Bulletin of the American Physical Society
2006 37th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 16–20, 2006; Knoxville, TN
Session V1: Ultracold Molecules |
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Chair: Cheng Chin, University of Chicago Room: Knoxville Convention Center Lecture Hall |
Friday, May 19, 2006 1:30PM - 2:06PM |
V1.00001: Ultracold Chromium: a dipolar quantum gas Invited Speaker: Tilman Pfau We report on experiments using a Bose-Einstein condensate of chromium atoms [1]. We produce up to $\sim $ 10$^{5}$ condensed $^{52}$Cr atoms after forced evaporation within a crossed optical dipole trap. Due to its large magnetic moment (6$\mu _{B})$, the dipole-dipole interaction strength in chromium is comparable with the one of the van der Waals interaction. We prove the anisotropic nature of the dipolar interaction by releasing the condensate from a cigar shaped trap [2]. This is the first experimental observation of mechanical dipolar effects in a quantum gas. We also report on the observation of 14 Feshbach resonances in elastic collisions between polarized ultra-cold $^{52}$Cr atoms [3]. This is the first observation of collisional Feshbach resonances in an atomic species with more than one valence electron. Moreover, such resonances constitute an important tool towards the realization of a purely dipolar interacting gas as they can be used to change strength and sign of the van der Waals interaction. \newline \newline \textbf{References} \newline 1. A. Griesmaier, J. Werner, S. Hensler, J. Stuhler, and T. Pfau, \textit{Phys. Rev. Lett. }\textbf{\textit{94}}\textit{, 160401 (2005)} \newline 2. J. Stuhler, A. Griesmaier, T. Koch, M. Fattori, T. Pfau, S. Giovanazzi, P. Pedri, and L. Santos, \textit{Phys. Rev. Lett. }\textbf{\textit{95}}\textit{, 150406 (2005)} \newline 3. J. Werner, A. Griesmaier, S. Hensler, J. Stuhler and T. Pfau, \textit{Phys. Rev. Lett. }\textbf{\textit{94}}\textit{, 183201 (2005)} [Preview Abstract] |
Friday, May 19, 2006 2:06PM - 2:42PM |
V1.00002: Optical production of ultracold polar molecules Invited Speaker: David DeMille We have recently demonstrated the production of ultracold polar RbCs molecules in their absolute vibronic ground state, via photoassociation of laser-cooled atoms followed by a laser-stimulated state transfer process [J. Sage \textit{et al.}, Phys. Rev. Lett. \textbf{94}, 203001 (2005)]. The resulting sample of $X{ }^1\Sigma ^+(v=0)$ molecules has a translational temperature of $\sim $100 $\mu $K and a narrow distribution of rotational states. With the method described here it should be possible to produce samples even colder in all degrees of freedom, as well as other bialkali species. Work is ongoing to separate and trap these ground-state molecules. Applications for such a trapped sample will be discussed. [Preview Abstract] |
Friday, May 19, 2006 2:42PM - 3:18PM |
V1.00003: Cold Molecule Spectroscopy for Constraining the Evolution of the Fine Structure Constant Invited Speaker: Current theories that attempt to unify gravity with the other fundamental forces predict spatial and temporal variations in the fundamental constants, including the fine structure constant, $\alpha$. Measurements of the variation of $\alpha$ by observation of multiple absorption lines from distant quasars are currently not in agreement. Due to the use of spatially diverse absorbers, these measurements are sensitive to relative Doppler shifts. Therefore an independent confirmation of the variation of $\alpha$ is important. Recently, there has been considerable interest in using spectroscopy of hydroxyl radical (OH) megamasers in interstellar space to constrain the evolution of fundamental constants. To aid in this work, we have performed precise laboratory-based measurements of ground-state, $\lambda$-doublet, microwave transitions in OH. Utilizing slow, cold molecules produced by a Stark decelerator, we have improved over the precision of the previous best measurement by twenty-five-fold for the F$' = 2 \rightarrow$ F = 2 transition and by ten-fold for the F$' = 1 \rightarrow$ F = 1 transition. Comparing these laboratory frequencies to those from OH megamasers in interstellar space will allow a sensitivity of 1 ppm for $\Delta\alpha/\alpha$ over $10^{10}$ years. [Preview Abstract] |
Friday, May 19, 2006 3:18PM - 3:54PM |
V1.00004: Quantum dynamics calculations on atom-diatom collisions: bosons versus fermions Invited Speaker: We have obtained new potential energy surfaces and carried out full quantum dynamics calculations for spin-polarized Li + Li$_{2}$ [1] and K + K$_{2}$ [2] collisions for both bosonic and fermionic isotopes. These are ``reactive'' scattering collisions because they include all possible arrangement channels. They are carried out in hyperspherical coordinates [3], which allow the full boson or fermion symmetry to be imposed. The potential energy surfaces are highly non-additive [4]. Our calculations give very high quenching rates for alkali dimers in excited vibrational states. For the \textit{low} vibrationally excited states that we can handle at present, we do \textit{not} see any suppression of inelastic scattering for fermionic atoms, even when the scattering length is large and positive. The low-temperature inelastic rate coefficients are typically above 10$^{-10}$ cm$^{3}$ s$^{-1}$. We conclude that Pauli blocking occurs only for molecules formed in the highest vibrational state in the potential well. Our results have important implications for experiments aimed at transferring molecules to lower vibrational states. We expect that it will be necessary to transfer them directly to the \textit{ground} vibrational state for them to be long-lived. Molecules produced in any intermediate vibrational state are likely to be ejected from the trap very quickly. We have also carried out calculations for mixed-isotope collisions involving alkali dimers [5]. For $^{7}$Li colliding with either $^{6}$Li$_{2}$ or $^{6}$Li$^{7}$Li, reactive scattering is possible even when the molecule is in its lowest rovibrational state because of the change in zero-point energy. For $^{7}$Li + $^{6}$Li$^{7}$Li, there is only one reactive channel and the reactive scattering rate is suppressed by a factor of 50 compares to the vibrational relaxation rates. \newline \newline [1] M. T. Cvita\v{s} et al., PRL 94, 033201 (2005). \newline [2] G. Qu\'{e}m\'{e}ner et al., PRA 71, 032722 (2005). \newline [3] P. Sold\'{a}n et al., PRL 89, 153201 (2002). \newline [4] P. Sold\'{a}n et al., PRA. 67, 054702 (2003). \newline [5] M. T. Cvita\v{s} et al., PRL 94, 200402 (2005). [Preview Abstract] |
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