Integrated photonic 3D waveguide arrays for quantum random walks on a circle

Quantum random walks (QRWs) can be used to perform both quantum simulations and quantum algorithms. In order to exploit this potential, quantum walks on different types of graphs must be physically implemented. To this end we design, model and experimentally fabricate, using the femtosecond laser direct-write technique, a 3D tubular waveguide array within glass to implement a photonic quantum walk on a circle. The boundary conditions of a QRW on a circle naturally suggests a 3D waveguide implementation - allowing much simpler device design than what could be achieved using a 2D waveguide architecture. We show that, in some cases, three-dimensional photonic circuits can be more suited to the simulation of complex quantum phenomena.Comment: 78 pages including title page, abstract, and references. 41 figures. Honours thesi

A Critical Look at the Evaluation of Knowledge Graph Question Answering

PhD thesis in Information technologyThe field of information retrieval (IR) is concerned with systems that “make a given stored collection of information items available to a user population” [111]. The way in which information is made available to the user depends on the formulation of this broad concern of IR into specific tasks by which a system should address a user’s information need [85]. The specific IR task also dictates how the user may express their information need. The classic IR task is ad hoc retrieval, where the user issues a query to the system and gets in return a list of documents ranked by estimated relevance of each document to the query [85]. However, it has long been acknowledged that users are often looking for answers to questions, rather than an entire document or ranked list of documents [17, 141]. Question answering (QA) is thus another IR task; it comes in many flavors, but overall consists of taking in a user’s natural language (NL) question and returning an answer. This thesis describes work done within the scope of the QA task. The flavor of QA called knowledge graph question answering (KGQA) is taken as the primary focus, which enables QA with factual questions against structured data in the form of a knowledge graph (KG). This means the KGQA system addresses a structured representation of knowledge rather than—as in other QA flavors—an unstructured prose context. KGs have the benefit that given some identified entities or predicates, all associated properties are available and relationships can be utilized. KGQA then enables users to access structured data using only NL questions and without requiring formal query language expertise. Even so, the construction of satisfactory KGQA systems remains a challenge. Machine learning with deep neural networks (DNNs) is a far more promising approach than manually engineering retrieval models [29, 56, 130]. The current era dominated by DNNs began with seminal work on computer vision, where the deep learning paradigm demonstrated its first cases of “superhuman” performance [32, 71]. Subsequent work in other applications has also demonstrated “superhuman” performance with DNNs [58, 87]. As a result of its early position and hence longer history as a leading application of deep learning, computer vision with DNNs has been bolstered with much work on different approaches towards augmenting [120] or synthesizing [94] additional training data. The difficulty with machine learning approaches to KGQA appears to rest in large part with the limited volume, quality, and variety of available datasets for this task. Compared to labeled image data for computer vision, the problems of data collection, augmentation, and synthesis are only to a limited extent solved for QA, and especially for KGQA. There are few datasets for KGQA overall, and little previous work that has found unsupervised or semi-supervised learning approaches to address the sparsity of data. Instead, neural network approaches to KGQA rely on either fully or weakly supervised learning [29]. We are thus concerned with neural models trained in a supervised setting to perform QA tasks, especially of the KGQA flavor. Given a clear task to delegate to a computational system, it seems clear that we want the task performed as well as possible. However, what methodological elements are important to ensure good system performance within the chosen scope? How should the quality of system performance be assessed? This thesis describes work done to address these overarching questions through a number of more specific research questions. Altogether, we designate the topic of this thesis as KGQA evaluation, which we address in a broad sense, encompassing four subtopics from (1) the impact on performance due to volume of training data provided and (2) the information leakage between training and test splits due to unhygienic data partitioning, through (3) the naturalness of NL questions resulting from a common approach for generating KGQA datasets, to (4) the axiomatic analysis and development of evaluation measures for a specific flavor of the KGQA task. Each of the four subtopics is informed by previous work, but we aim in this thesis to critically examine the assumptions of previous work to uncover, verify, or address weaknesses in current practices surrounding KGQA evaluation

An Ecosystem for Personal Knowledge Graphs: A Survey and Research Roadmap

This paper presents an ecosystem for personal knowledge graphs (PKG), commonly defined as resources of structured information about entities related to an individual, their attributes, and the relations between them. PKGs are a key enabler of secure and sophisticated personal data management and personalized services. However, there are challenges that need to be addressed before PKGs can achieve widespread adoption. One of the fundamental challenges is the very definition of what constitutes a PKG, as there are multiple interpretations of the term. We propose our own definition of a PKG, emphasizing the aspects of (1) data ownership by a single individual and (2) the delivery of personalized services as the primary purpose. We further argue that a holistic view of PKGs is needed to unlock their full potential, and propose a unified framework for PKGs, where the PKG is a part of a larger ecosystem with clear interfaces towards data services and data sources. A comprehensive survey and synthesis of existing work is conducted, with a mapping of the surveyed work into the proposed unified ecosystem. Finally, we identify open challenges and research opportunities for the ecosystem as a whole, as well as for the specific aspects of PKGs, which include population, representation and management, and utilization

Detecting Topological Entanglement Entropy in a Lattice of Quantum Harmonic Oscillators

The Kitaev surface-code model is the most studied example of a topologically ordered phase and typically involves four-spin interactions on a two-dimensional surface. A universal signature of this phase is topological entanglement entropy (TEE), but due to low signal to noise, it is extremely difficult to observe in these systems, and one usually resorts to measuring anyonic statistics of excitations or non-local string operators to reveal the order. We describe a continuous-variable analog to the surface code using quantum harmonic oscillators on a two-dimensional lattice, which has the distinctive property of needing only two-body nearest-neighbor interactions for its creation. Though such a model is gapless, satisfies an area law, and the ground state can be simply prepared by measurements on a finitely squeezed and gapped two-dimensional cluster state, which does not have topological order. Asymptotically, the TEE grows linearly with the squeezing parameter, and we show that its mixed-state generalization, the topological mutual information, is robust to some forms of state preparation error and can be detected simply using single-mode quadrature measurements. Finally, we discuss scalable implementation of these methods using optical and circuit-QED technology.Comment: 16 pages, 7 figures, added section about correlations length and study of the topological logarithmic negativity. Typos fixed. Comments welcom

Two-photon continuous-time quantum walk

1 page(s

Adiabatic transition from the cluster state to the surface code

"A thesis submitted to Macquarie University for the degree of Master of Philosophy""December 2012"Typeset in Latex2e (LaTeX2ε).Bibliography: pages 111-116.1. Introduction -- 2. Topological phases and the qubit toric code -- 3. Cluster states -- 4. Adiabatic evolution -- 5. Mapping qubit cluster states to the planar surface code -- 6. Quadratic interactions of quantum harmonic oscillators -- 7. Mapping continuous variable cluster states to the planar surface code -- 8. Implementation platform: circuit quantum electrodynamics -- 9. ConclusionThis project studies two different quantum phases of matter and how to design systems that adiabatically connect one phase with another. One phase corresponds to a cluster state which is a resource state for measurement-based quantum computation, and the other is a surface code which is a robust way to store quantum memory. Both phases are ground states of strongly correlated two-dimensional lattices of quantum systems, either two-level systems (qubits, fermions) or infinite-dimensional, continuous-variable (CV) systems (quantum modes, bosons), and both phases are gapped. However. the surface code has a special kind of non-local order, termed topological order, while the cluster phase does not. A key advantage of the cluster phase is that it can be relatively easily prepared in experiment using a constant depth circuit acting on an initially unentangled state. The surface code, in contrast, requires a number of preparation steps that scales with the system size; a consequence of the long range topological order in this phase.Remarkably, it has been shown that the surface code can be prepared from the cluster phase simply by performing a pattern of commuting single site measurements on the lattice. However, for any outcome of measurements, it is necessary to perform a set of corrections to the state such that the total preparation time is still extensive. The focus of this thesis is how to smoothly perform the entire preparation procedure for the surface code by deforming a Hamiltonian which encodes the state in the ground state. This avoids measurement altogether and moreover has the advantage that for CV systems the Hamiltonian involves only two-body near-neighbour interactions rather than the four-body interactions that are required in a spin encoding.In this thesis, we study a smooth, adiabatic transition from the cluster state to the surface code. We do this in a series of steps: We first consider the adiabatic evolution of a single qubit and a single qumode. We also calculate the iterative, discrete time step approximation of the continuous adiabatic evolution of states in the qubit case, and begin the work toward the adiabatic evolution of CV operators by first considering a single qumode transition Hamiltonian. Then we study the spectrum of au adiabatic transition from a bosonic CV cluster state Hamiltonian to a CV planar surface code Hamiltonian. In particular, we track the energy gap between the ground and first excited state during the transition.Mode of access: World wide web1 online resource (xviii, 116 pages) illustrations (some colour

Would You Ask it that Way? Measuring and Improving Question Naturalness for Knowledge Graph Question Answering

Knowledge graph question answering (KGQA) facilitates information access by leveraging structured data without requiring formal query language expertise from the user. Instead, users can express their information needs by simply asking their questions in natural language (NL). Datasets used to train KGQA models that would provide such a service are expensive to construct, both in terms of expert and crowdsourced labor. Typically, crowdsourced labor is used to improve template-based pseudo-natural questions generated from formal queries. However, the resulting datasets often fall short of representing genuinely natural and fluent language. In the present work, we investigate ways to characterize and remedy these shortcomings. We create the IQN-KGQA test collection by sampling questions from existing KGQA datasets and evaluating them with regards to five different aspects of naturalness. Then, the questions are rewritten to improve their fluency. Finally, the performance of existing KGQA models is compared on the original and rewritten versions of the NL questions. We find that some KGQA systems fare worse when presented with more realistic formulations of NL questions. The IQN-KGQA test collection is a resource to help evaluate KGQA systems in a more realistic setting. The construction of this test collection also sheds light on the challenges of constructing large-scale KGQA datasets with genuinely NL questions.Comment: 9 pages, 3 figures. Accepted for publication as a resource paper in Proceedings of the 45th International ACM SIGIR Conference on Research and Development in Information Retrieval (SIGIR '22), July 11-15, 2022, Madrid, Spain. For test collection, see https://github.com/iai-group/IQN-KGQ

Miljøgifter i restprodukter fra fiskeoljeindustrien. Vurderinger ved bruk i biogassanlegg

Restprodukter fra fiskeoljeindustrien som bleikejord og sape inneholder en lang rekke organiske miljogifter (POP) som brytes langsomt ned i naturen, akkumulerer i marine og terrestriske naringskjeder og er giftige. I denne rapporten gis en sammenstilling av analyser av sape, bleikejord og fiskeolje fra fiskeoljeindustrien. Resultatene brukes til a beregne konsentrasjoner i biorest hvor slike restprodukter brukes. Videre gis en vurdering av miljokonsekvensene ved bruk av denne bioresten pa dyrket jord.publishedVersio

Smart-sustainability:A new urban fix?

Urban policy increasingly positions smart urban development as a transformative approach to deliver sustainability. In this paper, we question the transformative credentials of smartness and argue that it is better understood as a partial fix for the economic, environmental and social challenges faced by cities. Drawing on the urban sustainability and smart city literatures, we develop the concept of the urban smart-sustainability fix. This concept focuses on how smart-sustainable city initiatives selectively integrate digital and environmental agendas via entrepreneurial forms of urban governance. We develop this concept by examining how the urban smart-sustainability fix is constructed in the European Commission's flagship smart cities and communities lighthouse projects, focusing on the Triangulum initiative. Our research reveals three elements of the urban smart-sustainability fix: (1) the spatial development of smart-sustainable districts; (2) the digitisation of urban infrastructure to reveal hidden processes; and, (3) collaborative experimentation with low-carbon and digital technologies. We argue that this has produced urban districts that are attempting to reduce their carbon emissions while promoting green economic growth. The main aim of the urban smart-sustainability fix is to make the urban realm more manageable resulting in amplification, rather than transformation, of the dominant ecological modernisation agenda of sustainable development