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 H08: Ion-Atom and Atom-Atom Collisions |
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Chair: John Tanis, Western Michigan University Room: Grand F |
Wednesday, May 30, 2018 8:00AM - 8:12AM |
H08.00001: Controlling cold atom-ion collisions using a Rydberg state Limei Wang, Markus Deiss, Johannes Hecker Denschlag With respect to quantum computation and quantum simulation, control of collisions is required. We present a method to control the cold collision between an ultracold atom and a trapped ion. A laser is used to excite the ground state atom to a repulsive Rydberg potential level once it approaches the ion to a certain distance. In this way the ion is effectively surrounded by a potential wall that the atom cannot cross. Once the atom leaves the interaction area, it is de-excited back to its original level. The adiabaticity of the scheme is analyzed as a function of different parameters such as laser frequency, laser power, initial atom-ion collision energy, as well as the direction of the collisional process with respect to the light field. By controlling e.g. the laser power and the laser frequency, as well as by addressing different Rydberg states, the properties of this shielding effect can be widely tuned. In particular, unwanted chemical reactions between atoms and ion can efficiently be suppressed, which is an important step towards realization of diverse quantum technological applications for hybrid atom-ion systems. [Preview Abstract] |
Wednesday, May 30, 2018 8:12AM - 8:24AM |
H08.00002: Radiative Double Electron Capture (RDEC) in 40 MeV $\rm{\bf F}^{\bf 8+}$ and $\rm{\bf F}^{\bf 9+}$ + Ne Collisions David La Mantia, Nuwan Kumara, Asghar Kayani, Anna Simon, John Tanis The capture of two electrons with the simultaneous emission of a single photon is known as radiative double electron capture (RDEC). This process is the time-inverse of double photoionization and gives insight into electron correlation. Preliminary RDEC cross sections were measured for $\rm{F}^{8,9+}$ colliding with neon. The corresponding RDEC cross section for $\rm{F}^{8+}$ is about 4 times smaller than that for $\rm{F}^{9+}$, as expected as capture of both electrons to the projectile K shell is not allowed. This work was performed at Western Michigan University (WMU) using the tandem Van de Graaff accelerator. Beams of 40 MeV $\rm{F}^{8+}$ and $\rm{F}^{9+}$ collided with neon inside a differentially pumped cell. Surface barrier detectors were used to observe the charge-changed projectiles and a Si(Li) x-ray detector, placed at $90^{\rm{o}}$ to the incident beam, was used to measure photons coincident with the charge-changed ions. Previous RDEC experiments with gaseous targets failed to find conclusive evidence for this event,\footnote{G. Bednarz, {\it et al}. NIM B, {\bf 205} 573 (2003)} while successful observations were performed at WMU using a solid carbon target.\footnote{A. Simon, {\it et al}. PRL {\bf 104}, 123001 (2010)} [Preview Abstract] |
Wednesday, May 30, 2018 8:24AM - 8:36AM |
H08.00003: Controling Excited-State Ion-Atom Reaction Ming Li, Alexander Petrov, Svetlana Kotochigova We investigate the control of the charge-exchange reaction between a neutral atom and a ground-state ion via light-induced coupling to their excited molecular states. In particular, we focus on Ca atoms in a magneto-optical trap (MOT) reacting with an Yb$^+$ ion controlled by an additional laser that is red-detuned from the Ca ground to 4s4p($^1$P) excited transition. Direct non-adiabatic charge-exchange reaction between an excited Ca atom and Yb$^+$ is limited by the Ca excited-state population in the MOT and the spontaneous decay of the excited atom. The additional laser, on the other hand, can efficiently transfer population from the ground-state potentials to excited potentials at shorter internuclear separations and enhance the charge-exchange reaction rate. The process relies on the extremely high density of states of the isotropic $-C_4/R^4$ induction and anisotropic $C_3/R^3$ charge-quadrupole potentials that govern the long-range molecular forces as well as the large transition dipole moment associated with the excited threshold. We theoretically demonstrate that the process, which can be controlled through changing laser detuning and intensity, can lead to enhancements of rate coefficients of the order of 10$^{-10}$ cm$^3/$s. [Preview Abstract] |
Wednesday, May 30, 2018 8:36AM - 8:48AM |
H08.00004: Heating dynamics in ultra-cold ion-atom system Meirav Pinkas, Ziv Meir, Tomas Sikorsky, Ruti Ben-Shlomi, Nitzan Akerman, Roee Ozeri Hybrid ultra-cold atom-ion experiments are a fascinating tool for studying quantum aspects of atom-ion collisions. However, even if the atoms are initially prepared in the $\mu K$ regime, the interaction energy at steady-state is limited to a few $mK$ since the ion is heated up by the collisions. An approaching atom shifts the ion from its equilibrium position and the collision occurs at a non-vanishing rf field which, on average, couples energy into the system. In this work we study the dependency of this heating mechanism on several ion trap parameters, for a ground state cooled $^{88}Sr^{+}$ ion immersed in an ultra-cold bath of $^{87}Rb$ atoms. We also investigated, using molecular dynamics simulation, the heating rates, the dynamics of the ion energy distribution and their dependency on various parameters such as the trapping potentials and atom-ion mass ratios. We find that the ion energy distribution evolves from the ground-state to a hot distribution with a high-energy power-law tail which depends on the various trap parameters. The measured heating rates, for different rf confinements of the Paul trap, were compared to the molecular dynamics simulation. [Preview Abstract] |
Wednesday, May 30, 2018 8:48AM - 9:00AM |
H08.00005: Spin-exchange and spin-relaxation in ultracold Rb-Sr$^+$ collisions Masato Morita, Tomas Sikorsky, Ziv Meir, Alexei Buchachenko, Ruti Ben-shlomi, Nitzan Akerman, Edvardas Narevicius, Timur V. Tscherbul, Roee Ozeri We present a joint experimental and theoretical study of collision-induced spin exchange and spin relaxation of a single trapped Sr$^+$ ion immersed in an ultracold gas of Rb atoms in different hyperfine states. We find that inelastic spin-relaxation of Sr$^+$ caused by the second-order spin-orbit coupling occurs much more slowly than in Rb-Yb$^+$ collisions. The calculated spin exchange rates are very sensitive to small variations of the Rb-Sr$^+$ interaction potential even in the multiple-partial-wave regime due to an unexpected correlation between the singlet and triplet scattering phase shifts. [Preview Abstract] |
Wednesday, May 30, 2018 9:00AM - 9:12AM |
H08.00006: Radiative double electron capture (RDEC) for F$^{\mathrm{8,9+}}$ ions colliding with N$_{\mathrm{2}}$* Nuwan Kumara, David La Mantia, Asghar Kayani, Prashanta Niraula, Shahid Iqbal, Anna Simon, John Tanis Radiative double electron capture (RDEC) is a one step atomic process in which two electrons are captured with the simultaneous emission of a single photon. RDEC can be considered as the time reversed process of double photoionization. The first observation of RDEC was reported in 2010 for 38 MeV O$^{\mathrm{8+}}$ colliding with a thin carbon foil$^{\mathrm{1}}$. The purpose of the present work is to observe RDEC for gas targets in which multiple collisions can be avoided. The experiment is performed using the Western Michigan University (WMU) accelerator from which 40 MeV F$^{\mathrm{8,9+}}$ projectiles were produced and then collided with nitrogen gas. Events for both F$^{\mathrm{8+}}$ and F$^{\mathrm{9+}}$ were observed in the calculated RDEC energy region of the spectrum for double capture coincident with x rays. The preliminary RDEC cross section for F$^{\mathrm{9+\thinspace }}$is consistent with the previously measured cross sections$^{\mathrm{1,2}}$ for fully stripped O and F projectiles colliding carbon. The preliminary F$^{\mathrm{8+}}$ RDEC cross section is about four times smaller because the capture of two electrons to the F$^{\mathrm{8+}}$ K shell is prevented due to the existing electron in the K shell. *Supported in part by NSF Grant PHY-1401429. $^{\mathrm{1}}$A. Simon et el., PRL \textbf{104}, 123001 (2010) $^{\mathrm{2}}$ T. Elkafrawy et al., Phys. Rev. A \textbf{94}, 042705 (2016). [Preview Abstract] |
Wednesday, May 30, 2018 9:12AM - 9:24AM |
H08.00007: Measurements of charge-exchange reaction rate constants between $\textrm{Ca}^+$ and Na in a hybrid atom-ion trap Jonathan Kwolek, Douglas Goodman, James Wells, Francesco Narducci, Winthrop Smith We present measurements of charge-exchage reaction rate constants between $\textrm{Ca}^+[^2\textrm{S}, {}^2\textrm{P}, {}^2\textrm{D}]$ and $\textrm{Na}[^2\textrm{S},{}^2\textrm{P}]$ using a hybrid trap. Our hybrid trap consists of a concentic magneto-optical trap MOT and linear Paul trap (LPT). The hybrid apparatus allows us to spatially overlap a trapped $\textrm{Ca}^+$ ion cloud or crystal with a cold Na MOT. $\textrm{Ca}^+$ ions that undergo charge-exchange or molecular photoassociation reactions with the Na atoms are lost from the LPT. An analysis of the trapped $\textrm{Ca}^+$ population's time-dependence yields the reaction rate constant between the trapped ions and co-trapped atoms. We can isolate the rate-constant for individual reaction pathways by independently controlling the internal electronic states of the Na atoms and/or the $\textrm{Ca}^+$ ions. Additionally, we explore the energy dependence of the rate constant by controlling the temperature of the laser-cooled $\textrm{Ca}^+$ ions. The reaction channel between $\textrm{Ca}^+[^2\textrm{S}]$ and $\textrm{Na}[^2\textrm{P}]$ is of particular interest, since an analysis of the Born-Oppenheimer potential energy curves reveal a barrier to the reaction for low temperature. [Preview Abstract] |
Wednesday, May 30, 2018 9:24AM - 9:36AM |
H08.00008: Cold and Controlled Chemical Reactions between Molecules and Ions Tiangang Yang, Gary Chen, Arthur Suits, Eric Hudson, Wesley Campbell Reactions between molecules and ions at low temperature are of significant importance in both fundamental chemistry as well as in interstellar medium. Control over reactant translational and internal energies are necessary for addressing these reactions experimentally. Recently, we have developed a new platform for quantum-state-resolved ion-molecule chemistry by utilizing a combination of cryogenic buffer gas cooling, laser-cooled ion sympathetic cooling, and integrated Time-of-Flight (TOF) mass spectrometer in an RF Paul trap. In this talk, I will provide our most recent results on cold beryllium/carbon ions' chemistry. [Preview Abstract] |
Wednesday, May 30, 2018 9:36AM - 9:48AM |
H08.00009: Study of Cold Phase Chemistry Using a Hybrid Atom-Ion Setup Kisra Egodapitiya, Jyothi Saraladevi, Zhubing Jia, Gang Shu, Robert Clark, Piero Chiappina, Kenneth Brown We report the first measurements in a cold potassium atom – calcium ion hybrid experiment. Hybrid atom-ion systems enable the study of processes such as charge exchange, cold molecular formation, and quenching of internal states of atoms and molecules at unprecedented low energies. The cold potassium atoms are produced in a Magneto Optical Trap (MOT), and cold calcium ions are produced by Doppler cooling calcium ions trapped in a linear ion trap (LIT). Cold atom-ion dynamics are probed using fluorescence of ions and atoms, and a radial ejection time of flight spectrometer that enables high-resolution detection of trapped ion species in the ion trap. We observe a fast decay of Calcium ions due to the interaction with cold potassium atoms. [Preview Abstract] |
Wednesday, May 30, 2018 9:48AM - 10:00AM |
H08.00010: Control of atom-ion reactions at low temperatures Michael Mills, Prateek Puri, Elizabeth West, Christian Schneider, Eric Hudson We discuss experiments performed in the MOTion trap, a hybrid atom-ion trap comprised of a linear quadrupole trap and a co-located magneto-optical trap. We first present the synthesis of BaOCa$^{+}$, the first molecule of its type to be observed. With the tools of the MOTion trap, we identify and investigate the mechanism of its formation via the barrierless reaction of Ca ($^{3}$P$_{J}$) with BaOCH_3$^{+}$. Next, we describe our studies of charge exchange reactions at low temperatures. We observe a suppression of the reaction rate at low temperatures due to the electric field of the ion shifting the transition energies of the neutral, and we propose a general method to eliminate this suppression, enabling control of low-temperature atom-ion reactions. Finally, we introduce a new method of controlling collision energy. By varying the axial confinement voltages of our ion trap, we shuttle the ions through the cloud of neutral atoms, providing a general technique with energy resolutions improved over current methods by an order of magnitude for collision temperatures ranging from a few mK to 10s of K. [Preview Abstract] |
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