <$10 $\mu $s) is evident which, by 600K, accounts for $\sim $45{\%} of the total $SF_6^- $ ion signal. These lifetimes are compared with those obtained using quasi-equilibrium theory and calculated $SF_6^- $ vibrational frequencies. Measurement and theory are being extended to other attaching targets to further examine the factors that govern negative ion lifetimes. [Preview Abstract] |
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R1.00101: Low energy electron scattering from N$_2$H molecules Brendan M. McLaughlin, Robert C. Forrey Electron collisions with the N$_2$H radical are an important constituent of understanding electron detachment in low energy H$^-$ + N$_2$ collisions. Potential energy curves for both the neutral N$_2$H and anion N$_2$H$^-$ molecules are calculated in C$_s$ symmetry for perpendicular, colinear and bent geometry using valence-CI and CASSCF approximations. Low energy electron scattering from the N$_2$H molecule are carried out using the R-matrix approach to determine the elastic scattering cross-section as a function of the colliding electron energy. Resonance energies and the autoionization linewidth ($\Gamma$) found in the elastic scattering cross sections are determined as a function of the stretching of the N$_2$ - H bond length, where the N$_2$ molecule is fixed at its equilibrium geometry. A complex potential is then constructed from the resonance parameters and used in the heavy particle dynamical calculations to determine the low energy electron detachment cross sections and rates. Results for isotopic replacement of H$^-$ by D$^-$ have also been obtained for this cold molecular complex. Further details will be presented at the meeting. [Preview Abstract] |
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R1.00102: Resonant positron annihilation in rings and substituted alkanes J.A. Young, C.M. Surko Energy-resolved positron-on-molecule annihilation rates have been measured for a variety of molecules by passing a cold positron beam through test gases [1,2]. In many cases, the annihilation rates exceed the free electron annihilation rate by orders of magnitude. In particular, when the positron energy equals a vibrational mode energy minus the binding energy, large vibrational Feshbach resonances (VFR) are observed. In alkane molecules, the height of the C-H stretch resonances grow exponentially and the binding energy grows linearly with the number of carbons [1]. In this paper, we report new results for benzene, d-benzene, and 1-chlorohexane. Specifically, we examine the relationship between binding, C-H peak height, and molecular size. All these molecules have deeper binding than alkanes with similar numbers of carbons or atoms. An empirical trend will be discussed such that molecules with the same number of atoms have similar C-H peak heights when the simple kinematic effects of the binding energy on VFR are normalized out. \newline [1] L. D. Barnes, \textit{et al.}, \textit{Phys. Rev. A} \textbf{67}, 032706 (2003). \newline [2] L. D. Barnes, \textit{et al.}, \textit{Phys. Rev. A} \textbf{74}, 012706 (2006). [Preview Abstract] |
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R1.00103: Resonant positron annihilation in the small molecule limit C.M. Surko, J.A. Young Energy-resolved measurements of positron-on-molecule annihilation have established the existence of vibrational Feshbach resonances (VFR) in alkanes and other large molecules [1,2]. Large annihilation rates occur whenever the incident positron energy is close to a vibrational mode energy minus the binding energy. Recently, Gribakin and Lee developed a quantitative model which successfully describes this process in halogen substituted methanes [3]. In this paper, we further examine VFR for small molecules. Using a cold positron beam from a Penning-Malmberg trap, we measured the energy resolved annihilation spectra of CD$_3$Cl, methanol, H$_2$O, and CO$_2$ and compared them to the predictions of the model. The presence or absence of resonances in these molecules is also discussed. CD$_3$Cl is compared to previous measurements of CH$_3$Cl. Since both should have identical binding, this provides a stringent test of the model. \\ ~[1] L. D. Barnes, \textit{et al.}, \textit{Phys. Rev. A} \textbf{67}, 032706 (2003). \\ ~[2] L. D. Barnes, \textit{et al.}, \textit{Phys. Rev. A} \textbf{74}, 012706 (2006). \\ ~[3] G. F. Gribakin and C. M. R. Lee, \textit{Phys. Rev. Lett.} \textbf{97}, 193201 (2006). [Preview Abstract] |
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R1.00104: Modified COLTRIMS Technique to Measure Electron Interactions with Atoms and Molecules J.B. Williams, J. Stewart, A. Bhandary, E.J. Clothiaux, A.L. Landers We have built a modified COLTRIMS apparatus to measure electron collisions with atoms and molecules. A beam from a pulsed electron gun passes through a diffuse target, followed by a synchronized electric field pulse which extracts the ions to a multi-channel plate detector with delay-line anode. By measuring positions and times of the extracted ions, relative cross sections differential in ion momentum can be determined. For example, this information can lead to both molecule orientation and dissociation energy. Preliminary results will be presented. [Preview Abstract] |
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R1.00105: A Simple Method to Calculate Elastic Scattering of Electrons by Molecules of any Size Mike Crabtree, Don Madison We have developed a simple method to calculate differential cross sections for elastic scattering of electrons from molecules. The computer program called General Atomic and Molecular Structure System, or GAMESS, is used to generate molecular charge densities. The charge densities are used to calculate spherically averaged static potentials for an external electron. To the static potential, we add approximate correlation, polarization and exchange potentials. The resulting molecular potential is then used to calculate L- dependent phase shifts and elastic scattering cross sections. The accuracy of this simple method will be examined by comparing theoretical results with absolute differential cross section measurements that have been made for several different molecules. [Preview Abstract] |
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R1.00106: Extension of the MCHF method to investigate electron Impact Ionization of Atoms near Threshold Haripada Saha Recently we have extended the multi-configuration Hartree-Fock (MCHF) method for multi-open channel wave functions [1] to calculate near threshold electron impact ionization of atoms. We have evaluated the triply differential cross sections for electron impact ionization of H and He using both the Hartree-Fock (HF) and the MCHF approximation. In particular, we will present results of triply differential cross sections for H and He for final state electrons sharing $\le $ 4 eV excess energy and leaving in opposite directions. In addition, we have also performed calculation with replacement of exact coulomb interaction between the two continuum electrons by a variationally determined screening potential [2-5]. We will compare our results calculated in the three approximations with the available experimental measurements. 1. H.P. Saha . D.J. Murray, J.Phys. B 38,3015 (2005). 2. M.R.H, Rudge and M.J. Seaton, Proc. R. Soc. London, Ser. A 283, 262 (1965). 3. R.K. Peterkop, Theory of Ionization of atoms by electron impact (Colorado Associated University Press, Boulder, 1977), pp. 128 and 129. 4. S. Jetzke, J. Zaremba, and F.H.M. Faisal, Z.Phys. D 11, 63 (1989). 5. Cheng Pan and Anthony F. Starace, Phys.Rev. Lett. 67,185 (1991); Phys. Rev. A 45, 4588(1992). [Preview Abstract] |
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R1.00107: Implications for Atomic Physics from New Ionization Balance Calculations and Solar Physics Observations Paul Bryans, Enrico Landi, Daniel Savin We have used state-of-the-art electron-ion recombination data for K-shell, L-shell, and Na-like ions of H through Zn to calculate improved collisional ionization equilibrium (CIE) fractional abundances for ions of all these elements. We present the implications of these new CIE results for observations of the solar atmosphere and discuss a number of atomic systems showing puzzling discrepancies between observations and solar models. These discrepancies suggest errors in the underlying atomic data. Based on this, we highlight those atomic processes that require improved theoretical or experimentally-derived rate coefficients. [Preview Abstract] |
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R1.00108: Out-of-plane~($e,2e$)~experiments~on helium autoionizating states. B.A. deHarak, N.L.S. Martin Recent COLTRIMS experiments on charged particle ionization have found substantial disagreement with theoretical predictions. In particular the angular distribution of electrons ejected into a plane perpendicular to the scattering plane disagreed with expectations by a factor of between three and five. A mechanism has been proposed to explain these results that invokes a second collision of the projectile in which it undergoes elastic scattering with the residual ion. We are investigating such phenomena when autoionization is present: the finite lifetime of the intermediate state will profoundly affect any such second collision and will influence the ejected electron angular distributions. Our experiments are being carried out on an existing ($e,2e$) apparatus modified to allow the electron gun to move on the surface of a (mathematical) cone. This permits the measurement of out-of-plane ($e,2e$) angular distributions, for a full 360$^{\circ}$, using a special geometry that allows out-of-plane conditions to be combined with the binary peak in a single measurement. Details of the apparatus, and the results of preliminary experiments on He $2s2p~^1P$, will be presented. [Preview Abstract] |
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R1.00109: Electron Impact Ionization of Noble Gas Atoms Radu Campeanu Electron impact single ionization of light noble gas atoms remains a formidable theoretical and computational challenge. Most experiments measuring total ionization cross sections are in agreement with each other, but on the theory side work is still needed for atoms heavier than helium. Distorted wave calculations, distorted-wave-R-matrix hybrid models, time-dependent close coupling calculations and coupled-channel-optical calculations produced total ionization cross sections which are in general significantly higher than the experimental data. Recent theoretical work on positron impact ionization of atoms and molecules was based on the use of several simple distorted-wave models. In these models the initial state of the atoms were represented in the Hartree-Fock approximation, while the incident and scattered positron and the ejected electron were described in a number of ways which tried to reproduce the pre and post-collision effects. We found that the inclusion in the final state representation of the electrostatic interaction between the ejected electron and scattered positron (model CPE4) produced good agreement with experiment for hydrogen and all the noble gases. In this paper we examine the possibility of employing electron impact ionization distorted-wave models similar to those successfully used in the positron impact ionization case. We find that when combined with the `maximum interference' model, these models produce good agreement with the experiments. [Preview Abstract] |
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R1.00110: Electron impact excitation of calcium. Oleg Zatsarinny, Klaus Bartschat, Victor Gedeon, Ludmila Bandurina We have used the $B$-spline $R$-matrix (close-coupling) method with non-orthogonal sets of orbitals~[1] to extend our recent calculation for low-energy elastic electron collisions with calcium atoms~[2] to excitation of the lowest few excited states. Our results for state-selected angle-integrated and angle-differential cross sections, as well as angle-differential electron-impact correlation parameters, measured in electron-photon coincidence or superelastic scattering setups, will be compared with recent experimental data~[3,4] and predictions from other theoretical methods~[5,6]. \par\vspace{0.1truecm}\noindent [1] O.~Zatsarinny, Comp. Phys. Commun. {\bf 174}, 273 (2006). \par\noindent [2] O.~Zatsarinny {\it et al.}, Phys. Rev. A {\bf 74}, 052708 (2006). \par\noindent [3] S. Milisavljevic {\it et al.}, J. Phys. B {\bf 37}, 3571 (2004). \par\noindent [4] A. Murray and D. Cvejanovic, J. Phys. B {\bf 36}, 4889 (2003). \par\noindent [5] R. Chauhan {\it et al.} J. Phys. B {\bf 38}, 2385 (2005). \par\noindent [6] S. Kawazoe {\it et al.}, J. Phys. B {\bf 39}, 493 (2006). [Preview Abstract] |
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R1.00111: A Study of Bremsstrahlung Produced From Solid Gold Films Scott Williams, C.A. Quarles We report the results of our on-going study of the thickness-dependence of bremsstrahlung from solid gold film targets. The incident electrons' energy is approximately 53 keV, and we have collected data from angles of 90 and 135 degrees. Target thicknesses ranging from 66 $\mu $g/cm$^{2}$ (where single interaction conditions apply) to more than twice the electron range (where a multiple interaction model applies) were studied. With this data, we can observe the transition from thin to thick film spectra, and compare it to data obtained using the Monte Carlo simulation, PENELOPE. This comparison could reveal whether there is any polarizational bremsstrahlung contribution for solid film targets. We also present results for the absolute doubly-differential cross section for the thin-film targets and compare the results with predictions of both ordinary bremsstrahlung and total bremsstrahlung including a polarizational contribution calculated in the stripping approximation. [Preview Abstract] |
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R1.00112: A Scaling for Differential Single and Multiple Ionization of Kr by Electron Impact O.G. de Lucio, J. Gavin, R.D. DuBois Differential measurements of Kr ionization by electron impact were performed for an electron beam of 240 eV and 500 eV energies, colliding with a Kr gas jet target. Results for absolute doubly differential cross sections (DDCS) of Kr$^{+}$, Kr$^{2+}$ and Kr$^{3+}$ ionization states are presented. Kr ions are pulled out of the interaction region by means of a pulsed field and recorded by means of a channeltron detector used in coincidence with a projectile detector in order to acquire differential information. DDCS plotted as a function of projectile energy loss and momentum transfer were investigated, some similarities were observed but in general no ``universal curves'' were found. By using a ``reduced momentum'' the DDCS for different angles, energy losses and even for different projectile energies could be compressed into two curves, corresponding to large ($90^\circ \ge \theta \ge 30^{\circ})$ and small ($\theta <30^{\circ})$ scattering angles. These different scalings and variables will be presented and discussed. [Preview Abstract] |
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R1.00113: Inner-shell Ionization With Relativistic Corrections By Electron Impact Bidhan Saha, M.A.R. Patoary, M. Alfaz Uddin, A.K.F. Haque, Arun K. Basak A simple method is proposed and tested by evaluating the electron impact inner-shell ionization cross sections of various targets up to ultra high energy region. In this energy region there are not many calculations due to lack of reliable method. In this work we extend the validity of the siBED model [1] in terms of targets and incident energies. The extension of our earlier RQIBED model [2] is also reported here and we examined its findings for the description of the experimental EIICS data of various targets up to E=1000 MeV. Details will be presented at the meeting. \newline [1] W. M. Huo, Phys. Rev A 64, 042719 (2001). \newline [2] M. A. Uddin, A. K. F. Haque, M. S. Mahbub, K. R. Karim, A. K. Basak and B. C. Saha, Phys. Rev. A 71, 032715 (2005). [Preview Abstract] |
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R1.00114: An Attempt to Observe Mott Scattering Optically in Krypton. J.W. Maseberg, T.J. Gay We present recent measurements of the relative Stokes parameters for the 811 nm Kr (4p$^{5}$5p)[5/2] $^{3}$D$_{3}\to $(4p$^{5}$5s)[3/2] $^{3}$P$_{2}$ transition excited by polarized electron impact. Of particular interest is the spin-normalized linear polarization fraction P$_{2}$/P$_{e}$. Because the upper excited state is well \textit{LS}-coupled, a near-threshold observable non-zero value of P$_{2}$ implies spin-orbit coupling between the target and continuum electron (an optical analog of Mott scattering) [1]. This work is a continuation of a previous paper wherein a cascade free measured P$_{2}$/P$_{e}$ of 0.028(26) is compared to a theoretical 31-state Breit-Pauli R-matrix calculation which predicts a value of 0.032 [2]. Thus our earlier data is consistent with both the theory and zero. Our current effort is to increase the precision of these measurements. \newline \newline [1] N. Anderson and K. Bartschat, \textit{Polarization, Alignment, and Orientation in Atomic Collisions}, (Springer-Verlag, New York, 2001). \newline [2] B.G. Birdsey \textit{et al}., Phys. Rev. A \textbf{60}, 1046 (1999). [Preview Abstract] |
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R1.00115: Elastic Electron Scattering from the 6P and 5D Levels of Ba Jeff Hein, Peter Zetner Measurements of elastic electron scattering from excited atoms are relatively scarce and, hence, the ability to test theoretical descriptions of such a scattering process is rather limited. Here, we present experimental data for the differential cross section (DCS) and the P$_{3}$ Stokes parameter for elastic scattering from the 6P and 5D levels of Ba at collision energies of 10 and 20 eV. The P$_{3}$ parameter quantifies the dependence of elastic scattering on the orientation of the atomic target state. Oriented target states (5D and 6P) are produced using circularly polarized light to prepare the excited atoms. The present measurements extend the work of Trajmar et al.$^{1}$ undertaken with aligned Ba 6P atoms prepared by linear polarized laser light. Excellent agreement with convergent close coupling theory $^{2,3}$ has been found for the DCS. Significant orientation dependence of elastic scattering has been observed but agreement with theory is less satisfactory. 1. S. Trajmar et al. J.Phys.B:At.Mol.Opt.Phys. \textbf{32} 2801 (1999) 2. I. Bray et al. J.Phys.B:At.Mol.Opt.Phys. \textbf{35} R117 (2002) 3. D. Fursa Private communication (2006) [Preview Abstract] |
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R1.00116: Electron Impact Induced Excited-State to Excited-State Transitions in Yb Jeff Hein, Peter Zetner The Yb atom (ground state electron configuration: [Xe]4f$^{14}$ 6s$^{2}$ $^{1}$S$_{0})$ is a heavy two-electron system in which spin-orbit coupling effects play a significant role in the electronic level structure. More experimental data for scattering from this atom are becoming available, motivating the application of recent theoretical methods to this system $^{1-4}$. The non-negligible role of spin-orbit coupling suggests that a relativistic theoretical formalism may be required. We have extended our scattering studies out of ground (6s$^{2} \quad ^{1}$S$_{0})$ state target atoms to excited (6s6p $^{3}$P$_{1})$ atoms using laser excitation of the atomic beam. Measurements of the inelastic differential cross section for the excitations 6s6p $^{3}$P$_{1}$ - 5d6s $^{3}$D and 6s6p $^{3}$P$_{1}$ - 6s7s $^{3}$S$_{1}$ are presented for 20 eV collision energy. Additionally, by employing circularly polarized laser light in the preparation of the $^{3}$P$_{1}$ target state, we are able to measure the P$_{3}$ Stokes parameter for these excitations. 1. P.V. Johnson et al. J. Phys. B: At. Mol. Opt. Phys. \textbf{31} 3027 (1998) 2. P.W. Zetner et al. J. Phys. B: At. Mol. Opt. Phys. \textbf{34} 1619 (2001) 3. B Predojevic et al J. Phys. B: At. Mol. Opt. Phys. \textbf{38} 1329 (2005) 4. B Predojevic et al J. Phys. B: At. Mol. Opt. Phys. \textbf{38} 3489 (2005) [Preview Abstract] |
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R1.00117: Elastic Differential and Integral Elastic Cross Sections for e$^-$-Fr Z. Felfli, D. Sokolovski, A.Z. Msezane Since an integral cross section is obtained by summing a partial wave series, singularities of the scattering matrix in the complex plane of the total angular momentum (Regge poles) are instrumental in understanding resonance effects in elastic, inelastic and reactive collisions. Typically, a resonance would not affect the energy dependence of an integral cross section $\sigma (E)$ if its angular life is much shorter than one full rotation of the metastable complex. In the opposite limit, a resonance would manifest itself as a sharp Breit-Wigner peak in $\sigma (E)$. We illustrate this on the Thomas-Fermi model foe e$^-$-Fr scattering[1]. Specifically, elastic partial and integral cross sections are investigated in the near threshold energy regime to understand the mechanism of electron attachment and predict new manifestations. We benchmark our approach by comparing the calculated results with those from the recent Dirac R-matrix method[2]. Results will be presented that highlight the existence of a shape resonance at E= 0.034~eV, in agreement with the Bahrim {\it et al.} results. Interestingly, a new sharp f-resonance appears at E = 0.354 eV and a p-wave Wigner threshold behaviour is identified. The general agreement with the Dirac R-matrix results gives credence to our simple approach. \newline [1] Z. Felfli {\it et al.}, J. Phys. B {\bf 39}, L353 (2006) \newline [2] C. Bahrim {\it et al.}, Phys. Rev. A {\bf 63}, 042710 (2001) [Preview Abstract] |
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R1.00118: New Manifestations in Near-Threshold Electron Attachment Cross Sections for K and Rb A.Z. Msezane, Z. Felfli, D. Sokolovski Regge trajectories$^{1}$ were employed for a fundamental understanding of the mechanism of electron attachment in electron-atom collisions, capturing with significantly less effort the low-energy results of the Dirac R-matrix$^{2}$. Here we demonstrate, following Macek et.al.$^{3}$ and Sokolovski et.al.$^{4}$ that for e - K and e -- Rb scattering the near-threshold electron attachment cross section is characterized by respectively, an s-wave and a d-wave Wigner threshold behavior, Ramsauer-Townsend minima, including the differential cross section's critical minima, and shape resonances, all discernible only through Regge partial cross sections scrutiny. Partial Regge cross sections, Differential and total cross sections at near threshold collision energies will be presented and discussed. [1] Z. Felfli, et. al., J. Phys. B At. Mol. Opt. Phys. \textbf{39,} L353-L359 (2006). [2] C. Barim, et. al. Phys. Rev. A\textbf{63}, 042710 (2001). [3] J. H. Macek, et. al., Phys. Rev. Lett. \textbf{93}, 183203 (2004). [4] D. Sokolovski, et. al., Phys. Rev. A, Submitted (2006) [Preview Abstract] |
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R1.00119: A Fully Relativistic Approach for Calculating the Top-Up Contribution to Electron-Impact Excitation Cross Sections for Transitions between Magnetic Sublevels Christopher J. Fontes, Hong Lin Zhang Previous work on relativistic electron-impact excitation calculations has been expanded to include transitions between magnetic sublevels. Specifically, a general expression has been derived for the relativistic plane-wave-Born (RPWB) cross section for electron-impact excitation between magnetic sublevels. This expression provides a convenient, accurate mechanism for estimating the high-$\ell$ partial-wave (or top-up) contribution to the corresponding relativistic distorted-wave (RDW) cross sections. This approach offers significant advantages over previous attempts to approximate the top-up contribution for RDW cross sections. For example, the RPWB top-up is fully relativistic and incorporates the correct kinematic description for relativistic collisions. Also, the RPWB approach is completely general in that it is applicable to any type of transition, while previous attempts employed the relativistic Coulomb-Bethe (RCB) approximation, which is valid only for dipole-allowed transitions. Another issue is that the RCB approach often converges slowly for $\Delta n$=0 transitions, while the RPWB approach always produces a converged result because it includes contributions from $\ell$ values up to infinity. Numerical examples will also be provided. This work was performed under the auspices of the US Department of Energy. [Preview Abstract] |
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R1.00120: POST-DEADLINE |
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R1.00121: An investigation of resonance involvement in electron circular dichroism of NMR shift reagent molecules Adam Scheer, Gordon Gallup, Timothy Gay We have measured the total scattering cross sections of several NMR shift reagent molecules, X(hfc)$_{3}$, where X = Yb, Er, Eu and Pr by means of electron transmission spectrometry (ETS) to determine their vertical attachment energies (VAEs). With the aid of restricted open-shell Hartree-Fock (ROHF) calculations on closely related molecules, we have assigned specific normally unoccupied orbitals to the resonances observed in ETS. Nolting \textit{et al}. [J. Phys. B \textbf{30}, 5491 (1997)] have demonstrated that the NMR shift reagents exhibit electron circular dichroism (ECD) between 1-10 eV. We reexamine their asymmetry spectra and provide a set of possible orbital assignments for major ECD structures. Inconsistencies in associating asymmetry features with resonances observed in the total scattering cross section are also discussed. Specifically, significant shifts to lower energy are observed in analogous ECD features as the atomic number of the central lanthanide atom decreases. However, similar shifts in VAEs are not seen as would be expected if resonance behavior were solely responsible for asymmetry. [Preview Abstract] |
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R1.00122: Extensive computation of allowed and forbidden transition probabilities in the potassium isoelectronic sequence Gopal Dixit, Pranawa C. Deshmukh, Steven T. Manson, Sonjoy Majumder Our primary aim in this work is to present both allowed and forbidden transition amplitudes and corresponding wavelengths and oscillator strengths for a few ions in the 19-electron potassium isoelectronic sequence. All of these ions have the configuration [Ar] 3$^{2}$D$_{3/2 }$as their ground state, except in the case of K and Ca$^{+}$, where it is [Ar] 4$^{2}$S$_{1/2}$.$_{ }$This difference in ground state configuration arises due to strong contributions of correlation effects in the energy levels of these systems [1]. Allowed and forbidden transitions in these systems are of great importance in astrophysics [2] and in laboratory plasma research [3]. We apply in the present work the relativistic coupled-cluster (RCC) theory [4] to evaluate the energy levels and wave functions of these systems and study amplitudes for electric and magnetic dipole transition amplitudes and also the electric quadrupole transition amplitudes. The contributions of various electron correlation effects to the transition amplitudes are estimated in some detail using the RCC theory. [1] Gopal Dixit et al., Astrophys. J (submitted); arXiv.org: physics/0702066. [2] C. R. Cowley and G. M. Wahlgern, Astronomy {\&} Astrophysics, \textbf{447}, 681 (2002). [3] J. E. Vernazza, E. M. Reeves, Astrophys. J. Suppl. \textbf{37}, 485 (1978) [4] I. Lindgren, Physics Scripta, \textbf{36}, 591 (1987). [Preview Abstract] |
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R1.00123: Quantum Process Tomography Kavan Modi, Cesar Rodriguez, Aik-Meng Kuah, George Sudarshan, Anil Shaji Quantum process tomography has become a very important tool in quantum information science. It is the way to study the detailed structure of a quantum channel. We will examine some recent experiment on quantum process tomography. We will point out some ambiguity in the way these experiments were preformed. We will show how these ambiguities lead to incorrect conclusion, namely the ``unphysical" result of not completely positive map. The notion that a dynamical map must be completely positive is erroneous. We will present specific examples in which this is not the case. We will also present a recipe that will resolve any ambiguity in the future. [Preview Abstract] |
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R1.00124: Electron-impact ionization rates for BF$_{3}$ fragments L. Vuskovic, M. Raskovic, S. Popovic We calculated electron-impact ionization rates of BF$_{3}$ and its fragments for electron energy distribution present in sheath mode of the repetitively pulsed d.c. diode system [1]. Data are being used for Ar/BF$_{3}$ discharge modeling. BF$_{3}$ and its fragments are reactive species that we are using to interact with niobium surface. The aim is to remove oxides and other impurities from the surface in the form of volatile compounds. This procedure of cleaning and smoothening improves the performance of the superconducting radiofrequency cavities used for particle accelerators. In our calculation electronic structures of BF$_{3}$ and its fragments were described with several empirical basis sets. After geometry optimization using density functional method B3LYP, MO parameters were calculated with UHF, CCSD(T) and OVGF methods [2]. Electron-impact ionization cross-sections were calculated employing the Binary-Encounter-Bethe approximation. Cross-section results were compared with available experimental data. Relative calculation errors were estimated, which was especially important for cross-sections obtained with CEP-31G basis set that is necessary to describe system containing niobium samples. [1] S. Radovanov, et al., J. Appl. Phys. 98, 113307 (2005). [2] Y-K. Kim, K.K. Irikura, AIP conferences proceedings, 543, 220 (2000). [Preview Abstract] |
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R1.00125: Correlation Functions and Multipartite Entanglement in Cavity QED Perry Rice, James Clemens, Luis Orozco Entanglement is essentially a quantum correlation between two systems, as such a cross-correlation function can be shown to indicate entanglement between two parts of a system. If the state of the system is a product state, with no entanglement, then the correlation function G is unity. If any cross correlation of the form above is not equal to one, then the two modes are entangled. Here we consider a multi-level atom, and two orthogonal polarization modes of the cavity. The atom is driven with polarization $a$. The atom can spontaneously emit into either the $a$ mode, or the $b$ mode. As the $b$ mode is undriven, light of that polarization can only arise from spontaneous emission. Hence perhaps one can measure the entanglement between the atom and field mode by a cross-correlation of the two modes $a$ and $b$. The problem with this is that we now have an atom and two field modes, and hence a tripartite system. In such systems, measures of entanglement are not well defined. Here we examine the use of correlation functions to discuss entanglement in this system. Work supported by NSF, NIST, and Research Corporation. [Preview Abstract] |
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R1.00126: Steering, Entanglement, Nonlocality, and the EPR Paradox Howard Wiseman, Steve Jones, Doherty Andrew The concept of steering was introduced by Schroedinger in 1935 as a generalization of the EPR paradox for arbitrary pure bipartite entangled states and arbitrary measurements by one party. Until now, it has never been rigorously defined, so it has not been known (for example) what mixed states are steerable (that is, can be used to exhibit steering). We provide an operational definition, from which we prove (by considering Werner states and Isotropic states) that steerable states are a strict subset of the entangled states, and a strict superset of the states that can exhibit Bell-nonlocality. For arbitrary bipartite Gaussian states we derive a linear matrix inequality that decides the question of steerability via Gaussian measurements, and we relate this to the original EPR paradox. [Preview Abstract] |
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R1.00127: Conditioned Homodyne Measurements and Entanglement for a Two-Level Atom in an OPO Perry Rice, Jeffrey Hyde It has been shown that entanglement between a two-level atom and a field mode can be characterized by correlations between transmitted and fluorescent light. A particularly useful quantity is the cross-correlation function $h_{\theta =0}^{FT} (0)$, a conditioned homodyne measurement of the transmitted field, conditioned on the detection of a fluorescent photon. Obviously it would be better to create the photons in pairs via a parametric process. A two-level atom in an optical parametric oscillator has been shown to have nonclassical spectra and photon statistics and be useful for teleportation and single photon storage. Here we demonstrate that various cross-correlation functions are an indication of entanglement, and that the conditioned homodyne measurement is an actual measure of entanglement. Work supported by NSF, NIST, and Research Corporation. [Preview Abstract] |
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R1.00128: ABSTRACT WITHDRAWN |
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R1.00129: Decay width of negative positronium ion Mariusz Puchalski, Andrzej Czarnecki, Savely Karshenboim We present a precise theoretical prediction for the decay width of the bound state of two electrons and a positron (a negative positronium ion). We include $O(\alpha^2)$ effects of hard virtual photons as well as soft corrections to the wave function and the decay amplitude. An outcome of a large-scale variational calculation, this is the first result for second-order corrections to a decay of a three-particle bound state. It will be tested experimentally in the new positronium-ion beam facility in Garching in Germany. [Preview Abstract] |
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R1.00130: Quantum Interferometry at the Heisenberg Limit Luca Pezze', Augusto Smerzi Entanglement can increase the precision of an interferometric phase measurement from the standard quantum limit up to the Heisenberg limit, which is the ultimate bound imposed by Quantum Mechanics. The quest requires two key ingredients: maximal quantum correlations engineered among the particles employed in the measurement process and a tailored phase estimation strategy. Here we present a rigorous Bayesian protocol for -unbiased- estimation of phases with confidences at the Heisenberg limit which overcomes basic difficulties present in previous approaches. We also demonstrate phase sensitivity beating the classical shot-noise limit with published experimental probabilities for Schroedinger cats up to N=6 beryllium ions. We report 0.8 db sub shot-noise implemented with an arbitrary large number of particles and maximum priori ignorance. Possible implementation of the protocol with trapped Bose-Einstein condensates will also be discussed. [Preview Abstract] |
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R1.00131: Optimal phase estimation for a Mach-Zehnder interferometer. Luca Pezze', Augusto Smerzi, George Khoury, Juan Hodelin, Dirk Bouwmeester We study a Mach-Zehnder interferometer fed by a coherent state in one input port and vacuum in the other. We explore a Bayesian phase estimation strategy to demonstrate that it is possible to achieve the standard quantum limit *independently* from the true value of the phase shift and specific assumptions on the noise of the interferometer. We have been able to implement the protocol using parallel operation of two photon-number-resolving detectors and multiphoton coincidence logic electronics at the output ports of a weakly-illuminated Mach-Zehnder interferometer. This protocol is unbiased and saturates the Cramer-Rao phase uncertainty bound and, therefore, is an optimal phase estimation strategy. [Preview Abstract] |
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R1.00132: Reduced Density Matrix Descriptions for Electromagnetically Induced Transparency in Atomic Systems Verne Jacobs Reduced density matrix descriptions are developed for electromagnetically induced transparency and related pump-probe optical phenomena in moving atomic systems, taking into account atomic collisions and external magnetic fields. Time- domain (equation-of-motion) and frequency-domain (resolvent-operator) formulations are developed in a unified manner. In a preliminary semiclassical perturbative treatment of the electromagnetic interaction, compact Liouville-space operator expressions are derived for the linear and the general (n$'$th order) non- linear electromagnetic-response tensors. These expressions are valid for coherent atomic excitations and for the full tetradic-matrix form of the collision operator in the Markov approximation. [Preview Abstract] |
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R1.00133: Evidence of Electron Spin-Dependent Terahertz Light Transport in Spintronic-Plasmonic Media Kenneth Chau, Mark Johnson, Abdulhakem Elezzabi Plasmonics and spintronics are actively pursued as means to sustain the continued miniaturization of information technology. Combining the advantages of both technologies could potentially pave the way for the development of highly integrated light-based devices. Here, we provide evidence of a new spin-dependent plasmonic phenomenon. Using a rudimentary plasmonic circuit, namely, a dense ensemble of ferromagnetic/nonmagnetic (F/N) metallic microparticles, we demonstrate that electron spin can influence terahertz plasmonic transport across the particles. In particular, by coating the ferromagnetic Co particles with nonmagnetic Au nano-layers, the terahertz transmission shows large magnetic field-dependent attenuation, enhanced relative to that of pure, uncoated Co particles. We show that enhanced magnetic attenuation in the F/N particles arises from dynamic spin accumulation in the nonmagnet. A quantitative measurement of the dependence of the attenuation on the N layer thickness is in good agreement with the spin diffusion length predicted by the spin accumulation model, as well as with other measurements of this length. The discovery may potentially lead to plasmonic devices operating in the visible regime that exploit electron spin. [Preview Abstract] |
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R1.00134: An Offset-Apertured Near-Field Scanning Optical Microscope Probe Michael Quong, Abdulhakem Elezzabi A novel hybrid apertured and scattering-type (``hybrid'') near-field scanning optical microscope (NSOM) probe design in the form of a cantilevered offset-apertured probe is presented. In the cantilever arm, a subwavelength aperture is located adjacent to the base of a metal-coated dielectric tip. Surface plasmon waves are coupled onto the tip's surface. The surface plasmon waves propagate to the tip's apex, where the fields are locally enhanced. As a result of the offset-apertured probe design, the low light throughput of typical apertured NSOMs and the background light-related problems of scattering-type NSOMs are circumvented. Unlike other hybrid NSOM probe designs, the offset-apertured probe's sharp apex allows for optical imaging in deep and narrow topographical features. To gain greater insight into the functioning of the offset-apertured probe, the dependences of the optical spot's intensity and full-width half-maximum on various geometrical parameters are characterized through numerical calculations. Results also demonstrate that an offset-apertured probe significantly improves throughput light intensity over a typical apertured NSOM probe having similar resolution. [Preview Abstract] |
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R1.00135: Large-Angle Deflection of MOT-Based Cold Cs Beam by Optical Molasses H. Wang, G. Iyanu We have generated a slow moving Cs atomic beam from a vapor-cell Cs MOT and deflected the cold Cs beam by an angle of 30 degrees using a 1-D optical molasses. The MOT-generated Cs atomic beam travels at a mean velocity of 7 m/s with a velocity spread of 1 m/s. At 18 cm down-stream from the Cs MOT, the Cs atomic beam interacts with a 1-D optical molasses formed by a pair of frequency-stabilized, retro-reflected laser beams. The 1-D optical molasses is set up in such a way that the molasses laser beams are perpendicular to the final atomic beam propagation path. Thus, the Cs beam velocity components along the molasses axis are efficiently damped to nearly zero, while the velocity component along the final atomic beam propagation path is unaffected. In a probe region about 34 cm down-stream from the optical molasses, laser induced fluorescence of the deflected Cs beam is obtained and used for studies of the atomic beam deflection efficiencies and beam manipulation parameters. This deflected Cs atomic beam will be used in our cold Cs beam atomic clock experiment. This work was supported under The Aerospace Corporation's Mission Oriented Investigation and Experimentation program, funded by the U.S. Air Force Space and Missile Systems Center under Contract No. FA8802-04-C-0001. [Preview Abstract] |
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R1.00136: Transfer of Ultracold 87Rb from a QUIC Magnetic Trap into a Far Off Resonance Optical Trap Ming He, William A. van Wijngaarden Ultracold 87Rb atoms were transferred from a QUIC magnetic trap into a far off resonance optical trap (FORT). FORTs were created by focusing a 150 mW laser beam having a wavelength of 852 nm to a spot having a radius of 20 and 30 $\mu $m. A probe laser then passed through the ultracold atom cloud after the magnetic trap was turned off to study the temporal evolution of the optically trapped atoms. Nearly a million atoms could be transferred into the FORT at temperatures as low as 1 $\mu $K with an efficiency as high as 50{\%}. [Preview Abstract] |
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R1.00137: Nanoscale Resolution Fluorescence Using Cold Atoms Deniz Yavuz, Nicholas Proite We suggest a new type of scanning fluorescence microscope that is capable of resolving nanometer size objects in the far field.~ The key idea is to use a position dependent Stark Shift of a Raman transition to produce atomic excitation tightly confined to nanometer spatial scales. We present numerical simulations that demonstrates a resolution that is 40 times smaller than the wavelength of light.~ We discuss in detail a possible first experiment where a nanoscale object is embedded in an ultracold atomic cloud and a high resolution image is obtained at the far field.~ [Preview Abstract] |
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R1.00138: Coherent Raman spectroscopy with incoherent laser pulses Xiaoji Xu, Stanislav Konorov, John Hepburn, Valery Milner Contrary to the common belief that noise and decoherence are detrimental to spectroscopic measurements, we propose and experimentally demonstrate a new method of coherent Raman spectroscopy with spectrally broad incoherent laser pulses. Laser induced molecular vibrations are probed by broadband laser pulses with intentionally introduced spectral phase noise. The vibrational resonances are identified through intensity correlations in the noisy spectrum of the scattered anti-Stokes photons. Spectral resolution is neither limited by the pulse bandwidth nor sensitive to the temporal profile quality of the pulses. The method does not require complicated pulse-shaping setups, spectral multiplexing or spatial beam arrangements. It enables full utilization of the broad bandwidth of femtosecond pulses, and quick scanless retrieval of the vibrational beating frequencies. [Preview Abstract] |
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R1.00139: Adiabatic passage with ultrashort laser pulses Sergey Zhdanovich, Evgeny Shapiro, Cian Menzel-Jones, Moshe Shapiro, John Hepburn, Valery Milner We develop a method of executing complete population transfer between quantum states using a series of femtosecond laser pulses. The method can be applied to a large class of problems as it benefits from the high peak power and large spectral bandwidth afforded by ultrashort pulses. The new type of ``piecewise adiabaticity'' is reflected by the robustness of the degree of population transfer to a wide variation in the intensities, durations, and time delays between the pulses. The method is studied in detail for two- and three-level systems, and demonstrated experimentally in atomic rubidium where piecewise adiabatic population transfer between two electronic states is observed. Piecewise adiabatic passage offers a new set of tools for manipulating the population of atomic and molecular states on ultrashort time scale. [Preview Abstract] |
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R1.00140: Investigation of xenon metastable atoms Tian Xia, Yuan-Yu Jau, William Happer The electron configuration of a xenon atom in its metastable state consists of tightly bound core electrons with a single missing electron in the 5P shell, and a loosely bound ``valence electron'' in the 6S shell. For our current work, we have been using pyrex cells with internal tungsten electrodes, filled with isotopically enriched Xe129 gas. Ti-sapphire laser is used to pump the metastable atom from 6S$_{2}$ to 6P$_{2 }$and 6P$_{3 }$at 823nm and 882nm respectively. The absorption spectrum is able to resolve the hyperfine structure of Xe129 in 6S$_{2}$, 6P$_{2 }$and 6P$_{3}$ state. The hyperfine coefficients for 6S$_{2}$, 6P$_{2 }$agree with previously reported measurements. And the hyperfine coefficient for 6P$_{3 }$state has not been reported before. If the pumping wavelength is locked at any one of the hyperfine transitions of Xenon129 atom, zero-field magnetic resonances of metastable Xenon atoms could be observed by pumping with circularly polarized laser beam. Since relaxation between magnetic sublevels is very fast due to the big depolarization collisional cross section, the linewidth of the magnetic resonant signal is broad. [Preview Abstract] |
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R1.00141: Soft x-ray driven femtosecond dynamics of ionic Rydberg states in N2 Etienne Gagnon, Arvinder S. Sandhu, Predrag Ranitovic, C. Lewis Cocke, Henry C. Kapteyn, Margaret M. Murnane We present the first direct observation of molecular dynamics initiated by a EUV pulse. A novel EUV pump- IR probe technique is used to observe these dynamics. The EUV pulse, with h(nu) = 42 eV, launches molecular nitrogen into highly-excited (N2)2+ core Rydberg states,~ the dynamics of which are previously unexplored. We use a time-delayed infrared pulse to promote the wavepacket from the Rydberg state to a dissociative (N2)2+ state via multiphoton ionization. The kinetic energy release of the N+/N+ channel is obtained as function of time delay. Having identified the final (N2)2+ state, we extract the potential energy curve corresponding to the evolving Rydberg state. The Rydberg state initially behaves the same as the (N2)2+ state. As the internuclear distance increases, we observe a fast decrease in the kinetic energy release on the time scale of 100 fs, corresponding to a transition from the molecular Rydberg state to N+ and N fragments. [Preview Abstract] |
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R1.00142: Resonant Association of Feshbach Molecules Thomas M. Hanna, Thorsten K\"ohler, Keith Burnett In recent experiments, Feshbach molecules have been associated using resonant modulation of a magnetic field close to a zero-energy resonance [1, 2]. We analyse the dependence of this process upon the duration, amplitude and frequency of the modulation, as well as the temperature and density of the gas. A modulation of angular frequency $\omega_{\mbox{L}}$ resonantly couples a pair of atoms with relative kinetic energy $p^2/m$ = $\bar{h}\omega_{\mbox{L}$ + $E_{\mbox{b}}^{\mbox{av}}$ to the molecular state, where $E_{\mbox{b}}^{\mbox{av}}$ is the molecular bound state energy. The presence of a continuum of modes around this energy has a strong influence on the final conversion efficiency. Shifts in the modulation frequency giving maximum conversion are created by the amplitude of the modulation and the temperature of the gas. We discuss the importance of mean-field effects at short times, and predict that resonant association can be effective for binding energies of order $h \times 1$ MHz. \newline \newline [1] S. T. Thompson, E. Hodby and C. E. Wieman, Phys. Rev. Lett. \textbf{95}, 190404 (2005). \newline [2] S. B. Papp and C. E. Wieman, Phys. Rev. Lett. \textbf{97}, 180404 (2006). [Preview Abstract] |
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R1.00143: An investigation of non-Brownian random walks in an optical lattice using polarization-selective intensity correlations Benjamin Agyare, Samuel Bish, Matthew Briel, Samir Bali We propose that Levy walks by cold atoms trapped in a near-resonance shallow optical lattice may be detected by measuring the polarization-selective intensity correlations of the scattered light. Experimental progress is reported. [Preview Abstract] |
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R1.00144: High resolution spectroscopy of Rydberg atom interactions K.C. Younge, A. Reinhard, P.R. Berman, G. Raithel We present progress toward a direct spectroscopic measurement of the dipole-dipole and van der Waals interactions between Rydberg atoms excited from a cold gas. We have collected $^{85}$Rb atoms in a broadband optical dipole trap (laser wavelength 1064nm) with a 15 micron FWHM diameter, and characterized the temperature, atom number, density, and size of the trapped sample using shadow imaging. The dipole trap will be employed to measure Rydberg-atom interactions using two independently tunable Rydberg excitation laser pulses. The first pulse is tuned to the interaction-free Rydberg excitation resonance; this pulse prepares a dilute gas of cold Rydberg atoms. The frequency of the second pulse is scanned relative to that of the first one, allowing us to map out the spectrum of energy-shifted collective states. In our poster, we will discuss methods and results, as well as potential applications in quantum information processing. [Preview Abstract] |
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R1.00145: Hyperfast time-resolved spectroscopy of electron correlation in excited states Cleanthes A. Nicolaides As a consequence of continuing developments in the science and technology of techniques that produce and control electromagnetic pulses with frequencies that are found in a broad part of the spectrum, from the ir to the soft X-rays, it is possible to have hyperfast pump-probe time delay spectroscopic techniques capable of time resolving the dynamics of various atomic and molecular systems involving excited states. In this context, it has been demonstrated via first principles solution of the time-dependent Schr\"odinger equation (TDSE), that effects which are caused by strong electron correlations in excited states, including the process of autoionization and the formation of resonances, can be time-resolved on a time scale of attoseconds [1-3]. By extending the investigations to polyelectronic atoms, we have obtained new results for various time resolved processes associated with the photo-ejection of inner (2s) electrons and of two electrons (LM) from the thirteen electron atom of Aluminum and with the electron correlation beats in bound and autoionizind states of N$^{+3}$ and Al. The theory and computations account for the interference of direct double ionization, inner hole states and Auger decay [4]. \newline [1] C. A. Nicolaides et al, J. Phys. \textbf{B 35}, L271 (2002). \newline [2] Th. Mercouris et al, Phys. Rev. \textbf{A 69}, 032502 (2004). \newline [3] Th. Mercouris, et al, Phys. Rev. \textbf{A 75}, 013407 (2007). \newline [4] Th. Mercouris, Y. Komninos and C. A. Nicolaides, unpublished. [Preview Abstract] |
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R1.00146: The Far-IR Beamline at the Canadian Light Source Dominique R.T. Appadoo The far-infrared (far-IR) beamline at the Canadian Light Source Inc. (CLSI) has been dedicated primarily to high-resolution spectroscopic studies of stable and unstable gas-phase molecules. The infrared radiation collected from a Bending Magnet is steered using long wavelength optics to a Br\"uker IFS125HR spectrometer which is able to record spectra at a resolution of 0.001 cm$^{-1}$. The far-IR beamline is presently being commissioned, and recent efforts in the optical alignment and noise reduction have rendered the beamline partially operational. The signal-to-noise ratio of data recorded with the synchrotron is better than that recorded with a thermal source by a factor of 8 around the 400 - 600 cm$^{-1}$ region. As a result, we are presently accepting proposals for the next cycle (July - Dec 2007) for experiments which can be conducted in this spectral region. [Preview Abstract] |
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R1.00147: KRb Feshbach Molecules Kang-Kuen Ni, J.J. Zirbel, S. Ospelkaus, J. Ye, S. Jin We have produced heteronuclear Feshbach molecules from an ultracold gas mixture of K40-Rb87 in an optical dipole trap. We can create more than 30,000 molecules at about 100 nK and we have observed molecule lifetimes as long as 20 ms near the Feshbach resonance. We will report on measurements of the Feshbach molecule lifetime as a function of magnetic-field detuning from resonance. These results are compared with theoretical predictions for vibrational quenching of heteronuclear Feshbach molecules. [Preview Abstract] |
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