Interatomic coulombic electron capture is a non-local process involving the environment-assisted attachment of a free electron with implied consequences for various systems. Starting from the established numerical model of quantum confinements in a nanowire, this dissertation sets out to deduce model-independent hypotheses for future investigations of theoretical or experimental nature and develops a generalised adaptation of the model to test whether the effective-two-electron treatment suffices to successfully capture a free electron in the experimentally motivated system of a barium (II) cation engulfed in a Bose-Einstein condensate of neutral rubidium atoms. Appearing associated to differing electronic states of the confinement region, two subprocesses can contrast in spatial preferences and resonant energies. For the investigated range of parameters, the energy levels of these associated states suggest to provide a starting point for a more comprehensive description beyond the particular parameters of an individual model. A rather simple electric dipole-dipole coupled adaptation of the model is then able to successfully show environment assisted electron attachment to a barium (II) cation aided by a surrounding cloud of ultracold rubidium atoms in typical experimental conditions.
Interatomic coulombic electron capture is a non-local process involving the environment-assisted attachment of a free electron with implied consequences for various systems. Starting from the established numerical model of quantum confinements in a nanowire, this dissertation sets out to deduce model-independent hypotheses for future investigations of theoretical or experimental nature and develops a generalised adaptation of the model to test whether the effective-two-electron treatment suffices to successfully capture a free electron in the experimentally motivated system of a barium (II) cation engulfed in a Bose-Einstein condensate of neutral rubidium atoms. Appearing associated to differing electronic states of the confinement region, two subprocesses can contrast in spatial preferences and resonant energies. For the investigated range of parameters, the energy levels of these associated states suggest to provide a starting point for a more comprehensive description beyond the particular parameters of an individual model. A rather simple electric dipole-dipole coupled adaptation of the model is then able to successfully show environment assisted electron attachment to a barium (II) cation aided by a surrounding cloud of ultracold rubidium atoms in typical experimental conditions.
Non-local energy transfer between bound electronic states close to the ionisation threshold is employed for efficient state preparation in dilute atom systems from technological foundations to quantum computing. The generalisation to electronic transitions into and out of the continuum is lacking quantum simulations necessary to motivate such potential experiments. Here, we present the first development of a electron-dynamical model simulating fully three-dimensional atomic systems for this purpose. We investigate the viability of this model for the prototypical case of recombination of ultracold barium(II) by environment-assisted electron capture thanks to a rubidium atom in its vicinity. Both atomic sites are modelled as effective one-electron systems using the Multi Configuration Time Dependent Hartree (MCTDH) algorithm and can transfer energy by dipole-dipole interaction. We find that the simulations are robust enough to realise assisted capture over a dilute interatomic distance which we are able to quantify by comparing to simulations without interatomic energy exchange. For our current parameters not yet optimised for reaction likelihood, an environment-ionising assisted capture has a probability of 1.9×10−5% over the first 15fs of the simulation. The environment-exciting assisted-capture path to [Ba+∗Rb∗] appears as a stable long-lived intermediate state with a probability of 8.2×10−4% for at least 20fs after the capture has been completed. This model shows potential to predict optimised parameters as well as to accommodate the conditions present in experimental systems as closely as possible. We put the presented setup forward as a suitable first step to experimentally realise environment-assisted electron capture with current existing technologies.
Interparticle Coulombic Electron Capture (ICEC) provides an environment-assisted pathway for electron attachment that can compete with photorecombination. Here, we present the first comprehensive survey of ICEC in atom-atom and atom-molecule systems, screening 2442 combinations in search of promising candidates for future experimental investigation.
We employ the efficient asymptotic approximation to predict ICEC cross sections and electron spectra. Intramolecular nuclear motion is included, while interparticle nuclear dynamics is neglected to permit an extensive survey.
We identify several classes of atom-atom and atom-molecule systems with favourable ICEC cross sections and ICEC-to-photorecombination ratios, including halogen-halide systems and systems involving a proton and diatomic molecules such as N2, O2, CO, and NO. These findings point to atmospheric and astrochemical environments in which ICEC may be relevant.
In this dissertation I describe a number of different computational investigations which I have undertaken during my time at Colorado State University. Perhaps the most significant of my accomplishments was the development of a general molecular dynamic model that simulates a wide variety of physical phenomena in ultracold plasmas (UCPs). This model formed the basis of most of the numerical investigations discussed in this thesis. The model utilized the massively parallel architecture of GPUs to achieve significant computing speed increases (up to 2 orders of magnitude) above traditional single core computing. This increased computing power allowed for each particle in an actual UCP experimental system to be explicitly modeled in simulations. By using this model, I was able to undertake a number of theoretical investigations into ultracold plasma systems. Chief among these was our lab's investigation of electron center-of-mass damping, in which the molecular dynamics model was an essential tool in interpreting the results of the experiment. Originally, it was assumed that this damping would solely be a function of electron-ion collisions. However, the model was able to identify an additional collisionless damping mechanism that was determined to be significant in the first iteration of our experiment. To mitigate this collisionless damping, the model was used to find a new parameter range where this mechanism was negligible. In this new parameter range, the model was an integral part in verifying the achievement of a record low measured UCP electron temperature of 1.57 ± 0.28K and a record high electron strong coupling parameter, Γ, of 0.35 ± 0.08. Additionally, the model, along with experimental measurements, was used to verify the breakdown of the standard weak coupling approximation for Coulomb collisions. The general molecular dynamics model was also used in other contexts. These included the modeling of both the formation process of ultracold plasmas and the thermalization of the electron component of an ultracold plasma. Our modeling of UCP formation is still in its infancy, and there is still much outstanding work. However, we have already discovered a previously unreported electron heating mechanism that arises from an external electric field being applied during UCP formation. Thermalization modeling showed that the ion density distribution plays a role in the thermalization of electrons in ultracold plasma, a consideration not typically included in plasma modeling. A Gaussian ion density distribution was shown to lead to a slightly faster electron thermalization rate than an equivalent uniform ion density distribution as a result of collisionless effects. Three distinct phases of UCP electron thermalization during formation were identified. Finally, the dissertation will describe additional computational investigations that preceded the general molecular dynamics model. These include simulations of ultracold plasma ion expansion driven by non-neutrality, as well as an investigation into electron evaporation. To test the effects of non-neutrality on ion expansion, a numerical model was developed that used the King model of the electron to describe the electron distribution for an arbitrary charge imbalance. The model found that increased non-neutrality of the plasma led to the rapid expansion of ions on the plasma exterior, which in turn led to a sharp ion cliff-like spatial structure. Additionally, this rapid expansion led to additional cooling of the electron component of the plasma. The evaporation modeling was used to test the underlying assumptions of previously developed analytical expression for charged particle evaporation. The model used Monte Carlo techniques to simulate the collisions and the evaporation process. The model found that neither of the underlying assumption of the charged particle evaporation expressions held true for typical ultracold plasma parameters and provides a route for computations in spite of the breakdown of these two typical assumptions.
We present an analytical model for intermolecular Coulombic electron capture (ICEC) which includes the internal nuclear dynamics of the molecules involved. In ICEC, an electron attaches to an atom or molecule by transferring excess energy to a neighbor, ionizing said neighbor. While previous theoretical investigations assumed fixed nuclei, recent studies indicate that relative motion between the two ICEC partners significantly influences the process. Here, we incorporate the internal nuclear motion of the molecules involved into an analytical equation of the ICEC cross section. We employ two approaches: 1. utilizing theoretical vibrationally resolved photoionization cross sections and 2. applying the Franck-Condon principle. Our theory yields electron spectra, ICEC cross sections for individual vibronic transitions, and temperature dependent cross sections. Nuclear dynamics lead to a distribution of the electronic cross section over several vibrational states and, in our model system H+ LiH, triggers dissociation of LiH during ICEC.
Electron capture by isolated atoms and ions proceeds by photorecombination. In this process, a species captures a free electron by emitting a photon which carries away the excess energy. It is shown here that in the presence of an environment a competing non-radiative electron capture process can take place due to long range electron correlation. In this interatomic (intermolecular) process the excess energy is transferred to neighbouring species. The asymptotic expression for the cross section of this process is derived. We demonstrate by explicit examples that under realizable conditions, the cross section of this interatomic process can clearly dominate that of photorecombination.
Quantum properties like coherence and entanglement can lead to enhanced performance characteristics in a wide range of applications including quantum computation, quantum memory storage, optical sensing, and energy harvesting. Entanglement is very sensitive to static and dynamical disorder. Similarly, the generation of highly-entangled states requires strong coupling or strong driving fields. Satisfying all of these requirements is generally quite difficult. In the first part of this thesis, we present an approach to overcome these limitations through the use of exotic light-matter states in hyperbolic media which provide a new approach to control quantum correlations and interatomic interactions. We reveal a class of excited-state, long-range interactions, referred to as Super-Coulombic interactions that are singular along a material-dependent resonance angle. In practical systems, the Super-Coulombic interaction achieves dipole-dipole coupling that is orders of magnitude larger than conventional approaches, while also occurring across a large frequency bandwidth making it robust to static energy-level disorder. This unique hyperbolic response is not only naturally occurring, found in materials like h-BN, BiTe2, BiSe2, and mono-layered black phosphorus, but can also be designed with artificial nanostructured materials (metamaterials) to create the desired hyperbolic dispersion across different parts of the electromagnetic spectrum. Our theoretical prediction motivated an intense search for the effect and was confirmed by an experimental demonstration at room temperature. To obtain agreement with experimental results, we present a rigorous theoretical framework that takes into account ensemble effects, finite-sized effects, and dimensional effects that arise from confined geometries ultimately modifying the Super-Coulombic spatial scaling law. In the second part of this thesis, we solve an outstanding theoretical problem dealing with the control of resonance energy transfer in nanophotonic environments in both the incoherent and coherent coupling limits. Resonance energy transfer is a fundamental process that is the subject of intense research across all sciences. For example, in chemistry for drug delivery and chemical monitoring, in engineering for photovoltatic and up-conversion devices, and in biology for exciton transport within photosynthetic complexes. First, we consider the disordered and weak coupling limit of resonance energy transfer often encountered in chemistry. We propose new design principles for enhancing and suppressing the energy transfer rate and efficiency quantitatively captured by a simple image dipole model. Our theory explains a wide range of experimental results which have been the subject of an ongoing debate for the past 15 years. Second, we present our recent result aimed at understanding the fundamental role of entanglement and quantum coherence in resonance energy transfer. To uncover the role of these effects, we develop a unified theory of energy transfer valid from the incoherent to quantum coherent coupling regimes. Ultimately, our theory reveals a fundamental bound ηmax = γa for energy transfer efficiency arising from γd+γa the spontaneous emission rates γd and γa of the donor and acceptor. This bound provides an upper limit to the efficiency of energy transfer regardless of quantum coherence or entanglement, suggesting new design principles for achieving near-unity energy transfer efficiency in coherent systems. The result has important implications for the two-chromophore model found in photosynthetic complexes and paves the way for nanophotonic analogues of efficiency-enhancing environments mimicking biological photosynthetic systems.