Bulletin of the American Physical Society
39th Annual Meeting of the APS Division of Atomic, Molecular, and Optical Physics
Volume 53, Number 7
Tuesday–Saturday, May 27–31, 2008; State College, Pennsylvania
Session B4: Photoassociation and Cold Collisions |
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Chair: Paul Julienne, National Institute of Standards and Technology Room: Nittany Lion Inn Ballroom AB |
Wednesday, May 28, 2008 11:00AM - 11:12AM |
B4.00001: Rate Saturation of Photoassociation in a Bose-Einstein Condensate J. Hitchcock, M. Junker, D. Dries, C. Welford, Y.P. Chen, T.A. Corcovilos, R.G. Hulet We present the first experimental evidence for saturation of the photoassociation (PA) rate constant, $K_p$, in a Bose-Einstein condensate (BEC). Atomic $^7$Li in the $F$ = 1, $m_F$ = 1 hyperfine state is condensed in an elongated optical trap and a PA pulse coupling the atoms to the $v^\prime$$^\prime$ = 83 vibrational level of the 1 $^3 \Sigma^+_g$ excited molecular state propagates along the long axis of the trap. On-resonant absorption imaging is used to measure the fraction of atoms remaining in the BEC after each PA pulse for a given duration and intensity. $K_p$ is then extracted as a fitting parameter to the time dependent loss. The PA rate is substantially enhanced by tuning to near a magnetic Feshbach resonance at 732G. The rate constant is observed to saturate to a value of $K_p$ $\sim$ 1.4 $\times$ 10 $^-$$^7$ cm$^3$/s for PA pulse intensities $>$ 5 W/cm$^2$. The saturation level is compared with the theories of quantum mechanical unitarity and rogue dissociation. [Preview Abstract] |
Wednesday, May 28, 2008 11:12AM - 11:24AM |
B4.00002: Giant formation rates of ultracold molecules via Feshbach optimized photoassociation Philippe Pellegrini, Mark Gacesa, Robin C\^ot\'e Since their first experimental realization, ultracold molecules have attracted a lot of attention due to their broad potential applications in metrology, high precision spectroscopy or quantum computing. However, even if the ability to produce and control ultracold molecules has improved drastically over the last decade, forming stable molecules in their ground lowest vibrationnal levels is still a difficult proposition. Here we present a theoretical investigation of the photoassociation of atoms in the vicinity of a Feshbach resonance for the production of ultracold stable molecules. We show that large molecular formation rates can be obtained, with enhancement of several orders of magnitude over off-resonance cases. Example with both homonuclear and heteronuclear dimers will be given. Future possible applications will be discussed as well. [Preview Abstract] |
Wednesday, May 28, 2008 11:24AM - 11:36AM |
B4.00003: Feshbach-optimized photoassociation in LiRb Marko Gacesa, Philippe Pellegrini, Robin C\^ot\'e We propose a realistic scheme for production of ultracold heteronuclear LiRb molecules in their lowest vibrational levels based on photoassociation in the vicinity of Feshbach resonances. To calculate the positions of Feshbach resonances we perform coupled-channel calculations using the best available molecular potentials, and the photoassociation rate is computed by multichannel mapped Fourier grid method. Li-Rb is an interesting mixture to study since it forms a polar molecule with a large dipole moment in its ground state. Polar molecules can be used in experiments related to e.g. quantum information and study of degenerate gases. [Preview Abstract] |
Wednesday, May 28, 2008 11:36AM - 11:48AM |
B4.00004: Light Assisted Collisional Losses in a $^{85/87}$Rb Optical Trap Anthony Gorges, Michael DeAngelo, Nicholas Bingham, Mathew Hamilton, Jacob Roberts Light-assisted collisional loss, loss due to the excitation of an atom-atom pair to a stronger interatomic potential, poses an interesting problem with respect to loading two isotopes into the same optical trap. By loading both $^{85}$Rb and $^{87}$Rb into a far off resonant trap (FORT), we have studied inter- and intraspecies excited state/ground state collisional losses. Because of the relatively weak confinement of the FORT we expect the hyperfine structure of the different isotopes to play a crucial role in the collisional loss rates. This allows us to directly compare losses associated with long range excited state potentials; from purely attractive to purely repulsive, long range to short range. We observe radically different loss rates for different excited state potentials. Additionally, we observe that some collisional channels' loss rates are heavily saturated at our operating intensities ($\sim$15 mW/cm$^{2}$). These losses are important limitations in loading dual isotope optical traps. [Preview Abstract] |
Wednesday, May 28, 2008 11:48AM - 12:00PM |
B4.00005: Control of Ultracold Collisions with Nonlinear Frequency Chirps J.A. Pechkis, J.L. Carini, C.E. Rogers III, P.L. Gould We report on measurements of ultracold excited-state collisions between Rb atoms induced by frequency-chirped laser light. The chirps, either positive or negative, sweep over 1 GHz in 100 ns and are centered at a variable detuning below the atomic resonance. If the laser light is resonant with an attractive potential of an atom-pair at some point during the chirp, the pair is excited, potentially resulting in loss from the trap. In previous work with linear chirps,$^{1}$ we observed that at certain center detunings, the negative chirp yielded a lower collisional loss rate than the positive chirp. We attribute this suppression to the fact that the negative chirp follows the excited atom-pair trajectory and can therefore de-excite the atom-pair during the collision. In the present work, we incorporate nonlinear frequency chirps. For the negative chirp, we find a significant dependence on the details of the nonlinearity. This indicates the importance of matching the chirp to the atom-pair trajectories. This work is supported by DOE. \\* \\*$^{1}$ M.J. Wright \emph{et al.}, Phys. Rev. A \textbf{75} 051401(R) (2007) [Preview Abstract] |
Wednesday, May 28, 2008 12:00PM - 12:12PM |
B4.00006: Spectral Phase Effects on Ultrafast Coherent Control H.U. Jang, M.L. Trachy, G. Veshapidze, C.W. Fehrenbach, B.D. DePaola A long-time goal in laser-matter interaction is the use of lasers to efficiently control chemical reactions. The newest tool in this field is the ultrafast laser. Using a genetic algorithm to guide laser parameters, specific pathways in certain chemical reactions have already been optimized, though later deducing exactly why those laser parameters were optimal has proven difficult. In the experiments described in this talk we examine the effects of spectral phase on the coherent control of a particular ultracold collision process, photoassociation followed by coherent excitation and ionization (PAI). We concentrate on step functions and pulses in the spectral phase. When combined with high resolution time-of- flight spectroscopy as a diagnostic, we find that such phases help in furthering our understanding of PAI, hopefully leading to a better understanding of the physics underlying the coherent control of this collision path. The experimental measurements will be compared with the results of simple calculations. [Preview Abstract] |
Wednesday, May 28, 2008 12:12PM - 12:24PM |
B4.00007: Ultracold collisions between Rb and excited NH Steven Wrathmall, Edmund Meyer, Daniel Haxton, Heather Lewandowski, Chris Greene Rb--NH is a system of both fundamental and current experimental interest. We investigate the prospect of collisional processes between the Rb (5p) + NH $\left(\rm{X}~^{3}\Sigma^{-}\right)$ and Rb (5s) + NH $\left(^{1}\Delta\right)$ states in the Rb--NH system. The inelastic collision processes inherently involve more than one Born-Oppenheimer potential surface, which is of general interest in the study of atomic and molecular collisions. [Preview Abstract] |
Wednesday, May 28, 2008 12:24PM - 12:36PM |
B4.00008: Photoassociation of $^{171}$Yb atoms Iris Reichenbach, Ivan Deutsch Photoassociation on the extremely narrow $^1S_0 \rightarrow {}^1P_0$ clock transition of fermionic alkaline-earth like elements allows for both the accurate examination of molecular states at large separation, and the manipulation of scattering properties via optical Feshbach resonances. The latter open new avenues to the control of ultracold atomic collisions by fine-tuning the scattering properties of the colliding atoms. We calculate the long-range molecular potentials of $^{171}$Yb that dissociate to $^1S_0 + ^1P_0$ for use in photoassociation, including hyperfine interactions and external magnetic fields. We investigate the existence of purely long-range bound states, caused by anticrossings induced by the hyperfine interaction, as well as shape resonances in the scattering eigenstates. [Preview Abstract] |
Wednesday, May 28, 2008 12:36PM - 12:48PM |
B4.00009: Spectroscopy of $^{1}$S$_{0 }$-- $^{3}$P$_{1} \quad ^{88}$Sr Atomic Transition in a 1.06 $\mu $m Optical Dipole Trap Y.N. Martinez de Escobar, P.G. Mickelson, A.J. Traverso, T.C. Killian We studied the effects of laser light near-resonant with the $^{1}$S$_{0}$-- $^{3}$P$_{1} \quad ^{88}$Sr transition in an optical dipole trap (ODT). We observe laser cooling of our ODT atomic sample as the atoms collide in the presence of red-detuned 689 nm light. Heating of the atoms was also observed at a different range of frequency detunings while performing spectroscopy. Both processes were accompanied with atom loss, but the increase of phase space density observed during 689 nm laser cooling could aid pursuits of quantum degeneracy with Sr. [Preview Abstract] |
Wednesday, May 28, 2008 12:48PM - 1:00PM |
B4.00010: Repumping of ultracold strontium atoms using the $^3$P$_2$ - $^3$D$_2$ transition P.G. Mickelson, Y.N. Martinez de Escobar, A.J. Traverso, T.C. Killian We discuss recent experiments involving ultracold strontium. Using a commercially-available 3 micron laser, we repump atoms out of the $^3$P$_2$ level via the $^3$D$_2$ state and gain almost a factor of 10 in the number of atoms in our system. This increase in the signal-to-noise ratio enables improved spectroscopy of strontium in our optical trap. [Preview Abstract] |
Wednesday, May 28, 2008 1:00PM - 1:12PM |
B4.00011: Fine-structure changing collisions in atomic titanium Mei-Ju Lu, Kyle Hardman, Jonathan Weinstein Fine-structure changing collisions are of interest for understanding interstellar evolution, and may play an important role in experiments with anisotropically- interacting atoms. We use helium buffer-gas cooling and optical pumping techniques to measure cold titanium--helium collisions that cause transitions between the fine- structure levels of the $[3d^2 4s^2] \ ^3F_J$ electronic ground state of atomic $^{48}$Ti, over a temperature range from 5 to 20 K. The Ti--He inelastic collision rate is strongly suppressed compared to collision rates of non-transition-metal atoms with noble gas atoms. [Preview Abstract] |
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