Quantum City: simulation of a practical near-term metropolitan quantum network

We present the architecture and analyze the applications of a metropolitan-scale quantum network that requires only limited hardware resources for end users. Using NetSquid, a quantum network simulation tool based on discrete events, we assess the performance of several quantum network protocols involving two or more users in various configurations in terms of topology, hardware and trust choices. Our analysis takes losses and errors into account and considers realistic parameters corresponding to present or near-term technology. Our results show that practical quantum-enhanced network functionalities are within reach today and can prepare the ground for further applications when more advanced technology becomes available

Near-term quantum-repeater experiments with nitrogen-vacancy centers: Overcoming the limitations of direct transmission

Quantum channels enable the implementation of communication tasks inaccessible to their classical counterparts. The most famous example is the distribution of secret key. However, in the absence of quantum repeaters, the rate at which these tasks can be performed is dictated by the losses in the quantum channel. In practice, channel losses have limited the reach of quantum protocols to short distances. Quantum repeaters have the potential to significantly increase the rates and reach beyond the limits of direct transmission. However, no experimental implementation has overcome the direct transmission threshold. Here, we propose three quantum repeater schemes and assess their ability to generate secret key when implemented on a setup using nitrogen-vacancy (NV) centers in diamond with near-term experimental parameters. We find that one of these schemes - the so-called single-photon scheme, requiring no quantum storage - has the ability to surpass the capacity - the highest secret-key rate achievable with direct transmission - by a factor of 7 for a distance of approximately 9.2 km with near-term parameters, establishing it as a prime candidate for the first experimental realization of a quantum repeater.Comment: 19+17 pages, 17 figures. v2: added "Discussion and future outlook" section and expanded introduction, published versio

Connecting Quantum Cities: Simulation of a Satellite-Based Quantum Network

We present and analyse an architecture for a European-scale quantum network using satellite links to connect Quantum Cities, which are metropolitan quantum networks with minimal hardware requirements for the end users. Using NetSquid, a quantum network simulation tool based on discrete events, we assess and benchmark the performance of such a network linking distant locations in Europe in terms of quantum key distribution rates, considering realistic parameters for currently available or near-term technology. Our results highlight the key parameters and the limits of current satellite quantum communication links and can be used to assist the design of future missions. We also discuss the possibility of using high-altitude balloons as an alternative to satellites

Conception et optimisation d'outils pour l'Internet quantique

Cette thèse s’inscrit dans l’effort international pour construire des réseaux quantiques utilisables par tous. Nous essayons de souligner les problématiques importantes ainsi que les paramètres expérimentaux pouvant être bloquants. Nous explorons différents aspects des réseaux quantiques en vue d’aider la communauté internationale à construire l’Internet quantique. Après avoir introduit certaines notions de base d’informatique quantique pour la compréhension de la suite, nous définissons l’Internet quantique, dégageons les principales problématiques et enjeux. Puis, nous nous penchons sur une série de protocoles, bipartites et multipartites, que nous explicitons. Ensuite, nous étudions la sécurité composable d’un protocole réseau de vérification d’intrication multipartite, utilisé comme bloc de base par de nombreux autres protocoles. Dans le chapitre suivant, nous simulons et analysons différents protocoles de répéteurs quantiques permettant de lier deux nœuds du réseau à grande distance. Ces répéteurs utilisent un défaut dans la structure cristalline du diamant, que nous modélisons. Enfin, les deux derniers chapitres sont dédiés à la construction et à la simulation d’une architecture de réseau quantique transnational qui minimise la quantité de matériel nécessaire pour les utilisateurs du réseau. Nous étudions d’abord un réseau métropolitain, dont nous simulons une instance dans un contexte parisien. Nous exposons les paramètres expérimentaux ainsi que les performances actuelles. Ensuite nous étudions la possibilité d’établir une connexion entre différentes villes quantiques distantes de plusieurs centaines de kilomètres à l’aide de satellites.This thesis is written in the context of quantum Internet development. We try here to contribute to the community by discussing some security concerns and by providing detailed models and simulation studies of quantum internet architectures and protocols. We explore different aspects of quantum networks on the path to the Quantum Internet. After introducing basic quantum information notions, we define the Quantum Internet and highlight the main goals and challenges. Then, we list a few bipartite and multipartite applications. After that, we study the composable security of a multipartite entanglement verification protocol, that is used as a building block by many other protocols. In the following chapter, we perform simulations of different quantum repeater protocols allowing connection between two distant nodes. These repeaters use a defect in the crystalline structure of the diamond, that we model. Finally, the last two chapters are dedicated to building and simulating an international quantum network architecture that minimizes the necessary hardware for the end users. We first study a metropolitan network, called the Quantum City, that we simulate in a Parisian context. We highlight the main parameters and today’s performances. Then, we study the feasibility of connecting different quantum cities separated by hundred of kilometers using satellites

Data underlying the publication: Near-term quantum-repeater experiments with nitrogen-vacancy centers: Overcoming the limitations of direct transmission

This is the python notebook that generates the figures in the article "Near-term quantum-repeater experiments with nitrogen-vacancy centers: Overcoming the limitations of direct transmission", online preprint at arXiv:1809.0036

Financing mental health in low and middle-income countries: making an economic case to support investment

The main objective of this work is to provide a book with high quality content that becomes a reference and support for graduate course (Mental Health, Public Health and Epidemiology) and for research in the domain of health economics applied to mental health. Also this book might be useful for policymakers on formulating mental health policies. Key messages of this book are based on: a) mental illness represent a huge cost for society and for health care; b) health economics applied to mental health could help in the optimization of resource allocation for mental health care and for better decision making in terms of balancing costs and benefits; c) interventions and treatment should be also chosen in general medical practice and in public decision-policy according to cost-effectiveness, burden of disease and equity principles; d) quality of care is related with better outcomes, higher quality of life for clients, and with lower costs for society and health system (best value for money); e) it is possible to decrease the burden of mental disorders with cost-effective treatments. The book is divided in four main topics: 1. Introduction to Health Economics applied to Mental Health – this section is an overview of basic principles, concepts and methods used in Economics and Health Economics to enable students to make critical appraisal of Health Economics texts and also to design research studies in this topic. 2. Health Economics applied to the evaluation of quality and costs of Mental Health Services – this section presents results of Brazilian studies on the costs of mental health care (hospital, outpatient care, residential care, informal care), methods on the measurement of costs and it discusses issues related with public policies decisions and quality of mental health car in the low and middle income countries context. There is also an overview of quality indicators of mental health care and instruments to evaluate mental health services and costs.3. Health Economics applied to evaluate treatment of mental disorders - This section presents a review of cost-effectiveness of pharmacological treatments and other interventions applied for treating the most burdensome mental disorders such as depressive and anxiety disorders, bipolar disorders, psychosis, alcohol and drug disorders, dementia, and hyper attention deficit disorders. 4. Health Economics, burden and indirect costs of mental disorders - This section highlights the social and economic burden caused by mental illness under societal perspective focusing on stigma, unemployment, indirect costs in the workplace (absenteeism and presenteeism), the relationship between poverty and mental disorders, global health and social determinants of mental health and on the costs of mental disorders (depression, anxiety, psychosis, alcohol and drug disorders). We present some instruments to measure indirect costs of mental disorders