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Atoms
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Low Energy Interactions between Ions and Ultracold Alkali Atoms
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Low Energy Interactions between Ions and Ultracold Alkali Atoms

A special issue of Atoms (ISSN 2218-2004).

Deadline for manuscript submissions: closed (30 April 2021) | Viewed by 15194

Special Issue Editors

Prof. Dr. Winthrop W. Smith

E-Mail Website
Guest Editor
Department of Physics, University of Connecticut unit 3046, 196 Auditorium Road, Storrs, CT 06269-3046, USA
Interests: laser spectroscopy; collision studies; laser-excited atomic and molecular beams; nonlinear dynamics; chaos
Prof. Dr. Douglas S. Goodman

E-Mail Website
Guest Editor
Department of Chemistry and Physical Sciences, Quinnipiac University, Hamden, CT 06518-1908, USA
Interests: laser cooling and trapping; cold ion-neutral collisions; microparticle ion trapping; physics education

Special Issue Information

Dear Colleagues,

The study of low-energy ion-neutral collisions is fundamental to understanding the behavior, control, and applications of cold, atomic, molecular, and ionic gaseous systems. At long range, universal charge-induced polarization effects dominate the ion-neutral elastic, inelastic, reactive, and charge-transfer cross sections. Neutral alkali targets are of particular importance due to their ubiquitous use in cold atomic molecular and optical experiments, as well as their uniquely large polarizability. As their collision energy is lowered, ion-alkali reaction cross sections approach millions of atomic units, many orders of magnitude larger than typical neutral-atom van der Waals cross sections at the same energy scale. However, cold ion-alkali reactions had remained relatively unexplored until the early 2000s, at which time advances in laboratory and computational techniques such as cold hybrid ion-neutral traps and many-body excited-state quantum chemistry modeling were developed. Since then, the cold ion-neutral collision regime has rapidly blossomed. Researchers continue to explore and demonstrate quantum-limited control over a wide variety of ion-neutral partners, investigating ion-neutral sympathetic heating and cooling, formation and cooling of cold molecular ions, probing of quantum gases, and quantum chemistry, simulations, and computations. This Special Issue aims to highlight recent experimental and theoretical work in the field of low-energy ion-neutral studies, review progress, and discuss the outlook for future developments. Authors are invited to submit original research papers for the Special Issue as well as short, tutorial reviews emphasizing new developments not included in previous reviews.

Prof. Winthrop W. Smith
Prof. Douglas S. Goodman
Guest Editors

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Keywords

  • cold ion-neutral collisions
  • ion-neutral collision dynamics
  • hybrid ion-neutral traps
  • charge transfer collisions
  • quantum simulations and computing
  • ion impurities in ultracold quantum gases
  • sympathetic cooling of ions
  • molecular association
  • quantum chemistry
  • Langevin orbiting collisions
  • long-range polarization interactions
  • ion-Rydberg atom interactions

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Published Papers (4 papers)

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Research

15 pages, 2666 KiB  
Article
Interactions of Ions and Ultracold Neutral Atom Ensembles in Composite Optical Dipole Traps: Developments and Perspectives
by Leon Karpa
Atoms 2021, 9(3), 39; https://doi.org/10.3390/atoms9030039 - 4 Jul 2021
Cited by 4 | Viewed by 3138
Abstract
Ion–atom interactions are a comparatively recent field of research that has drawn considerable attention due to its applications in areas including quantum chemistry and quantum simulations. In first experiments, atomic ions and neutral atoms have been successfully overlapped by devising hybrid apparatuses combining [...] Read more.
Ion–atom interactions are a comparatively recent field of research that has drawn considerable attention due to its applications in areas including quantum chemistry and quantum simulations. In first experiments, atomic ions and neutral atoms have been successfully overlapped by devising hybrid apparatuses combining established trapping methods, Paul traps for ions and optical or magneto-optical traps for neutral atoms, respectively. Since then, the field has seen considerable progress, but the inherent presence of radiofrequency (rf) fields in such hybrid traps was found to have a limiting impact on the achievable collision energies. Recently, it was shown that suitable combinations of optical dipole traps (ODTs) can be used for trapping both atoms and atomic ions alike, allowing to carry out experiments in absence of any rf fields. Here, we show that the expected cooling in such bichromatic traps is highly sensitive to relative position fluctuations between the two optical trapping beams, suggesting that this is the dominant mechanism limiting the currently observed cooling performance. We discuss strategies for mitigating these effects by using optimized setups featuring adapted ODT configurations. This includes proposed schemes that may mitigate three-body losses expected at very low temperatures, allowing to access the quantum dominated regime of interaction. Full article
(This article belongs to the Special Issue Low Energy Interactions between Ions and Ultracold Alkali Atoms)
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14 pages, 1057 KiB  
Article
Analysis of Multipolar Linear Paul Traps for Ion–Atom Ultracold Collision Experiments
by M. Niranjan, Anand Prakash and S. A. Rangwala
Atoms 2021, 9(3), 38; https://doi.org/10.3390/atoms9030038 - 29 Jun 2021
Cited by 7 | Viewed by 3446
Abstract
We evaluate the performance of multipole, linear Paul traps for the purpose of studying cold ion–atom collisions. A combination of numerical simulations and analysis based on the virial theorem is used to draw conclusions on the differences that result, by considering the trapping [...] Read more.
We evaluate the performance of multipole, linear Paul traps for the purpose of studying cold ion–atom collisions. A combination of numerical simulations and analysis based on the virial theorem is used to draw conclusions on the differences that result, by considering the trapping details of several multipole trap types. Starting with an analysis of how a low energy collision takes place between a fully compensated, ultracold trapped ion and an stationary atom, we show that a higher order multipole trap is, in principle, advantageous in terms of collisional heating. The virial analysis of multipole traps then follows, along with the computation of trapped ion trajectories in the quadrupole, hexapole, octopole and do-decapole radio frequency traps. A detailed analysis of the motion of trapped ions as a function of the amplitude, phase and stability of the ion’s motion is used to evaluate the experimental prospects for such traps. The present analysis has the virtue of providing definitive answers for the merits of the various configurations, using first principles. Full article
(This article belongs to the Special Issue Low Energy Interactions between Ions and Ultracold Alkali Atoms)
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15 pages, 2130 KiB  
Article
Long-Range Atom–Ion Rydberg Molecule: A Novel Molecular Binding Mechanism
by Markus Deiß, Shinsuke Haze and Johannes Hecker Denschlag
Atoms 2021, 9(2), 34; https://doi.org/10.3390/atoms9020034 - 21 Jun 2021
Cited by 26 | Viewed by 3836
Abstract
We present a novel binding mechanism where a neutral Rydberg atom and an atomic ion form a molecular bound state at a large internuclear distance. The binding mechanism is based on Stark shifts and level crossings that are induced in the Rydberg atom [...] Read more.
We present a novel binding mechanism where a neutral Rydberg atom and an atomic ion form a molecular bound state at a large internuclear distance. The binding mechanism is based on Stark shifts and level crossings that are induced in the Rydberg atom due to the electric field of the ion. At particular internuclear distances between the Rydberg atom and the ion, potential wells occur that can hold atom–ion molecular bound states. Apart from the binding mechanism, we describe important properties of the long-range atom–ion Rydberg molecule, such as its lifetime and decay paths, its vibrational and rotational structure, and its large dipole moment. Furthermore, we discuss methods of how to produce and detect it. The unusual properties of the long-range atom–ion Rydberg molecule give rise to interesting prospects for studies of wave packet dynamics in engineered potential energy landscapes. Full article
(This article belongs to the Special Issue Low Energy Interactions between Ions and Ultracold Alkali Atoms)
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15 pages, 341 KiB  
Article
Loading a Paul Trap: Densities, Capacities, and Scaling in the Saturation Regime
by Reinhold Blümel
Atoms 2021, 9(1), 11; https://doi.org/10.3390/atoms9010011 - 29 Jan 2021
Cited by 3 | Viewed by 2908
Abstract
Providing ideal conditions for the study of ion-neutral collisions, we investigate here the properties of the saturated, steady state of a three-dimensional Paul trap, loaded from a magneto-optic trap. In particular, we study three assumptions that are sometimes made under saturated, steady-state conditions: [...] Read more.
Providing ideal conditions for the study of ion-neutral collisions, we investigate here the properties of the saturated, steady state of a three-dimensional Paul trap, loaded from a magneto-optic trap. In particular, we study three assumptions that are sometimes made under saturated, steady-state conditions: (i) The pseudopotential provides a good approximation for the number, Ns, of ions in the saturation regime, (ii) the maximum of Ns occurs at a loading rate of approximately 1 ion per rf cycle, and (iii) the ion density is approximately constant. We find that none of these assumptions are generally valid. However, based on detailed classical molecular dynamics simulations, and as a function of loading rate and trap control parameter, we show where to find convenient dynamical regimes for ion-neutral collision experiments, or how to rescale to the pseudo-potential predictions. We also investigate the fate of the electrons generated during the loading process and present a new heating mechanism, insertion heating, that in some regimes of trapping and loading may rival and even exceed the rf-heating power of the trap. Full article
(This article belongs to the Special Issue Low Energy Interactions between Ions and Ultracold Alkali Atoms)
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