Bulletin of the American Physical Society
49th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 63, Number 5
Monday–Friday, May 28–June 1 2018; Ft. Lauderdale, Florida
Session U04: Ultracold Collisions and Photoassociation Processes |
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Chair: Jacob Roberts, Colorado State University Room: Grand C |
Friday, June 1, 2018 8:00AM - 8:12AM |
U04.00001: Observation of cold dipolar collisions between centrifuge decelerated molecules Thomas Gantner, Xing Wu, Manuel Koller, Martin Zeppenfeld, Sotir Chervenkov, Gerhard Rempe Understanding molecular collisions at low energies is a prerequisite for future sympathetic and evaporative cooling of naturally occurring molecules. However, experimental investigation of collisions in this temperature regime is still in its infancy. Our cryofuge setup, the combination of cryogenic buffer gas cooling and centrifuge deceleration $\footnote{S. Chervenkov et al., \textbf{Phys. Rev. Lett.} 112, 013001 (2014)}$, produces slow molecular beams with densities of over $10^{9}/cm^{3}$. This allowes the observation of cold molecule-molecule collisions with large observed cross sections $> 10^{-12} cm^{2}$ for $CH_3F$ and $ND_3$ $\footnote{X. Wu et al., \textbf{Science} 358, 645-648, (2017)}$. Our experimental findings agree with theoretically modeled elastic and inelastic collisional loss rates. The low absolute velocity enables the straightforward loading of molecules into an electrostatic trap $\footnote{B.G.U. Englert et al., \textbf{Phys. Rev. Lett.} 107, 263003 (2011)}$ making much more detailed studies possible due to longer interaction times. Such measurements are important, e.g., for future evaporative cooling experiments. [Preview Abstract] |
Friday, June 1, 2018 8:12AM - 8:24AM |
U04.00002: Ion-ion correlation impacts on electron-ion collision rates in plasmas John Guthrie, Wei-Ting Chen, Puchang Jiang, Craig Witte, Jacob Roberts Ultracold plasmas can be created at sufficiently cold temperatures that spatial correlations in the electron and ion components can become significant with respect to many plasma properties in the so-called strong coupling regime. In recent experimental work, we measured a discrepancy between predicted and measured electron-ion collision rates. Subsequent simulations of this experimental measurement have indicated that ion-ion correlations need to be taken into account in computing the electron-ion collision rate. This is despite the fact that there is a mass ratio of approximately $10^5$ between the ion and electron masses in the ultracold plasma. We discuss the significance of these results in the context of both ultracold plasmas and other plasmas in general. [Preview Abstract] |
Friday, June 1, 2018 8:24AM - 8:36AM |
U04.00003: Rydberg molecules for ion-atom scattering in the ultracold regime Michal Tomza, Thomas Schmid, Christian Veit, Nicolas Zuber, Robert Löw, Tilman Pfau, Michal Tarana We propose a novel experimental method to extend the investigation of ion-atom collisions from the so far studied cold, essentially classical regime to the ultracold, quantum regime [1]. Key aspect of this method is the use of Rydberg molecules to initialize the ultracold ion-atom scattering event. We exemplify the proposed method with the lithium ion-atom system, for which we present simulations of how the initial Rydberg molecule wavefunction, freed by photoionization, evolves in the presence of the ion-atom scattering potential. We predict bounds for the ion-atom scattering length from ab initio calculations of the interaction potential. We demonstrate that, in the predicted bounds, the scattering length can be experimentally determined from the velocity of the scattered wavepacket in the case of $^6$Li$^+$-$^6$Li, and from the molecular ion fraction in the case of $^7$Li$^+$-$^7$Li. The proposed method to utilize Rydberg molecules for ultracold ion-atom scattering, here particularized for the lithium ion-atom system, is readily applicable to other ion-atom systems as well. [1] T. Schmid, C. Veit, N. Zuber, R. L\"ow, T. Pfau, M. Tarana, M. Tomza, Phys. Rev. Lett. 120 (2018), arXiv:1709.10488 [Preview Abstract] |
Friday, June 1, 2018 8:36AM - 8:48AM |
U04.00004: Experimental realization of a Rydberg optical Feshbach resonance in a quantum many-body system Tanita Eichert, Oliver Thomas, Carsten Lippe, Herwig Ott Tuning the scattering length between two particles via Feshbach resonances led to some of the most important advances in atomic physics. We have realized a Rydberg optical Feshbach resonance in rubidium by coupling two ground state atoms to an ultra-long range Rydberg molecular state using a laser field and demonstrate their exemplary application leading to different revival times in collapse and revival experiments in an optical lattice. Long lifetimes of Rydberg molecular states allow us to maintain long sample lifetimes on the order of milliseconds while changing the background scattering length of 99 Bohr radii by up to 50 Bohr radii. Rydberg optical Feshbach resonances open up a whole new field: In contrast to optical Feshbach resonances using intercombination transitions in strontium and ytterbium, Rydberg optical Feshbach resonances are feasible with a plenitude of Rydberg molecular states and all atomic species that are able to create Rydberg molecules. This large number of available molecular states allows to optimize the ratio between the change in scattering length and loss rates in further research. [Preview Abstract] |
Friday, June 1, 2018 8:48AM - 9:00AM |
U04.00005: Study of collisional processes of magnetically trapped cold Methyl radicals. Manish Vashishta, Takamasa Momose Cold atomic collisions have been characterized by known interatomic potentials, and various quantum effects such as resonance scattering have been explained by the standard scattering theories. On the other hand, collisions of cold molecules, especially those of reactive molecules, have been studied less than those of atoms due to the difficulties in making cold molecules, and information is still lacking to fully understand cold collisional processes of molecules with complex internal structures. Recently, we demonstrated that methyl radicals, one of the fundamental and important reactive intermediates, can be trapped in a magnetic trap at 200 mK. We determine the collision cross section of different gases with the trapped methyl radicals by measuring the loss rate of methyl radicals from the trap to study their collision dynamics. \\ References: \begin{enumerate} \item Yang Liu, Manish Vashishta, Pavle Djuricanin, Sida Zhou, Wei Zhong, Tony Mittertreiner, David Carty, and Takamasa Momose. ``Magnetic Trapping of Cold Methyl Radicals'' Phys. Rev. Lett.~\textbf{118}, 093201 (2017). \end{enumerate} [Preview Abstract] |
Friday, June 1, 2018 9:00AM - 9:12AM |
U04.00006: Updated photoassociation spectroscopy and mass-scaling of bosonic strontium Benjamin Reschovsky, Brandon Ruzic, Hiro Miyake, Neal Pisenti, Gretchen Campbell, Paul Julienne We present an updated investigation into the mass-scaling behavior of photoassociation resonances relative to the $^3P_1$ state in bosonic strontium. A previous mass-scaling model [Borkowski \textit{et al.}, Phys.\ Rev.\ A \textbf{90}, 032713 (2014)] was able to incorporate a large number of photoassociation resonances for $^{88}$Sr, but at the time only a handful of resonances were known for $^{84}$Sr and $^{86}$Sr. In this work, we perform a more thorough measurement of $^{84}$Sr and $^{86}$Sr bound states, identifying multiple new resonances at deeper binding energies out to -5~GHz. We also identify several previously measured resonances that cannot be reproduced and provide alternative binding energies instead. With this improved spectrum, we develop a mass-scaled model that accurately reproduces the observed binding energies of $^{86}$Sr and $^{88}$Sr to within 1~MHz. In order to accurately reproduce the deeper bound states, our model includes a second $1_u$ channel to more faithfully reproduce the depth of the potential. In addition, the optical lengths of the $^{84}$Sr $0_u^+,\ \nu=-2$ to $\nu=-5$ states are measured and compared to numerical estimates to characterize their use as optical Feshbach resonances. [Preview Abstract] |
Friday, June 1, 2018 9:12AM - 9:24AM |
U04.00007: Atom-molecule coherence in heteronuclear Li-Yb Alaina Green, Jun Hui See Toh, Khang Ton, Subhadeep Gupta We have demonstrated coherent coupling between Li+Yb free atom pairs and LiYb molecules in the electronic ground state via two-photon free-bound Raman processes. Coherent control is manifest in the creation of a dark atom-molecule superposition state. Evidence for this dark state is observed in a crossed optical dipole trap containing a mixture of ultracold $^6$Li and $^{174}$Yb, as the suppression of photoassociative loss within a narrow (sub-natural) frequency range. We intend to utilize this dark state to perform Stimulated Raman Adiabatic Passage (StiRAP) to create ultracold samples of LiYb in the electronic ground state. The non-bialkali LiYb molecule possesses both electric and magnetic dipole moments, and the unpaired electron degree of freedom could be utilized towards magnetic trapping of ultracold molecules as well as tuning of molecular collisions and reactions. [Preview Abstract] |
Friday, June 1, 2018 9:24AM - 9:36AM |
U04.00008: Effects of quantum superposition and interference in spin-dependent photoassociation of 87Rb Bose-Einstein condensates. David Blasing, Jesus Perez-Rios, Yangqian Yan, Chuan-Hsun Li, Sourav Dutta, Qi Zhou, Yong Chen We have studied spin-dependent photoassociation in 87Rb Bose-Einstein condensates both with and without Raman induced spin-momentum coupling. Such Raman induced spin-momentum coupling creates superpositions of the bare m\textunderscore f spin states within the F$=$1 hyperfine manifold of 87Rb. These m\textunderscore f spin superposition states simultaneously access two photoassociation channels, thus opening the possibility to observe quantum interference effects. I will report our experimental results in comparison with a theoretical model considering the interference effects. [Preview Abstract] |
Friday, June 1, 2018 9:36AM - 9:48AM |
U04.00009: Non-adiabatic quantum reactive scattering in hyperspherical coordinates Brian K. Kendrick A new methodology for performing electronically non-adiabatic quantum reactive scattering calculations in hyperspherical coordinates is presented for A + B$_2$ $\leftrightarrow$ AB + B and AB + B $\to$ AB + B reactive systems. The methodology accurately treats all six degrees of freedom relative to the center of mass on two coupled Born-Oppenheimer electronic potential energy surfaces which exhibit a conical intersection (degeneracy). The non-adiabatic coupling between the two electronic states is equivalent to a U(2) non-abelian gauge potential and a particular choice of gauge is shown to remove the troublesome singularities which occur at the conical intersection. The new methodology is applied to ultracold collisions of H/D with vibrationally excited HD(v=4, j=0). For high vibrational excitation of HD, the H/D + HD system is a barrierless exoergic reaction which exhibits significant reactivity in the Wigner threshold regime. The total, vibrationally, and rotationally resolved reaction rate coefficients are reported as a function of collision energy between 1uK and 100K. Interesting constructive and destructive quantum interference effects are shown to alter the ultracold reaction rates by several orders of magnitude which confirm recently reported results for this system. [Preview Abstract] |
Friday, June 1, 2018 9:48AM - 10:00AM |
U04.00010: Restricted-basis-set calculations on atom-molecule collisions in external fields Timur Tscherbul, Masato Morita Rigorous quantum scattering calculations on molecular collisions in external fields are computationally demanding due to the need to account for a large number of coupled channels. We show that by restricting the number of helicity states in the basis set, it is possible to obtain highly accurate quantum dynamical results for low-temperature atom-molecule collisions in a magnetic field at a reduced computational cost. [Preview Abstract] |
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