Thesis (Ph. D.)--University of Texas at Austin, 2009. / Title from PDF title page (University of Texas Digital Repository, viewed on Aug. 6, 2009). Vita. Includes bibliographical references.

Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: High-temperature (HTc) SQUID magnetometers are used in the biomedical field of magnetocardiography (MCG). The use of MCG enables a much earlier diagnosis of potentially dangerous conditions than the use of electrocardiography (EeG). For the use of MCG, high-quality HTc SQUIDs are necessary. These SQUIDs can only be realised if the design and fabrication processes are well defined and understood. In this thesis an extensive literature review on the design process explains all the concepts necessary to understand and design a high-quality HTc SQUID. Then the fabrication process is redefined and characterised. The SQUIDs are fabricated with YBCO thin films on MgO substrates. The relevant steps in the process are the pulsed laser deposition (PLD), UV lithography and argon ion milling. The characterisation of the fabrication process is based on a statistical method called Design of Experiment (DOE). This enables more information to be obtained about the fabrication process than before. For the PLO process the important parameters are determined and an initial optimisation is done. During the characterisation process it is proven that the use of ozone during PLO has a positive effect on the quality of the YBCO thin film. On the PLD apparatus the substrate heater and laser-beam profile is improved. The UV lithography process is analysed and a DOE is proposed for optimisation. A temperature bath is added to the process to enable better reproducibility. An rf multicusp ion mill is built for argon-ion milling, this device is tested and shown to provide the required etching capability. / AFRIKAANSE OPSOMMING: Hoë-temperatuur (HTc) SQUID magnetometers word in die biomediese rigting vir magnetokardiografie (MKG) gebruik. Met MKG kan 'n mens potensieel gevaarlike toestande heelwat vroeër diagnoseer as wat moontlik is met elektrokardiografie (EKG). HTc SQUIDs van hoë kwaliteit word benodig vir MKG. Sulke SQUIDs kan slegs vervaardig word as die vervaardiging en ontwerpsprosesse goed gedefinieer en verstaan word. In hierdie tesis verduidelik 'n omvattende literatuurstudie oor die ontwerpsproses al die konsepte wat nodig is om 'n SQUID van hoë kwaliteit te verstaan en te ontwerp. Verder word die vervaardigingsproses geherdefinieer en gekarakteriseer. Die SQUIDs word vervaardig met YBCO-dunfilm op MgO-substrate. Die relevante stappe tydens die vervaardiging is: gepulseerde laser deposisie (PLO), UV-litografie en argon-ioonstraling. Die karakterisering van die vervaardigingsproses is gebaseer op 'n statistiese metode genaamd "Design of Experiment" (DOE). Hierdie metode laat 'n mens toe om meer inligting oor die proses te verkry as wat voorheen moontlik was. Gedurende die karakterisering word bewys dat die gebruik van osoon gedurende die PLO-proses 'n positiewe invloed op die kwaliteit van die YBCO-dunfilm het. Die PLO-apparaat se substraatverwarmer en laserstraalprofiel word verbeter. Die UV-litografieproses word geanaliseer en 'n DOE word voorgestel vir die optimisering daarvan. Daar word 'n temperatuurbad by die proses gevoeg om die herhaalbaarheid te verbeter. 'n "Rf multicusp ion mill" word gebou, die toestel word getoets en daar word aangetoon dat dit die nodige etsvermoë het.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The Superconducting Quantum Interference Device (SQUID) is one of the most sensitive magnetic field sensors in the world. These instruments can only be used optimally for geomagnetic research if placed far from man-made magnetic signals. Moving the SQUID to a remote site leads to several infrastructure-related problems including construction, power, data connectivity, and cryogenic cooling. This thesis investigates possible solutions to these problems and develops guidelines for designing future remote SQUID stations. A remote SQUID observatory typically consists of three structures placed approximately 40 m apart. These include: the control room, which houses all computers and supporting electronics, the power hut, which contains a regulated battery bank charged from a solar array that delivers DC power to the rest of the system, and the SQUID hut itself, which is thermally insulated by cavity walls. The SQUID is placed on an isolation pillar that decouples it from structural vibrations due to wind and outside temperature uctuations. The temperature inside the SQUID hut is also monitored as changes in temperature can result in small deformations of the SQUID mounting system which lead to changes in the SQUID's orientation. The changes in the orientation will appear as slow varying magnetic signals on the SQUID output. In principle, it is possible to compensate for these variations through post-processing. The SQUID needs to be cryogenically cooled to function. The SANSA SQUID is a High Temperature Superconductor (HTS) and operates using liquid nitrogen. Immersion cooling is used, as it is the simplest method, and produces the least amount of mechanical and electrical noise. Over time the liquid nitrogen will evaporate and needs to be replaced without significantly disrupting SQUID operations. A simple yet effective pumping scheme was developed that can transfer approximately 1.8 litres of liquid nitrogen every minute from a refill dewar. Monitoring of the liquid nitrogen level is an important management tool for a remote station, as refilling will be the primary reason for technicians to visit the site. The monitoring is achieved by placing the SQUID dewar on a specially designed non-magnetic load cell scale. The scale has been designed to limit the amount of tilting as the weight changes since this would also change the SQUID orientation. When a HTS SQUID is cooled in a large magnetic field, such as the Earth's field, Abrikosov vortices are likely to form in the superconducting material. As these vortices jump between pinning sites in the material, they increase the 1/f noise of the device and have been found to reduce the stability of the SQUID. Metal shields can be used to reduce the magnetic field, but are awkward to use and also reduce the magnitude of the signals of interest. In this thesis, a shielding method using Helmholtz coils is investigated. These coils are relatively simple and inexpensive to construct and do not attenuate the signals of interest. It was found that by cooling the SQUID in the reduced magnetic field, generated by the Helmholtz coils, the stability of the SQUID can be improved significantly. / AFRIKAANSE OPSOMMING: Die SQUID is die mees sensitiewe magneetveld sensors in die wêreld. Hierdie instrument kan slegs optimaal vir geometriese navorsing gebruik word indien dit ver van mensgemaakte magneetvelde opgestel word. Om die SQUID in 'n afgesonderde area op te stel veroorsaak verskeie probleme met betrekking tot infrastruktuur sover dit konstruksie, kragvoorsiening, en kriogeniese afkoeling aangaan. Hierdie tesis ondersoek moontlike oplossings vir die probleme en riglyne te ontwikkel vir die oprigting van toekomstige SQUID stasies. 'n Tipiese afgele SQUID observatorium bestaan gewoonlik uit 3 strukture wat 40m van mekaar opgestel is. Die beheerkamer bevat al die elektroniese apperaat, die kragkamer bevat 'n stel gereguleerde batterye wat deur sonpanele helaai word en DS krag verskaf aan die stasie en die SQUID-kamer wat deur middel van spoumure teen hitte gensoleer is. Die SQUID word op 'n gesoleerde pilaar geplaas om die invloed van vibrasies a.g.v. wind en wisselende buite temperature te verminder. Die temperatuur binne die SQUID kamer word ook noukeurig gemonitor aangesien wisseling in temperatuur geringe vervorming van die SQUID se montering kan veroorsaak wat 'n verandering van die SQUID se orintasie veroorsaak. Hierdie veranderings sal waargeneem word as stadige varirende sein in die SQUID se lesings. In beginsel is dit moontlik om vir dit te kompenseer deur middel van naprosessering. Die SQUID moet kriogenies afgekoel word om te funksioneer. Die SANSA SQUID is 'n Ho Temperatuur Supergeleier (HTS) en vloeibare stikstof word gebruik vir verkoeling. Afkoeling deur middel van indompeling word gebruik omdat dit die kleinste hoeveelheid meganiese en elektroniese versteuring veroorsaak. Die vloeibare stikstof verdamp mettertyd em moet vervang word sonder om die werking van die SQUID merkbaar te onderbreek. 'n Eenvoudige tog effektiewe oorpompstelsel is ontwikkel wat ongeveer 1.8 liter/minuut vloeibare stikstof vanuit 'n hervullings vakuum es kan oorpomp. Die meting van die vloeibare stikstof vlak is 'n belangrike aspek van die instandhouding van 'n afgele stasie aangesien dit die hoof rede sal wees vir tegnici om die perseel te besoek. Die meting word bewerkstellig deur die plasing van die SQUID se vakuum es op 'n spesiale ontwerpte, nie-magnetiese vrag sel skaal. Hierdie skaal is ontwerp om die mate van kanteling te beperk aangesien dit die orentasie van die SQUID kan benvloed. Wanneer 'n HTS SQUID binne in 'n groot magnetiese veld afgekoel word, is dit waarskynlik dat Abrikosov vortekse in die supergeleidende materiaal sal ontstaan. Soos hierdie vortekse rondspring in die materiaal vermeerder dit die 1/f ruis en daar is gevind dat die stabiliteit van die SQUID nadelig benvloed word. Metaal skilde kan gebruik word om die invloed van die magneetveld te verminder, maar is ongerie ik om te gebruik en verminder ook die sterkte van die seine wat waarneem wil word. In hierdie tesis word Helmholtz spoele ondersoek as 'n afskermings metode. Hierdie spoele is eenvoudig om te vervaardig en verminder nie die sterkte van waarneembare seine nie. Daar is gevind dat die stabiliteit van die SQUID merkbaar verbeter word deur afkoeling in 'n lae magnetiese veld soos bewerkstellig deur die Helmholtz spoele.

付記する学位プログラム名: 京都大学卓越大学院プログラム「先端光・電子デバイス創成学」 / 京都大学 / 新制・課程博士 / 博士(工学) / 甲第24621号 / 工博第5127号 / 新制||工||1980(附属図書館) / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 竹内 繁樹, 教授 川上 養一, 教授 木本 恒暢 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

No / A system consisting of two Josephson qubits coupled through a quantum monochromatic electromagnetic field mode of a resonant tank circuit is studied. It is shown that for certain values of the parameters, it can be used as an entangling gate, which entangles the two qubits whilst the electromagnetic field remains disentangled. The gate operates with decent fidelity to a gate and could form the basis for initial experimental investigations of coupled superconducting qubits.

The study of quantum interference in solid-state systems yields insight in fundamental properties of mesoscopic systems. Electron quantum interference constitutes an important method to explore mesoscopic physics and quantum decoherence. This dissertation focuses on two-dimensional (2D) electron systems in $delta-$Si doped n-type In$_{0.64}$Ga$_{0.36}$As/In$_{0.45}$Al$_{0.55}$As, 2D hole systems in Si-doped p-type GaAs/Al$_{0.35}$Ga$_{0.65}$As and C-doped p-type GaAs/\Al$_{0.24}$Ga$_{0.76}$As heterostructures. The low temperature experiments study the magnetotransport of nano- and micro-scale lithographically defined devices fabricated on the heterostructures. These devices include a single ring interferometer and a ring interferometer array in 2D electron system, Hall bar geometries and narrow wires in 2D hole systems. The single ring interferometer yields pronounced Aharonov-Bohm (AB) oscillations with magnetic flux periodicity of h/e over a wide range of magnetic field. The periodicity was confirmed by Fourier transformation of the oscillations. The AB oscillation amplitude shows a quasi-periodic modulation over applied magnetic field due to local magnetic flux threading through the interferometer arms. Further study of current and temperature dependence of the amplitude of the oscillations indicates that the Thouless energy forms the measure of excitation energies giving quantum decoherence. An in-plane magnetic field was applied to the single ring interferometer to study the Berry's phase and the Aharonov-Casher effect. The ring interferometer array yields both AB oscillations and Altshuler-Aronov-Spivak (AAS) oscillations, the latter with magnetic flux periodicity of h/2e. The AAS oscillations require time-reversal symmetry and hence can be used to qualify time-reversal symmetry breaking. More importantly, the fundamental mesoscopic dephasing length associated with time-reversal symmetry breaking under applied magnetic field, an effective magnetic length, can be obtained by the analysis of the AAS oscillations over magnetic field. A theoretical model for confined ballistic system is confirmed by experimental data fitting. The AAS oscillations are barely resolved above 0.16 T and their amplitude decays with increasing magnetic field. The AB oscillations exist till above 2 T and their amplitude doesn't show the monotonic decay with increasing magnetic field. The different behavior of the AAS and AB oscillations originates in the different symmetries, respectively temporal and spatial, that they are sensitive to. The p-type 2D GaAs system has strong spin-orbit interaction (SOI). Antilocalization in a Hall bar geometry was analyzed by the 2D Hikami-Larkin-Nagaoka (HLN) theory to obtain the spin coherence time and phase coherence time. The 2D hole systems we studied have low density and high mobility, quite different from the 2D electron systems. These high-quality 2D hole systems demonstrate semi-classical ballistic phenomena in mesoscopic structures preferentially to quantum-coherence phenomena. / Ph. D.

Quantum trajectories are investigated within the complex quantum Hamilton-Jacobi formalism. A unified description is presented for complex quantum trajectories for one-dimensional time-dependent and time-independent problems. Complex quantum trajectories are examined for the free Gaussian wave packet, the coherent state in the harmonic potential, and the the barrier scattering problems. We analyze the variations of the complex-valued kinetic energy, the classical potential, and the quantum potential along the complex quantum trajectories. For one-dimensional time-independent scattering problems, we demonstrate general properties and similar structures of the complex quantum trajectories and the quantum potentials. In addition, it is shown that a quantum vortex forms around a node in the wave function in complex space, and the quantized circulation integral originates from the discontinuity in the real part of the complex action. Although the quantum momentum field displays hyperbolic flow around a node, the corresponding Polya vector field displays circular flow. Moreover, local topologies of the quantum momentum function and the Polya vector field are thoroughly analyzed near a stagnation point or a pole (including circular, hyperbolic, and attractive or repulsive structures). The local structure of the quantum momentum function and the Polya vector field around a stagnation point are related to the first derivative of the quantum momentum function. However, the magnitude of the asymptotic structures for these two fields near a pole depends only on the order of the node in the wave function. Finally, quantum interference is investigated and it leads to the formation of the topological structure of quantum caves in space-time Argand plots. These caves consist of the vortical and stagnation tubes originating from the isosurfaces of the amplitude of the wave function and its first derivative. Complex quantum trajectories display helical wrapping around the stagnation tubes and hyperbolic deflection near the vortical tubes. Moreover, the wrapping time for a specific trajectory is determined by the divergence and vorticity of the quantum momentum field. The lifetime for interference features is determined by the rotational dynamics of the nodal line in the complex plane. Therefore, these results demonstrate that the complex quantum trajectory method provides a novel perspective for analysis and interpretation of quantum phenomena. / text

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2014-08-01T15:13:17Z No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Disseertacao Luciano Paulo de Araujo Maia.pdf: 1329124 bytes, checksum: b9e2abb00156f6dd57d05cd14dbacbb1 (MD5) / Made available in DSpace on 2014-08-01T15:13:17Z (GMT). No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Disseertacao Luciano Paulo de Araujo Maia.pdf: 1329124 bytes, checksum: b9e2abb00156f6dd57d05cd14dbacbb1 (MD5) Previous issue date: 2002 / In this paper we present a new quantum state of light, obtained from an asymmetric superposition of coherent states in circular stationary mode. The generation of this state was proposed and the experimental apparatus required is presented. General expressions describing various properties (statistical distribution, variances, atomic inversion, etc..) Were obtained for arbitrary generations. We observed how they behave their properties by varying the phase between the components of superpo- sition states. We show that the statistical properties do not fully characterize the resulting state, showing different states with the same statistics. Alternative ways to distinguish these states were considered. Based on quantum interference in phase space, we show how we can generate an approximation of the number state N2 thru a process called "quantum sculpture,"and check the influence of the stage in this process. Finally, we measured the classicalidade not analyze this state and its representation in phase space. / Neste trabalho, apresentamos um novo estado quântico da luz, obtido de uma su- perposição assimétrica de estados coerentes circulares no modo estacionário. A ger- ação deste estado foi proposta e o aparato experimental necessário é apresentado. Expressões gerais descrevendo diversas propriedades (distribuição estatística, vari- anças, inversão atômica, etc.) foram obtidas para arbitrárias gerações. Verificamos como se comportam suas propriedades, variando a fase entre os estados componentes da superposição. Mostramos que as propriedades estatísticas não caracterizam com- pletamente o estado resultante, exibindo estados distintos com mesma estatística. Formas alternativas para distinguir estes estados foram consideradas. Baseado na interferência quântica no espaço de fase, mostramos como podemos gerar uma aprox- imação ao estado de número N2 , atravéz de um processo denominado “escultura quântica” e verificamos a influência da fase neste processo. Finalmente, medimos a não classicalidade deste estado e analisamos a sua representação no espaço de fase.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: This work discusses the design of a 3-axis Geomagnetometer SQUID System (GSS), in which HTS SQUIDs are used unshielded. The initial GSS installed at SANSA was fully operable, however the LN2 evaporation rate and SQUID orientation required improving. Magnetic shields were also developed in case the SQUIDs would not operate unshielded and to test the system noise with geomagnetic variations removed. To enable removing the double layer shield from the probes while the SQUIDs remain submerged in LN2, the shield was designed to disassemble. The shields proved to be effective, however due to icing the shields could not be removed without removing the SQUIDs from the LN2. / AFRIKAANSE OPSOMMING: Hierdie werk bespreek die ontwerp van 'n 3-as Geomagnetometer SQUID Sisteem (GSS), waarin HTS SQUIDs sonder magnetiese skilde aangedryf word. Die aanvanklike GSS geïnstalleer by SANSA was ten volle binnewerking, maar die LN2 verdamping en SQUID oriëntasie benodig verbetering. Magnetiese skilde was ook ontwikkel vir die geval dat die SQUIDs nie sonder skilde wou werk nie en om die ruis te toets na geomagnetiese variasies verwyder is. Die dubbele laag skild was ontwerp om uitmekaar gehaal te word terwyl die SQUIDs binne die LN2 bly. Die skild was doeltreffend, maar ys het verhoed dat die skild verwyder kon word vanaf die LN2 sonder om die SQUIDs ook te verwyder.

In this thesis we investigate, experimentally and theoretically, many classical and quantum coherence effects of the light. Initially we investigate the interference patterns formation by nonlocal double slit using classical light sources and comparing the results with those using a twin photos light source generated by Spontaneous Parametric Down Conversion (SPDC). We demonstrate that the classical correlation in wave vectors, in beam splitter outs, is a sufficient condition to the interference pattern to exist. In this work we also investigate experimentally the influence of polarized nonlocal double slit and local double slit. Here is present a alternative Fano based interpretation to explain the reason why the polarization of correlated beam has not influence on pattern fringes. We presented also an investigation about the light source parameters influence on the ghost interference interference. We demonstrate experimentally the relationship between, the coherence and source size, and fringes visibility. We extended the concept of complementarity related to coherence and correlation using the changes of the reference beam coherence and observing it’s influence on the interference patterns of the local double slit. In near-field limit, we investigate the existence of conditionality in the wave vector limited by the aperture of objects placed on the classically correlated beams paths. We demonstrate that is possible to find conditionality between the light emitted through the slits apertures. All these experiments performed using the Brown Twiss intensity interferometer (HBT) served to investigate the difference between the transversal effects with quantum and classical incoherent light. Finally, we demonstrate the first experimental measurement demonstrating the polarization changes on the partially coherent light propagation induced by the coherence source changes. This phenomenom was investigated for the free space propagation and for a nonlinear medium modeled by a Kerr medium. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Nesta tese investigamos, experimentalmente e teoricamente, diversos efeitos clássicos e quânticos da coerência da luz. Inicialmente investigamos a formação do padrão de interferência por uma fenda dupla não local utilizando fontes clássicas de luz e comparando com os resultados obtidos usando fótons gêmeos gerados na Conversão Paramétrica Espontânea Descendente (CPED). Nós demonstramos que uma correlação clássica nos vetores de onda, nas saídas de um divisor de feixes, é uma condição suficiente para a existência do padrão de interferência. Neste trabalho nós também investigamos experimentalmente a influência da polarização na fenda não local e na fenda dupla local. Apresentamos uma interpretação alternativa, baseada na interpretação de Fano para o experimento de Hanbury-Brown e Twiss, explicando porque as polarizações dos feixes não influenciam na visibilidade das franjas de interferência. Ainda apresentamos, uma investigação sobre a influência do grau de coerência e o tamanho da fonte sobre as franjas de interferência fantasma. Demonstramos experimentalmente a relação entre coerência e tamanho da fonte na visibilidade das franjas. Estendemos o conceito de complementaridade relacionando coerência e correlação, mostrando que a mudança do grau de coerência do feixe de referência influencia nos padrões de interferência da fenda local. No limite de campo próximo investigamos a existência da condicionalidade nos vetores de onda limitados pela abertura dos objetos colocados no caminho dos feixes de luz classicamente correlacionados. Demonstramos a possibilidade de encontrar a condicionalidade entre a luz emitida pelas aberturas das fendas.Todos os experimentos realizados utilizando o interferômetro de intensidades de Browne Twiss (HBT) serviram para investigar a diferença entre os efeitos transversais com luz clássica e luz quântica. Finalmente, apresentamos a primeira medida experimental demonstrando a mudança da polarização na propagação da luz parcialmente coerente induzida por meio da mudança da coerência da fonte. Este fenômeno foi investigado para a propagação no ar livre e em um meio não linear aproximado por tipo Kerr.