Bulletin of the American Physical Society
2005 36th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 17–21, 2005; Lincoln, Nebraska
Session J4: Ultracold Collisions I |
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Chair: Phillip L. Gould, University of Connecticut Room: Burnham Yates Conference Center Hawthorne |
Friday, May 20, 2005 8:00AM - 8:12AM |
J4.00001: Slowing and Focusing of Molecules and Atoms in Pulsed Optical Fields Ray Fulton, Alexis Bishop, Peter Barker We demonstrate a general scheme for the deceleration of molecules in a high intensity (1.6 x 10$^{16}$ W/m$^{2})$ pulsed optical field. Using this method we have reduced the translational energy of cold benzene molecules in a molecular beam by 15 {\%} in a single pulse of 10 ns duration$^{[1]}$.$^{ }$The large gradient force from a focused beam of an injection seeded Q-switched Nd:YAG laser was used to decelerate the benzene molecules seeded in a supersonic jet from 320 m/s to 295 m/s without ionization or dissociation. This 25 m/s reduction in velocity corresponds to an average deceleration of 10$^{8}$g. The same high intensity Gaussian laser beam was used to focus ground state xenon atoms in a supersonic jet to a spot size of 7.6 $\mu $m indicating that this very general scheme can be used to manipulate a wide range of atomic and molecules species. References: [1] R. Fulton, A.I. Bishop, P.F. Barker. Phys. Rev. Lett. \textbf{93}, 243004 (2004) [Preview Abstract] |
Friday, May 20, 2005 8:12AM - 8:24AM |
J4.00002: Cold molecular NO from a Stark guide Bryan Bichsel, Jason Alexander, Neil Shafer-Ray, Michael Morrison, Eric Abraham Although the success of laser cooling and trapping has had a major impact on atomic physics, the requirements of simple internal structure have limited its use to a few atomic species. A modified Stark guide can be used as a source for cold polar molecules by filtering the cold fraction from a thermal source. Our hexapole Stark guide is constructed from straight copper rods with $\pm $ 4.5 kV on alternating wires. We present experimental results for creating a controlled (65-80K) molecular source of NO, the enhancement of the lowest ro-vibrational states of this source by the Stark guide capturing those particles with the lowest transverse temperature, as well as a new technique for measuring the speed distribution of a cold molecular sample. Furthermore, we discuss progress towards extracting and isolating longitudinally cold ($<$1K) molecules. [Preview Abstract] |
Friday, May 20, 2005 8:24AM - 8:36AM |
J4.00003: Time-dependent coherent multiple light scattering in ultracold atomic $^{85}$Rb S. Balik, R. Olave, C.I. Sukenik, M.D. Havey, V.M. Datsyuk, D.V. Kupriyanov, I.M. Sokolov Multiple light scattering creates mesoscopic coherences in optically dense ultracold atomic gases. Considerable interest has been generated by the possibility that at high densities strong localization, in which coherences collapse into localized subradiant excitations, may occur. At lower density, the main observable is the coherent backscattering (CBS) effect. In CBS, the intensity of resonance radiation scattered from the sample shows enhancement in the nearly backwards direction. We report polarization and time dependent studies of light scattering from the F = 3 - F$'$ = 4 hyperfine transition in ultracold atomic $^{85}$Rb. Studies include measurement of the time dependence of light scattered from the sample as a function of polarization and detuning from resonance excitation. Among other things, the measurements demonstrate frequency-dependent depolarization due to multiple scattering. The data is analyzed to obtain the long-lived decay modes of the sample, and also the fractional contribution of single scattering to the measured signals. Second, time dependent-simulations of the resonance CBS enhancement factor show the influence of time-separation of the emergence of light from different scattering orders. Supported by the National Science Foundation and NATO. [Preview Abstract] |
Friday, May 20, 2005 8:36AM - 8:48AM |
J4.00004: State-Selective Detection of Ultracold High-$v$ Ground-State Rb$_2$, and Spectroscopy of the (2)$\,\,^1\Sigma_u^+$ State Y. Huang, H. Kim, J. Qi, D. Wang, E.E. Eyler, P.L. Gould, W.C. Stwalley We have used single-color photoassociation (PA), followed by radiative stabilization, to form ultracold Rb$_2$ molecules in either the metastable triplet state, $a\,\,^3\Sigma_u^+$, or the true ground state, $X\,\,^1\Sigma_g^+$. Individual near-dissociation levels of the $X\,\,^1\Sigma _g^+$ state from $v''$=111 to $v''$=117 have been detected by resonant multiphoton ionization (REMPI) through the (2)$\,\,^1\Sigma_u^+$ state. The (2)$\,\,^1\Sigma_u^+$ state, which we have observed for the first time, has been studied over the wavelength range from 585 nm to 609 nm. The observed vibrational levels are determined to range from $v'$=26 to $v'$=60. Similarly, we have formed $a\,\,^3\Sigma_u^+$ molecules by PA and detected them via REMPI through the (1) $^3\Pi_g$ state. This work was supported by the National Science Foundation. [Preview Abstract] |
Friday, May 20, 2005 8:48AM - 9:00AM |
J4.00005: Passage time statistics in the formation of ultracold dimers from fermionic atoms Hermann Uys, Takahiko Miyakawa, Dominic Meiser, Pierre Meystre We investigate the temporal fluctuations characteristic of the formation of molecular dimers from ultracold fermionic atoms via either photoassociation or a Feshbach resonance. The quantum fluctuations inherent to the initial atomic state result in large fluctuations in the passage time from atoms to molecules. A heuristic classical stochastic model yields an excellent agreement with the full quantum treatment in the initial stages of the dynamics. We also show that in contrast to the association of atoms into dimers, the reverse process of dissociation from a condensate of bosonic dimers exhibits little passage time fluctuations. [Preview Abstract] |
Friday, May 20, 2005 9:00AM - 9:12AM |
J4.00006: Cold Cs Rydberg Atom Collisions: Line Shifts, Broadening and Inelastic Processes K. Richard Overstreet, Jonathan Tallant, Jeff Crawford, Arne Schwettmann, James P. Shaffer Results of collision experiments involving Cs atoms excited to Rydberg states will be presented. We report observations of the onset of dipole-dipole interactions by measuring spectral line broadening and line shift. The results are compared to a static line broadening theory appropriate for weak long range interactions. Experiments on resonant inelastic collisions between Rydberg atoms, 89D + 89D $\to $ 90P + 89D, will also be described. The inelastic collisions are studied by measuring photofragment velocity distributions. [Preview Abstract] |
Friday, May 20, 2005 9:12AM - 9:24AM |
J4.00007: Interactions between bosonic and fermionic metastable He atoms J. F. Babb Mixtures of spin-polarized metastable ${}^3\textrm{He}$ atoms and ${}^4\textrm{He}$ atoms are unique systems of current interest for studies of ultra-cold gases. The $s$-wave scattering length for collisions of ${}^4\textrm{He}$ atoms was measured to be ${}^{4-4}a=11.3$~nm ($+2.5,-1$~nm)~[1] and recent calculations find $8<{}^{4-4}a<12$~nm~[2]. The scattering length ${}^{3-4}a$ for fermion-boson collisions is presently indeterminate in sign and magnitude, but it has been predicted to fall in the ranges ${}^{3-4}a<-25$~nm or ${}^{3-4}a>46$~nm~[2,3]. In this talk, with regard to improving the theoretical value of ${}^{3-4}a$, the data characterizing ${}^3\textrm{He}(2\,{}^3S)$--${}^4\textrm{He}(2\,{}^3S)$ interactions primarily in the molecular ${}^5\Sigma_g^+$ state are reevaluated and additional calculations are presented. Supported in part by the NSF. [1]~S. Seidelin, \textit{et al.}, Phys. Rev. Lett. \textbf{93} (2004), 090409. [2]~A.~S. Dickinson, F.~X. Gad\'{e}a, and T. Leininger, J. Phys. B \textbf{37} (2004), 587. [3]~R.~J.~W. Stas, J.~M. McNamara, W. Hogervorst, and W. Vassen, Phys. Rev. Lett. \textbf{93} (2004), 053001. [Preview Abstract] |
Friday, May 20, 2005 9:24AM - 9:36AM |
J4.00008: Impact of three-body collisions on molecules in ultracold Bose-Fermi mixtures Jose D'Incao, Brett Esry We have investigated ultracold three-body collisions in quantum degenerate Bose-Fermi gas mixtures. In this regime, the three-body collision rates can be deduced analytically to determine their energy and scattering length dependence. For large and positive values of the scattering length, we demonstrate that relaxation of weakly bound boson-fermion molecules is strongly suppressed when colliding with an identical femionic atom. This suppression depends strongly on the mass ratio of the bosons and fermions. On the other hand, relaxation induced by collisions with the bosonic atoms is not suppressed. The main behavior of the total rate will thus be dictated by the relative densities of the two atomic species. (Supported by the National Science Foundation.) [Preview Abstract] |
Friday, May 20, 2005 9:36AM - 9:48AM |
J4.00009: Zeeman relaxation of CaF in low-temperature collisions with helium Scott V. Nguyen, Kenneth Maussang, Dima Egorov, Joel S. Helton, John M. Doyle The collision-induced Zeeman relaxation rate for collisions of CaF $X^{2}\Sigma~(v\prime\prime=0)$ with $^3$He is measured at 2~K. $10^{12}$ CaF molecules, produced via laser ablation, are cooled by a cold \3he buffer-gas inside a 3.44~T magnetic field. By monitoring the populations of the low-field and high- field seeking states, we extract a Zeeman relaxation rate of $\Gamma_{Z} = (7.7\,+5.4/-2.5)\times 10^{-15}$ cm$^{3}/s$ and a ratio of diffusion and inelastic cross-section of $\sigma^{CaF- He}_{diff} \Big/ \sigma^{CaF-He}_{Z}~=~(1.3 \,+1.3/-0.5)\times 10^4$. This rate is a direct measurement of the influence of spin-rotation coupling on Zeeman relaxation in the ground and first rotational level of CaF. The relationship of this inelastic rate to known molecular constants is consistent with recent theory of cold molecular collisions~[1] and outlines the $^2\Sigma$ molecules conducive to magnetic trapping. [1] R. V. Krems and A. Dalgarno, J.~Chem.~Phys.{\bf 120}, 2296 (2004). [Preview Abstract] |
Friday, May 20, 2005 9:48AM - 10:00AM |
J4.00010: Quantum statistical effects in the dissociation of a Bose-Einstein condensate of molecules Michael Jack, Han Pu We consider the dissociation of a molecular Bose-Einstein condensate transfered to the unstable side of a Feshbach resonance by rapidly tunning the magnetic field back through the resonance. The dissociation of the molecular condensate into correlated pairs of atoms exhibits very rich quantum dynamics which depends on the quantum statistics of the constituent atoms when the mode occupation gets large. A unified treatment of this dissociation is presented which includes both dissociation into pairs of bosonic and fermionic atoms. We show that in the case of bosonic atoms, Bose-enhancement can lead to stimulated dissociation, whereas, in the case of fermions, Pauli-blocking of the available states can give rise to incomplete dissociation of the molecules and a non-trivial oscillating final state. This work is applicable to narrow Feshbach resonances as it is easier, experimentally, to rapidly tune across the resonance and, secondly, they have a narrow dissociation linewidth which reduces the effective density of available states and therefore enhances the effects of quantum statistics. [Preview Abstract] |
Friday, May 20, 2005 10:00AM - 10:12AM |
J4.00011: The role of van der Waals interaction in O($^{3}$P)+H$_{2}$ reaction at low temperatures Balakrishnan Naduvalath, Philippe Weck, Jo\~ao Brand\~ao, W. Wang, C. J. Rosa We report quantum scattering calculations of the O($^3P$)+H$_2(v)$ reaction with an aim of determining sensitivity of the results to details of the interaction potential. We use two different analytic representations of the $^3A''$ potential energy surface (PES)\ -\ the GLDP surface reported by Rogers et al. (J. Phys. Chem. A {\bf 104}, 2308 (2000)) that provides a partial description of the van der Waals region and the more recent BMS1 and BMS2 PESs by Brand\~ao et al. (J. Chem. Phys {\bf 121}, 8861 (2004)) which explicitly include the van der Waals part. The ab initio data of Rogers et al. form the basis of all three surfaces. We report cross sections and rate coefficients on the three PESs using accurate quantum calculations. We also perform quasiclassical trajectory calculations on all three surfaces to explore quantum effects at low temperatures. [Preview Abstract] |
Friday, May 20, 2005 10:12AM - 10:24AM |
J4.00012: Production and Decay of Ultracold Feshbach Molecules in Bosonic and Fermionic Species. E. Hodby, S. Thompson, C. Regal, M. Greiner, A. Wilson, D.S. Jin, E.A. Cornell, C.E. Wieman We investigate the production efficiency of weakly-bound, ultracold molecules in bosonic $^{85}$Rb and also fermionic $^{40}$K when the magnetic field is swept across a Feshbach resonance [1]. For adiabatic sweeps of the magnetic field, our novel model shows that the conversion efficiency of \textit{both} species is solely determined by the phase space density of the atomic cloud, in contrast to a number of theoretical predictions. In the non-adiabatic regime our measurements of the $^{85}$Rb molecule conversion efficiency follow a Landau-Zener model. The spontaneous dissociation of these $^{85}$Rb molecules has also been observed [2]. The molecular lifetime shows a strong dependence on magnetic field, varying by three orders of magnitude between 155.5 G and 162.2 G. Our measurements are in good agreement with theoretical predictions in which molecular dissociation is driven by inelastic spin relaxation [3]. Molecule lifetimes of tens of milliseconds can be achieved close to resonance. [1] Cond-mat/0411487 [2] Phys. Rev. Lett. \textbf{94}, 020401 (2005) [3] Phys. Rev. Lett. \textbf{94}, 020402 (2005) [Preview Abstract] |
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J4.00013: Polarizabilities of $^3$P atoms and van der Waals coefficients for their interaction with helium atoms Xi Chu, Alex Dalgarno The effectiveness of the buffer gas cooling depends on the relative efficiency of elastic and inelastic collisions of the atoms with $^3$He atoms at temperatures below 0.4 K. Inelastic collisions lead to trap loss. The inelastic cross sections are controlled by the energy separations of the interaction potentials of the different symmetries of the molecular system formed by the approach of the helium atom and the gas atom. Scattering at low temperatures is sensitive to the interactions at large internuclear distances R and the range of candidate atoms can be explored through calculations of the long range anisotropy. Time-dependent density functional theory with self-interaction correction is applied to obtain the scalar and tensor dynamic polarizabilities of atoms in $^3$P states. The static polarizabilities are in good agreements with previous values. The dynamic polarizabilities are then used to evaluate the leading term in the long range interaction between the $^3$P atoms and helium. They are significant in determining the likelihood that the $^3$P atoms can be trapped in a helium buffer gas. [Preview Abstract] |
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