Bulletin of the American Physical Society
42nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 56, Number 5
Monday–Friday, June 13–17, 2011; Atlanta, Georgia
Session K4: Few-body and Molecular Collisions |
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Chair: Phillip Stancil, University of Georgia Room: A704 |
Wednesday, June 15, 2011 2:00PM - 2:12PM |
K4.00001: Universal Relations for Identical Bosons from 3-Body Physics Daekyoung Kang, Lucas Platter, Eric Braaten Systems consisting of identical bosons with a large scattering length satisfy universal relations determined by 2-body physics that are similar to those for fermions with two spin states. They require the momentum distribution to have a large-momentum $1/k^4$ tail and the radio-frequency transition rate to have a high-frequency $1/\omega^{3/2}$ tail, both of which are proportional to the 2-body contact. Identical bosons also satisfy additional universal relations that are determined by 3-body physics and involve the 3-body contact, which measures the probability of 3 particles being very close together. The coefficients of the 3-body contact in the $1/k^5$ tail of the momentum distribution and in the $1/\omega^2$ tail of the radio-frequency transition rate are log-periodic functions of $k$ and $\omega$ that depend on the Efimov parameter. [Preview Abstract] |
Wednesday, June 15, 2011 2:12PM - 2:24PM |
K4.00002: Three-Body-Recombination Interference Minima in the Midst of Three Overlapping Feshbach Resonances E.L. Hazlett, Y. Zhang, R.W. Stites, K.M. O'Hara We report on our investigation of three-body recombination (3BR) in a three component $^6$Li gas between 700 and 800~G. Over this field range, two of the three scattering lengths are large and positive and the third is large and negative due to three broad Feshbach resonances centered at 690, 811 and 834~G. In this situation, there can exist 3BR to either deep dimers or one of two shallow dimers. The release in binding energy from these 3BR events can result in atom loss and/or heating. In our experiment, the dipole trap is sufficiently deep that shallow dimers produced in 3BR events remain trapped and only cause heating, whereas 3BR into deep dimers primarily result in loss with minimal heating. Thus, a measurement of the heating rate provides a sensitive technique for discriminating between 3BR events to shallow dimers and those to deep dimers. We see two minima in the heating rate at 752 and 762~G. The location of these minima are in agreement with theoretical predictions for St\"{u}ckleburg interference minima associated with the Efimov effect in $^6$Li. [Preview Abstract] |
Wednesday, June 15, 2011 2:24PM - 2:36PM |
K4.00003: Three-body recombination of two-dimensional ultracold polar molecules Fatima Anis, B.D. Esry In the wake of enormous ongoing efforts on both experimental and theoretical fronts for creating and understanding the behavior of ultracold dipolar gases, we have studied the recombination of three dipoles in two dimensions. We first derived the recombination rate expressions for three particles restricted to two dimensions and compared these analytical results with numerical calculations performed within the hyperspherical formalism. We extended this analysis to three dipoles in two dimensions for both bosonic and fermionic species. The comparison between analytical and numerical results will be presented for this case as well. [Preview Abstract] |
Wednesday, June 15, 2011 2:36PM - 2:48PM |
K4.00004: Efimov trimers in Lithium 6 Pascal Naidon, Masahito Ueda Three atoms can form unusual three-body bound states called Efimov trimers due to a universal attraction arising whenever the scattering lengths between the atoms are much larger than the range of their interactions. Various indirect signatures and first-time direct spectroscopy of such Efimov trimers have been demonstrated in recent experiments [1] using lithium 6 in three different spin states, where the scattering lengths are enhanced by magnetic Feshbach resonances. We found that all these measurements are indeed consistent with the universal Efimov effect, but non-universal deviations at negative energy remain to be understood and have been quantified by a variation of a short-range 3-body paramater [2].\\[4pt] [1] T. B. Ottenstein et al., Phys. Rev. Lett. {\bf 101}, 203202 (2008); J. H. Huckans et al., Phys. Rev. Lett. {\bf 102}, 165302 (2009); S. Nakajima, et al., Phys. Rev. Lett. {\bf 105}, 023201 (2010); T. Lompe et al., Phys. Rev. Lett. {\bf 105}, 103201, 2010); T. Lompe et al., Science {\bf 330}, 940 (2010).\\[0pt] [2] P. Naidon and M. Ueda, arXiv:1008.2260 (2010); S. Nakajima, M. Horikoshi, T. Mukaiyama, P. Naidon, and M. Ueda, arXiv:1010.1954 (2010). [Preview Abstract] |
Wednesday, June 15, 2011 2:48PM - 3:00PM |
K4.00005: Efimov and non-Efimov physics of 2+1 particles Shimpei Endo, Pascal Naidon, Masahito Ueda Three-body bound states called Efimov states are associated with remarkable features such as discrete scale invariance of their spectrum, and have attracted a lot of interest since their recent experimental realizations with ultracold atoms [1]. These states are characterized by the scattering length between particles and a short-range parameter. Recently, however, universal trimers [2] which depend only on the scattering length have been theoretically predicted for systems of two heavy and one light particles. Although the origin of these trimers is closely related to the Efimov effect, they have a distinct nature. We will discuss on the relationship between these universal trimers and Efimov trimers.\\[4pt] [1] F. Ferlaino, and R. Grimm, Physics, {\bf 3}, 9 (2010)\\[0pt] [2] O. I. Kartavtsev, and A. V. Malykh, J. Phys. B, {\bf 40}, 1429 (2007). [Preview Abstract] |
Wednesday, June 15, 2011 3:00PM - 3:12PM |
K4.00006: Multichannel Quantum Defect Theory for State-Resolved Molecular Collisions Michael Mayle, Brandon P. Ruzic, John L. Bohn With the advent of state-resolved, ultracold samples of ground state molecules, novel opportunities arise to explore the physics of cold and ultracold molecular collisions. We revisit state- resolved molecular scattering by employing a Multichannel Quantum Defect Theory treatment that allows us to describe long-range interactions by means of a few quantum defect parameters while the short-range physics can be modeled energy-independently. Being valid over a wide range of collision energies, the theory enables us to assess the effect of magnetic and electric fields on scattering resonances without the necessity of large-scale computations. Furthermore, a careful mapping of the resonances in cold collision experiments has the potential to provide insights on the physics of the short-range collision complex and its influence on the threshold scattering behavior. [Preview Abstract] |
Wednesday, June 15, 2011 3:12PM - 3:24PM |
K4.00007: Cold Chemical Reactions of CaH and Li Vijay Singh, Kyle Hardman, Mei-Ju Lu, Aja Ellis, Muir Morrison, Jonathan Weinstein We have observed cold chemical reactions between ground-state molecular CaH ($^2\Sigma$) and atomic Li ($^2S$) at cryogenic temperatures. The molecules and atoms are created by laser ablation of CaH$_2$ and Li targets, respectively, and cooled by buffer-gas cooling. The densities of the reactants are continuously monitored via laser absorption spectroscopy, and a reaction rate coefficient of $10^{-11}$~cm$^3$~s$^{-1}$ is observed for unpolarized reactants. Progress towards controlling the reaction through polarization of the electron spins will be presented. [Preview Abstract] |
Wednesday, June 15, 2011 3:24PM - 3:36PM |
K4.00008: Ultracold collisions and reactions of vibrationally excited OH radicals with oxygen atoms Juan Carlos Juanes-Marcos, Goulven Qu\'em\'ener, Brain K. Kendrick, Balakrishnan Naduvalath We report quantum dynamics calculations of O + OH ($v=1,j=0$) collisions on two different representations of the electronic ground state potential energy surface. A time-independent quantum mechanical method has been applied, using hyperspherical coordinates. Probabilities and cross sections are calculated for the elastic, inelastic, and reactive channels, and for $J=0$ total angular momentum. Results show that the reaction outcome is strongly influenced by long-range forces, and that the competition between vibrational quenching and chemical reactivity is found to be sensitive to the choice of the potential energy surface. [Preview Abstract] |
Wednesday, June 15, 2011 3:36PM - 3:48PM |
K4.00009: The effect of energy and angular momentum gaps in cold and ultracold collisions of H$_2$ molecules Samantha Fonseca dos Santos, Balakrishnan Naduvalath, Stephen Lepp, Goulven Qu\'em\'ener, Robert C. Forrey, Phillip Stancil We present a full quantum mechanical treatment of collisions between distinguishable (ortho-para) and indistinguishable (ortho-ortho) H$_2$ molecules over a wide range of energies and for different initial rovibrational levels of the molecules. For the indistinguishable case, it has been found that a quasi-resonant rotation-rotation (QRRR) transfer that involves the least energy and angular momentum gaps dominates at cold and ultracold temperatures. For the distinguishable case for which exchange of rotational energy between the two molecules is not allowed, a quasi-resonant vibration-vibration (QRVV) transfer dominates inelastic collisions, albeit with less efficiency. When inelastic collisions are dominated by a QRRR or QRVV transition, calculations using a reduced basis set involving only the quasiresonant channel yield nearly identical results as the full basis set calculation, leading to dramatic savings in computational cost. [Preview Abstract] |
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