Hybrid ion-atom systems combine the well-controllable platforms of trapped ions and ultracold quantum gases and link them together by the intermediate-range ion-atom interaction. These quantum systems offer opportunities for buffer gas cooling, quantum simulation of many-body systems, as well as state-to-state quantum chemistry [1]. To fully benefit from the combination, it is essential to understand, characterize, and control the interactions between the atoms and ions. At TU/e, a new experimental setup is being built to go beyond alkali hybrid atom-ion systems and exploit the novel combination of a trapped ion – Yb+ - with dipolar atoms - Dy. This mixture offers new opportunities and here we present the progress made on developing it.
Hybrid ion-atom systems combine the well-controllable platforms of trapped ions and ultracold quantum gases and link them together by the intermediate-range ion-atom interaction. These quantum systems offer opportunities for buffer gas cooling, quantum simulation of many-body systems, as well as state-to-state quantum chemistry [1]. To fully benefit from the combination, it is essential to understand, characterize, and control the interactions between the atoms and ions. At TU/e, a new experimental setup is being built to go beyond alkali hybrid atom-ion systems and exploit the novel combination of a trapped ion – Yb+ - with dipolar atoms - Dy. This mixture offers new opportunities and here we present the progress made on developing it.
Hybrid ion-atom systems combine the well-controllable platforms of trapped ions and ultracold quantum gases and link them together by the intermediate-range ion-atom interaction. These quantum systems offer opportunities for buffer gas cooling, quantum simulation of many-body systems, as well as state-to-state quantum chemistry. To fully benefit from the combination, it is essential to understand, characterize, and control the interactions between the atoms and ions. At TU/e, a new experimental setup to go beyond alkali atom-ion hybrid system and exploit the combination of a trapped ion – Yb+ - with dipolar atoms - Dy. This mixture offers new opportunities and here we present the most recent results.
Hybrid quantum systems represent one of the most promising routes in the progress of experimental quantum physics and in the development of quantum technologies. In a hybrid quantum system two (or more) different quantum systems interact in the same experimental setup. Therefore, these composite systems benefit from both the properties of each single system and from the presence of an interaction term, leading to the emergence of new variables that can be experimentally manipulated. \nA promising hybrid quantum system is the one realized by the com- bination of an ultracold atomic gas and trapped ions. Ultracold atoms and trapped ions are two of the most studied physical systems for the implementation of several quantum technologies, like e.g. quantum simulation, quantum computa- tion, and quantum metrology. When trapped together, atoms and ions interact via an interaction potential that scales asymptotically with R^(−4), where R is the inter- particle distance, due to the electrostatic (attractive) force between the ion’s electric monopole and the atom’s induced dipole. Interestingly, this potential has a typical range on the order of hundreds of nm, i.e. approx. two orders of magnitude longer than the range of atom-atom interactions. Several studies have proposed to use this interaction to realize new quantum simulations, study few-body physics, and control atom-ion chemical reactions. \nElastic collisions between ions and atoms can be exploited to sympathetically cool the ions and try to reach the so-far elusive s-wave scattering regime, in which atom- ion collisions can lead to a quantum coherent evolution of the composite system. However, the ultracold atom-ion mixtures realized so far were not brought to the s-wave scattering regime because of the so-called “micromotion”, a driven motion affecting the dynamics of the ions trapped in Paul traps. Atom-ion collisions in the presence of micromotion cause a coupling of energy from the oscillating field of the Paul trap to the colliding particles, which can be heated up in the collision. In order to realize an atom-ion experiment in which the system could reach the s-wave scattering regime, the choice of the atomic species and the ion trapping strategy are crucial. \nWe decided to build a new experimental apparatus for the realization of an ultracold atom-ion quantum hybrid system made of a quantum gas of fermionic Lithium and trapped Barium ions. The choice for the elements ensures that atoms and ions in their electronic ground state will not undergo charge- exchange collisions, i.e. inelastic processes for which an electron is “exchanged” be- tween the two colliding particles. Additionally, the large mass ratio ensures an efficient cooling of the ion in the ultracold gas. \nFor what regards the ion trapping strategy, in order to remove the limitations set by micromotion, we conceived a new trap. This is formed by the superposition of an electric quadrupole static potential and an optical lattice along the untrapping direction of the electric quadrupole. The ions are moved into this electro-optical trap (EOT) from a standard Paul trap, in which the ions are first trapped after their production through photoionization. \nIn this thesis, I will describe how this new experimental apparatus for the real- ization of an ultracold atom-ion quantum hybrid system was conceived, designed and assembled. I will first describe the motivations for investigating atom-ion interactions in the ultracold regime. Then, I will describe the experimental techniques to trap and cool Barium ions and Lithium atoms, and how we plan to make them interact. The largest part of the thesis will be dedicated to the description of the parts of the experimental setup that I designed and realized, like the Lithium optical setup, the Barium imaging system and the electrical setup of the ion trap, including a compact RF drive based on interdependent resonant circuits that I developed for operating the Paul trap. The last chapter of the thesis is dedicated to this innovative drive.
Ultracold atoms and trapped ions are among the most formidable sources of coherent matter available in a laboratory. In a hybrid quantum system of atoms and ions, ultracold atoms and trapped ions are combined in a single experimental apparatus, thus realizing an innovative platform to experimentally investigate open problems of quantum physics from a new standpoint. An atom-ion hybrid system not only brings together the advantages of each single physical system, but moreover gives rise to atom-ion interactions, which are two orders of magnitude longer-ranged than atom-atom interactions. Despite a strong interest in atom-ion experiments in recent years, atom-ion systems have not yet been brought to an s-wave scattering regime in which atoms and ions experience a long-living coherent evolution. I will report on the advancements in the realization of an experimental apparatus in which a single trapped Barium ion will be immersed into an ultracold gas of fermionic Lithium. In particular, I will report on the a number of technical advancements that we have realized in order to achieve the highest possible level of control over the atom-ion quantum mixture. These include a new ion trap for creating confining potentials for the ions with a combination of optical and electric fields [1], and a high-finesse optical cavity for confining and rapidly cool neutral atoms via unconventional sideband cooling [2]. Notably, this apparatus was recently used to successfully trap Ba+ ions, thus realizing the first ion trapping experiment in Italy. [1] E. Perego, L. Duca, C. Sias Appl. Sci. 10, 2222 (2020) [2] F. Berto, E. Perego, L. Duca, C. Sias arXiv:2107.04110 Phys. Rev. Research (in press)
Merging trapped ions with cold atomic clouds offers intriguing prospects for quantum chemistry and many-body quantum simulations. Especially when going beyond the standard alkali atomic baths by using lanthanide atoms, opportunities arise to study the interplay between the intermediate-range atom-ion interaction and the tunable long-range dipolar atom-atom interactions. However, the high total angular momentum of the ground-state of open-shell lanthanides, e.g. 5I8 for dysprosium, affects the atom-ion potential. Here, we discuss the implications for long- and short-range atom-ion interactions and present a novel apparatus which combines an ytterbium ion (Yb+) with dipolar dysprosium (Dy) atoms. We highlight the consequences of this novel Dy-Yb+ mixture for observing buffer gas cooling, (non-) radiative charge transfer, and three-body recombination. While the energy-averaged rates are dominated by radiative charge transfer, particularly radiative association, we find that three-body recombination can compete with molecular-ion formation at Dy densities n≳1012 cm−3. This competition is further enhanced by the expected non-thermal distribution of ion energies. These processes could be experimentally characterised through controlled variation of the atom-ion interaction parameters, providing a direct test of our theoretical predictions.
In recent years, ultracold atoms have emerged as an exceptionally controllable experimental system to investigate fundamental physics, ranging from quantum information science to simulations of condensed matter models. Here we go one step further and explore how cold atoms can be combined with other quantum systems to create new quantum hybrids with tailored properties. Coupling atomic quantum many-body states to an independently controllable single-particle gives access to a wealth of novel physics and to completely new detection and manipulation techniques. We report on recent experiments in which we have for the first time deterministically placed a single ion into an atomic Bose Einstein condensate. A trapped ion, which currently constitutes the most pristine single particle quantum system, can be observed and manipulated at the single particle level. In this single-particle/many-body composite quantum system we show sympathetic cooling of the ion and observe chemical reactions of single particles in situ.
Over the last decade there has been rapid progress in studying ultracold mixtures of trapped ions and neutral atoms. These systems are particularly interesting for studying quantum impurity physics and quantum chemistry, and may find applications in buffer gas cooling of trapped ions. In these lecture notes I review some of the recent progress and give relevant background information that may be useful for students who are considering working in this research area, but already have a firm knowledge of quantum and atomic physics. The notes are written from the Amsterdam perspective and therefore are not meant as a comprehensive review. I introduce the interaction potential between atoms and ions as well as some relevant atomic physics background. Then I explain how ion traps work. I treat the problem of a trapped ion in a neutral buffer gas and under what circumstances the gas can cool the ion. Next, I explain how the motional state of trapped ions can be measured. For applications in quantum technology, it will be of vital importance to be able to control the interactions between ion and atoms. I treat the case of using Rydberg dressing or excitation to boost the range and strength of the atom-ion interactions. Finally, I treat a number of applications in quantum chemistry that were studied in the group in Amsterdam, followed by a brief outlook.