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 H4: Two and Few-body Collisions of Ultracold Atoms and Molecules |
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Chair: R. Cote, University of Connecticut Room: TELUS Convention Centre Glen 206 |
Thursday, June 7, 2007 10:30AM - 10:42AM |
H4.00001: A new method for calculation of Efimov resonances Francoise Masnou-Seeuws, Juan Blandon, Viatcheslav Kokoouline The recent observation of Efimov resonances in a cold gas [1] opens a new field. We have developed a method to calculate accurately the positions, widths and wave functions of three-body resonances. The calculations combine the hyperspherical adiabatic approach [2] and the slow variable discretization method of Ref.[3]. A sine grid basis set is used with a mapping procedure to introduce a variable grid step in the hyper-radius and in the two hyperangles; moreover, a complex absorbing potential is introduced. The method can be used to determine accurately both the short range and the long range wavefunctions. It has been checked on a model potential and compared with a R-matrix method [4] which necessitates a much larger basis set: the two calculations are in good agreement. [1] T. Kraemer \textit{et al.}, Nature \textbf{440}, 315 (2006), [2] V.Kokoouline and F.Masnou-Seeuws, Phys. Rev. A \textbf{73}, 012702 (2006), [3] O.I.Tolstikhin, S.Watanabe, and M.Matsuzawa, J. Phys. B: At. Mol. Opt. Phys. \textbf{29}, L389 (1996), [4] E. Nielsen, H. Suno, and B. D. Esry, Phys. Rev. A \textbf{66}, 012705 (2002). [Preview Abstract] |
Thursday, June 7, 2007 10:42AM - 10:54AM |
H4.00002: Signatures of Efimov's effect in ultracold gases Thorsten Koehler, Mark Lee, Paul Julienne Based on the approach of G. Smirne et al. [e-print cond-mat/0604183 (Phys. Rev. A, in press)], we present numerically exact calculations of resonance-enhanced three-body recombination in ultracold 133Cs Bose gases. We discuss associated atom-loss-rate constants at low magnetic-field strengths in comparison with recent experiments on Efimov's effect by Kraemer et al. [Nature (London) 440, 315 (2006)]. We interpret these measurements in terms of their relation to similar studies on helium trimers in molecular beams. We show how, as yet unobserved, excited Efimov-trimer molecules could be detected in ultracold gases of 85Rb, as well as 133Cs at high fields in the vicinity of 800 G. [Preview Abstract] |
Thursday, June 7, 2007 10:54AM - 11:06AM |
H4.00003: Weakly bound tetra-atomic molecules: attaching neutral atoms to Efimov states Yujun Wang, B.D. Esry We discuss the conditions under which a neutral atom can be attached to an Efimov state to form a tetra-atomic molecule. We use the adiabatic hyperspherical representation and obtain the the four-body adiabatic hyperspherical potentials by treating the interactions between the atoms in the Efimov state and the fourth atom perturbatively via a Fermi contact potential with an energy-dependent scattering length. These adiabatic potentials are then used to determine the binding energies of the tetra-atomic molecules which, in turn, allow us to determine the combinations of scattering length and effective range that result in binding. These molecules are expected to have long lifetimes and sizes comparable to the Efimov molecules themselves. We will also discuss the atom-Efimov state scattering length and speculate about collisionally induced quenching of the Efimov states. These results --- the latter in particular --- address the increasingly relevant and interesting question of the behavior of Efimov states in ultracold quantum gases. [Preview Abstract] |
Thursday, June 7, 2007 11:06AM - 11:18AM |
H4.00004: ABSTRACT WITHDRAWN |
Thursday, June 7, 2007 11:18AM - 11:30AM |
H4.00005: Trimer formation in ultracold gases of bosonic and fermionic molecules Bout Marcelis, Dmitry Petrov, Servaas Kokkelmans, Gora Shlyapnikov We consider weakly bound bosonic and fermionic heteronuclear molecules (dimers) in ultracold atomic gases, where the interspecies interaction is characterized by a large positive scattering length. We develop a new theoretical approach to solve the four-body scattering problem, which is valid when the mass ratio between the constituent atoms is sufficiently large. This approach is then used to study elastic and inelastic dimer- dimer scattering processes in the case that the light constituent atoms are fermions, while the heavy atoms can be either fermions or bosons. Due to the Fermi statistics of the light atoms, the heavy atoms experience a strong repulsion at large intermolecular distances. This leads to suppression of the collisional relaxation to universal trimer (Efimov) states and/or deeply bound molecular states. We present the formation rate of Efimov trimers as a function of the three-body parameter for several experimentally interesting systems. The competition between the formation of trimers and relaxation to deeply bound molecules is analyzed, and prospects for future studies of these systems are discussed. [Preview Abstract] |
Thursday, June 7, 2007 11:30AM - 11:42AM |
H4.00006: Ultracold four-body collisions of two-spin fermionic atoms Jose P. D'Incao, Nirav P. Mehta, Seth T. Rittenhouse, Chris H. Greene We have performed {\em ab initio} calculations for the four fermions system in two different spin states. From these calculations we were able to extract the scattering length dependence for the scattering observables which are relevant for current experiments in ultracold fermionic quantum gases. We have calculated, for instance, the dimer-dimer scattering length and explored the finite energy dependence concening the experimental range of temperatures in the strongly interacting regime. Due to the finite range of our interatomic model we also were able to explore finite scattering length corrections to the dimer-dimer scattering length. This work was supported by the National Science Foundation. [Preview Abstract] |
Thursday, June 7, 2007 11:42AM - 11:54AM |
H4.00007: Ultracold Feshbach molecules: energy structure and scattering length Cheng Chin Recent experiments on ultracold Feshbach molecules have revealed detailed and intriguing molecular energy structure near the continuum. Based on the quantum nature of the molecules, they are generally classified into two types: open-channel dominated and closed channel dominated A simple picture exists to unify and describe BOTH types of molecules. We report excellent agreements between our results and the full multi-channel calculation over a wide range of molecular binding energies: from 0 (continuum) to $\sim $ h$\times $1GHz. Comparison to measurements on $^{6}$Li, $^{40}$K, $^{85 }$Rb, $^{87 }$Rb and $^{133}$Cs will be presented. In particular, we will address the issue of associating molecular binding energies and atomic scattering lengths and the case of $^{133}$Cs where multiple s-, d- and g-wave resonances overlap. [Preview Abstract] |
Thursday, June 7, 2007 11:54AM - 12:06PM |
H4.00008: Effects of nonintegrability on stabilization of Feshbach molecules in atom waveguides Vladimir Yurovsky Deactivation of broad quasi-1D molecules [1,2] is analyzed. Deactivation of tightly bound molecules can be considered to be a two-body inelastic collision, which is suppressed at low collision energies [3,5]. If broad molecules are described by the integrable Lieb-Liniger-McGuire (LLMG) model with attractive interactions, an exact expression for the deactivation rate has a non-zero limit at low collision energy. (This behavior differs from the free-atom case [3], since bound atoms have non-vanishing imaginary momenta.) This absence of deactivation suppression can be related to non-diffraction of the LLMG model, which forbids atom-dimer reflection, and the atom and dimer can approach each other. Solution of Faddeev equations (using the approach of [4]) demonstrates that when the symmetry of the LLMG model is lifted due to a Feshbach resonance and reflection becomes allowed [4], the deactivation of broad molecules becomes suppressed. Thus, both the presence [4] and the suppression of certain processes are among the observable effects of non-integrability. [1] H. Moritz {\it et al.}, Phys. Rev. Lett. {\bf 94}, 210401 (2005). [2] T. Bergeman, M. G. Moore, and M. Olshanii, {\it ibid.} {\bf 91,} 163201 (2003). [3] D. M. Gangardt and G. V. Shlyapnikov, {\it ibid.} {\bf 90}, 010401 (2003). [4] V. A. Yurovsky, A. Ben-Reuven, and M. Olshanii, {\it ibid.} {\bf 96}, 163201 (2006). [5] V. A. Yurovsky and Y. B. Band, Phys. Rev. A, {\bf 75}, 012717 (2007). [Preview Abstract] |
Thursday, June 7, 2007 12:06PM - 12:18PM |
H4.00009: Calculation of the two-body scattering T-matrix in Configuration Space George Rawitscher Three-body Faddeev calculations require as input two-body T-matrices. For atomic physics applications configuration space is preferable over momentum space, since the potentials are given in the former. A recently developed solution of the Lippmann-Schwinger integral equation for the one-variable scattering wave function in configuration space [1] has now been extended to obtain the two variable scattering T-matrix, as will be shown with numerical examples. The method is based on spectral expansions into Chebyshev Polynomials of two auxiliary functions in each radial partition, in terms of which the T-matrix is obtained. The result is an important ingredient for the solution of the Faddeev integral equations in configuration space [2]. \newline [1] G. Rawitscher and I. Koltracht, Computing in. Sc. and Eng., \textbf{7}, 58 (2005); \newline [2] W. Gl\"{o}ckle, and G. Rawitscher; ``Three-atom scattering via the Faddeev scheme in configuration space,'' physics/0512010 at arxiv.com; [Preview Abstract] |
Thursday, June 7, 2007 12:18PM - 12:30PM |
H4.00010: A Measurement of the s-Wave Scattering Length in a $^7$Li Bose-Einstein Condensate D. Dries, M. Junker, J. Hitchcock, C. Welford, Y.P. Chen, R.G. Hulet The s-wave scattering length, $a_s$, parameterizes the effective interatomic interactions in a Bose-Einstein condensate (BEC). The sign and magnitude of $a_s$ have important consequences for the observable properties of the condensate and, consequently, $a_s$ needs to be accurately known in order to correctly interpret many experimental results. In our experiment, we create an optically trapped $^7$Li BEC in the $F=1$, $m_F=1$ hyperfine state. Using a Feshbach resonance, we are able to change the value of $a_s$ by nearly two orders of magnitude over the magnetic field range of 507-730 G. We extract $a_s$ from absorption images of the condensate by fitting to the Thomas-Fermi radius. Furthermore, the condensate suddenly disappears at fields above $730\pm1$ G, placing a lower bound on the location of the Feshbach resonance. [Preview Abstract] |
Thursday, June 7, 2007 12:30PM - 12:42PM |
H4.00011: Isotopic tuning of scattering lengths of ultracold Yb atoms Paul Julienne, R. Ciurylo, M. Kitagawa, K. Enomoto, K. Kasa, Y. Takahashi The species Yb has 5 stable spinless bosonic isotopes and two fermionic ones, $^{171}$Yb with I=1/2 and $^{173}$Yb with I=5/2. Two-color photoassociation spectroscopy of ultracold Yb atomic gases has been used to measure the binding energies of 7 J=0 and 5 J=2 bound states near the dissociation threshold of the homonuclear molecular dimers $^{170}$Yb$_{2}$, $^{171}$Yb$_{2}$, $^{172}$Yb$_{2}$, $^{173}$Yb$_{2}$, $^{174}$Yb$_{2}$, and $^{176}$Yb$_{2}$. Fitting 3 binding energies from $^{174}$Yb$_{2}$ and $^{176}$Yb$_{2}$ determines the C$_{6}$ and$_{ }$C$_{8}$ van der Waals constants and the absolute number of bound states in the single ground state potential. Our mass-scaled model then accurately predicts the binding energies of the other 9 measured levels, and determines accurate scattering lengths of all 28 different isotopic combinations, including $^{168}$Yb. As the reduced mass varies from 168/2 to 176/2, the scattering lengths vary through a complete cycle from --$\infty $ to +$\infty $. Thus, scattering length can be widely ``tuned'' by varying isotopic composition. Since all 6 species from mass 170 to 176 can be brought to the quantum degenerate regime, this gives a wide variety of mixtures for new studies of ultracold quantum gases and lattices. [Preview Abstract] |
Thursday, June 7, 2007 12:42PM - 12:54PM |
H4.00012: High Intensity 2-Photon Photoassociation Spectroscopy of Strontium S.B. Nagel, Y.N. Martinez, P.G. Mickelson, T.C. Killian We perform high intensity, 2-photon photoassociation spectroscopy near the 461 nm $^1$S$_0$-$^1$P$_1$ transition of strontium to determine the binding energy of the least bound level in the ground state atomic potential. Previous work by our group has constrained the value of the s-wave scattering length in both $^{86}$Sr and $^{88}$Sr. This work provides a more precise value of the s-wave scattering lengths using the newly-determined binding energy, thus informing efforts to attain quantum degeneracy in strontium. [Preview Abstract] |
Thursday, June 7, 2007 12:54PM - 1:06PM |
H4.00013: Three-body physics with multichannel two-body interactions Nirav Mehta, Seth Rittenhouse, Jose D'Incao, Chris Greene Atoms with internal hyperfine states (denoted by A, A', etc.) split by an external magnetic field are governed by complicated multichannel pair-wise interactions. We consider a simplified zero-range multichannel model designed to mimic atom-atom scattering near a Feshbach resonance. Our simple two-body interaction leads to a wide variety of rich physics at the three-body level absent in single channel models. Using a novel approach, we solve the three-body hyperangular Lippman-Schwinger equation and obtain adiabatic potential curves showing all available reaction channels and pathways for three-body proceses. This work is funded in part by the NSF. [Preview Abstract] |
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