Quantum information processors have the ability to drastically change our world. By manipulating bits of information ruled by the laws of quantum mechanics, computational devices can perform some computations that are classically intractable. Most quantum algorithms rely on pure qubits as inputs and require entanglement throughout the computation. In this thesis, we explore a model of computation that uses mixed qubits without entanglement known as DQC1 (deterministic quantum computation with one quantum bit), using the physical system of liquid-state Nuclear Magnetic Resonance (NMR). Throughout our research, we experimentally implement an algorithm that completely encapsulates the DQC1 model, and take a close look at the quantum nature of DQC1-states as given by the quantum discord and geometric quantum discord, which are measures of non-classicality that capture correlations weaker than those measured by entanglement. We experimentally detect and quantify these correlations in an NMR DQC1 quantum information processor.

Quantum information processors have the ability to drastically change our world. By manipulating bits of information ruled by the laws of quantum mechanics, computational devices can perform some computations that are classically intractable. Most quantum algorithms rely on pure qubits as inputs and require entanglement throughout the computation. In this thesis, we explore a model of computation that uses mixed qubits without entanglement known as DQC1 (deterministic quantum computation with one quantum bit), using the physical system of liquid-state Nuclear Magnetic Resonance (NMR). Throughout our research, we experimentally implement an algorithm that completely encapsulates the DQC1 model, and take a close look at the quantum nature of DQC1-states as given by the quantum discord and geometric quantum discord, which are measures of non-classicality that capture correlations weaker than those measured by entanglement. We experimentally detect and quantify these correlations in an NMR DQC1 quantum information processor.

This thesis explores the role of non-classical correlations in bipartite continuous variable quantum systems, and the approach taken is three-fold. We show that given two initially entangled atomic ensembles, it is possible to probabilistically increase the entanglement between them using a beamsplitter-like interaction formed from two quantum non-demolition (QND) interactions with auxiliary polarised light modes. We then develop an elegant method to calculate density matrix elements of non-Gaussian bipartite quantum states and use this to show that the entanglement in a two mode squeezed vacuum can be distilled using QND interactions and non-Gaussian elements. Secondly, we introduce a potential new measure of quantum entanglement in bipartite Gaussian states. This measure has an operational meaning in quantum cryptography and provides an upper bound on the amount of a secret key that can be distilled from a Gaussian probability distribution shared by two conspirators, Alice and Bob, given the presence of an eavesdropper, Eve. Finally, we go beyond the realm of quantum entanglement to explore other non-classical correlations in continuous variable systems. We provide solutions for a number of these measures on two mode Gaussian states and introduce the Gaussian Ameliorated Measurement Induced Disturbance (GAMID). The interplay between these different measures and quantum entanglement is examined. We then attempt to take small steps into the non-Gaussian regime by computing these non-classicality measures on the three-parameter continuous variable Werner states.

Correlations and entanglement in a chain of three oscillators A,B,C with nearest neighbour coupling is studied. Oscillators A,B and B,C are coupled but there is no direct coupling between oscillators A,C. Examples with initial factorizable states are considered, and the time evolution is calculated. It is shown that the dynamics of the tri-partite system creates correlations and entanglement among the three oscillators and in particular, between oscillators A,C which are not coupled directly. We have performed photon number selective and non-selective measurements on oscillator A and we investigated their effects on the correlations and entanglement. It is shown that, before the measurement, the correlations between oscillators A,C can be stronger than the correlations of oscillators A,B. Moreover, some entanglement witness shows that oscillators A,C are entangled but the oscillators A,B might or might not be entangled. By using quantum discord, which measures the quantumness of correlations, it is shown that there are quantum correlations between oscillators A,B and after the measurements in both cases of selective and non-selective measurements, oscillators A,B and A,C become classically correlated.

In this thesis, I study bipartite discord between A and B in terms of the structure formed by the bipartite and tripartite entanglement found in the purified system ABC. I find that discord manifests itself only when there is both tripartite and bipartite entanglement present in the purification. This allows one to understand the asymmetry of quantum discord, D(A|B) ≠ D(B|A) in terms of entanglement monogamy. For the cases where AB has rank two and for two-mode Gaussian states, I find that discord also necessarily appears whenever there is tripartite and bipartite entanglement in ABC. As a result of this, some light is shed on a counter-intuitive property of Gaussian states: the presence of classical correlations necessarily requires the presence of quantum discord. Finally, these results are found to be closely linked to the protocol for remote activation of entanglement by a third party.

Conflict and agriculture have a long, shared history. The purpose of this research is to look at the relationships between agriculture, agricultural technologies, and conflict during current and recent conflicts, large scale and localized. Agriculture and its related technologies are often affected by conflict, but rarely acknowledged as a cause or solution to conflict. Literature reviews in six topic areas illustrate various facets of the relationship between agriculture and conflict. Research conducted in Santa Cruz del Quiché, Guatemala illustrates the ways farmers were impacted by the country’s civil war. It also examines farmer survival strategies during the war, and reveals the presence of minor localized conflict over water resources. Conflict over land is not a major concern at present. Market access for inputs and outputs are shown to have been a problem for a number of farmers during the civil war. The poverty of Santa Cruz farmers indicates that much could be gained by rural development. Research is unable to support the hypotheses that agricultural technologies have prevented or caused conflict in Santa Cruz del Quiché, or that they have played a large role in recovery from the country’s civil war. The author recommends that future research be undertaken in regions with a diverse set of agricultural technologies, and/or a recent history of significant technological change in agriculture. Policy recommendations include providing secure access to markets during war time, increasing capacity for home-based rural production, and continuing research into resilient crops. Finally, the author suggests that the responsible decision to develop, adopt, or introduce an agricultural technology must take into account the social consequences of that decision, including how the new technology may alleviate or contribute to conflict.

This study examined issues of measurement equivalence in a cross-national study using the Marital Satisfaction Inventory-Revised (MSI-R). Overall findings supported cross-cultural similarities across the Spain, Germany, Korea, and the U.S. standardization samples. The Spanish, German, and Korean translations of the MSI-R demonstrated moderate to strong internal consistency, inter-scale correlations, and discriminative validity overall. Confirmatory factor analyses revealed configural and metric invariance across the original measure and the German, Spanish, and Korean translations. Mean profile comparisons between the current German, Spanish, and Korean samples and the original standardization sample revealed significant differences on several scales. Test characteristic similarities between the U.S. and the Spanish, German, and Korean clinical samples suggest the clinical utility of the MSI-R for identifying couples for secondary prevention or intervention protocols, and treatment planning in Spain, Germany, and Korea. Implications for cross-national clinical and research applications of the MSI-R are discussed.

In this thesis, I study bipartite discord between A and B in terms of the structure formed by the bipartite and tripartite entanglement found in the purified system ABC. I find that discord manifests itself only when there is both tripartite and bipartite entanglement present in the purification. This allows one to understand the asymmetry of quantum discord, D(A|B) ≠ D(B|A) in terms of entanglement monogamy. For the cases where AB has rank two and for two-mode Gaussian states, I find that discord also necessarily appears whenever there is tripartite and bipartite entanglement in ABC. As a result of this, some light is shed on a counter-intuitive property of Gaussian states: the presence of classical correlations necessarily requires the presence of quantum discord. Finally, these results are found to be closely linked to the protocol for remote activation of entanglement by a third party.

Doctor en Ciencias, Mención Computación / Este trabajo de tesis presenta soluciones para al problema de detección de anomalı́as en flujo de datos multivariantes. Dado una subsequencia de serie temporal (una pequeña parte de la serie original) como entrada, uno quiere conocer si este corresponde a una observación normal o es una anomalı́a, con respecto a la información histórica. Pueden surgir dificultades debido principalmente a que los tipos de anomalı́a son desconocidos. Además, la detección se convierte en una tarea costosa debido a la gran cantidad de datos y a la existencia de variables de dominios heterogéneos. En este contexto, se propone un enfoque de detección de anomalı́as basado en Discord Discovery, que asocia la anomalı́a con la subsecuencia más inusual utilizando medidas de similitud. Tı́picamente, los métodos de reducción de la dimensionalidad y de indexación son elaborados para restringir el problema resolviéndolo eficientemente. Adicionalmente, se propone técnicas para generar modelos representativos y consisos a partir de los datos crudos con el fin de encontrar los patrones inusuales. Estas técnicas también mejoran la eficiencia en la búsqueda mediante la reducción de la dimensionalidad. Se aborda las series multivariantes usando técnicas de representación sobre subsequencias no- normalizadas, y se propone nuevas técnicas de discord discovery basados en ı́ndices métricos. El enfoque propuesto es comparado con técnicas del estado del arte. Los resultados ex- perimentales demuestran que aplicando la transformación de translación y representación de series temporales pueden contribuir a mejorar la eficacia en la detección. Además, los métodos de indexación métrica y las heurı́sticas de discord discovery pueden resolver eficien- temente la detección de anomalı́as en modo offline y online en flujos de series temporales multivariantes. / Este trabajo ha sido financiado por beca CONICYT - CHILE / Doctorado para Extranjeros, y apoyada parcialmente por el Proyecto FONDEF D09I1185 y el Programa de Becas de NIC Chile

This thesis studies continuous variable mixed states with the aim of better understanding the fundamental behaviour of quantum correlations in such states, as well as searching for applications of these correlations. I first investigate the interesting phenomenon of discord increase under local loss and explain the behaviour by considering the non-orthogonality of quantum states. I then explore the counter-intuitive result where entanglement can be created by a passive optical beamsplitter, even if the input states are classical, as long as the input states are part of a larger globally nonclassical system. This result emphasises the importance of global correlations in a quantum state, and I propose an application of this protocol in the form of quantum dense coding. Finally, I develop a quantum digital signature protocol that can be described entirely using the continuous variable formalism. Quantum digital signatures provide a method to ensure the integrity and provenance of a message using quantum states. They follow a similar method to quantum key distribution (QKD), but require less post-processing, which means they can sometimes be implemented over channels that are inappropriate for QKD. The method I propose uses homodyne measurement to verify the signature, unlike previous protocols that use single photon detection. The single photon detection of previous methods is designed to give unambiguous results about the signature, but this comes at the cost of getting no information much of the time. Using homodyne detection has the advantage of giving results all the time, but this means that measurement results always have some ambiguity. I show that, even with this ambiguity, the signature protocol based on homodyne measurement outperforms previous protocols, with the advantage enhanced when technical considerations are included. Therefore this represents an interesting new direction in the search for a practical quantum digital signature scheme.