This thesis is a collection of theoretical works aiming at adjusting quantum algorithms to the hardware of quantum computers. The overarching topic of these efforts is to enable digital quantum... Show moreThis thesis is a collection of theoretical works aiming at adjusting quantum algorithms to the hardware of quantum computers. The overarching topic of these efforts is to enable digital quantum simulation, the process of approximating the ground state of an arbitrary physical system with elementary operations of a quantum computer. For fermionic systems, a class including molecules and materials, the impact of quantum computing would be undoubtedly high, and algorithms exist for their simulation. However, there is a certain gap between the requirements of those algorithms and what actual quantum devices can provide: it seems that our expectations of a fully-fledged quantum computer still exceed our capabilities to build it. To make quantum simulation feasible, we seek to adapt quantum algorithms to three different types of device limitations within this thesis. Show less
The thesis describes experimental steps towards reduction of friction on the macroscopic scale by scenarios of thermo- and superlubricity well-known on the nanoscale. The friction study involves... Show moreThe thesis describes experimental steps towards reduction of friction on the macroscopic scale by scenarios of thermo- and superlubricity well-known on the nanoscale. The friction study involves experiments on tailored Si nanopillar arrays, micropatterned Diamond-Like Carbon coating and high-quality graphene. Show less
The lipid membrane is a basic structural component of all living cells. Embedded in this nanometer-thin barrier, membrane proteins shape the membrane and at the same time respond to the shape... Show moreThe lipid membrane is a basic structural component of all living cells. Embedded in this nanometer-thin barrier, membrane proteins shape the membrane and at the same time respond to the shape of the membrane. This two-way interaction gives rise to a force between membrane-deforming objects that is mediated by the membrane. In this thesis, this effect is measured by employing micron-sized colloidal particles. In Chapters 2 and 3, methods for extracting local forces from video images of colloidal particles are described. Then, in Chapter 4, the development of colloidal particles that strongly attach to specific lipid membranes is described. These are then used in Chapters 5 and 6, in which membrane-mediated forces and assembly pathways between membrane-attached colloidal particles are investigated and quantified. Finally, in Chapters 7 and 8, the preparation of micron-sized oil droplets is studied and their use as lipid monolayer support is demonstrated. The results from this thesis contribute to fundamental microbiological questions about forces between membrane proteins, as well as to the understanding of the toxicity of microplastics. Show less
We study the interplay of topology and geometry with chirality for several passive and active systems, employing both analytical and numerical methods. In chapter 1, we explain how nematic liquid... Show moreWe study the interplay of topology and geometry with chirality for several passive and active systems, employing both analytical and numerical methods. In chapter 1, we explain how nematic liquid crystals confined in toroidal geometries undergo structural phase transitions depending on the slenderness of the confining toroid. In chapter 2, we consider a system of active polar swimmers that align with their neighbors. When confined in the right geometry, the system will self-assemble into a state with topologically protected chiral acoustic modes. The chirality in this system manifests itself as a temporal one, rather than a spatial chirality. Chapter 3 shows how systems of Yukawa charged active spinning dimers self-assemble into a crystal phase with spatiotemporal order, a liquid phase or a glass phase depending on the density. Depending on the phase and the confinement geometry of these systems of actively spinning dimers, the system will allow for rigid body rotations or edge currents. Finally, in chapter 4 we introduce a novel method of doing molecular dynamics on curved surfaces by developing a symplectic integrator. We present preliminary results on two-dimensional crystal melting in the presence of curvature. We find that the crystal may melt inhomogeneously. Show less
A plasma is an ionized gas with very low electrical resistivity. As such, magnetic field lines are 'frozen in' and move with the fluid. Magnetic field lines that are linked, knotted and... Show moreA plasma is an ionized gas with very low electrical resistivity. As such, magnetic field lines are 'frozen in' and move with the fluid. Magnetic field lines that are linked, knotted and tangled, cannot be undone by the fluid motions. In this thesis we investigate how this linking and knottedness influences the plasma dynamics through numerical simulations. One of the main results is the identification of a novel, self-organizing equilibrium, where every field line is linked with every other one. In such a structure all the field lines lie on toroidal magnetic surfaces, and the entire structure resembles the famous topological structure of the Hopf fibration. This magnetic equilibrium is localized, and kept in balance by a finite external pressure. Through resistive effects the structure slowly expands while the magnetic energy is dissipated. This research, and the novel structures identified have implications for nuclear fusion research and the study of astrophysical plasma phenomena. Show less
Combining ferromagnetism and superconductivity can lead to the development of a completely new generation of technology, with unique and powerful characteristics, called superconducting spintronics... Show moreCombining ferromagnetism and superconductivity can lead to the development of a completely new generation of technology, with unique and powerful characteristics, called superconducting spintronics. The task of developing this, however, is challenging because at the microscopic level the superconducting and ferromagnetic states are intrinsically incompatible. Under certain conditions, however, the conventional (singlet) superconducting state can be converted into the triplet one, with the spins of the electrons forming the Cooper pairs aligned parallel. The triplet state can coexist with ferromagnetism and is very interesting both for applications and from a fundamental point of view. In this thesis we study the electrical properties of small hybrid devices that mainly consist of superconducting and ferromagnetic layers. By measuring the electrical resistance of these devices as a function of parameters such as the temperature or the applied magnetic field, it is possible to indirectly infer important information about the state of the (super)conductivity in the different layers. We investigate different types of devices (multilayers, triplet spin valves and Josephson junctions), in order to address different aspects related to the generation of the triplet state, for a better and better control of the process. Show less
Dissertation. We study the topological properties of strongly externally driven quantum non-interacting quantum systems, focussing on the example of the quantum walk and closely related systems.
