An Observational Theory for Mobile Ad Hoc Networks

AbstractWe propose a process calculus to study the observational theory of Mobile Ad Hoc Networks. The operational semantics of our calculus is given both in terms of a Reduction Semantics and in terms of a Labelled Transition Semantics. We prove that the two semantics coincide. The labelled transition system is then used to derive the notions of simulation and bisimulation for ad hoc networks. As a main result, we prove that the (weak) labelled bisimilarity completely characterises (weak) reduction barbed congruence, a standard, branching-time, contextually-defined program equivalence. We then use our (bi)simulation proof methods to formally prove a number of non-trivial properties of ad hoc networks

SMART Cables for Observing the Global Ocean: Science and Implementation

The ocean is key to understanding societal threats including climate change, sea level rise, ocean warming, tsunamis, and earthquakes. Because the ocean is difficult and costly to monitor, we lack fundamental data needed to adequately model, understand, and address these threats. One solution is to integrate sensors into future undersea telecommunications cables. This is the mission of the SMART subsea cables initiative (Science Monitoring And Reliable Telecommunications). SMART sensors would “piggyback” on the power and communications infrastructure of a million kilometers of undersea fiber optic cable and thousands of repeaters, creating the potential for seafloor-based global ocean observing at a modest incremental cost. Initial sensors would measure temperature, pressure, and seismic acceleration. The resulting data would address two critical scientific and societal issues: the long-term need for sustained climate-quality data from the under-sampled ocean (e.g., deep ocean temperature, sea level, and circulation), and the near-term need for improvements to global tsunami warning networks. A Joint Task Force (JTF) led by three UN agencies (ITU/WMO/UNESCO-IOC) is working to bring this initiative to fruition. This paper explores the ocean science and early warning improvements available from SMART cable data, and the societal, technological, and financial elements of realizing such a global network. Simulations show that deep ocean temperature and pressure measurements can improve estimates of ocean circulation and heat content, and cable-based pressure and seismic-acceleration sensors can improve tsunami warning times and earthquake parameters. The technology of integrating these sensors into fiber optic cables is discussed, addressing sea and land-based elements plus delivery of real-time open data products to end users. The science and business case for SMART cables is evaluated. SMART cables have been endorsed by major ocean science organizations, and JTF is working with cable suppliers and sponsors, multilateral development banks and end users to incorporate SMART capabilities into future cable projects. By investing now, we can build up a global ocean network of long-lived SMART cable sensors, creating a transformative addition to the Global Ocean Observing System

Application of advanced on-board processing concepts to future satellite communications systems: Bibliography

Abstracts are presented of a literature survey of reports concerning the application of signal processing concepts. Approximately 300 references are included

Belle II Technical Design Report

The Belle detector at the KEKB electron-positron collider has collected almost 1 billion Y(4S) events in its decade of operation. Super-KEKB, an upgrade of KEKB is under construction, to increase the luminosity by two orders of magnitude during a three-year shutdown, with an ultimate goal of 8E35 /cm^2 /s luminosity. To exploit the increased luminosity, an upgrade of the Belle detector has been proposed. A new international collaboration Belle-II, is being formed. The Technical Design Report presents physics motivation, basic methods of the accelerator upgrade, as well as key improvements of the detector.Comment: Edited by: Z. Dole\v{z}al and S. Un

The distinct element analysis of soil masses

The conventional Distinct Element Analysis of Cundall and Belytschko and their respective co-workers are prone to vibrations which must be damped out artificially if numerical problems are to be avoided. An alternative approach to this method is developed which eliminates such problems by allowing the elements to consolidate without gain in velocity. In the method employed here the contact forces, together with body forces due to gravity give rise to accelerations of the elements which in turn cause them to change position. Normally this change in position will produce an increase in the contact forces. Once these new contact forces have been calculated the elements are then returned to their original positions prior to the next iteration. The contact forces, therefore, increase during the analysis to counter the effects of gravity. Two methods using this new approach are described, for which computer programs have been written. The first program, SLICES, is designed to analyse slopes divided in to slices with a predetermined failure arc. During the analysis the program generates the stress profile acting on the failure arc and predicts the stability or otherwise of the slope. Program SLICES is compared with a traditional slice method under conditions of total and effective stress with cohesive and frictional soils. An analysis using a non-linear failure criterion is also carried out with program SLICES. The second program, CIRCLES, uses circles as the distinct element type and does not require a predetermined failure arc. It is shown that edge effects cause an incorrect stress regime to be set up that masks the failure process. However a sliding type failure is demonstrated where the edge effects do not mask the analysis. Submitted in accordance with the regulations for the degree of Ph. D. of the University of Durham. October 1989

SMART cables for observing the global ocean: Science and implementation

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150639/1/fmars-06-00424.pdfDescription of fmars-06-00424.pdf : Main articl

Detection of a single erbium ion in a nanoparticle

Encoding information into quantum mechanical properties of a system can lead to applications many fields, including computing and communication. Devices that will enable these applications could be part of a quantum network in the future. Quantum networks can be implemented using nodes that have the ability to generate and store entanglement efficiently for long durations as well as to process quantum information. The nodes also need to be interfaced with photons, which can faithfully carry information over long distances. Single rare-earth ions doped in crystals offer all these capabilities. The main goal of this thesis was to detect a single erbium ion, which operates in the telecommunication wavelength, and to investigate its feasibility as a spin-photon interface. Detecting a single erbium is challenging due to its low emission rate, but it can be aided by Purcell-enhancing its emission via coupling to an optical cavity. In this thesis, we utilize erbium ions doped into nanoparticles, which facilitates their integration into cavities with small mode-volumes. In addition, nanoparticles provide the confinement required to individually manipulate spatially close-by single ion qubits, which is required for dipolar quantum gates. We hence first study the optical coherence properties of Er:Y2O3 nanoparticles at cryogenic temperatures. We identify the limiting mechanisms and identify avenues for improvement in the future. We also study the optical and spin coherence properties of Pr:Y2O3, which is a promising alternative to erbium. Fiber-based microcavities can achieve high Purcell factors as they can simultaneously realize high finesse and small mode-volume. They are also ideally suited to be coupled to nanoparticles due to their tuning capabilities. However, stabilizing such a cavity inside a cryogenic environment is challenging. We hence first describe the construction of a custom setup, which enables us to stabilize the cavity while being coupled to a suitable nanoparticle. Utilizing the first iteration of this setup, we then report on the coupling of Er:Y2O3 nanoparticles to a fiber-based high finesse microcavity. We achieve an average Purcell factor of 14 for a small ensemble of ions, while a small subset of ions show Purcell factor up to 70. We explain the obtained multi-exponential decay behaviour using a detailed model. Furthermore, we demonstrate dynamic control of the Purcell-enhanced emission by tuning the cavity resonance on a time-scale faster than the spontaneous emission rate of the ions. This allows us to extract the natural lifetime of the ions as well as to shape the waveform of the emitted photons. However, we conclude that the achieved signal-to-noise ratio is not high enough to resolve single erbium ions. For the final experiment, we operate the second iteration of the setup, which improves our sensitivity to single erbium ions by more than a factor 50. This enables us to demonstrate the first detection of a single erbium ion in a nanoparticle. The ion exhibits a Purcell factor of 60, leading to a cavity enhanced lifetime of 225 us, and a homogeneous linewidth of 380 MHz. The counts received from the ion show a clear saturation and we measure the second-order auto-correlation of the emitted photons to be 0.59, which reduces to 0.29 after background-subtraction. This is strong evidence that the photons are emitted by a single erbium ion. Our work opens the path for exploring single rare-earth-ions doped into nanoparticles as spin-photon interfaces for quantum information processing.La codificación de la información en las propiedades mecánico-cuánticas de un sistema puede dar lugar a aplicaciones en muchos campos, como la informática y la comunicación. Podemos imaginar que los dispositivos que permitan estas aplicaciones formen parte de una red cuántica en el futuro. Las redes cuánticas pueden implementarse utilizando nodos que tengan la capacidad de generar y almacenar el entrelazamiento de forma eficiente durante largos periodos de tiempo, así como de procesar la información cuántica. Los nodos también necesitan una interfaz con fotones, ya que estos pueden transportar fielmente la información a largas distancias. Los iones individuales de tierras raras dopados en cristales ofrecen todas estas capacidades. El objetivo principal de esta tesis fue detectar un ion individual de erbio, que opera en la longitud de onda de las telecomunicaciones, e investigar su viabilidad como interfaz espín-fotón. La detección de un ion individual de erbio es un reto debido a su baja tasa de emisión, pero esta puede mejorarse mediante el acoplamiento a una cavidad óptica, debido al efecto Purcell. En esta tesis, utilizamos iones de erbio dopados en nanopartículas, lo que facilita su integración a cavidades con volúmenes de modo pequeños. Además, las nanopartículas proporcionan el confinamiento necesario para manipular bits cuánticos de iones individuales cercanos espacialmente, lo cual es necesario para construir puertas cuánticas dipolares. Por ello, estudiamos primero las propiedades de coherencia óptica de las nanopartículas de Er:Y2O3 a temperaturas criogénicas. Identificamos los mecanismos limitantes e identificamos las vías de mejora en el futuro. También estudiamos las propiedades de coherencia óptica y de espín de Pr:Y2O3, que es una alternativa prometedora al erbio. Las microcavidades basadas en fibra pueden alcanzar elevados factores de Purcell, ya que pueden lograr simultáneamente una gran finura y un pequeño volumen de modo. También son idóneas para ser acopladas a nanopartículas debido a su capacidad para ajustar la frecuencia de resonancia. Sin embargo, estabilizar una cavidad de este tipo en un entorno criogénico es un reto. Primero, describimos la construcción de un sistema personalizado que nos permitió estabilizar la cavidad mientras se acoplaba a una nanopartícula adecuada. Utilizando la primera iteración de esta configuración, informamos sobre el acoplamiento de nanopartículas de Er:Y2O3 a una microcavidad de alta precisión basada en fibra. Conseguimos un factor Purcell medio de 14 para un pequeño conjunto de iones, mientras que un pequeño subconjunto de iones mostró un factor Purcell de hasta 70. Explicamos el comportamiento de decaimiento multiexponencial obtenido utilizando un modelo detallado. Además, demostramos el control dinámico de la emisión potenciada por el efecto Purcell ajustando la resonancia de la cavidad en una escala de tiempo más rápida que la tasa de emisión espontánea de los iones. Esto nos permitió extraer el tiempo de vida natural de los iones, así como moldear la forma de onda de los fotones emitidos. Para el experimento final, operamos la segunda iteración de la configuración, que mejoró nuestra sensibilidad a los iones individuales de erbio en más de un factor 50. Esto nos permitió demostrar la primera detección de un ion de erbio en una nanopartícula. El ión presentó un factor Purcell de 60, lo que da un tiempo de vida realzado por la cavidad de 225 us, y un ancho de línea homogéneo de 380 MHz. Los recuentos recibidos del ion mostraron una clara saturación y la medida de autocorrelación de segundo orden de los fotones emitidos resultó en 0,59, que se reduce a 0,29 tras la sustracción de fondo. Esto es una fuerte evidencia de que los fotones son emitidos por un ion individual de erbio. Nuestro trabajo abre el camino para explorar los iones individuales de tierras raras dopados en nanopartículas como interfaces de espín-fotón para el procesamiento de información cuánticaPostprint (published version

Polarization-preserving quantum frequency conversion for trapped-atom based quantum networks

The scope of this thesis is the development of efficient and low-background polarization- preserving quantum frequency converters (PPQFC) and their integration into trapped-atom based quantum network nodes to demonstrate building blocks of a quantum network (QN). We constructed four PPQFC devices to transduce the emission wavelengths of single trapped 40Ca+-ions at 854 nm and neutral 87Rb-atoms at 780 nm to the low-loss telecom bands between 1260 nm and 1625 nm. Upon the conversion process, the quantum information encoded in the photon polarization has to be preserved. To this end, we rely on difference frequency generation in ridge waveguides, which are inserted into polarization interferometers arranged in Sagnac- or Mach-Zehnder-type configuration. For the conversion of single and entangled photons we achieved external device efficiencies between 26.5 % and 57.4 %, low background levels, which allow for signal-to-background ratios above 20, and process fidelities > 99.5 %. Employing the PPQFC devices, we were able to demonstrate several key elements of long-distance QNs: photon-photon entanglement over 40 km of fiber via 2-step QFC with a fidelity of 98.9 %, ion-telecom-photon entanglement with high fidelities up to 97.8 %, an atom-to-telecom-photon state transfer, and the distribution of atom-photon entanglement over 20 km of fiber with a fidelity of 78.9 %. These results hold great promise to extend small QNs with ≥ 2 nodes to a metropolitan scaleIn dieser Arbeit werden effiziente und hintergrundarme polarisationserhaltende Quan- tenfrequenzkonverter (PPQFC) entwickelt und in Quantennetzwerkknoten basierend auf gefangenen Atomen integriert, um Bausteine eines Quantennetzwerks (QN) zu demonstrieren. Wir haben vier PPQFC gebaut um die Emissionswellenlängen von einzelnen 40Ca+-Ionen bei 854 nm und neutralen 87Rb-Atomen bei 780 nm in die verlustarmen Telekombänder zwischen 1260 nm und 1625 nm umzuwandeln. Im Konversionsprozess muss die Quanteninformation, kodiert in der Polarisation der Photonen, erhalten bleiben. Dazu nutzen wir Differenzfrequenzerzeugung in Kantenwellenleitern, welche in Polarisationsinterferometer in Form von Sagnac- oder Mach-Zehnder-Aufbauten integriert werden. Für die Konversion einzelner und verschränkter Photonen erreichten wir externe Geräteeffizienzen zwischen 26.5 % und 57.4 %, geringe Hintergrundbeiträge, die Signal-zu-Hintergrund-Verhältnisse über 20 ermöglichen, sowie Prozess-Fidelities > 99.5 %. Mit Hilfe der Konverter konnten wir eine Reihe von Kernelementen von langreichweitigen QNn zeigen: Photonen-Photonen-Verschränkung über 40 km Faser mittels 2-Schritt QFC mit einer Fidelity von 98.9 %, Ion-Telekom-Photon-Verschränkung mit hohen Fidelities bis zu 97.8 %, einen Atom-zu-Telekom-Photon Zustandstransfer, und die Verteilung von Atom-Photon-Verschränkung über 20 km Faser mit einer Fidelity von 78.9 %. Diese Resultate sind vielversprechend um kleine QN mit ≥ 2 Knoten auf die Längenskala einer Stadt auszuweiten