Quantum computing is an emerging technology, which holds the potential to simulate complex quantum systems beyond the reach of classical numerical methods.Despite recent formidable advancements in... Show moreQuantum computing is an emerging technology, which holds the potential to simulate complex quantum systems beyond the reach of classical numerical methods.Despite recent formidable advancements in quantum hardware, constructing a quantum computer capable of performing useful calculations remains challenging.In the absence of a reliable quantum computer, the study of potential applications relies on mathematical methods, ingenious approximations, and heuristics derived from the fields of application. This thesis focuses on developing new quantum algorithms, targeting some of the key challenges in the simulation of complex quantum systems.The techniques introduced in this thesis span from quantum state preparation to mitigation of hardware and algorithmic noise, from efficient expectation value measurement to noise-resilient applications in quantum chemistry. A common thread connecting all these algorithms is the introduction of a single auxiliary qubit – a fundamental unit of quantum information – which has an active and distinctive role in the task at hand. Show less
Biological cells, the basic building blocks of all life forms, are surrounded by a lipid membrane. More than half of the membrane is occupied by membrane proteins, which can regulate the cell... Show moreBiological cells, the basic building blocks of all life forms, are surrounded by a lipid membrane. More than half of the membrane is occupied by membrane proteins, which can regulate the cell functionality through specific arrangements. To regulate the arrangements several proteins have to work together. In addition to direct forces, there exists an indirect force between the proteins, which stems from their deformation of the membrane and contributes to their self-organization. Since the actual membrane is very crowded and proteins are too tiny and complex to measure this interaction, in this thesis we used a model system consisting of lipid membranes and solid particles to study the deformation-mediated interaction. We experimentally confirmed for the first time that, unlike many known forces, this deformation-mediated interaction is not additive, i.e. the strength and range of three (or more) deformations cannot be obtained by simple addition of the interactions between pairs of deformations. We found that the interaction weakens with increasing number of membrane-deforming particles and that the particle become less ordered. We investigated deformations in both directions of the membrane and found that the interaction can be both repulsive and attractive, and furthermore depends on the shape of the deformation. This thesis helps to better understand the organization of proteins that deform cellular membranes. Show less
Detecting nanoscopic objects plays an important role in nanoscience in particular, in the rapidly growing field of nanobiology. The forebear to modern super-resolution microscopy for single... Show moreDetecting nanoscopic objects plays an important role in nanoscience in particular, in the rapidly growing field of nanobiology. The forebear to modern super-resolution microscopy for single molecule investigation, is fluorescence microscopy. Fluorescence as a contrast mechanism, however, brings several restrictions. These include (1) the use of the label itself, which may introduce artifacts to the interpretation, (2) the limited photoemission caused by photobleaching and photoblinking as well as (3) low bandwidth of the emission. Fluorescence-free alternatives are thus highly desirable to overcome these limitations. Optical detection of individual proteins with high bandwidth holds great promise for understanding important biological processes on the nanoscale. In this thesis, we investigate label-free optoplasmonic detection of single proteins and particles in motion. Analysing the data provide information about the hydrodynamic volume of the diffuser and interaction such as binding events. Show less
A single self-assembled semiconductor quantum dot in a high-finesse optical microcavity - the subject of this thesis - is an interesting quantum-mechanical system for future quantum applications.... Show moreA single self-assembled semiconductor quantum dot in a high-finesse optical microcavity - the subject of this thesis - is an interesting quantum-mechanical system for future quantum applications. For instance, this system allows trapping of an extra electron and thus can serve as a spin quantum memory, or enables high-fidelity and high-rate single-photon production. We investigate several aspects in this thesis:First, the operation and manipulation of the system is achieved using resonant laser spectroscopy. This requires filtering out of the relatively strong excitation laser, which is often done using the cross-polarization technique. This approach, however, is complicated in optical setups by spin-orbit coupling of light at the beamsplitter. We experimentally firstly explore this effect in a cryogenic optical microscope and demonstrate its importance for quantum dot based single photon sources. Next, we develop a unique setup with a cold permanent magnet and firstly realise trapping of a single electron in our particular quantum dot - cavity devices and show spin control. Then we show how true single photons from our device can be used to create novel quantum states of light. First, we investigate theoretically single photon addition to coherent laser light including several experimental imperfections - we find an universal behaviour of the photon correlation function. Finally, we demonstrate entanglement of several consecutive photons by repeatedly using Hong-Ou-Mandel quantum interference of single photons with a photon quantum memory in the form of an optical delay loop. We show that this results in quantum states of light that have Poissonian photon statistics like laser light - therefore we call them artificial coherent states - but also that they are more complicated than ordinary coherent states and contain multi-photon quantum entanglement in the form of linear cluster states, a potential resource for universal quantum computing. Show less
The first direct detection of gravitational waves opened the possibility of mapping the Universe via this new and independent messenger. Indeed, during their propagation, gravitational waves pick... Show moreThe first direct detection of gravitational waves opened the possibility of mapping the Universe via this new and independent messenger. Indeed, during their propagation, gravitational waves pick up information about the spacetime as they are affected by its expansion and by the matter structures along the propagation path. The aim of this Thesis is to investigate which cosmological information is accessible from a gravitational wave detection, with a specific interest in the late time Universe. Show less
Mechanical metamaterials are carefully engineered materials whose properties are controlled by their structure, not by their composition, which allows using metamaterials to study and control... Show moreMechanical metamaterials are carefully engineered materials whose properties are controlled by their structure, not by their composition, which allows using metamaterials to study and control physical effects in detail. Here we develop metamaterials to study the sequential, complex response of frustrated materials that are cyclically driven. In particular, we focus on metamaterials that act as collections of hysteretic, bistable elements called hysterons. We create hysterons in metamaterials by using local frustration at defects and by using a competition between two global, incompatible deformations modes. We show how we can tune these hysterons, both by rational design and by using spatial gradients in the mechanical driving. Then we show that collectively, our samples exhibit complex transition pathways, including those with avalanches, and study the role of hysteron interactions. Finally, we explore how to control the frustration by local defects in so-called monoholar metamaterials. Show less
In this thesis, we have used numerical approaches to study the effects of translational symmetry breaking on strange metallic systems as realised by the holographic duality. This involves solving... Show moreIn this thesis, we have used numerical approaches to study the effects of translational symmetry breaking on strange metallic systems as realised by the holographic duality. This involves solving for large-scale coupled partial differential equations, describing the physics of corrugated black holes in negatively curved space-times.We show that the strong-coupling nature of the physics of these holographic systems produces some unique behaviours, which are suggestively close to experimental observations that have been done in the lab. We speculate that strong-coupling physics is what is at the heart of the mysteries that shroud the strange metal. Show less
In this thesis I describe the results of Pulsed Interleaved Excitation and Fluorescence (Cross) Correlation Spectroscopy (PIE-F(C)CS) combined with single-pair Förster Resonance Energy Transfer ... Show moreIn this thesis I describe the results of Pulsed Interleaved Excitation and Fluorescence (Cross) Correlation Spectroscopy (PIE-F(C)CS) combined with single-pair Förster Resonance Energy Transfer (spFRET) used to study dynamics in single nucleosomes, which depends on subtle differences in the length of DNA ends, DNA sequence, histone variants and specific and non-specific protein interactions. This technique, which can resolve distances between two fluorophores of only a few nanometers, is an excellent technique to monitor changes in nucleosomal compaction, as the nucleosome is only ten nanometers in diameter. In combination with F(C)CS and PIE, spFRET makes it possible to monitor conformational dynamics on a timescale of micro- to milliseconds. Show less
In condensed matter systems electron-electron interactions, negligible in everyday metals, can dramatically alter the electronic behavior of the system. Examples of such altered behavior include... Show moreIn condensed matter systems electron-electron interactions, negligible in everyday metals, can dramatically alter the electronic behavior of the system. Examples of such altered behavior include high-temperature superconductivity and modulation of the electron density. A common feature of this correlation driven behavior is the tendency of the spatial electronic structure to vary on the nanometer scale. In this thesis we explore the nanoscale variation of the electronic structure of various correlated electron systems. We use the wave-like oscillations in the electron density of states to probe fundamental properties of the system providing insights into when various experimental probes disagree with each other. Turning our attention to high-temperature superconductors we find that close to the transition between superconductor and metal a granular superconductor emerges, small nanoscale patches of superconductivity interlaces with a metallic matrix. A careful examination of the wave-like oscillations hints at the presence of spatial ordering of the electrons. Finally we study how the presence of strong interactions can alter the way electrons flow through a material such that concepts usually reserved for everyday fluids become relevant. Show less
Despite being the object of intense study, embryonic development has been difficult to model due to a number of reasons. First, complex tissues can be comprised of many cell types, of which we... Show moreDespite being the object of intense study, embryonic development has been difficult to model due to a number of reasons. First, complex tissues can be comprised of many cell types, of which we probably only know a subset. Therefore, we first focused on the discovery of cell types by single-cell RNA-sequencing (scRNA-seq). Cell types are routinely identified by clustering scRNA-seq data, however, there was no principled way to determine the right number of clusters. To improve cell type classification, we developed phiclust, a clusterability measure for scRNA-seq. Another challenge in a developing tissue is that many signaling processes and morphogenic events occur simultaneously, which makes it hard to isolate the individual contributions. For this purpose, I looked at stem cell derived in vitro systems, in which a small number of specific cell types can be combined deliberately and studied in isolation. My analysis of different model systems shows that cellular communication causes structural and transcriptional changes in the developing cells. Finally, while tissue organization has been characterized extensively, we lack generative models that can relate specific patterns to the underlying gene regulatory mechanisms. Therefore, I later focused on deep learning-based approaches to infer gene regulatory networks from observed spatial patterns. Show less
We find ourselves in an era of transition, not just towards a more computing- and data-driven society but also away from unsustainable fossil fuels as an energy source. This leads to a rapidly... Show moreWe find ourselves in an era of transition, not just towards a more computing- and data-driven society but also away from unsustainable fossil fuels as an energy source. This leads to a rapidly increasing demand for computing power on an ever more tight energy budget. Therefore, it is imperative to investigate novel energy-efficient computing techniques, like superconducting spintronics or neuromorphic computing using correlated electron matter. Naturally, understanding the physics governing these processes at the sub-micrometer (i.e., device) scale is crucial for this development to succeed. This thesis examines the effects of size reduction and geometry on ferromagnetic Josephson junctions and highly correlated electron matter through transport experiments. Specifically, it describes how spin-polarized supercurrents can be generated using spin texture, stabilized by carefully tuning the geometry of planar Josephson junctions, and how the bistability of these spin textures can be employed to create non-volatile superconducting memory elements. Furthermore, it reports a strong size dependence of the current density that drives the Mott-insulating-to-metal transition in Ca2RuO4 and shows how various constricted geometries can be used to localize and examine the properties of superconducting chiral domain walls in Sr2RuO4. Show less
The way organisms develop from the initial single-cellular state to a complex final assembly like the human body, and how the final body is maintained throughout life, is one of the greatest... Show moreThe way organisms develop from the initial single-cellular state to a complex final assembly like the human body, and how the final body is maintained throughout life, is one of the greatest mysteries and it’s understanding one of the biggest scientific challenges. Lately, it came as a surprise that the initial assembly and the later maintenance of integrity is not only determined by intricate biochemical communication networks, but in part by physical forces that cells, their neighbors, and their environment apply in a bidirectional manner. The resulting collectivity of cell behavior determines the development of organisms, and are crucial to the health and disease state of the organism.In this thesis, we developed and utilized concepts from physics to quantitatively understand forces that develop between cells and their environment, and towards neighboring cells, and how the interplay between these forces regulates the arrangement, shape, and topology of tissue. The topics range from the development of novel experimental methods to the combination of experimental observations with theoretical descriptions. Our results contribute to a better understanding of cell and tissue integrity. Show less
In my thesis I study Majorana fermions from three different perspectives. The first one corresponds to non-interacting Majorana fermions that, however, pose non-trivial topological properties. The... Show moreIn my thesis I study Majorana fermions from three different perspectives. The first one corresponds to non-interacting Majorana fermions that, however, pose non-trivial topological properties. The second one corresponds to strongly interacting Majoranas and the third to relic neutrinos. No one knows for sure if they have Dirac or Majorana nature. Show less
Pericytes, the mural cells of blood microvessels, are important regulators of vascular morphogenesis and function that have been postulated to mechanically control microvascular diameter through as... Show morePericytes, the mural cells of blood microvessels, are important regulators of vascular morphogenesis and function that have been postulated to mechanically control microvascular diameter through as yet unknown mechanisms. Their disfunction has been implicated in several pathologies, including cerebral ischemia, Alzheimer's disease and diabetic retinopathy.To reveal mechanisms used by pericytes for mechanical interactions within microvessels we designed models bringing human induced pluripotent stem cell (hiPSC)-derived pericytes in contact with various micropatterned substrates representing the microvascular basement membrane organization. Our findings shed light on how pericytes can mechanically regulate microvascular morphogenesis and function, and open possibilities for testing therapeutic strategies. Show less
In this PhD thesis, the recombination of different atomic lattices in stacked 2D materials such as twisted bilayer graphene is studied. Using the different possibilities of Low-Energy Electron... Show moreIn this PhD thesis, the recombination of different atomic lattices in stacked 2D materials such as twisted bilayer graphene is studied. Using the different possibilities of Low-Energy Electron Microscopy (LEEM), the domain forming between the two atomic layers with small differences is studied. Superlattices in three such 2D material systems are studied. In twisted bilayer graphene, the small difference is caused by a twist of approximately one degree between the layers. In graphene on SiC, the difference is caused by the lattice mismatch between a buffer layer bound to the substrate and the next graphene layer. For both, we show that domains of different shapes and sizes occur and relate them to strain and lattice mismatch. The third system studied is tantalum disulfide. In this layered material, two different superlattices occur: a superlattice between atomic layers with different atomic arrangements in the layers, so-called polytypes, and the superlattices between the atomic lattice and the Charge Density Waves (CDW). CDWs cause a large temperature dependent resistivity change. The influence of a mixture of different polytypes on the precise CDW states is studied using LEEM spectroscopy and local Low-Energy Electron Diffraction. Show less
This thesis covers several aspects of quantum algorithms for near-term quantum computers and its applications to quantum chemistry and material science. These aspects range from error mitigation... Show moreThis thesis covers several aspects of quantum algorithms for near-term quantum computers and its applications to quantum chemistry and material science. These aspects range from error mitigation and error modeling of a quantum computing device to a measurement scheduling to extract the relevant information of a quantum state for quantum chemistry calculations.It also presents a benchmarking study of classical optimization methods for variational quantum algorithms. Additionally, a small quantum simulation is performed on a cloud-based quantum computer to understand the bottlenecks of such infrastructure. Finally, a method to calculate energy derivatives on a quantum computer, a relevant figure for quantum chemistry calculations. Show less
The ultimate goal of cosmologists is to find a cosmological model able to explain the current observational data. In this sense, the Standard Cosmological model establishes that our universe is... Show moreThe ultimate goal of cosmologists is to find a cosmological model able to explain the current observational data. In this sense, the Standard Cosmological model establishes that our universe is mainly composed of two unknown components: a type of matter that is known to only interact through gravitation, Cold Dark Matter, and a substance responsible for the current accelerated expansion of the universe that can be modelled by a cosmological constant. Still, this model, though successful, fails to answer hot-burning questions in the field. For this reason, theoretical cosmologists focus on developing further modifications of the model to test them against astrophysical data and check whether alternative scenarios can provide a better explanation of the observations.This thesis is dedicated to the Bayesian statistical analyses of extensions of the Standard Cosmological model using several astronomical data sets, and to the forecast of new observables and experiments. The first part focuses on data science and inflation, and it aims to constrain inflationary models using advanced inference techniques. The second part of the thesis is dedicated to the novel concept of cross-correlations of gravitational-wave physics and large scale structure observables. The third part of this thesis is dedicated to the incoming ESA Euclid satellite, and in particular, it focuses on a crucial data science analysis software for the mission: the code “Cosmological Likelihood for Observables in Euclid”, also known as CLOE. Show less
My PhD research is devoted to studies of the conjectural cluster-algebraic symmetry in the theory of topological string, which is the simplest, however already non-trivial sector in the theory of... Show moreMy PhD research is devoted to studies of the conjectural cluster-algebraic symmetry in the theory of topological string, which is the simplest, however already non-trivial sector in the theory of string. The language of cluster algebras is the modern tool which was initially developed for solving problems in linear algebra, and has recently been applied to the theory of integrable systems. In this dissertation we identify the cluster-algebraic nature of new classes of integrable systems of string-theoretic origin. We then show how the partition functions of topological string on the corresponding geometries can be naturally fit into a cluster-algebraic context. Show less
Because thin systems can deform along the thickness with relative ease, the interplay between surface mechanics and geometry plays a fundamental role in sculpting their three-dimensional shape.... Show moreBecause thin systems can deform along the thickness with relative ease, the interplay between surface mechanics and geometry plays a fundamental role in sculpting their three-dimensional shape. Often, deformations arise as a consequence of elastic pre-stress in the material, for example because of the small-scale geometry of the constituents or their local arrangement. In this thesis, we look at the connection between geometry, local and global, and mechanics in thin closed shells and open sheets which we consider as two-dimensional solids that we study using linear elasticity theory. In particular, we investigate the elasticity-driven shape deformations in the context of three soft matter systems: dense single-layered crystals, oil-in-water emulsions, and biological thin assemblies of tubulin. Show less
In the thesis we demonstrated an 85% state transfer efficiency between two mechanical modes coupled to a common optical mode via stimulated Raman adiabatic passage (STIRAP) in the classical regime.... Show moreIn the thesis we demonstrated an 85% state transfer efficiency between two mechanical modes coupled to a common optical mode via stimulated Raman adiabatic passage (STIRAP) in the classical regime. We also showed possibilities to manipulate quantum states of the mechanical modes via STIRAP. Show less
