Bulletin of the American Physical Society
52nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 66, Number 6
Monday–Friday, May 31–June 4 2021; Virtual; Time Zone: Central Daylight Time, USA
Session M06: Ion-Neutral and Electron-Neutral CollisionsLive
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Sponsoring Units: GEC Chair: Mark Zammit, LANL |
Wednesday, June 2, 2021 2:00PM - 2:12PM Live |
M06.00001: Transport of a Single Cold Ion Immersed in a Bose-Einstein Condensate Moritz Berngruber, Thomas Dieterle, Christian Hölzl, Robert Loew, Krzysztof Jachymski, Tilman Pfau, Florian Meinert Transport processes are ubiquitous in nature but their understanding on a microscopic level still forms a prime challenge to explain macroscopic phenomena in complex many body systems. |
Wednesday, June 2, 2021 2:12PM - 2:24PM Live |
M06.00002: Stability of long ion chains versus catastrophic melting collisions: a combined numerical and experimental study Yue Shi For scalable quantum computing with trapped atomic ions, a stable ion chain held in ultrahigh vacuum conditions is a pre-requsite. However, collisions with the residual background gas molecules can ''melt'' the ion chain: the imparted kinetic energies are high enough such that the Coulomb crystal is heated to the gas phase. Currently this problem presents a significant challenge to the number of qubits for compact trapped ion quantum computers in room temperature setups. It is also an interesting classical Floquet many-body problem in its own right: under periodic driving and non-linear Coulomb interactions, the trajectories of the ions can be classically chaotic. Here, we study the dynamics of multiple ions in a linear Paul-trap through combined numerical and experimental approaches, and find how different regions of the trap parameter space affect the dynamics of the ion chains and the melting probabilities. Contrary to the commonly held belief of radio-frequency heating induces melting, we show that the melting arise from the driven-dissipative competitions in the many-body system. |
Wednesday, June 2, 2021 2:24PM - 2:36PM Live |
M06.00003: Differential cross sections for electron-impact ionization of neon James P Colgan, Mark C Zammit, Nathan Garland, Chris J Fontes, Xianzhu Tang, Mitch Pindzola We extend the time-dependent close-coupling method to the calculation of triple differential cross sections for electron impact ionization of neon. Our calculations explore some effects of scattering from a p-orbital target compared to other s-orbital targets. We also present single differential cross sections and compare to previous measurements. |
Wednesday, June 2, 2021 2:36PM - 2:48PM Live |
M06.00004: Quantum control of entangled photon-pair generation in electron-ion collisions driven by laser-synthesized photoelectron wave packets R. Esteban Goetz, Klaus R Bartschat Correlated electron-dynamics resulting from electron-ion collisions appears in a variety of competing rearrangement channels, such as inelastic scattering and dielectronic recombination, i.e., capture of the incident electron via compound resonance states. These transient doubly-excited resonance states may, in turn, decay via two competing processes: autoionization or radiative stabilization. Here, we propose an extension of coherent control using laser-synthesized photoelectron wave packets as the incident projectile to control competing rearrangement channels as well as the various processes within each channel. Most notably, this enables us to control the emission of photons in electron-ion collisions via two mechanisms: (i) radiative decay involving a manifold of different de-excitation pathways contributing to the same photon mode within an isolated rearrangement channel [1], or (ii) decay of a coherent superposition thereof, prepared by the projectile. Using a time-dependent two-Hilbert space formulation of multichannel scattering theory of rearrangement collisions, we demonstrate quantum control of entangled photon-pair generation in radiative cascade decay for both cases. The coherence of the incident electron wave packet is engineered by pulse-shaping the ionizing laser field promoting interferometric resonantly-enhanced multi-photon ionization. [1] arXiv:2011.09649 |
Wednesday, June 2, 2021 2:48PM - 3:00PM Live |
M06.00005: Electron collisions with H2 from electronically excited states using the R-matrix method Thomas Meltzer Electron collisions with H2 are important for the semiconductor plasma industry, magnetically confined fusion reactors and astrophysical modelling. In previous work [1], R-matrix calculations for electron impact electronic excitation of H2 from its ground state were presented. The results were in agreement with recent experimental data and accurate theoretical calculations obtained by the Molecular Convergent Close-Coupling approach. This presentation covers our latest work [2] where the R-matrix approach has been used to produce integrated cross-sections for electron collisions with H2 from an initially excited state. Our calculations suggest that previous theoretical results overestimate the cross-sections by as much as a factor of 5 for certain transitions. This work has been made possible by recent developments in the UKRMol+ code [3] which now supports B-spline type orbitals for use in the continuum. In this work we required a radius of 100 Bohr in order to support the extremely diffuse, highly-excited target states that were of interest. Cross-sections for the first 12 excited states are discussed with a focus on the metastable triplet a and c states. |
Wednesday, June 2, 2021 3:00PM - 3:12PM Live |
M06.00006: Comparisons and fits of electron angular distribution approximations for elastic scattering from neutral fusion-relevant targets William Kupets, Nathan Garland, James P Colgan, Xianzhu Tang, Liam Scarlett, Dmitry Fursa, Igor Bray, Mark C Zammit Accurate elastic differential cross sections are essential for modeling many plasma scenarios, particularly in low temperature plasma technologies or the cooler edge regions of tokamaks. Currently, few models have reported the ability to accurately predict elastic electron scattering from neutral targets at low energies. We tested several models presented in low temperature plasmas literature and developed new expressions, based on CCC calculations, that successfully predicts both (high-energy) forward scattering and (low-energy) backward scattering for He, H, and H2. It is shown that the proposed approximations reliably predict elastic scattering dynamics, while also offering a straightforward analytic expression that can be implemented efficiently in particle-in-cell (PIC) / Monte Carlo (MC) modeling. |
Wednesday, June 2, 2021 3:12PM - 3:24PM Live |
M06.00007: Semiclassical theory of laser-assisted dissociative recombination Ilya I Fabrikant, Harindranath B Ambalampitiya, Ioan Schneider We study the process of laser-assisted dissociative recombination of an electron with a molecular cation |
Wednesday, June 2, 2021 3:24PM - 3:36PM On Demand |
M06.00008: Evidence for radiative double-electron capture (RDEC) by F9+ ions in collisions with single-layer graphene Prashanta M Niraula, Khushi Bhatt, Asghar Kayani, John A. Tanis, D. S. La Mantia Evidence for radiative double-electron capture (RDEC) has been observed for F9+ ions in collisions with single-layer graphene. To our knowledge this the first such experiment for RDEC with this novel target. RDEC occurs when a highly-charged ion captures two electrons from a target while simultaneously emitting a photon and can be considered the time inverse of double photoionization. The experiment was done at Western Michigan University using a 40 MeV F9+ beam to interact with the graphene. X rays were observed at 90o to the incident beam in coincidence with the outgoing ions after separation with a dipole magnet. Selecting the graphene target was a challenge, resulting in using a ~0.35 nm thick graphene sample mounted on a 200 nm thick silicon nitride supporting grid with ~6400 holes of 2 mm diameter. This entire assembly (purchased commercially) was mounted on 200 mm thick 3.0 mm hexagonal silicon substrate with a 0.5 x 0.5 mm aperture. X rays attributed to RDEC were seen for three separate graphene samples and the results are compared with our previous gas target1 and C-foil target2 results. For single-layer graphene, the foil thickness is close to that of the gas target and about a hundred times smaller than the thin-foil carbon used. Despite this, surprisingly, the graphene produced results appearing similar to those of the foil target. *Supported in part by NSF Grant No. 1707467. 1D. S. La Mantia et al., Phys. Rev. Lett. 124, 133401 (2020). 2D. S. La Mantia et al., Phys. Rev. A 102, 060801(R) (2020). |
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