Bulletin of the American Physical Society
43rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 57, Number 5
Monday–Friday, June 4–8, 2012; Orange County, California
Session H3: Theory and Computation of Atomic and Molecular Interactions |
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Chair: Shaohao Chen, Lousiana State University Room: Grand Ballroom E |
Wednesday, June 6, 2012 10:30AM - 10:42AM |
H3.00001: Universal bound states of two atoms near a Feshbach resonance Shina Tan The Efimov effect was traditionally thought to exist for three or more particles only. It will be shown how to make universal shallow bound states of TWO atoms only, which will exhibit a universal energy spectrum reminiscent of the Efimov effect, by using potentials to constrain the spatial motion of atoms. The two atoms must be tuned near a scattering resonance. Several related types of such two-body states will be described. These diatomic ``artificial molecules,'' if isolated from each other, will be free from three-body recombination, and can have long lifetimes in principle, in contrast with the Efimov bound states of three atoms. [Preview Abstract] |
Wednesday, June 6, 2012 10:42AM - 10:54AM |
H3.00002: Controlling the group velocity of colliding ultracold atoms and Bose-Einstein condensates using Feshbach resonances Ranchu Mathew, Eite Tiesinga Over the last ten years progress has been made in creating atoms lasers, sources of coherent atoms, based on atomic Bose-Einstein condensates in analogy to optical lasers. The analog of nonlinear four-wave mixing has also been experimentally observed when three Bose-Einstein condensates with carefully tuned or phase-matched relative velocities collide. Here, we report on a theoretical proposal to change the group velocity upon collision between two ultracold atom clouds in analogy to slowing of light in dispersive media. We make use of ultracold collisions near a Feshbach resonance, which gives rise to a sharp variation in scattering length with collision energy and thereby changes the group velocity. We also present an initial analysis of the practicality of the proposal. [Preview Abstract] |
Wednesday, June 6, 2012 10:54AM - 11:06AM |
H3.00003: Laser assisted electron-atom scattering in critical geometries Nathan Morrison, Chris H. Greene We investigate the scattering of electrons off of neutral targets in the presence of a linearly polarized, low frequency laser field. The laser has large enough extent for the wavefunction to be treated in the Floquet expansion. The scattering geometries of interest are small angles where momentum transfer is nearly perpendicular to the field, and the Kroll Watson approximation breaks down. We use the eigenchannel R matrix method to solve the Schr\"odinger equation, employing Hamiltonians in both the length and the velocity gauges in different regions. The target atom is represented by a model potential including a screened coulomb term near the origin and a longer range induced dipole interaction. The short range reaction matrix in the Kramers-Henneberger (acceleration) representation is found by matching the velocity gauge R matrix to spherical Gordon-Volkov states, and from this the cross section is derived. Experiments have shown emission and absorption cross sections at small angles to be much higher than the approximation predicts, and we hope to gain insight into the cause of this phenomenon. [Preview Abstract] |
Wednesday, June 6, 2012 11:06AM - 11:18AM |
H3.00004: Angular momentum changing transitions in proton-Rydberg hydrogen atom collisions D. Vrinceanu, R. Onofrio, H.R. Sadeghpour Collisions between electrically charged particles and neutral atoms are central for understanding the dynamics of neutral gases and plasmas in a variety of physical situation. Specifically, redistribution of angular momentum states within the degenerate shell of highly excited Rydberg atoms occurs efficiently in distant collisions with ions. This process is crucial in establishing the validity of the local thermal equilibrium assumption and may also play a role in determining a precise ionization fraction in primordial recombination. We provide an accurate, non-perturbative rate coefficient for collisions between protons and H($n\ell)$ ending in a final state H($n\ell')$, represented by the formula \[ q_{n\ell\rightarrow n\ell'}(T) = \frac{3.922\times10^{-4}}{\sqrt{T[K]}}\;\; \frac{n^2 \left[ n^2(\ell + \ell') - \ell_<^2 (\ell + \ell' + 2|\Delta \ell|) \right]} {(\ell+1/2)|\Delta \ell|^3}\;\;\mbox{cm$^3$/s}, \] where $\ell_<$ is the smallest between $\ell$ and $\ell'$, and $\Delta \ell=\ell-\ell'$. The validity of this formula is confirmed by results of classical trajectory Monte Carlo simulations. [Preview Abstract] |
Wednesday, June 6, 2012 11:18AM - 11:30AM |
H3.00005: Analytical Solution for 3D Stationary Schr\"{o}dinger Equation: application to scattering Marzieh Zare, Yuri Rostovtsev We have derived and studied the generalized Ricatti equation for the WKB approximation in three dimensions. A new approximated solution of Schrodinger equation is obtained. We show that this solution is more accurate than that of the WKB method. Writing Schrodinger differential equation in an integral form which is suitable for scattering theory, we discuss some applications of the obtained results, in particular, to the scattering problem. [Preview Abstract] |
Wednesday, June 6, 2012 11:30AM - 11:42AM |
H3.00006: Excitation ionization of atoms and diatoms as a test of the all-active-electron MCTDHF method Daniel Haxton, Keith Lawler, C. William McCurdy We have developed an implementation of the Multiconfiguration Time-Dependent Hartree-Fock (MCTDHF) method [PRA 83, 063416 (2011)]. MCTDHF is an adaptive method for solving the time-dependent Schrodinger equation and we apply it to atoms and diatoms in ultrafast laser pulses. The method is built to describe nonlinear phenomena and incorporates both an all-active-electron representation and the ability to include diatomic nuclear motion without the Born-Oppenheimer approximation. As a diagnostic of the method, we have calculated photoionization cross sections for: valence ionization of Beryllium, and of HF, LiH, and N2 in the fixed nuclei approximation; 1s ionization of Beryllium; and dissociative ionization of H2+ including nuclear motion with full nonadiabatic coupling. We will present results that demonstrate the convergence of the method with respect to the number of time-dependent orbitals and discuss the prospects of the method for describing nonlinear phenomena. [Preview Abstract] |
Wednesday, June 6, 2012 11:42AM - 11:54AM |
H3.00007: Chaotic Energy Hopping in Bidirectionally Kicked Rydberg Atoms Korana Burke, Kevin Mitchell, Shuzhen Ye, F. Barry Dunning A highly excited (n~306) quasi one-dimensional Rydberg atom exposed to periodic alternating external electric field pulses exhibits chaotic behavior. Time evolution of this system is governed by a geometric structure of phase space called a homoclinic tangle and its turnstile. The turnstile is responsible for organizing chaotic ionization. We present and explain the results from an experiment designed to probe the structure of the phase space turnstile. We create time-independent Rydberg wave packets, subject them to alternating electric field kicks, and measure the ionization fraction. We present the behavior of the ionization fraction as a function of the applied kick strength and show that this behavior is directly connected to the size and shape of the underlying turnstile. For short kicking periods the ionization fraction as a function of the applied kick strength exhibits step-function-like behavior that changes into s-shape behavior for large kicking periods. Next we use the geometric structure of phase space to design a short pulse sequence that quickly and efficiently transfers electronic wave packet from a high energy state to a much lower energy state. Finally, we show how the phase space geometry influences the efficiency of the transport between energy states. [Preview Abstract] |
Wednesday, June 6, 2012 11:54AM - 12:06PM |
H3.00008: ABSTRACT WITHDRAWN |
Wednesday, June 6, 2012 12:06PM - 12:18PM |
H3.00009: Trends in correlation and confinement impacts on the e-Xe@C$_{60}$ generalized oscillator strengths Valeriy Dolmatov, Miron Amusia, Larissa Chernysheva The response of endohedral Xe@C$_{60}$ to fast electron impact ionization is theoretically studied by calculating its 4d, 5s and 5p generalized oscillators strengths (GOS). The calculation methodology combines the plane wave Born approximation, single-electron Hartree-Fock approximation, and multi-electron random phase approximation with exchange, all in the presence of the C$_{60}$ confinement. The confinement is accounted for in the framework of both a spherical $\delta$-potential [1] and square-well-potential [2] models to evaluate the effect of the finite thickness of the C$_{60}$ cage on said GOS's. Impressive confinement brought impact on the latter is revealed. Vitality of accounting for electron correlation in calculations of the Xe@C$_{60}$ 5s and 5p GOS's is demonstrated. Trends in contributions of multipolar transitions beyond dipole transitions in the calculated GOS's are unraveled. We challenge experimentalists to conduct corresponding measurements.\\[4pt] [1] M.Ya. Amusia, A.~S.~Baltenkov, and B. G. Krakov, Phys. Lett. A, \textbf{243}, 99 (1998).\\[0pt] [2] V.~K.~ Dolmatov, Adv. Quant. Chem. \textbf{58}, 13 (2009). [Preview Abstract] |
Wednesday, June 6, 2012 12:18PM - 12:30PM |
H3.00010: Optically controllable photonic structures with zero absorption Christopher O'Brien, Olga Kocharovskaya We show the possibility to periodically modulate the refractive index in a homogeneous resonant atomic medium in space or/and time while simultaneously maintaining vanishing absorption/gain.\footnote{C. O'Brien and O. Kocharovskaya, Phys. Rev. Lett. {\bf 107}, 137401 (2011).} Such modulation is based on periodic resonant enhancement of the refractive index via the matching of an effective absorption resonance to an effective gain resonance, controlled by external optical fields, and opens the way to produce coherently controllable photonic structures. We suggest the possible implementation of the proposed scheme in rare-earth doped crystals with excited state absorption. Providing a particular example of how the refractive index can be periodically changed along the optical axis of an Er3+:YAG crystal to optically produce in a homogenous media, a distributed Bragg reflector with a very high reflectivity and very narrow bandwidth. [Preview Abstract] |
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