| 1. |
- Andersson, H. Ingemar, 1950-
(author)
-
Chronic pain : epidemiological studies in a general population
- 1998
-
Doctoral thesis (other academic/artistic)abstract
- The aim was to study the epidemiology of chronic pain (> 3 months duration) and factors associated to pain prevalence, prognosis, health care and medication in a general population. A cross-sectional mailed survey to a random population sample (n = 1806) was followed by a clinical examination and a prospective study of three selected groups. Pain related diagnoses from primary health care was monitored and compared with pain prevalence. The most important findings were: - a high total prevalence of chronic pain, 55.2%, without gender difference but varying by age and socioeconomic level. About one fourth (12.8%) reported high pain intensity and functional impairments. Women experienced pain at more locations and with higher intensity. - in a multivariate analysis increasing age, female gender, low education, high work strain, depression and insomnia were associated with chronic pain. - widespread pain showed a worse 2- year prognosis compared with neck shoulder pain. - musculoskeletal location of pain dominated, myalgia and myofascial pain being the most common symptom descriptions. - co-morbidity with chronic pain was common. More hypertensives and an increased level of serum uric acid associated to widepread pain indicated possible metabolic connections to pain. - smoking (current and previous) was associated with low-back and widespread pain. - chronic pain had a substantial influence of primary health care-seeking and medication; high pain intensity being the most important predictor of care and medication. - pain related diagnoses in primary health care increased between 1987 and 1996. Chronic pain, mainly with musculoskeletal location, is a community health problem. A multi-factorial approach in prevention and treatment on the basis of present knowledge is necessary.
|
|
| 2. |
- Andersson, Ole
(author)
-
Holonomy in Quantum Information Geometry
- 2018
-
Licentiate thesis (other academic/artistic)abstract
- In this thesis we provide a uniform treatment of the two most popular non-adiabatic geometric phases for dynamical systems of mixed quantum states, namely those of Uhlmann and of Sjöqvist et al. We develop a holonomy theory for the latter which we also relate to the already existing theory for the former. This makes it clear what the similarities and differences between the two geometric phases are. We discuss and motivate constraints on the two phases. Furthermore, we discuss some topological properties of the holonomy of `real' quantum systems, and we introduce higher-order geometric phases for not necessarily cyclic dynamical systems of mixed states. In a final chapter we apply the theory developed for the geometric phase of Sjöqvist et al. to geometric uncertainty relations, including some new "quantum speed limits''.
|
|
| 3. |
- Blanchfield, Kate
(author)
-
Configurations in Quantum Information
- 2012
-
Licentiate thesis (other academic/artistic)abstract
- Measurements play a central role in quantum information. This thesis looksat two types: contextual measurements and symmetric measurements. Contextualityoriginates from the Kochen-Specker theorem about hidden variablemodels and has recently undergone a subtle shift in its manifestation. Symmetricmeasurements are characterised by the regular polytopes they formin Bloch space (the vector space containing all density matrices) and are thesubject of several investigations into their existence in all dimensions.We often describe measurements by the vectors in Hilbert space ontowhich our operators project. In this sense, both contextual and symmetricmeasurements are connected to special sets of vectors. These vectors areoften special for another reason: they form congurations in a given incidencegeometry.In this thesis, we aim to show various connections between congurationsand measurements in quantum information. The congurations discussedhere would have been well-known to 19th and 20th century geometers andwe show they are relevant for advances in quantum theory today. Specically,the Hesse and Reye congurations provide proofs of measurement contextuality,both in its original form and its newer guise. The Hesse congurationalso ties together dierent types of symmetric measurements in dimension3called SICs and MUBswhile giving insights into the group theoreticalproperties of higher dimensional symmetric measurements.
|
|
| 4. |
- Blanchfield, Kate, 1986-
(author)
-
Geometry and foundations of quantum mechanics
- 2014
-
Doctoral thesis (other academic/artistic)abstract
- This thesis explores three notions in the foundations of quantum mechanics: mutually unbiased bases (MUBs), symmetric informationally-complete positive operator valued measures (SICs) and contextuality. MUBs and SICs are sets of vectors corresponding to special measurements in quantum mechanics, but there is no proof of their existence in all dimensions. We look at the MUB constructions by Ivanović and Alltop in prime dimensions and highlight the important role played by the Weyl-Heisenberg and Clifford groups. We investigate how these MUBs are related, first invoking the third level of the Clifford hierarchy and then examining their geometrical features in probability simplices and Grassmannian spaces. There is a special connection between SICs and elliptic curves in dimension three, known as the Hesse configuration, which we discuss before looking for higher dimensional generalisations. Contextuality is introduced in relation to hidden variable models, where sets of vectors show the impossibility of assigning non-contextual outcomes to their corresponding measurements in advance. We remark on geometrical properties of these sets, which sometimes include MUBs and SICs, before constructing inequalities that can experimentally rule out non-contextual hidden variable models. Along the way, we look at affine planes, group theory and quantum computing.
|
|
| 5. |
- Dumitru, Irina, 1989-
(author)
-
Studies in the Geometry of Quantum Measurements
- 2020
-
Doctoral thesis (other academic/artistic)abstract
- Quantum information studies quantum systems from the perspective of information theory: how much information can be stored in them, how much the information can be compressed, how it can be transmitted. Symmetric informationally-Complete POVMs are measurements that are well-suited for reading out the information in a system; they can be used to reconstruct the state of a quantum system without ambiguity and with minimum redundancy. It is not known whether such measurements can be constructed for systems of any finite dimension. Here, dimension refers to the dimension of the Hilbert space where the state of the system belongs.This thesis introduces the notion of alignment, a relation between a symmetric informationally-complete POVM in dimension d and one in dimension d(d-2), thus contributing towards the search for these measurements. Chapter 2 and the attached papers I and II also explore the geometric properties and symmetries of aligned symmetric informationally-complete POVMs.Chapter 3 and the attached papers III and IV look at an application of symmetric informationally-complete POVMs, the so-called Elegant Bell inequality. We use this inequality for device-independent quantum certification, the task of characterizing quantum scenarios without modelling the devices involved in these scenarios. Bell inequalities are functions that are bound in classical theories more tightly than in quantum theories, and can thus be used to probe whether a system is quantum. We characterize all scenarios in which the Elegant Bell inequality reaches its maximum quantum value. In addition, we show that this inequality can be used for randomness certification.
|
|
| 6. |
- Fragkos, Vasileios, 1992-
(author)
-
Quest for quantum signatures in Axion Dark Matter and Gravity
- 2022
-
Licentiate thesis (other academic/artistic)abstract
- This licentiate thesis in theoretical physics focuses on the existence of quantum features in physical systems such as axion dark matter and gravity. Our focus is mostly on effects which appear at low energies, a regime in which our models can be confronted with current experiments or within the foreseeable future.In our first project, we focus on squeezing of axion dark matter, a quantum mechanical effect which accompanies the standard mean field description of axions. We have showed that within a reasonable set of assumptions, the quantum state of axions is highly squeezed. This theoretical finding suggests that the mean field description of axion dark matter is incomplete, since the latter conceals many interesting and possibly experimentally relevant phenomena, and paves the way for axion dark matter studies beyond the mean field approximation. Moreover, in this thesis, some ongoing work on axion dark matter decoherence is presented. Our goal is to test whether axion dark matter squeezing is robust against decoherence. Preliminary results indicate that squeezing is not diminished in presence of environmental interactions. Our results stem from an interdisciplinary approach at the intersection between cosmology, quantum optics, quantum open systems and cold atoms.Our second work focuses on quantum features of gravity. An almost century old question is how gravity can be reconciled with the laws of quantum mechanics. This question remains still open and part of the reason is the lack of experimental evidence. However, in recent years, the rapid progress of experimental techniques allows for quantum control and manipulation of larger and larger quantum systems. These new experimental routes have sparkled an interest in testing such fundamental questions with tabletop experiments. One particularly interesting proposal aims to test whether gravity can mediate entanglement between two spatially superposed mesoscopic masses. This proposal, in order to deduce the existence of quantized gravitational mediators, relies on a quantum-information-theoretic argument, the so-called LOCC (Local Operations and Classical Communication). In our work, we critically assess this proposal, its underlying assumptions and what teaches about quantum gravity. We conclude that the LOCC argument is not useful and by invoking it, one cannot unambiguously infer the existence of quantum mediators unless the principle oflocality is elevated to a fundamental principle of nature. We support our claim by explicitly showing that well known relativistic field theories, apart from local formulations can also admit non-local ones. Therefore, the entanglement generating quantum channel can be either local or non-local.
|
|
| 7. |
- Jakobsson, Emma, 1985-
(author)
-
Shapes of Spacetimes : Collected tales of black holes
- 2017
-
Doctoral thesis (other academic/artistic)abstract
- In theory, the existence of black holes is predicted by general relativity. In reality, there is a general consensus that they exist in space; in particular at the center of many galaxies. The theory of black holes has been around for decades, but there are still interesting questions calling for attention. This doctoral thesis and its four contributions touches upon some of these questions.One challenging theoretical aspect of black holes lies in their definition, the event horizon. For several reasons, this definition is not satisfactory in many contexts, and alternative horizons based on the concept of trapped surfaces have been suggested to take its place. The question raised in Paper I has to do with the location of such surfaces in a simple model of gravitational collapse, the Oppenheimer-Snyder model.A different scenario of gravitational collapse, that of a null shell of dust collapsing in flat spacetime, is the starting point of the original formulation of the Penrose inequality. By a reformulation, this inequality can be turned into a purely geometric relation in Minkowski space. In Paper IV we formulate and prove a (2+1)-dimensional version in anti-de Sitter space.The Penrose inequality sometimes goes under the name of the "isoperimetric inequality for black holes". In Paper III a different kind of isoperimetric inequality is discussed (with less rigour), namely that of the volume contained in a black hole with a given area.In Paper II, the subject of limits of spacetimes is visualized. Again, (2+1)-dimensional anti-de Sitter space finds its use, as a one parameter family of surfaces, capturing the geometry of charged black hole spacetimes, is embedded in it. Thus different limiting procedures are illustrated.Finally, interesting models can be constructed by cutting and gluing in spacetimes, but in doing so one needs to take care, in order to obtain a physically realistic model. With this background as motivation, a study of Lorentzian cones is given.Taken together, all of these contributions make up a collection of interesting aspects of black hole geometry, or, shapes of spacetimes.
|
|
| 8. |
- Pidokrajt, Narit, 1979-
(author)
-
Information geometries in black hole physics
- 2009
-
Doctoral thesis (other academic/artistic)abstract
- In this thesis we aim to develop new perspectives on the statistical mechanics of black holes using an information geometric approach (Ruppeiner and Weinhold geometry). The Ruppeiner metric is defined as a Hessian matrix on a Gibbs surface, and provides a geometric description of thermodynamic systems in equilibrium. This Ruppeiner geometry exhibits physically suggestive features; a flat Ruppeiner metric for systems with no interactions i.e. the ideal gas, and curvature singularities signaling critical behavior(s) of the system. We construct a flatness theorem based on the scaling property of the black holes, which proves to be useful in many cases. Another thermodynamic geometry known as the Weinhold geometry is defined as the Hessian of internal energy and is conformally related to the Ruppeiner metric with the system’s temperature as a conformal factor. We investigate a number of black hole families in various gravity theories. Our findings are briefly summarized as follows: the Reissner-Nordström type, the Einstein-Maxwell-dilaton andBTZ black holes have flat Ruppeiner metrics that can be represented by a unique state space diagram. We conjecture that the state space diagram encodes extremality properties of the black hole solution. The Kerr type black holes have curved Ruppeiner metrics whose curvature singularities are meaningful in five dimensions and higher, signifying the onset of thermodynamic instabilities of the black hole in higher dimensions. All the three-parameter black hole families in our study have non-flat Ruppeiner and Weinhold metrics and their associated curvature singularities occur in the extremal limits. We also study two-dimensional black hole families whose thermodynamic geometries are dependent on parameters that determine the thermodynamics of the black hole in question. The tidal charged black hole which arises in the braneworld gravity is studied. Despite its similarity to the Reissner-Nordström type, its thermodynamic geometries are distinctive.
|
|
| 9. |
- Smania, Massimiliano, 1990-
(author)
-
Bell tests and the no-signalling assumption
- 2018
-
Licentiate thesis (other academic/artistic)abstract
- Bell's theorem was originally meant for testing fundamental properties of Nature, namely local realism. However, through the years it has become a powerful device for certifying encryption security, randomness, and entanglement among other properties. Especially after the series of loophole-free violation papers at the end of 2015, these applications are becoming more and more relevant. In most of these scenarios, additional assumptions - as fair-sampling - are set forth in order to achieve the required near-optimal violations. However, it turns out that many of the experiments realised so far suffer from apparent signalling. We say “apparent” because we do not believe that the issue comes from actual communication between different measurement stations, but rather, as we show in this work, from systematic issues related to the particular experimental realisation.After making a point for the importance of correcting these errors, we identify and address some of the most common sources of signalling in a set of experiments based on single photon polarisation qubits. Finally, we report a reliable CHSH violation which is free from apparent signalling.While the core results are contained in the attached Paper I, we first provide the reader with a brief introduction to the concepts involved in this work, in addition to supplementary unpublished experimental work.
|
|
| 10. |
- Dumitru, Irina, 1989-
(author)
-
Exploring the Elegant Bell Inequality
- 2017
-
Licentiate thesis (other academic/artistic)abstract
- In quantum information, device independent certification is a matter of both practical and fundamental interest. In this thesis, we explore the use of a particular Bell inequality, known as the elegant Bell inequality, in device independent certification. We first characterize all states and measurements that can lead to a maximal violation of the elegant Bell inequality. It turns out that, in all cases, the state involved in a maximal violation is a generalized singlet state, and the measurements of one of the parties are always maximally spread out on the Bloch sphere, forming a complete set of mutually unbiased bases. The measurements involved on the other party form two pairs of symmetric informationally complete vectors. The elegant Bell inequality, then, can be used to certify the presence of these elements.We also explore the usefulness of the elegant Bell inequality in randomness certification, in particular in a protocol for certification of maximal randomness from one entangled bit.The last part of this thesis is dedicated to a study of some of the special geometricstructures involved in the maximal violation of the elegant Bell inequality, namely the symmetric informationally complete vectors. The problem of the existence and of the construction of these sets of vectors in Hilbert spaces of any dimension is open, but there are solutions available in many dimensions. We look at these structures from both a geometric and an algebraic number theory perspective, and conjecture a relation between vectors in different dimensions. We introduce the relation of "alignment" between such sets of vectors.
|
|
