A coupling of an atomic quantum system to a mesoscopic solid-state object constitutes a so called hybrid quantum system.
The present thesis focuses on a fundamental hybrid quantum system consisting of ultracold atoms interacting with a cylindrical geometry.
A thorough understanding of the scattering process gives insight into the underlying physics and thus promotes a deeper understanding of nanowire-based hybrid systems of higher complexity.
A coupling of an atomic quantum system to a mesoscopic solid-state object constitutes a so called hybrid quantum system.
The present thesis focuses on a fundamental hybrid quantum system consisting of ultracold atoms interacting with a cylindrical geometry.
A thorough understanding of the scattering process gives insight into the underlying physics and thus promotes a deeper understanding of nanowire-based hybrid systems of higher complexity.
Quantum reflection refers to the reflection of particles by attractive long-range potentials in nonclassical regions of coordinate space without reaching a classical turning point. Recent advances in nanotechnology and in cooling processes of atoms and molecules give rise to the creation of hybrid systems involving ultracold atoms and nanostructures, where quantum reflection might play an important role. In this work we review some fundamental aspects of quantum reflection. These include the description of atom-surface interactions -which are originated from the vacuum fluctuations of the electromagnetic field-, the near-threshold characterization of quantum reflection, possible applications for trapping and guiding ultracold atoms, and the description of scattering processes in a basic hybrid system: ultracold atoms interacting with nanotubes.
We study inelastic processes in the hybrid quantum system constituted by a carbon nanotube (CNT) in contact with an ultracold quantum gas, such as a cloud of thermal atoms or a Bose-Einstein condensate (BEC). We present a parameter-free ab initio approach for the loss rate based on the underlying scattering process, considering the two-dimensional character of the system as well as the exact Casimir-Polder potential. The predicted loss rates are in perfect agreement with recent experimental results, obtained both for a thermal cloud of rubidium atoms and for a BEC. For the trap loss of a thermal cloud, we find that retardation effects become important and contribute significantly, which emphasises the crucial role of the exact interaction potential. Copyright (C) EPLA, 2013
We investigate theoretically how cold atoms, including Bose–Einstein condensates, are scattered from, or absorbed by, nanotubes with a view to analysing recent experiments. In particular, we consider the role of potential strength, quantum reflection, atomic interactions and tube vibrations on atom loss rates. Lifshitz theory calculations deliver a significantly stronger scattering potential than that found in experiment and we discuss possible reasons for this. We found that the scattering potential for dielectric tubes can be calculated to a good approximation using a modified pairwise summation approach, which is efficient and easily extendable to arbitrary geometries. Quantum reflection of atoms from a nanotube may become a significant factor at low temperatures, especially for non-metallic tubes. Interatomic interactions are shown to increase the rate at which atoms are lost to the nanotube and lead to non-trivial dynamics. Thermal nanotube vibrations do not significantly increase loss rates or reduce condensate fractions, but lower frequency oscillations can dramatically heat the cloud.
We study inelastic processes in the hybrid quantum system constituted by a carbon nanotube (CNT) in contact with an ultracold quantum gas, such as a cloud of thermal atoms or a Bose-Einstein condensate (BEC). We present a parameter-free ab-initio approach for the loss rate based on the underlying scattering process, considering the two-dimensional character of the system as well as the exact Casimir-Polder potential. The predicted loss rates are in perfect agreement with recent experimental results, obtained both for a thermal cloud of rubidium atoms and for a BEC. For the trap loss of a thermal cloud, we find that retardation effects become important and contribute significantly, which emphasises the crucial role of the exact interaction potential.
Quantum information science involves the use of precise control over quantum systems to explore new technologies. However, as quantum systems are scaled up they require an ever deeper understanding of many-body physics to achieve the required degree of control. Current experiments are entering a regime which requires active control of a mesoscopic number of coupled quantum systems or quantum bits (qubits). This thesis describes several approaches to this goal and shows how mesoscopic quantum systems can be controlled and utilized for quantum information tasks.
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.