Theory of filtered type-II PDC in the continuous-variable domain: Quantifying the impacts of filtering

Parametric down-conversion (PDC) forms one of the basic building blocks for quantum optical experiments. However, the intrinsic multimode spectral-temporal structure of pulsed PDC often poses a severe hindrance for the direct implementation of the heralding of pure single-photon states or, for example, continuous-variable entanglement distillation experiments. To get rid of multimode effects narrowband frequency filtering is frequently applied to achieve a single-mode behavior. A rigorous theoretical description to accurately describe the effects of filtering on PDC, however, is still missing. To date, the theoretical models of filtered PDC are rooted in the discrete-variable domain and only account for filtering in the low gain regime, where only a few photon pairs are emitted at any single point in time. In this paper we extend these theoretical descriptions and put forward a simple model, which is able to accurately describe the effects of filtering on PDC in the continuous-variable domain. This developed straightforward theoretical framework enables us to accurately quantify the trade-off between suppression of higher-order modes, reduced purity and lowered Einstein-Podolsky-Rosen (EPR) entanglement, when narrowband filters are applied to multimode type-II PDC.Comment: 15 pages, 13 figure

Three-dimensional hybrid vortex solitons

We show, by means of numerical and analytical methods, that media with a repulsive nonlinearity which grows from the center to the periphery support a remarkable variety of previously unknown complex stationary and dynamical three-dimensional solitary-wave states. Peanut-shaped modulation profiles give rise to vertically symmetric and antisymmetric vortex states, and novel stationary hybrid states, built of top and bottom vortices with opposite topological charges, as well as robust dynamical hybrids, which feature stable precession of a vortex on top of a zero-vorticity base. The analysis reveals stability regions for symmetric, antisymmetric, and hybrid states. In addition, bead-shaped modulation profiles give rise to the first example of exact analytical solutions for stable three-dimensional vortex solitons. The predicted states may be realized in media with a controllable cubic nonlinearity, such as Bose-Einstein condensates.Comment: To appear in the New Journal of Physic

Increasing knowledge-intensity and complexity :nanotechnology and the future of public participation and policy making

PhD ThesisIn recent years, both policy-makers and politicians have been confronted with increasing obstacles towards the interpretation, usage, prediction and application of data, information and of knowledge. This has often resulted in surprises, for instance, as predicted outcomes of introduced policy changes, either did not take effect or simply took on other forms that were not desired. Added to that, new developments and advances in a number of key technological areas have led to the emergence of new knowledge-intensive and technologically-complex disciplines, such as Nanotechnology, Genetic Engineering or Synthetic Biology. The complexity that is inherent in any of these new disciplines poses new challenges to both policy-making and public participation. This thesis focuses on the question of whether increasing complexity and knowledge-intensity that follow current and future technological developments will lead to a decrease in both the public’s interests and ability to participate in the public debate. In addition, this thesis will investigate how policy recommendations are affected when the dependency on expertise, which is due to the inherent knowledge-intensity of these new disciplines, is on the rise. Nanotechnology has been chosen as an example case of one of these new knowledge-intensive and technologically-complex disciplines. By developing and employing a knowledge framework that is based on a practical approach to distinguishing various types of knowledge; public and expert opinions as well as policy recommendations will be analysed in order to determine whether a new approach for involving the public and for the future of policy recommendation is required. Furthermore, by applying this knowledge framework to three selected theories of policy process, special emphasis is placed on the applicability of different types of knowledge and information in policy contexts. An additional aim is to assess the use of terms, such as information and knowledge, in the policy sciences. Using these different types of knowledge, for instance, by making a deliberate distinction between knowledge by acquaintance and knowledge by description, or between tacit knowledge and explicit knowledge, allows identifying what can be known by whom, and thus will shed new light on both policy recommendations and on what can be expected from the public’s involvement in the future. This thesis will suggest that when dealing with knowledge-intensive and technologically-complex disciplines, the importance of acknowledging different types of knowledge is a prerequisite for improving the quality of policy-making, policy recommendations as well as public engagement. Also, a case will be made against a generic use of the terms knowledge and information in policy literature. As much as policy information does not equal any generic type of information, lacking specificity with regards to information and knowledge in the theories of policy may invalidate or at least challenge some claims made policy scientists, as expected outcomes that apply to one particular type of information may not automatically apply to another

Increasing knowledge-intensity and complexity : nanotechnology and the future of public participation and policy making

In recent years, both policy-makers and politicians have been confronted with increasing obstacles towards the interpretation, usage, prediction and application of data, information and of knowledge. This has often resulted in surprises, for instance, as predicted outcomes of introduced policy changes, either did not take effect or simply took on other forms that were not desired. Added to that, new developments and advances in a number of key technological areas have led to the emergence of new knowledge-intensive and technologically-complex disciplines, such as Nanotechnology, Genetic Engineering or Synthetic Biology. The complexity that is inherent in any of these new disciplines poses new challenges to both policy-making and public participation. This thesis focuses on the question of whether increasing complexity and knowledge-intensity that follow current and future technological developments will lead to a decrease in both the public’s interests and ability to participate in the public debate. In addition, this thesis will investigate how policy recommendations are affected when the dependency on expertise, which is due to the inherent knowledge-intensity of these new disciplines, is on the rise. Nanotechnology has been chosen as an example case of one of these new knowledge-intensive and technologically-complex disciplines. By developing and employing a knowledge framework that is based on a practical approach to distinguishing various types of knowledge; public and expert opinions as well as policy recommendations will be analysed in order to determine whether a new approach for involving the public and for the future of policy recommendation is required. Furthermore, by applying this knowledge framework to three selected theories of policy process, special emphasis is placed on the applicability of different types of knowledge and information in policy contexts. An additional aim is to assess the use of terms, such as information and knowledge, in the policy sciences. Using these different types of knowledge, for instance, by making a deliberate distinction between knowledge by acquaintance and knowledge by description, or between tacit knowledge and explicit knowledge, allows identifying what can be known by whom, and thus will shed new light on both policy recommendations and on what can be expected from the public’s involvement in the future. This thesis will suggest that when dealing with knowledge-intensive and technologically-complex disciplines, the importance of acknowledging different types of knowledge is a prerequisite for improving the quality of policy-making, policy recommendations as well as public engagement. Also, a case will be made against a generic use of the terms knowledge and information in policy literature. As much as policy information does not equal any generic type of information, lacking specificity with regards to information and knowledge in the theories of policy may invalidate or at least challenge some claims made policy scientists, as expected outcomes that apply to one particular type of information may not automatically apply to another.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Accelerating the analysis of optical quantum systems using the Koopman operator

The prediction of photon echoes is an important technique for gaining an understanding of optical quantum systems. However, this requires a large number of simulations with varying parameters and/or input pulses, which renders numerical studies expensive. This article investigates how we can use data-driven surrogate models based on the Koopman operator to accelerate this process. In order to be successful, we require a model that is accurate over a large number of time steps. To this end, we employ a bilinear Koopman model using extended dynamic mode decomposition and simulate the optical Bloch equations for an ensemble of inhomogeneously broadened two-level systems. Such systems are well suited to describe the excitation of excitonic resonances in semiconductor nanostructures, for example, ensembles of semiconductor quantum dots. We perform a detailed study on the required number of system simulations such that the resulting data-driven Koopman model is sufficiently accurate for a wide range of parameter settings. We analyze the L2 error and the relative error of the photon echo peak and investigate how the control positions relate to the stabilization. After proper training, the dynamics of the quantum ensemble can be predicted accurately and numerically very efficiently by our methods