Bulletin of the American Physical Society
2013 Joint Meeting of the APS Division of Atomic, Molecular & Optical Physics and the CAP Division of Atomic, Molecular & Optical Physics, Canada
Volume 58, Number 6
Monday–Friday, June 3–7, 2013; Quebec City, Canada
Session P5: Atom-Atom and Atom-Molecule Collisions |
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Chair: Samantha Fonseca dos Santos, University of California, Davis Room: 301 |
Thursday, June 6, 2013 2:00PM - 2:12PM |
P5.00001: Inelastic studies of Th and ThO collisions below 1 K Colin Connolly, Yat Shan Au, Wolfgang Ketterle, John Doyle The actinide series is among very few parts of the periodic table that is virtually unexplored at low temperatures. We present the first experimental investigations of cold collisions of actinide atoms and actinide-containing molecules below 1~K. Using atomic thorium (Th), we measure Zeeman relaxation due to collisions with $^3$He. Although ground-state Th has ``submerged shell'' structure---with a spherical outer valence electron shell---these collisions proceed about 100 times faster than those of the lanthanide series, while still about 100 times slower than anisotropic open-shell atoms. In contrast, we find that the first excited state ($^3P_0$) is collisionally stable (no quenching observed within $>10^6$ collisions with $^3$He) and has a long radiative lifetime exceeding 200~ms. We also investigate collisions of the molecule ThO (ground state and metastable $H$-state\footnote{ThO($H$) is used in the ACME search for the electron EDM (Vutha, A.~C.~\textit{et al.} \textit{Journal of Physics B} \textbf{43}, 074007 (2010))}) with $^3$He. No quenching of the metastable $H$-state is observed within $>3\times10^4$ collisions, allowing for a new measurement of the ThO($H$) radiative lifetime. Evidence is presented for formation of ThO-He van der Waals molecules. [Preview Abstract] |
Thursday, June 6, 2013 2:12PM - 2:24PM |
P5.00002: Theoretical studies of rovibrational quenching in atom-diatom collisions: New results on old problems P.C. Stancil, B.H. Yang, N. Balakrishnan, R.C. Forrey, J.M. Bowman Accurate rotational and vibrational deexcitation rate coefficients due to molecular collisions are necessary for the interpretation of observations of interstellar gas from the microwave to the infrared (IR). The far-IR and submillimeter are particularly useful for studying the formation of stars, from nearby nebulae to high-redshift galaxies, which are current observational targets for the Herschel Space Observatory and the Atacama Large Millimeter/submillimeter Array (ALMA). Astrophysical models rely heavily on theoretical estimates due to the difficulty of direct measurements of collisional rate coefficients. We report on our recent calculations of cross sections and rate coefficients for state-to-state transitions of CO induced by H collisions and HCl and HF induced by He collisions using quantum coupled-channel methods. In particular, issues related to the accuracy of potential energy surfaces, the effect of vibrational excitation on pure rotational quenching, and scalings by rotation, vibration, and chemical similarity will be discussed. [Preview Abstract] |
Thursday, June 6, 2013 2:24PM - 2:36PM |
P5.00003: Reactive collisions of ultracold polar molecules Constantinos Makrides, Svetlana Kotochigova, Alexander Petrov There has been a recent increase in the number of experimental and theoretical efforts in describing and controlling ultra cold chemistry. A number of groups have been able to create and trap a number of cold molecules and are now looking to move into controlling more exotic molecular systems. Critical to this movement is understanding the various interactions between the atoms and molecules in the trap. We offer here a study of the these interactions using Li + LiYb as a test system of interest. Using ab initio calculations we are able to obtain the long range interactions for the current system and connect to the short range interactions to provide a description of the interaction landscape. With this information, chemical reactions such as the exchange reaction (Li + LiYb $\to$ Yb + Li$_2$) can be practically approached in scattering calculations. [Preview Abstract] |
Thursday, June 6, 2013 2:36PM - 2:48PM |
P5.00004: Effect of p-wave resonances on the threshold behavior of ultracold chemical reactions R. C\^ot\'e, I. Simbotin, J. Wang, S. Ghosal In previous work we have studied the effects of s-wave resonances on the threshold behavior for ultracold chemical reactions, and we now extend our analysis to higher partial waves. Although s-wave is dominant in the limit $k\rightarrow 0$, p-wave or d-wave contributions can be resonantly enhanced at ultralow energy. If the corresponding partial wave has a resonance pole very close to the threshold, the ultracold regime is divided in two separate domains. The Wigner regime will be displaced towards much lower energies, while the remaining part of the ultracold regime is characterized by an anomalous $k$-dependence for the inelastic and reaction cross sections; the newly found behavior, $\sigma_{\ell}(k)\sim k^{2\ell-5}$, is valid for $k_{\mathrm{pole}} \ll k \ll k_{\mathrm{low}}$. For $k\approx k_{\mathrm{pole}}$ the behavior changes over into the familiar Wigner threshold law, $\sigma_{\ell}(k)\sim k^{2\ell-1}$, which is now valid only for $k\ll k_{\mathrm{pole}}$. We illustrate our findings with numerical results of reaction cross sections for benchmark systems, such as H$_2$ + Cl and H$_2$ + D. [Preview Abstract] |
Thursday, June 6, 2013 2:48PM - 3:00PM |
P5.00005: Generalized confinement-induced resonances(CIR) in quasi-1D system Chen Zhang, Chris Greene Reduced dimension systems have been realized in ultracold atomic gases to explore new physics, and the scattering properties of atoms in these systems are particularly interesting. Confinement-induced resonances occur in quasi-1D systems when the quasi-1D scattering phase shift of a particle scattered by a infinitely massive particle in the center of a quasi-1D tube jumps by Pi. In this project, we analytically derive the position of this quasi-1D CIR for different transverse trapping potentials at low energy under the frame transformation approximation [2], which generalizes the well-known results for an isotropic harmonic oscillator trap in the transverse plane [1,2]. We isolate the contribution from all the closed channels by regularizing a divergent summation of all closed channel components. We have verified our analytical results for a square-hard-wall transverse trap system numerically using short range model potentials, and shows finite range corrections of the zero-range model. [1] M. Olshanii, Phys. Rev. Lett. 81 938 (1998) [2] B. Granger and D. Blume, Phys. Rev. Lett. 92 13(2004) [Preview Abstract] |
Thursday, June 6, 2013 3:00PM - 3:12PM |
P5.00006: Dipolar confinement-induced resonances of ultracold gases in waveguides Panagiotis Giannakeas, Vladimir Melezhik, Peter Schmelcher Exploring the impact of anisotropic dipolar interactions for ultracold collisions in quasi-one-dimensional traps we derive and analyze dipolar confinement-induced resonances (DCIRs) attributed to different angular momentum states. Our analysis is based on an extended $K$-matrix approach for quasi-one dimensional geometries. An analytically derived resonance condition allows us to predict the positions of DCIRs. The results obtained within the $K$-matrix theory are in excellent agreement with corresponding exact numerical calculations. [Preview Abstract] |
Thursday, June 6, 2013 3:12PM - 3:24PM |
P5.00007: Avalanche Mechanism for the Enhanced Loss of Ultracold Atoms D. Hudson Smith, Christian Langmack, Eric Braaten In several experiments with ultracold trapped atoms, a narrow loss feature has been observed near an {\it atom-dimer resonance}, at which there is an Efimov trimer at the atom-dimer threshold. The conventional interpretation of these loss features is that they are produced by the {\it avalanche mechanism}, in which the energetic atom and dimer from 3-body recombination undergo secondary elastic collisions that produce additional atoms with sufficient energy to escape from the trapping potential. We use Monte Carlo methods to calculate the average number of atoms lost and the average heat generated by recombination events in a Bose-Einstein condensate and in a thermal gas. We improve on previous models by taking into account the energy-dependence of the cross sections, the spacial structure of the atom cloud, and the elastic scattering of the atoms. We show that the avalanche mechanism cannot produce a narrow loss feature near the atom-dimer resonance. The number of atoms lost from a recombination event can be more than twice as large as the 3 that would be obtained in the absence of secondary collisions. However the resulting loss feature is broad and its peak is at a scattering length that is larger than the atom-dimer resonance and depends on the trap depth. [Preview Abstract] |
Thursday, June 6, 2013 3:24PM - 3:36PM |
P5.00008: Frequency Domain Control by the Autler-Townes Effect Ergin Ahmed, Xinhua Pan, Marjatta Lyyra In recent years Quantum Optics has been expanded from atomic to molecular systems despite much weaker oscillator strengths and complex relaxation pathways that have presented serious challenges in the past. The richness of molecular excitation pathways and the variety of molecular interactions combined with the Autler-Townes (AC Stark) effect has made it possible to develop novel applications in this field,\footnote{E. H. Ahmed et al., Adv. At., Mol., Opt. Phys., Vol. 61, 467 - 514, (2012).} such as control of molecular angular momentum alignment\footnote{J. Qi, \textit{et al.}, PRL 83, 288-291 (1999).} and the electronic transition dipole moment function.\footnote{J. Qi, \textit{et al.}, PRL 88, 173003 (2002).} In addition, the electric field amplitude of the control laser Rabi frequency can be used as a ``tuning'' mechanism for the mixing coefficients of energy levels that are weakly perturbed by the spin-orbit interaction,\footnote{E. H. Ahmed, \textit{et al.}, PRL 107, 163601 (2011).} i.e. to control the valence electron spin polarization and the spin multiplicity of molecular quantum states. Experimentally we demonstrate that the enhancement of the spin-orbit coupling between a pair of weakly interacting singlet-triplet rovibrational levels depends on the Rabi frequency (laser power) of the control laser. We will discuss how this mechanism can be used to optimize collisional population flow between singlet and triplet electronic states, through such control of the spin-orbit perturbation based gateway levels. [Preview Abstract] |
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