Bulletin of the American Physical Society
48th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 62, Number 8
Monday–Friday, June 5–9, 2017; Sacramento, California
Session U3: Cold Collisions and Spectroscopy |
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Chair: Eite Tiesinga, Joint Quantum Institute, NIST and UMD Room: 308 |
Friday, June 9, 2017 10:30AM - 10:42AM |
U3.00001: Observation of a triplet structure in d-wave Feshbach resonances Yue Cui, Min Deng, Chuyang Shen, Shen Dong, Cheng Chen, Bo Gao, Meng Khoon Tey, Li You A d-wave Feshbach resonance between the $^{85}$Rb$|2, -2\rangle$+$^{87}$Rb$|1, -1\rangle$ scattering channel is observed in a mixture of ultracold $^{85}$Rb and $^{87}$Rb atoms. Analogous to the well-known doublet splitting of the p-wave resonance in $^{40}$K [1], we find a triplet structure originating from the magnetic dipole-dipole interaction between the valence electron spins of the two heteronuclear atoms. The three components of the resonance are respectively associated with the partial wave projections onto the direction of the magnetic field being $m_{l}$=0, $|m_{l}|$=1 and $|m_{l}|$=2. Such an interpretation and our observations are well characterized using the semi-analytic multichannel quantum-defect theory [2]. This work opens up new possibilities of studying the anisotropy in d-wave interaction dominated physics. \vspace{3ex} \newline [1] C. Ticknor, C. A. Regal, D. S. Jin, and J. L. Bohn, Phys. Rev. A 69, 042712 (2004). \newline [2] Bo Gao, Phys. Rev. A 84, 022706 (2011). [Preview Abstract] |
Friday, June 9, 2017 10:42AM - 10:54AM |
U3.00002: ABSTRACT WITHDRAWN |
Friday, June 9, 2017 10:54AM - 11:06AM |
U3.00003: Final state distribution in three-body recombination of three ultracold $^{87}$Rb atoms B. Ruzic, Y. Wang, J. D'Incao, P. Julienne, J. Wolf, A. Kr{\"u}kow, M. Deiss, E. Tiemann, J. Hecker Denschlag We use numerical calculations of coupled 3-body equations to obtain predictions of the distribution of Rb$_2$ dimer vibrational-rotational states when three ultracold Rb atoms undergo 3-body recombination. We assume the three body potentials at long range are given by pairwise addition of the known two-body potentials having the known van der Waals coefficient and scattering length for two Rb atoms and having a number $N$ of s-wave bound states. We solve the 3-body equations in the adiabatic hyperspherical representation to obtain the product distributions as $N$ increases from unity and compare them to recently measured product distributions at the University of Ulm. We find points of agreement as well as difference with the observations, and use these to get insights into the nature of threshold three-body recombination of ultracold Rb atoms. [Preview Abstract] |
Friday, June 9, 2017 11:06AM - 11:18AM |
U3.00004: Three-body scattering dynamics of ultracold magnetic lanthanides Svetlana Kotochigova, Ming Li, Constantinos Makrides, Alexander Petrov, Eite Tiesinga We theoretically investigate the origin of an extremely strong temperature dependence of the Feshbach-Fano (FF) resonance profiles observed experimentally [1,2] in atom-loss spectra of magnetic lanthanides, Dy and Er. This temperature dependence leads to a rapid increase of resonance density in these recombination spectra. We show with a resonant scattering model that the Wigner-threshold power law of the three-body recombination rate as a function of collision energy is very different for $s$- and $d$-wave entrance channels. Our resonance profiles for the Er loss features are in good agreement with experimental measurements [2] for temperatures from 230 nK to 2 $\mu$K indicating that the entrance channel has long-range repulsive three-body potentials, governed by the asymptotic behavior of the grand-angular-momentum operator and the total orbital angular momentum of the three atoms. [1] K. Bauman, N. Q. Burdick, M. Lu, and B. L. Lev, Phys. Rev. A {\bf 89}, 020701 (2014); [2] T. Maier, H. Kadau, M. Schmitt, M. Wezel, I. Ferrier-Barbut, T. Pfau, S. Baier, K. Aikawa, L. Chomaz, M. J. Mark, F. Ferlaino, C. Makrides, E. Tiesinga, A. Petrov, and S. Kotochigova, Phys. Rev. X {\bf 5}, 041029 (2015). [Preview Abstract] |
Friday, June 9, 2017 11:18AM - 11:30AM |
U3.00005: Analytical coupled-channels treatment of two-body scattering in the presence of three-dimensional isotropic spin-orbit coupling Qingze Guan, Doerte Blume It is shown that the single-particle spin-orbit coupling terms, which---in the cold atom context---are associated with synthetic gauge fields, can significantly and non-trivially modify the phase accumulation at small interparticle distances even if the length scale $(k_{\text{so}})^{-1}$ associated with the spin-orbit coupling term is significantly larger than the van der Waals length $r_{\text{vdW}}$ that characterizes the two-body interaction potential. A theoretical framework, which utilizes a generalized local frame transformation and accounts for the phase accumulation analytically, is developed. Comparison with numerical coupled-channels calculations demonstrates that the phase accumulation can, to a very good approximation, be described over a wide range of energies by the free-space scattering phase shifts---evaluated at a scattering energy that depends on $k_{\text{so}}$---and the spin-orbit coupling strength $k_{\text{so}}$. [Preview Abstract] |
Friday, June 9, 2017 11:30AM - 11:42AM |
U3.00006: Energetics and control of ultracold isotope-exchange reactions between heteronuclear dimers in external fields Michal Tomza We show that isotope-exchange reactions between ground-state alkali-metal, alkaline-earth-metal, and lanthanide heteronuclear dimers consisting of two isotopes of the same atom are exothermic with an energy change in the range of 1-8000 MHz, thus resulting in cold or ultracold products. For these chemical reactions, there are only one rovibrational and at most several hyperfine possible product states. The number and energetics of open and closed reactive channels can be controlled by the laser and magnetic fields. We suggest a laser-induced isotope- and state-selective Stark shift control to tune the exothermic isotope-exchange reactions to become endothermic, thus providing the ground for testing models of the chemical reactivity. The present proposal opens the way for studying the state-to-state dynamics of ultracold chemical reactions beyond the universal limit with a meaningful control over the quantum states of both reactants and products. [1] M. Tomza, Phys. Rev. Lett. 115, 063201 (2015) [Preview Abstract] |
Friday, June 9, 2017 11:42AM - 11:54AM |
U3.00007: Controlled state-to-state atom-exchange reaction in ultracold atom-dimer mixture Huan Yang Ultracold molecules offer remarkable opportunities to study chemical reactions at nearly zero temperature. Although significant progresses have been achieved in exploring ultracold bimolecular reactions, the investigations are usually limited to measurements of the overall loss rates of the reactants. Detection of the reaction products will shed new light on understanding the reaction mechanism and provide a unique opportunity to study the state-to-state reaction dynamics. Here we report on the direct observation of an exoergic atom-exchange reaction in an ultracold atom-dimer mixture. Both the atom and molecule products are observed and the quantum states are characterized. By changing the magnetic field, the reaction can be switched on or off, and the reaction rate can be controlled. The reaction is efficient and we have measured a state-to-state reaction rate of up to 7.2(7)\texttimes 10$^{\mathrm{-10}}$ cm$^{\mathrm{3}}$/s from the time evolution of the reactants and products. The atom-exchange reaction observed is also an effective spin-exchange interaction between the Feshbach molecules and the fermionic atoms and may be exploited to implement quantum simulations of the Kondo effect with ultracold atoms and molecules. [Preview Abstract] |
Friday, June 9, 2017 11:54AM - 12:06PM |
U3.00008: Full-dimensional quantum dynamics of ultracold Li-CaH collisions in a magnetic field Timur Tscherbul, Jacek Klos, Masato Morita We present a theoretical study of ultracold Li-CaH collisions in a magnetic field using a full-dimensional potential energy surface with an explicit dependence on the CaH vibrational coordinate. Elastic and inelastic cross sections will be presented as a function of magnetic field and implications will be discussed for sympathetic cooling of $^2\Sigma$ molecular radicals with ultracold alkali-metal atoms in a magnetic trap. [Preview Abstract] |
Friday, June 9, 2017 12:06PM - 12:18PM |
U3.00009: The $C \: ^1 \Sigma ^+$, $A \: ^1 \Sigma ^+$, and $b \: ^3 \Pi_{0^+}$ states of LiRb Ian Stevenson, David Blasing, Yong Chen, Daniel Elliott We present the first spectroscopic studies of the $C \ ^1\Sigma^+$ electronic state and the $A \ ^1\Sigma^+$ - $b \ ^3\Pi_{0^+}$ complex in $^7$Li - $^{85}$Rb. Using resonantly-enhanced, two-photon ionization, we observed $v = 7$, 9, 12, 13 and $26-45$ of the $C \ ^1\Sigma^+$ state. We augment the REMPI data with a form of depletion spectra in regions of dense spectral lines. The $A \ ^1\Sigma^+$ - $b \ ^3\Pi_{0^+}$ complex was observed with depletion spectroscopy, depleting to vibrational levels $v=0 \rightarrow 29$ of the $A \ ^1\Sigma^+$ state and $v=8 \rightarrow 18$ of the $b \ ^3\Pi_{0^+}$ state. For all three series, we determine the term energy and vibrational constants. Finally, we outline several possible future projects in ultracold molecules based on the data presented here. [Preview Abstract] |
Friday, June 9, 2017 12:18PM - 12:30PM |
U3.00010: Geometric phase effects in ultracold collisions of H/D with rotationally excited HD Brian K. Kendrick, James F. E. Croft, Jisha Hazra, N. Balakrishnan Quantum reactive scattering calculations for the H/D + HD($v=4$, $j=1,2$)$\to$ H/D + HD($v'$, $j'$) and H + H$_2$($v=4$, $j=1,2$) $\to$ H + H$_2$($v'$, $j'$) exchange reactions are presented for the ground electronic state of H$_3$. A numerically exact three-dimensional time-independent scattering method based on hyperspherical coordinates is used to compute rotationally resolved reaction cross sections and non-thermal rate coefficients for collision energies between $1\,\mu {\rm K}$ and $100\,{\rm K}$. The geometric (Berry) phase associated with the D$_{3h}$ conical intersection in H$_3$ is included using a $U(1)$ vector (gauge) potential approach. It is shown that the geometric phase leads to a significant (up to three orders of magnitude) enhancement or suppression of the ultracold reaction rate coefficients depending upon whether the interference between the reaction pathways encircling the conical intersection is constructive or destructive. The nature of the interference is governed by a newly discovered mechanism which leads to an effective quantization of the ultracold scattering phase shifts. Interesting behavior due to rotational excitation of the HD and H$_2$ is observed which might be exploited by experimentalists to control the reaction outcome. [Preview Abstract] |
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