Optimized state independent entanglement detection based on geometrical threshold criterion

Experimental procedures are presented for the rapid detection of entanglement of unknown arbitrary quantum states. The methods are based on the entanglement criterion using accessible correlations and the principle of correlation complementarity. Our first scheme essentially establishes the Schmidt decomposition for pure states, with few measurements only and without the need for shared reference frames. The second scheme employs a decision tree to speed up entanglement detection. We analyze the performance of the methods using numerical simulations and verify them experimentally for various states of two, three and four qubits.Comment: 13 pages, 12 figure

An Improved Experiment to Determine the `Past of a Particle' in the Nested Mach-Zehnder Interferometer

We argue that the modification proposed by Li et al. [Chin. Phys. Lett. 32, 050303 (2015)] to the experiment of Danan et al. [Phys. Rev. Lett. 111, 240402 (2013)] does not test the past of the photon as characterised by local weak traces. Instead of answering the questions: (i) Were the photons in A? (ii) Were the photons in B? (iii) Were the photons in C? the proposed experiment measures a degenerate operator answering the questions: (i) Were the photons in A? (ii) Were the photons in B and C together? A negative answer to the last question does not tell us if photons were present in B or C. A simple variation of the modified experiment does provide good evidence for the past of the photon in agreement with the results Danan et al. obtained.Comment: 3 pages, accepted for publication in Chinese Physics Letter

Systematic errors in current quantum state tomography tools

Common tools for obtaining physical density matrices in experimental quantum state tomography are shown here to cause systematic errors. For example, using maximum likelihood or least squares optimization for state reconstruction, we observe a systematic underestimation of the fidelity and an overestimation of entanglement. A solution for this problem can be achieved by a linear evaluation of the data yielding reliable and computational simple bounds including error bars.Comment: 8 pages, 8 figure

Genuine multipartite entanglement without multipartite correlations

Physical Review Letters1141818050

Developing Countries and the Global Dairy Sector Part I Global Overview

Globally, the dairy sector is probably one of the most distorted agricultural sectors: producer subsidies are in place in many developed countries, encouraging surplus production, export subsidies are paid by governments to place the excess production on the world markets, and tariff and non-tariff barriers are erected both by developed and developing countries to protect their dairy sector from 'unfair' competition. These market distortions are having significant and different impacts on producers and consumers in developing and developed countries, which are however extremely difficult to quantify. This paper is the first volume of a study on the impacts of global dairy trade on developing countries, giving an overview of global dairy production, consumption, industry structure, trade, applied policies and international standards. Different developments are occurring in the global dairy sector at the moment: Production in developed countries is falling (together with the number of dairy cows and farms), while productivity is rising. Simultaneously milk production in developing countries is growing strongly and numbers of cows are increasing. This development is mirrored in consumption. Dairy consumption levels in developed countries are constant or falling, whereas in many developing countries, foremost in East and Southeast Asia and driven by population growth and growing per capita incomes, dairy consumption is rapidly increasing. With consumer demand in developing countries rising faster than domestic production, global dairy trade volumes are increasing as well with import demand of developing countries being the major driver. In the second volume of the study, the dairy sectors of six developing countries (Bangladesh, Jamaica, Peru, Senegal, Tanzania and Thailand) will be analyzed in order to identify the impacts of (subsidized) milk powder imports on milk producers and consumers.Livestock Production/Industries,

Practices and values regarding milk consumption among pre-schoolers in Bangkok

Purpose: Thai government agencies and the business sector have been promoting milk consumption. Considering the robust and continual movements by those actors to promote milk consumption among children in Thailand at the national level, this study aims to investigate milk-consumption practices and values towards milk consumption at pre-school, family and individual levels. Methods: This cross-sectional qualitative study employs observation and interview methods, along with the Ecological System Theory as a framework. Data were collected from three kindergartens used by families of varying socio-economic status, and the homes of 18 pre-schoolers, aged 3-5 years old, attending these kindergartens, from October 2013-September 2014. Results: Findings reveal kindergartens implemented daily routines to make children drink milk. Practices at home include (i) overfeeding of milk, (ii) preference for fortified milk and (iii) using sweetness to make children drink milk. These practices were underpinned by values that milk is good for children and good parents feed their children milk. These values, in combination with other macro-level measures such as the government’s milk-promotion campaigns and the milk industry’s marketing, influence the milk-drinking practices of pre-schoolers. Conclusion: The promotion of the benefits of milk prompted children to exceed the recommended milk consumption of 400ml per day. Balanced information on moderation in milk drinking was absent

Efficient quantum state analysis and entanglement detection

Entanglement is one of the most fascinating features of quantum theory, as it fundamentally distinguishes quantum systems from classical systems. It not only might play a role in natural processes, but provides an especially powerful resource for a plethora of quantum information protocols, including quantum state teleportation, superdense coding as well as quantum computation schemes. However, for larger systems involving more than two parties, it is a challenging task to verify and characterize entanglement. In this thesis, efficient means for detecting genuine multipartite entanglement in multiqubit quantum systems will be derived, demonstrated, and discussed. Beyond that, methods for quantum state and process tomography will be introduced, which allow to analyze and investigate prepared multipartite states or even the performance of whole setups. Some typical obstacles for reliable state tomography will be pointed out, together with new means to understand experimentally obtained data. Finally, the measurement problem, which describes the unavoidable backaction of a measurement process to the quantum state under investigation, will be illustrated. Together with the discussion of different methods of quantum measurements, the optimal measurement instruments for binary qubit measurements will be derived. These optimal measurement instruments allow to perform a quantum measurement, providing a tunable amount of information about the quantum state, while avoiding any unnecessary disturbance to the state. This set of optimal instruments will be compared to other measurement schemes, such as measurements based on the optimal quantum cloning protocol.Verschränkung ist eines der grundlegendsten Phänomene der Quantentheorie und lässt sich nur unzureichend durch einen klassischen Formalismus beschreiben. Verschränkung spielt nicht nur möglicherweise eine Rolle in natürlichen Prozessen, sondern stellt insbesondere eine sehr mächtige Ressource für eine Vielzahl an Anwendungen bereit. So beruhen Quanteninformationsprotokolle wie Quantenzustandsteleportation, superdense coding sowie diverse Ansätze für quantum computation darauf. Dennoch ist es gerade in größeren Systemen, die aus mehr als zwei Teilchen bestehen, äußerst schwierig, Verschränkung nachzuweisen. In der hier vorliegenden Arbeit werden verschiedene Methoden vorgestellt, mit denen Vielteilchenverschränkung effizient detektiert werden kann. Diese Methoden werden experimentell untersucht und anschließend in Hinblick auf ihre Verwendbarkeit diskutiert. Darüber hinaus werden Methoden für Quantenzustands- und Quantenprozesstomographie eingeführt, mit deren Hilfe experimentelle Aufbauten genauestens untersucht werden können. Die dabei typischen Herausforderungen werden aufgezeigt, wobei Methoden präsentiert werden, die neue Einblicke in experimentell gewonnene Daten erlauben. Abschließend wird das sogenannte Messproblem beleuchtet, das die unvermeidbare Störung eines Quantensystems durch einen Messprozess beschreibt. Es werden verschiedene Methoden für Quantenmessungen diskutiert, wobei schließlich die optimalen Messinstrumente hergeleitet werden. Mit diesen kann Information über einen Zustand gewonnen werden, während die dadurch verursachte Störung gleichzeitig minimiert wird. Diese optimalen Instrumente werden mit anderen Messschemata verglichen, die beispielsweise auf dem optimalen Quantenkloner beruhen