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 B4: Photoassociation and Chemical Reaction of Molecules |
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Chair: Paul Lett, JQI/NIST Room: 309 |
Tuesday, June 6, 2017 10:30AM - 10:42AM |
B4.00001: Microwave dressing of ultracold $^{\mathrm{23}}$Na$^{\mathrm{40}}$K molecules Zoe Yan, Yiqi Ni, Jee Woo Park, Sebastian Will, Huanqian Loh, Kang Kuen Ni, Martin Zwierlein Ultracold molecules with tunable dipolar interactions are a promising platform for quantum simulation and the creation of novel states of matter. Previously, we have demonstrated the creation of a spin-polarized ensemble of fermionic $^{\mathrm{23}}$Na$^{\mathrm{40}}$K molecules in their rovibronic and hyperfine ground state. One way to induce strong dipole moments is microwave dressing, which has been proposed to allow shielding of inelastic collisions and the realization of topological superfluids. By applying microwave fields near the frequency of the transition to the first rotationally excited state, we can induce an oscillatory dipole moment of up to 1.1 Debye in the molecules. We characterize this microwave dressing via the Autler-Townes splitting it induces in a rotational transition. We will present recent work exploring how microwave dressing affects the collision rate in the molecular gas. [Preview Abstract] |
Tuesday, June 6, 2017 10:42AM - 10:54AM |
B4.00002: Dipolar collisions of ultracold $^{\mathrm{23}}$Na$^{\mathrm{87}}$Rb molecules. Mingyang Guo, Xin Ye, Junyu He, Goulven Quéméner, Maykel González-Martínez, Olivier Dulieu, Dajun Wang Although ultracold polar molecules have long been proposed as a primary candidate for investigating dipolar many body physics, many of their basic properties, like their collisions in external electric fields, are still largely unknown. In fact, despite the successful production of several new ultracold molecular species in the last two years, so far the only available dipolar collision data is still from JILA's fermionic $^{\mathrm{40}}$K$^{\mathrm{87}}$Rb experiment in 2010. In this talk, we will describe our investigation on dipolar collisions of ultracold bosonic and chemically stable $^{\mathrm{23}}$Na$^{\mathrm{87}}$Rb molecules which possess a large permanent electric dipole moment. With a moderate electric field, an effective dipole moment large enough to strongly couple higher partial waves into the collisions can be achieved. We will report the influence of this effect on the molecular collisions observed in our experiment. Our theoretical model for understanding these observations will also be presented. [Preview Abstract] |
Tuesday, June 6, 2017 10:54AM - 11:06AM |
B4.00003: Collisions of ultracold $^{\mathrm{23}}$Na$^{\mathrm{87}}$Rb molecules with controlled chemical reactivity Xin Ye, Mingyang Guo, Junyu He, Dajun Wang, Goulven Quemener, Maykel Gonzalez-Martinez, Oliver Dulieu The recent successful creation of several ultracold absolute ground-state polar molecules without chemical reaction channel has opened a new playground for investigating the so far poorly understood collisions between them. On one hand, these collisions are indispensable for the exploration of dipolar physics, on the other hand, they are direct manifestations of the brand-new field of ultracold chemistry. Here, we report on the study on molecular collisions with ultracold ground-state $^{\mathrm{23}}$Na$^{\mathrm{87}}$Rb molecules prepared by transferring weakly bound Feshbach molecules with STIRAP. By tuning the Raman laser wavelength to control the internal states, samples with distinctly different chemical reactivity and inelastic channels can be prepared. Surprisingly, we found that the trap loss of the non-reactive case is nearly identical to that of the reactive case. We also developed a model based on the collision complex formation mechanism. The comparison between experiment and theory will also be presented. [Preview Abstract] |
Tuesday, June 6, 2017 11:06AM - 11:18AM |
B4.00004: Abstract Withdrawn
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Tuesday, June 6, 2017 11:18AM - 11:30AM |
B4.00005: Photoassociation of cold (RbCs)$_2$ tetramers in the ground electronic state Marko Gacesa, Robin C\^ot\'e We theoretically investigate prospects for photoassociative formation of cold (RbCs)$_2$ tetramers from a pair of ultracold RbCs molecules. The long-range region of the potential energy surface (PES) of the lowest electronic state of (RbCs)$_2$ can be affected by orienting both RbCs molecules by an external electric field. In fact, we find a long-range barrier that supports long-range shelf states for relative angles between the dimers' internuclear axes smaller than about 20$^{\circ}$. We show that these shelf states can be populated by spontaneous decay from the first excited electronic state which can be efficiently populated by photoassociation from the scattering continuum at ultracold temperatures. The vibrationally excited ground-state tetramer molecules formed this way have sufficiently long lifetimes to allow experimental detection. Moreover, for the relative angles between the dimers close to 20$^{\circ}$, the proposed approach may result in production of deeply bound tetramers. [Preview Abstract] |
Tuesday, June 6, 2017 11:30AM - 11:42AM |
B4.00006: Short-range photoassociation of LiRb David Blasing, Ian Stevenson, Jesús Pérez-Ríos, Daniel Elliott, Yong Chen We have observed short-range photoassociation of $^7$Li$^{85}$Rb to the two lowest vibrational states of the $d\,^3\Pi$ potential. We have also observed several $a^3\,\Sigma^+$ vibrational levels with generation rates between $\sim10^2$ and $\sim10^3$ molecules per second, resulting from the spontaneous decay of these $d\,^3\Pi$ molecules. This is the first observation of many of these $a\,^3\Sigma^+$ levels. We observe an alternation of the peak heights in the rotational photoassociation spectrum that depends on the parity of the excited molecular state. Franck-Condon overlap calculations predict that photoassociation to higher vibrational levels of the $d\,^3\Pi$, in particular the sixth vibrational level, should populate the lowest vibrational level of the $a\,^3\Sigma^+$ state with a rate as high as $10^4$ molecules per second. This work also motivates an experimental search for short-range photoassociation to other bound molecules, such as the $c\,^3\Sigma^+$ or $b\,^3\Pi$, as prospects for preparing ground-state molecules. [Preview Abstract] |
Tuesday, June 6, 2017 11:42AM - 11:54AM |
B4.00007: Direct photoassociation of halo molecules in ultracold $^{86}Sr$ J. A. Aman, Joshua Hill, T. C. Killian We investigate the creation of $^1S_0\!+\!^1S_0$ halo molecules in strontium 86 through direct photoassociation in an optical dipole trap. We drive two photon Raman transitions near-resonance with a molecular level of the $^1S_0\!+\!^3P_1$ interatomic potential as the intermediate state. This provides large Frank-Condon factors and allows us to observe resonances for the creation of halo molecules through higher order Raman processes. The halo molecule is bound by $E_B\approx85$ kHz at low excitation-laser intensity, but experiments show large AC Stark shifts of the molecular binding energy. These conditions suggest that STIRAP should be very effective for improving molecular conversion efficiency. Further experiments in a 3D lattice will explore molecular lifetimes and collision rates. [Preview Abstract] |
Tuesday, June 6, 2017 11:54AM - 12:06PM |
B4.00008: Continuous Production of Rovibronic Ground State RbCs Molecules via Short-Range Photoassociation to the $B^{\mathrm{1}}\Pi $, $c^{\mathrm{3}}\Sigma^{\mathrm{+}}$, and $b^{\mathrm{3}}\Pi $ states Toshihiko Shimasaki, Jin-Tae Kim, Yuqi Zhu, David DeMille Electronic states with strong singlet-triplet mixing can be useful for efficient direct molecule production in the rovibronic ground state via short-range photoassociation (PA). We have observed rovibronic levels of the strongly mixed $B^{\mathrm{1}}\Pi (\Omega =$1), $c^{\mathrm{3}}\Sigma^{\mathrm{+}}(\Omega =0^{-}$ and 1), and $b^{\mathrm{3}}\Pi (\Omega =0^{-}$, 0$^{\mathrm{+}}$, and 1) states of $^{\mathrm{85}}$Rb$^{\mathrm{133}}$Cs in the energy range of 13950 -14200 cm$^{\mathrm{-1}}$ using short-range PA. For selected PA states, vibrational branching and rotational branching in the $X^{\mathrm{1}}\Sigma ^{\mathrm{+}}$ ($v=$0) state have been investigated using resonance-enhanced multiphoton ionization and depletion spectroscopy [1], respectively. Efficient production of the rovibronic ground state $X^{\mathrm{1}}\Sigma^{\mathrm{+}}(v=$0, $J=$0) has been observed for some of the PA states in this energy range. Molecule production rate up to $\sim $1$\times $10$^{\mathrm{4}}$ molecules /s into the rovibronic ground state has been achieved, which is a factor of 5 improvement compared to previously observed PA states [2]. [1] T. Shimasaki \textit{et al}., Phys. Rev. A \textbf{91}, 21401 (2015). [2] T. Shimasaki \textit{et al}., ChemPhysChem \textbf{17}, 3677 (2016). [Preview Abstract] |
Tuesday, June 6, 2017 12:06PM - 12:18PM |
B4.00009: Ultracold atom-molecular ion systems: a photo-asisted spin-dependent polyatomic chemical reaction Ionel Simbotin, John A. Montgomery, Jr., Robin C\^ot\'e In recent years, rapid progress in cooling and trapping of hybrid atom-ion systems has led to studies of atom-ion processes. These range from charge transfer, recombination, internal state conversion, to the possibility of changing cross sections and corresponding rates with tunable Feshbach resonances. A recent experiment from the group of Eric Hudson at UCLA explored how ultracold Ca atoms interact with a trapped polyatomic molecular ion, namely BaOCH$_3^+$. We computed stationary points of the potential energy surface (PES) for this complex system, and reaction paths for different spin states, and found that a large barrier prevents the reaction to form BaOCa$^+$ and CH$_3$ in the singlet channel. We also found a barrier corresponding to a transition state for the triplet channel corresponding asymptotically to Ca($^3P$)\,+\,BaOCH$_3^+$, but low enough to allow reactions. We computed reaction rates based on a Langevin model, taking into account the different $J$ values of the initial $^3P_J$ state of Ca, and found that this photo-assisted reaction depends not only on the singlet/triplet spin state, but also on the fine structure of the initial reactants. [Preview Abstract] |
Tuesday, June 6, 2017 12:18PM - 12:30PM |
B4.00010: Formation of ultracold molecules induced by a high-power single frequency fiber laser Henry Fernandes Passagem, Ricardo Colin-Rodriguez, Paulo Ventura da Silva, Nadia Bouloufa-Maafa, Olivier Dulieu, Luis Marcassa Photoassociation of a pair of ultracold atoms is a quite simple and rapid approach for cold molecule formation. The main limitation of PA is that the latter step is incoherent, so that the population of the created molecules is spread over many vibrational levels with weak or moderate binding energies. If the excited electronic molecular state exhibits a peculiar feature at short internuclear distance like a potential barrier or an avoided crossing, the population of deeply-bound ground state levels may be significantly enhanced. In this work, the influence of a high-power single frequency fiber laser on the formation of ultracold $^{85}$Rb$_2$ molecules is investigated as a function of its frequency (in the 1062-1070~nm range) in a magneto optical trap. We found evidence for the formation of ground state $^{85}$Rb$_2$ molecules in low vibrational levels ($v\leq 20$) with a maximal rate of 10$^4$~s$^{-1}$, induced by short-range photoassociation by the fiber laser followed by spontaneous emission. When this laser is used to set up a dipole trap, we measure an atomic loss rate at a wavelength far from the PA resonances only 4 times smaller than the one observed at a PA resonance wavelength. This work may have important consequences for atom trapping using lasers around 1060 nm. [Preview Abstract] |
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