Rozprawy doktorskie: „Superconducting quantum devices”

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Baker, Luke James. "Superconducting nanowire devices for optical quantum information processing". Thesis, University of Glasgow, 2018. http://theses.gla.ac.uk/8440/.

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Near infrared photons are a promising choice for quantum information processing; their low transmission loss is necessary for applications such as long distance Quantum Key Distribution (QKD) in optical fibre and integrated quantum optics. An ideal proof-of-concept test of such applications would be to create, manipulate and detect single photons on a monolithic chip. Superconducting nanowire single photon detectors promise high system detection efficiencies, low dark count and low jitter under near-infrared photon illumination. Superconducting nanowire devices using NbTiN films show improved coupling efficiencies with the aid of oxidized silicon cavities. NbTiN devices were characterised in a fibre-coupled package, achieving high SDE (43%) coherent key generation rates over 200km in a T12 QKD protocol simulation. Hairpin superconducting nanowires offer excellent integration with silicon waveguide optics and can achieve near unity absorption efficiencies. Hairpin devices fabricated from MoSi films were characterised using a custom pulse tube He-3 cryostat engineered for low vibration operation at 350mK and capable of near-infrared optical maps of superconducting nanowires. The devices exhibited high critical currents 40uA), low jitter (51ps) and a dark count rate <10cps. Tests of perpendicular coupling efficiencies yield low system detection efficiencies due to high coupling losses. Using an alternative coupling method via grating couplers or cleave mounting, it is expected a much higher system detection efficiency can be achieved.

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Judge, Elizabeth Eileen. "Direct measurement of dissipative forces in superconducting BSCCO". Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3035957.

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Akram, Uzma. "Quantum interference and cavity QED effects in a V-system /". [St. Lucia, Qld.], 2003. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe17140.pdf.

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Kilian, Anton Theo. "3-Axis geomagnetic magnetometer system design using superconducting quantum interference devices". Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86452.

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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.

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Abi-Salloum, Tony Y. Narducci L. M. "Interference between competing pathways in the interaction of three-level atoms and radiation /". Philadelphia, Pa. : Drexel University, 2006. http://dspace.library.drexel.edu/handle/1860%20/858.

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Marthaler, Michael [Verfasser], i G. [Akademischer Betreuer] Schön. "Study of Quantum Electrodynamics in Superconducting Devices / Michael Marthaler. Betreuer: G. Schön". Karlsruhe : KIT-Bibliothek, 2009. http://d-nb.info/1014099854/34.

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Graf, zu Eulenburg Alexander. "High temperature superconducting thin films and quantum interference devices (SQUIDs) for gradiometers". Thesis, University of Strathclyde, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366689.

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Egger, Daniel J. [Verfasser], i Frank K. [Akademischer Betreuer] Wilhelm-Mauch. "Optimal control and quantum simulations in superconducting quantum devices / Daniel J. Egger. Betreuer: Frank K. Wilhelm-Mauch". Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2014. http://d-nb.info/1060715961/34.

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Podd, Gareth James. "MicroSQUIDs with independently controlled Josephson junctions". Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613267.

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Ogunyanda, Kehinde. "A superconducting quantum interference device (SQUID) magnetometer for nanosatellite space weather missions". Thesis, Cape Peninsula University of Technology, 2012. http://hdl.handle.net/20.500.11838/1164.

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Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Electrical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology, 2012
In order to effectively determine the occurrences of space weather anomalies in near Earth orbit, a highly sensitive space-grade magnetometer system is needed for measuring changes in the Earth’s magnetic field, which is the aftermath of space weather storms. This research is a foundational work, aimed at evaluating a commercial-off-the-shelf (COTS) high temperature DC SQUID (superconducting quantum interference device) magnetometer, and establishing the possibility of using it for space weather applications. A SQUID magnetometer is a magnetic field measuring in strument that produces an electrical signal relative to the sensed external magnetic field intensity.

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Hutson, D. "The design, construction and operation of practical thin film superconducting quantum interference devices (SQUIDs)". Thesis, University of Strathclyde, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382345.

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Cottle, Amy. "Development of a SQUID magnetometry system for a cryogenic neutron electric dipole moment experiment". Thesis, University of Oxford, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.711932.

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Bothner, Daniel [Verfasser], i Reinhold [Akademischer Betreuer] Kleiner. "Micropatterned Superconducting Film Circuitry for Operation in Hybrid Quantum Devices / Daniel Bothner ; Betreuer: Reinhold Kleiner". Tübingen : Universitätsbibliothek Tübingen, 2014. http://d-nb.info/1162897465/34.

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DE, LEO MARIA. "Realization of superconducting quantum devices based on tunnel Josephson junctions by micro and nanofabrication techniques". Doctoral thesis, Politecnico di Torino, 2013. http://hdl.handle.net/11583/2506305.

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This PhD Thesis is focused on the realization of superconducting quantum devices based on overdamped Nb/Al-AlOx/Nb SNIS (Superconductor - Normal metal - Insulator - Superconductor) tunneling Josephson junctions, interesting for several application fields (voltage metrology, digital electronics, radiation sensors, nanoSQUID, etc.). The challenges faced by quantum electronics and metrology are directing the new generations of devices towards smaller dimensions and higher levels of integration. Taking into account this requirement, the fabrication of SNIS-based devices has been addressed on downscaling the junction dimensions form the micro to the nanoscale. In particular, the effective area of junctions has been reduced exploiting three different lithographic techniques: the optical lithography to realize SNISs for a micrometer resolution, the Electron Beam Lithography (EBL) at the subµm and, finally, the Focused Ion Beam (FIB) sculpting method to achieve nanometer sizes. Specifically, prototypes have been realized exploiting the thin film technology, to guarantee a good control of electrical parameters of junctions, a higher reproducibility of their current-voltage I-V characteristics, and an accurate dimension control. Reliable and simpler fabrication processes have been implemented and validated, and the device downscaling was pursued without affecting the fundamental properties of SNIS junctions such as the non hysteretic I-V response and the skill on generating quantised voltage steps under radiofrequency irradiation. This work has thereby led to the definition and validation of a new generation of devices and processes down to the nanometer scale, and these approaches represent precious experiences of nanofabrication valuable for new research activities and projects.

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Murrell, Jonathan Kenneth Jeffrey. "Non-linear behaviour of a Superconducting Quantum Interference Device coupled to a radio frequency oscillator". Thesis, University of Sussex, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366212.

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Esmail, Adam Ashiq. "Charge dynamics in superconducting double dots". Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/270018.

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The work presented in this thesis investigates transitions between quantum states in superconducting double dots (SDDs), a nanoscale device consisting of two aluminium superconducting islands coupled together by a Josephson junction, with each dot connected to a normal state lead. The energy landscape consists of a two level manifold of even charge parity Cooper pair states, and continuous bands corresponding to charge states with single quasiparticles in one or both islands. These devices are fabricated using shadow mask evaporation, and are measured at sub Kelvin temperatures using a dilution refrigerator. We use radio frequency reflectometry to measure quantum capacitance, which is dependent on the quantum state of the device. We measure the quantum capacitance as a function of gate voltage, and observe capacitance maxima corresponding to the Josephson coupling between even parity states. We also perform charge sensing and detect odd parity states. These measurements support the theoretical model of the energy landscape of the SDD. By measuring the quantum capacitance in the time domain, we observe random switching of capacitance between two levels. We determine this to be the stochastic breaking and recombination of single Cooper pairs. By carrying out spectroscopy of the bath responsible for the pair breaking we attribute it to black-body radiation in the cryogenic environment. We also drive the breaking process with a continuous microwave signal, and find that the rate is linearly proportional to incident power. This suggests that a single photon process is responsible, and demonstrates the potential of the SDD as a single photon microwave detector. We investigate this mechanism further, and design an experiment in which the breaking rate is enhanced when the SDD is in the antisymmetric state rather than the symmetric state. We also measure the quantum capacitance of a charge isolated double dot. We observe 2e periodicity, indicating the tunnelling of Cooper pairs and the lack of occupation of quasiparticle states. This work is relevant to the range of experiments investigating the effect of non-equilibrium quasiparticles on the operation of superconducting qubits and other superconducting devices.

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Al-Khawaja, Sameer. "Time dependent phenomena in squid ring circuits". Thesis, University of Sussex, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298105.

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Espinosa, Jorge D. "Roughening of cobalt thin films on sapphire (110) upon annealing and superparamagnetic behavior of cobalt nanodots on sapphire (001)". Morgantown, W. Va. : [West Virginia University Libraries], 2004. https://etd.wvu.edu/etd/controller.jsp?moduleName=documentdata&jsp%5FetdId=3801.

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Thesis (M.S.)--West Virginia University, 2004
Title from document title page. Document formatted into pages; contains vi, 30 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 29-30).

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Skacel, Sebastian Tobias [Verfasser], i Ustinov A. [Akademischer Betreuer] V. "Development of superconducting devices employing coherent Quantum Phase Slip = Entwicklung supraleitender Bauelemente zur Untersuchung von kohärenten Quanten-Phasenschlupf Drähten / Sebastian Tobias Skacel ; Betreuer: A. V. Ustinov". Karlsruhe : KIT-Bibliothek, 2019. http://d-nb.info/1202076726/34.

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Rottier, P. A. (Pieter Adriaan). "Establishing a process for the fabrication of high-quality HTc SQUIDs". Thesis, Stellenbosch : Stellenbosch University, 2002. http://hdl.handle.net/10019.1/52828.

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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.

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Muller, Benjamin John Frederick. "The development of a SQUID-based gradiometer". Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/4378.

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Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010.
ENGLISH ABSTRACT: This thesis presents an attempt at creating a fully functional SQUID for the purposes of a predefined application. The goal of the work is to provide a method of development, primarily utilising the facilities of the Engineering Faculty of the University of Stellenbosch, with minimal assistance from other departments. This method is then analysed and the successes and failures discussed in order to provide guidelines and recommendations for future research. The device consists of a gradiometric SQUID, as well as electronics which provide the SQUID bias current, output linearisation and output signal filtering. YBCO is used for the superconducting material, allowing the use of liquid nitrogen as coolant which eases the operation and portability of the device. Various methods of creating Josephson junctions are tested, such as constriction bridges using AFM lithography and step-edge junctions, with and without different buffer layers. Proof of concept simulations demonstrate the viability of the device. Unfortunately, a functional device could not be constructed, mostly due to the design requiring higher levels of resolution and process control than some of the available facilities can provide. Recommendations are provided for future researchers.
AFRIKAANSE OPSOMMING: Hierdie tesis beskryf ’n poging om ’n volledige funksionele SQUID te vervaardig vir die doeleindes van ’n vasgestelde toepassing. Die doel van die werk is om ’n metode te voorsien wat hoofsaaklik gebruik maak van die fasiliteite van die Ingenieurswese Fakulteit van die Universiteit van Stellenbosch, met minimale hulp van ander departemente. Hierdie metode word dan ondersoek en die suksesse en mislukkings bespreek om riglyne en voorstellings te voorsien vir toekomstige navorsing. Die toestel bestaan uit ’n gradiometriese SQUID, sowel as elektronika wat voorsiening maak vir voorspanning, uittree-linearisering en ’n uittree-filter. YBCO is as supergeleidende materiaal gebruik, wat die gebruik van vloeibare stikstof as verkoeler moontlik maak en dus die hantering en draagbaarheid van die toestel vergemaklik. Verskillende metodes om Josephson-vlakke te vervaardig is getoets, onder andere vernouingsbrugvlakke deur middel van AFM litografie en stapvlakke met en sonder bufferlae. Bewys van konsep simulasies demonstreer die lewensvatbaarheid van die toestel. Ongelukkig kon ’n funksionele weergawe van die toestel nie vervaardig word nie, hoofsaaklik as gevolg van die ontwerp wat hoër resolusievlakke en beter prosesbeheer benodig as wat sekere van die beskikbare fasiliteite kan voorsien. Aanbevelings word voorsien vir toekomstige navorsers.

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Graser, Ferdl Wolfgang. "A reproducible design and manufacturing process for SQUID magnetometers". Thesis, Stellenbosch : University of Stellenbosch, 2005. http://hdl.handle.net/10019.1/1865.

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Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005.
A process was developed to design and manufacture a dc SQUID magnetometer. Superconductor theory is given as a foundation to explain the Josephson junction. This knowledge is applied to explain the ideal and practical dc SQUID. The design of the dc SQUID is done with inductance calculation formulas. Each step of the manufacturing process is discussed in detail. Many improvements have been made to the process to make each step reproducible. The steps in the manufacturing process that were done in-house are: manufacturing an YBa2Cu3O7−d pellet, depositing the thin film with the pulsed laser deposition process, creating a mask with the UV lithography process, wet etching the circuit and depositing silver contact pads with thermal evaporation. The device is packaged on a printed circuit board device holder and shielded with a mu-metal shield. A test setup is developed to test the final device. Each step in the manufacturing process was successful. The final device did not work, due to oxidisation of the YBa2Cu3O7−d thin film.

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Phiri, Temwani-Joshua. "Correlation between SQUID and fluxgate magnetometer data for geomagnetic storms". Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80364.

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Thesis (MScEng)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: Geomagnetic storms are primarily driven by the rapid transfer of energy from the solar wind to the magnetosphere. The mechanism of energy transfer involves the merging of the interplanetary magnetic field to the geomagnetic field in a process known as magnetic reconnection. This leads to an influx of energetic, charged particles into the magnetosphere so that current systems are enhanced. Specifically, an increase in the equatorial ring current leads to a decrease in the surface field. Geomagnetic storms are thus characterized by a strong decline in the horizontal components of the geomagnetic field, lasting from several hours to days. The intensity of a storm is described by the disturbed storm-time index, which is essentially a measure of the deviation from the typical quiet day variation along the equator. Severe storms can lead to the disruption of high frequency (HF) communications as a consequence of a strongly perturbed ionosphere. By the same token, the global positioning system (GPS) can become highly unreliable during magnetically disturbed conditions, yielding distance errors as large as 50 meters. The impact of geomagnetic activity and other solar-driven processes on technology systems are collectively known as space weather. Magnetic field sensing thus forms an important part of space weather forecasting and is vital to space science research as a means of improving our understanding of solar wind-magnetosphere interactions. This study examines the use of magnetometers built as SQUIDs (Superconducting Quantum Interference Devices) for monitoring the geomagnetic field for space weather forecasting purposes. A basic theory of superconductivity is presented and subsequently the key aspects governing the operation of SQUIDs are discussed. Space weather is also introduced with respect to the various processes on the sun that perturb the magnetosphere and hence the geomagnetic field. The method of analysis was basically to Fourier-transform the data using the Wiener-Khintchine theorem. A systematic approach to Fourier analysis is thus presented, demonstrating the superiority of the Wiener-Khintchine theorem in noise reduction. The suitability of SQUID magnetometers for space science research is demonstrated by a comparative study between SQUID and fluxgate datasets for magnetic storms during 2011. Strong correlation was observed between the frequency content of the SQUID and fluxgate signals. This result supports South Africa’s SQUID project, currently undertaken as a collaborative effort between SANSA Space Science and the Department of Electrical and Electronic Engineering at Stellenbosch University. This thesis thus lays a foundation for future research involving advanced magnetometry using SQUIDs.
AFRIKAANSE OPSOMMING: Geomagnetiese storms word hoofsaaklik gedryf deur die vinnige oordrag van energie van die sonwind na die magnetosfeer. Die meganisme van energie oordrag behels die samesmelting van die interplanetêre magneetveld met die geomagneetveld, in 'n proses wat bekend staan as magnetiese heraansluiting. Dit lei tot 'n instroming van energieke elektries-gelaaide deeltjies, tot in die magnetosfeer, met die gevolg dat magnetosferiese elektriese stroomstelsels versterk word. 'n Toename in die ekwatoriale ringstrome lei spesifiek tot 'n afname in die horisontale komponent van die geomagnetiese veld. Geomagnetiese storms word dus gekenmerk deur 'n sterk afname in die horisontale komponent van die geomagnetiese veld, ‘n afname wat etlike ure tot dae kan duur. Die intensiteit van 'n storm word beskryf deur die storm-tyd versteurings indeks , 'n maatstaf van die afwyking van die tipiese stil dag magnetiese variasie langs die ewenaar. Ernstige storms kan lei tot die ontwrigting van hoë frekwensie (HF) kommunikasie as 'n gevolg van 'n erg versteurde ionosfeer. Soortgelyk kan die Globale Posisionering Stelsel (GPS) hoogs onbetroubaar word tydens magneties versteurde toestande, en posisiefoute so groot as 50 meter veroorsaak. Die impak van geomagnetiese aktiwiteit en ander sonkrag gedrewe prosesse op tegnologie is gesamentlik bekend as ruimteweer. Magneetveldmetinge vorm dus 'n belangrike deel van ruimteweervoorspelling en is noodsaaklik vir ruimtewetenskaplike navorsing as 'n middel om die sonwind-magnetosfeer interaksies beter te verstaan. Hierdie studie ondersoek die gebruik van SQUID (Engels: Superconducting Quantum Interference Device) magnetometers vir die monitering van die geomagnetiese veld vir ruimteweervoorspellingsdoeleindes. ’n Basiese teorie van supergeleiding word aangebied, waarvolgens die sleutelaspekte van SQUIDs bespreek word. Ruimteweer word ook voorgestel in terme van die verskillende prosesse op die son wat die aarde se magnetosfeer en dus die geomagnetiese veld versteur. Die analisemetode wat hier gebruik word, is om die Fourier-transform van data met die Wiener-Khintchine theorema te bereken. A sistematiese metode vir Fourier-analise word aangebied, wat die superiorireit van die Wiener-Khintchine teorema vir ruisvermindering demonstreer. Die geskiktheid van SQUID magnetometers vir ruimtewetenskaplike navorsing word gedemonstreer deur ’n vergelykende studie tussen SQUID- en vloedhek-datastelle vir magnetiese storms gedurende 2011. Sterk korrelasie is waargeneem tussen die frekwensie-inhoud van die SQUID- en vloedhekseine. Hierdie resultate ondersteun Suid-Afrika se SQUID-projek, wat tans as ’n samewerkingspoging tussen SANSA Space Science en die Departement Elektriese en Elektroniese Ingenieurswese aan die Universiteit van Stellenbosch bedryf word. Hierdie tesis lê ’n fondasie vir toekomstige navorsing oor gevorderde magnetometrie met SQUIDs.

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Schoellmann, Volker. "Quantum classical interactions of a superconducting quantum interference device". Thesis, University of Sussex, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264634.

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Nturambirwe, Jean Frederic Isingizwe. "Non-destructive measurement of internal fruit quality using SQUID-NMR techniques". Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/71801.

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Thesis(MScEng)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: The SQUID-NMR technique has been increasingly recommended by many researchers as holding a lot of potential, and it is believed it will become an invaluable tool for non-destructive evaluation in the future. Most of its potential is yet to be exploited. Non-destructive quality control of food products is one of the applications where such a system is being tried. Much of the progress that has been made in improving such a system to the present degree of user friendliness and cost effectiveness shows that, with more effort, it would be possible to implement the technology for on-line sorting, and possibly to reduce it down to hand-held devices. The goal was to investigate the feasibility of the internal fruit quality measurements using the NMR technique, and to develop a SQUID system suitable for SQUID-NMR application, intended for a later integration in a full SQUID-NMR system. A working dc SQUID was manufactured on an YBCO (Y Ba2Cu3O7􀀀 ) thin film deposited on a 10 mm x 10 mm MgO substrate. The SQUID was made of microbridge Josephson junctions, patterned by using the double resist laser lithography method, implemented during the course of this manufacturing process. The test of the SQUID showed a non-hysteretic current-voltage characteristic. Under the action of bringing a magnet closer to the SQUID under test, and then retracting it, the modulation of the I-V curve was observed. The critical current of the SQUID was 20 A and the resistance was 5.5 A series of experiments were performed on destructive measurements of the sugar content in table grapes using NMR, in order to evaluate the feasibility of this technique. The total sugars(TSS) measurements of the same samples were carried out by refractometry, chosen as a conventional method for validation. The NMR measurements were evaluated to be 5.4% precise and have an accuracy of 9.3% relative to the refractometry measurements. A further series of experiments were carried out on a high-Tc SQUID-NMR system. A high correlation coefficient (0.85) of the increasing values of the T1 and T2 relaxation times to the decreasing concentration of sugar (sucrose) in water was obtained. Non-destructive measurements T1 and T2 in table grapes suggested a possible prediction of sugar content in table grapes from the values of T1 or T2. This technique also presented many advantages compared to the conventional high field NMR technique, such as the fast measurements that do not require spectral processing, the ease of sample preparation, and its non-destructive nature.
AFRIKAANSE OPSOMMING: Die SQUID-NMR tegniek word al hoe meer aanbeveel deur navorsers oor die groot potensiaal, en dit beloof om in die toekoms van onskatbare waarde te wees in nie vernietigende evaluering. Die potensiaal moet grotendeels nog ontgin word, en die nie vernietigende kwaliteitsbeheer van voedselprodukte is een van die toepassings wat hier getoets word. Die vooruitgang tot dusver om die stelsel te verbeter wat die gebruikersvriendelikheid en koste-effektiwiteit betref, toon dat met effens meer moeite dit moontlik sal wees om die tegnologie aan te pas vir lynsortering van vrugte, en om dit dalk ook as handtoestel beskikbaar te stel. Die vooruitgang tot dusver om die stelsel te verbeter wat die gebruikersvriendelikheid en koste-effektiwiteit betref, toon dat met effens meer moeite dit moontlik sal wees om die tegnologie aan te pas vir lynsortering van vrugte, en om dit dalk ook as handtoestel beskikbaar te stel. Die doel is om die uitvoerbaarheid van interne vrugtekwaliteit metings deur hierdie tegniek te ondersoek en om ’n SQUID stelsel te ontwikkel wat gepas is vir SQUIDNMR toepassing, met die doel om dit later in ’n volledige SQUID-NMR stelsel te kan integreer. ’n Werkende GS-SQUID is vervaardig op ’n YBCO dunfilm wat op ’n 10 mm x 10 mm MgO substraat gedeponeer is. Die SQUID is van mikro-brug Josephson aansluitings/ voegvlakke, waarop in die loop van die vervaardigingsproses ’n patroon m et dubbelweerstand laser litografie neergelê is. Toets van die SQUID het ’n niehisterese stroom-spanning as kenmerkend getoon. Die nader bring en terugtrekking van ’n magneet het gelei tot waarneming van die modulasie van die I-V kurwe. Die kritieke stroom van die SQUID was 20 A en die weerstand was 5.5 ohm. ’n Reeks eksperimente is uitgevoer oor vernietigende metings van die suikerinhoud van tafeldruiwe met gebruik van NMR, om die gangbaarheid van hierdie tegniek te evalueer. Totale suikers (TSS) metings van dieselfde monsters is uitgevoer deur refraktometrie, wat gekies is as gebruiklike metode vir geldigheidsbepaling. Die NMR metings is as 5.4% presies/noukeurig evalueer, en met ’n akkuraatheid van 9.3% teenoor die refraktometrie metingsyfers. ’n Verdere reeks eksperimente is uitgevoer op ’n hoë-Tc SQID-NMR stelsel. ’n Hoë korrelasiekoëffisiënt van 0.85 van die toenemende waardes van T1 en T2 ontspantye teenoor die afname in konsentrasie van sukrose in water is waargeneem. Nie-vernietigende metings van T1 eb T2 in tafeldruiwe het gelei tot die moontlikheid van gebruik van hierdie tegniek om suikerinhoud van tafeldruiwe te voorspel. Die tegniek het ook baie voordele getoon in teenstelling met die gebruiklike hoëveld NMR tegniek, onder andere dat hierdie metings vinniger is, nie verdere verwerking van die spektrum benodig nie, die maklike voorbereiding van die monsters en die nie-vernietigende aard van die proses.

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Matladi, Thabang-Kingsley. "Correlation between SQUID and Fluxgate Magnetometer Data-sets for Geomagnetic Storms: Hermanus". Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86627.

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Thesis (MEng)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Superconducting QUantum Interference Devices (SQUIDs) are fairly recent types of magnetometers that use flux quantization combined with Josephson tunnelling to detect very faint (< 10¯15 T) magnetic fields. Recent scientific studies have shown that these highly sensitive magnetometers, located in an ultra-low-noise environment, are capable of observing Earth-ionosphere couplings, such as P waves emitted during earthquakes or magnetic storms in the upper atmosphere, S and T breathing modes of the Earth during quiet magnetic and seismic periods, signals in time correlating with sprites. Since SQUIDs are much more sensitive than conventional magnetometers, they are arguably the best tool for understanding space weather and natural hazards, whether they are produced from space or within the ionosphere by magnetic storms for instance, or natural disturbances, including magnetic disturbances produced by earthquakes or as a result of the dynamics of the earth's core. A study was conducted at SANSA Space Science in Hermanus, Western Cape, in 2012, to find the correlation between SQUID and Fluxgate data-sets, with the aim of validating the use of a SQUID as a reliable instrument for Space Weather observations. In that study, SQUID data obtained from the Low Noise Laboratory (LSBB) in France was compared to Fluxgate data-sets from the three closest magnetic observatories to LSBB, namely Chambon la For êt (France), Ebro (Spain) and Fürstenfeldbruck (Germany), all further than 500 km from LSBB. As a follow-up study, our aim is to correlate the SANSA Space Science SQUID data at Hermanus with Fluxgate magnetic data also recorded on-site (at Hermanus). There are notable di_erences between the previous study and the current study. In the previous study, the three-axis SQUID used comprised of three low-Tc devices operated in liquid helium (4.2 K) in an underground, low noise environment shielded from most human interferences. The SQUID magnetometer operated at Hermanus for the duration of this study is a high-Tc two-axis device (measuring the x and z components of the geomagnetic field). This SQUID magnetometer operates in liquid nitrogen (77 K), and is completely unshielded in the local geomagnetic field of about 26 uT. The environment is magnetically clean to observatory standards, but experiences more human interference than that at LSBB. The high-Tc SQUIDs also experience excessive 1/f noise at low frequencies which the low-Tc SQUIDs do not suffer from, but the big advantage of the current study is that the SQUIDs are located within 50 m from the observatory's fluxgate. We thus expect far better correlation between SQUID and fluxgate data than what was obtained in the previous study, which should improve the isolation of signals detected by the SQUID but not by the fluxgate.
AFRIKAANSE OPSOMMING: SQUIDs (supergeleidende kwantuminterferensietoestelle) is redelik onlangse tipes magnetometers wat vloedkwantisering saam met Josephson-tonneling gebruik om baie klein (< 10¯15 T) magnetiese velde waar te neem. Onlangse wetenskaplike studies het getoon dat hierdie hoogs sensitiewe magnetometers die vermoë het om Aarde-ionosfeerkoppeling waar te neem wanneer dit in 'n ultra-laeruisomgewing geplaas word. Sodanige koppeling sluit in: P-golwe wat deur aardbewings or magnetiese storms in die boonste atmosfeer veroorsaak word; S- en T-asemhalingsmodusse van die Aarde gedurende stil magnetiese en seismiese periodes; en seine in tyd wat korreleer met weerligeffekte in die boonste atmosfeer. Aangesien SQUIDs heelwat meer sensistief is as konvensionele magnetometers, is dit moontlik die beste gereedskap om ruimteweer en geassosieerde natuurlike gevare mee te analiseer; hetsy sulke toestande veroorsaak word vanaf die ruimte (deur die son) of binne die ionosfeer deur magnetiese storms of natuurlike steurings wat deur aardbewings of die dinamika van die Aardkern veroorsaak word. 'n Studie is in 2012 gedoen by SANSA Space Science in Hermanus in die Wes-Kaap om die korrelasie tussen SQUID- en vloedhekdatastelle te vind met die doel om SQUIDs as betroubare instrumente vir ruimteweerwaarneming te bevestig. In daardie studie is SQUID-data verkry vanaf die Laeruis Ondergrondse Laboratorium (LSBB) in Frankryk, en is dit vergelyk met vloedhekdatastelle vanaf die drie naaste magnetiese observatoriums aan LSBB, naamlik: Chambon la Forêt (Frankryk), Ebro (Spanje) en Fürstenfeldbruck (Duitsland). Al drie hierdie observatoriums is verder as 500 km vanaf LSBB. As 'n opvolgstudie is ons doelwit om SQUID- en vloedhekdata wat beide op die terrein van SANSA Space Science in Hermanus waargeneem word, te korreleer. Daar is merkbare verskille tussen hierdie en die vorige studies. In die vorige studie is 'n drie-as lae-Tc SQUID-magnetometer in vloeibare helium (4.2 K) in 'n laeruis ondergrondse laboratorium, afgeskerm teen menslike steurings, gebruik. Die SQUID-magnetometer wat vir die duur van die huidige studie by Hermanus gebruik is, is 'n hoë-Tc twee-as toestel (wat die x - en z -komponente van die geomagnetiese veld meet). Hierdie SQUID-magnetometer opereer in vloeibare stikstof teen 77 K, sonder enige afskerming in die geomagnetiese veld van ongeveer 26 uT. Die omgewing is magneties skoon volgens observatoriumstandaarde, maar ondervind meer menslik-veroorsaakde steurings as LSBB. Die hoë-Tc SQUIDs tel ook heelwat 1/f ruis op (wat lae-frekwensiemetings beïnvloed); iets wat nie 'n rol speel by die lae-Tc SQUIDs nie. Die groot voordeel van die huidige studie is dat die SQUIDs binne 50 meter vanaf die observatorium vloedhekke geleë is. Ons verwag dus heelwat beter korrelasie tussen SQUID- en vloedhekdata as wat met die vorige studie verkry is, wat dit makliker sal maak om die isolasie te verbeter van seine wat deur die SQUIDs waargeneem is, maar nie deur die vloedhekke nie.

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Van, Zyl Derrick Steven. "SQUID detected low-field NMR for the evaluation of internal fruit quality". Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/5208.

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Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010.
ENGLISH ABSTRACT: Assessing the quality of fruit has become vitally important for farmers and growers. With retailers placing ever stricter requirements on fresh produce, growers have to spend a greater amount of time and effort sorting and grading their harvest. Increasingly, vendors are placing requirements not only on external factors like colour, and firmness, but on internal quality factors such as sugar content and acidity, because, although consumers buy fruit based on their external appearances, the taste of the fruit is what determines whether the consumer will buy again. Different techniques exist that probe the internal quality of fruit non-destructively. The technique most widely used today is Near Infrared Spectroscopy. This technique is powerful, but has certain limitations such as poor reliability and the need for constant recalibration. This thesis suggests an alternative method for evaluating internal fruit quality based on low-field nuclear magnetic resonance detected by superconducting quantum interference devices. It introduces the theory of SQUIDs and NMR, and evaluates the use of SQUID detected NMR spectroscopy as a method for determining the internal quality of fruit. The fabrication techniques and processes are explained in detail and a design for a SQUID detected NMR spectrometer is given. Relevant simulations and simulation results are also given. No working SQUID could be fabricated and, as such, no working NMR spectrometer was demonstrated. This thesis serves as a reference work for future research.
AFRIKAANSE OPSOMMING: Bepaling van die gehalte van vrugte het vir boere uiters belangrik geword. Met kleinhandelaars wat al strenger vereistes plaas op vars produkte moet boere meer tyd en inspanning bestee met die sortering en gradering van hul oes. Handelaars plaas nie net vereistes op eksterne kwaliteitsfaktore soos kleur en fermheid nie, maar begin al hoe strenger vereistes plaas op interne kwaliteitsfaktore soos suikerinhoud en suurgehalte, want, hoewel verbruikers vrugte koop op grond van hul eksterne kwaliteitsfaktore, is dit die smaak van die vrug wat bepaal of die verbruiker weer die vrug sal koop. Verskillende tegnieke bestaan wat die interne kwaliteit van vrugte op ’n nie-destruktiewe manier kan bepaal. Die mees algemene tegniek is Naby Infrarooi Spektroskopie. Hierdie tegniek is kragtig maar het sekere beperkings soos swak betroubaarheid en die noodsaaklikheid van konstante herkalibrasie. Hierdie tesis stel ’n alternatiewe metode vir die evaluering van interne vrugkwaliteit gebaseer op lae-veld kernmagnetiese resonans waargeneem deur supergeleidende kwantum inmenging toestelle voor. Dit stel die teorie van SKWITs en KMR bekend, en evalueer die gebruik van SKWIT-bespeurde KMR spektroskopie as ’n metode vir die bepaling van die interne kwaliteit van vrugte. Die fabrikasie tegnieke en prosesse word in detail verduidelik en ’n ontwerp vir ’n SWKIT opgevangde KMR spektrometer word gegee. Toepaslike simulasies en simulasie resultate word ook gegee. Geen werkende SKWIT kon vervaardig word nie en as gevolg daarvan kon geen werkende KMR spektrometer gedemonstreer word nie. Hierdie tesis dien as ’n naslaan werk vir toekomstige navorsing.

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Xue, Zhengyuan, i 薛正远. "Implementation of fault-tolerant quantum computation with superconducting device". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B43085465.

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Xue, Zhengyuan. "Implementation of fault-tolerant quantum computation with superconducting device". Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B43085465.

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Figueiredo, José Jadsom Sampaio de. "Estudo das propriedades magnéticas de nanopartículas de AuPd". [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277189.

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Orientadores: Abner de Siervo e Flavio Garcia
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin.
Made available in DSpace on 2018-08-12T11:00:44Z (GMT). No. of bitstreams: 1 Figueiredo_JoseJadsomSampaiode_M.pdf: 4194889 bytes, checksum: 489e23ac30c4fa90808ef2de00ae46d4 (MD5) Previous issue date: 2008
Resumo: Nanopartículas (NPs) metálicas, filmes ultrafinos e sistemas nano-estruturados têm motivado vários estudos teóricos e experimentais devido a novas propriedades eletrônicas, óticas e magnéticas destes materiais. Nas NPs, tais propriedades estão diretamente relacionadas aos efeitos de tamanho (size effect) e superfície, os quais afetam suas estruturas eletrônica e cristalográfica, concentrando um maior número de átomos na superfície em relação ao seu volume. Estudos recentes têm sugerido que alguns metais nobres sem nenhum tipo de ordenamento ferromagnético espontâneo podem apresentá-lo, mesmo a temperatura ambiente, quando segmentados em forma de nanopartículas. Exemplos desses metais são Au e Pd. Apesar dos esforços para provar a existência de comportamento ferromagnético nestes materiais, não existem medidas que demonstrem de forma não ambígua a polarização ferromagnética nos átomos de Pd. Na maioria dos trabalhos mostrados na literatura, o ferromagnetismo é quantificado por magnetometria SQUID. Faz-se necessário, portanto, verificar a existência de ferromagnetismo nestes materiais utilizando-se de técnicas elemento específicas, tais como XMCD (dicroísmo circular magnético de raios X). Esta técnica é muito importante para determinação quantitativa e seletiva dos momentos magnéticos de spin e orbital para cada elemento separadamente. O nosso trabalho se diferencia em relação a estes, pois ao invés de estudarmos cada elemento individualmente trabalhamos com nanopartículas do composto bimetálico Aux Pd1-x (x =0,00, 0,25, 0,50, 0,75) passivadas por tiol. Medidas de SQUID indicaram claramente um sinal magnético nestas nanopartículas, inclusive à temperatura ambiente. Neste trabalho apresentaremos os resultados preliminares da caracterização destas nanopartículas por medidas de SQUID, XANES, XPS, bem como XMCD nas bordas L2,3 do Pd e L3 do Au . Ressaltamos também, o desenvolvimento de uma instrumentação para medidas de XMCD em ambientes de UHV onde é possível submeter às amostras a altos campos magnéticos e condições de baixas temperaturas. Com base nos resultados obtidos discutiremos a possibilidade de ferromagnetismo nestas nanopartículas e sua origem.
Abstract: Metallic Nanoparticles (NP's), ultra-thin films and nano-structured systems have motivated several theoretical and experimental works because of their new electronic optical and magnetic properties of these materials. In NP's, such properties are directly related to the size and surface effects, which affect its electronic and crystallographic structures, by concentrating a larger number of atoms on the surface in relation to their volume. Recent studies have suggested that some noble metals without any kind of spontaneous ferromagnetic order can exhibit it, even at room temperature, when segmented as nanoparticles. Examples of these metals are Au and Pd. Despite the efforts to prove the existence of a ferromagnetic behavior in such materials, there are no measurements that demonstrate unambiguously the ferromagnetic polarization in Pd atoms, for example. Most of the works shown in the literature have used SQUID measurements to characterize the ferromagnetism in these materials. It is therefore necessary to verify the existence of ferromagnetism in these materials by using element specific techniques, such as XMCD (X-ray magnetic circular dichroism). XMCD is a very important technique, which is element selective and performs quantitative determination of the spin and orbital magnetic contributions for each element separately. Our work has a particular difference when compared to others in literature because instead of studying each element individually we have worked with NP's of the bimetallic compound Aux Pd1-x (x = 0.00, 0.25, 0.50, 0.75) capped by thiol. SQUID measurements clearly showed ferromagnetic behavior in these nanoparticles, even at room temperature. In this thesis we will present results of a systematic characterization of these nanoparticles by a multi-technique approach which involves measurements with SQUID, XANES, XPS and XMCD in the L2,3 edges of the Pd and Au L3 edge. We also emphasize the development of a new instrumentation for XMCD measurements at UHV where samples can be submitted to high magnetic fields and conditions of low temperatures. Based on these findings we discuss the possibility of ferromagnetism in these nanoparticles and its origin.
Mestrado
Física da Matéria Condensada
Mestre em Física

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LOLLI, LAPO. "Photon-Number Resolving by Superconductive Devices". Doctoral thesis, Politecnico di Torino, 2012. http://hdl.handle.net/11583/2497951.

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Strong interests on optical quantum based metrology, quantum information and particularly in quantum cryptography are continuously growing. The main limitations to the developments in these fields are due to non-ideal devices: both single photon sources and single photon detectors. In these field of applications, detectors require to be able to resolve the number of photons in a light pulse. Presently state of the art indicates that classical semiconductor light detectors (i.e. avalanche photodiode or single photon avalanche diode) are not able to discriminate the number of photon arriving at the same time. In the meanwhile, superconducting devices have shown the possibility to resolve single photon pulses. One of the most promising superconducting detectors is the Transition-Edge Sensor (TES): a microcalorimeter that takes advantage of the sharp transition (few millikelvin) from the superconducting to the normal phase; for this reason it is sometimes called Superconductive Phase Thermometer (SPT). In the ultraviolet (UV) to infrared (IR) wavelength range, the photons are absorbed directly by the superconductive thin film and the absorbed energy induces an increase of the TES resistance. Thanks to the applied bias voltage, which maintains the device in the transition region the photon absorption induces a decrease of the TES current, measured by a dc-SQUID amplifier, and the pulse integral of the bias power reduction corresponds to the absorbed energy. This means that TESs have the very interesting properties to be able to detect single photons with an intrinsic energy resolution, without filters or gratings, that limit the quantum efficiency. By contrary of classical detectors, if monochromatic light irradiates TESs, as usually happens in communication systems, they show the photon-number resolving (PNR) capability and due to the good signal to noise ratio TESs are almost free from dark counts. Moreover, in the superconducting detector family, TESs are the only true photon-number resolving detectors operating in the VIS-NIR range. Together with quantum information science, the PNR property results useful even for optical radiometry too. In the optical community, the candela - the International System (SI) unit for the luminous intensity - has not a common consensus whether its present definition fully satisfies the current and future needs of growing associated technology. Furthermore, actually there are substantial efforts directed toward a new definitions of four base SI units: the proposal wants to link the SI units to fundamental constants, leaving f.i. material artifact. Considering the recent advances in optical radiometry and in quantum technologies, for the candela world it means redefine its unit linking to the Planck constant and consequently expressing the luminous intensity unit in terms of photon number rather than optical power. This challenge has been accepted by several national metrology institutes to demonstrate the feasibility of redefining the candela. Inside this research project called `qu-candela', the TES PNR capability has been considered to build the bridge between the quantum and classical world of radiometry: i.e. the detector possibility to measure optical powers from one single photon per second to the lower limits of cryogenic radiometry, 104 photons per second. The theme of this work of thesis is to investigate both optical and electrical characterization of different kind of TESs based on a titanium/gold multilayer film, produced and developed at the National Institute of Metrological Research (INRIM) of Torino. Thanks to the proximity effect, the multilayer allows to lower with continuity the critical temperature from that of the Ti bulk (Tc ~ 390 mK) to those of interest: ~ 300 mK and ~ 100 mK. Detectors with higher Tc have shown a faster response pulse with a relaxing time constant of the order of 200 ns, while for the lower Tc sensors, the time constant is about 10 µs. By contrary to the response time, the detector intrinsic energy resolution is proportional to its film critical temperature. Our sensors work to discriminate incident photon from UV wavelengths to those typical of the telecommunications, 1310 nm and 1550 nm. Irradiating a TES with an active area of 10x10 µm^2 by incident photons of 0.79 eV (corresponds to a wavelength 1570 nm), the best energy resolution obtained has been 0.18 eV. Detectors with higher active area 20x20 µm^2 have a worse energy resolution, because it is also proportional to the material film heat capacity. In the meanwhile due to the same reason these kind of sensors present a bigger saturation energy. This has allowed to investigate on the TES capability to discriminate up to 29 incident photons simultaneously. Until now, such count represents the bigger amount of photons discriminated by single photon detectors, without reaching the device saturation, with a linear behaviour. From this count it has been estimated 12 photons on average, per pulse, at 9 kHz repetition rate; this results in a photon flux of about 105 photons/s, demonstrating the possibility of having a detector able to work from low flux regime to 1 photon/s to flux measurable by conventional semiconductor device (f.i. single photon avalanche detector SPAD). An innovative absolute calibration technique for PNR detector has been demonstrated. The absolute technique is based on the Klyshko's efficient solution to measure detection efficiency in photon counting rate and well know for common click-no-click detector. In fact, exploiting the recent developments in quantum state world, it is possible to work with quasi single photon state, by using a parametric down conversion heralded single photon source, and calibrate PNR detectors without requiring reference standards. The best detection efficiency, of ca. 50%, has been reached by coupling the smaller active area detectors with a 9 µm core optical fiber, single mode at telecom wavelengths.

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Millar, Alasdair J. "Step edge Josephson junctions and high temperature superconducting quantum interference device (SQUID) gradiometers". Thesis, University of Strathclyde, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249130.

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This thesis is concerned with the development of Superconducting Quantum Interference Device (SQUID) gradiometers based on the high temperature superconductor YBa2Cu3O7-o (YBCO). A step-edge Josephson junction fabrication process was developed to produce sufficiently steep (> 60°) step-edges such that junctions exhibited RSJ-like current-voltage characteristics. The mean I(RN product of a sample of twenty step-edge junctions was 130jtV. Step-edge dc SQUIDs with inductances between 67pH and 114pH were fabricated. Generally the SQUIDs had an intrinsic white flux noise in the 10-30μ(Do/ Hz range, with the best device, a 70pH SQUID, exhibiting a white flux noise of 5μ4bo/ Hz. Different first-order SQUID gradiometer designs were fabricated from single layers of YBCO. Two single-layer gradiometer (SLG) designs were fabricated on 10 x 10mm2 substrates. The best balance and lowest gradient sensitivity measured for these devices were 1/300 and 308fT/cm Hz (at 1kHz) respectively. The larger baseline and larger flux capture area of the pick-up loops in a large area SLG design, fabricated on 30 x 10mm2 substrates, resulted in significant improvements in the balance and gradient sensitivity with 1/1000 and 50fT/cm Hz (at 1kHz) measured respectively. To reduce the uniform field effective area of SLGs and therefore reduce the direct pick-up of environmental field noise when operated unshielded, a novel gradiometric SQUID (G-SQUID) device was developed. Fabricated from a single layer of YBCO, the G-SQUIDs, with inductances of 67pH, had small uniform field effective areas of approximately 2μm2 - more than two orders of magnitude smaller than the uniform field effective areas of conventional narrow-linewidth SQUIDs of similar inductance. Two designs of G-SQUID SLGs were fabricated on 10 x 10mm2 substrates. Due to their small effective areas, when cooled unshielded these devices showed no increase in their white flux noise. The best balance achieved for a G-SQUID SLG was approximately 1/5000 - an order of magnitude better than the balance of similar SLGs incorporating conventional narrow-linewidth SQUIDs.

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Ngankio, Njila Joël Roméo. "Analyse d'une nouvelle architecture pipeline de convertisseur analogique numérique supraconducteur". Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENT006/document.

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L'objectif de ce travail était d’élaborer la brique de base d'un convertisseur analogique numérique supraconducteur à architecture pipeline, fonctionnant à 30GHz de fréquence d’échantillonnage. Ce convertisseur est constitué d’un bloc de N comparateurs disposés en cascade le long d’une ligne de transmission. Chaque étage de comparaison est constitué d'un SQUID rf mutuellement couplé à un tronçon de ligne de transmission. Lorsque le signal à convertir arrive à la hauteur d'un comparateur, il génère un champ magnétique qui induit un courant dans le SQUID rf. Ce courant pourra faire commuter la jonction Josephson du SQUID rf dans certains cas, en fonction des caractéristiques internes de la jonction Josephson du SQUID et de son environnement. La commutation, qui s’accompagne de l’apparition d’une impulsion de tension quantifiée SFQ, a été étudiée de manière théorique et expérimentale en fonction des différents paramètres du problème
Superconductive analogue to digital converters (ADC) generally have speed and power dissipation advantages which should enable their application in telecommunication, medicine, and where an analogue signal (delivered e.g. by a sensor) needs to be digitized for post-processing.We are developing a new concept of analogue to digital converter using high critical temperature (Tc=90K) superconductors and operating at 30GHz; this converter is based an original structure, the pipeline architecture. The principle is to place a cascade of N comparators along a transmission line on which propagates the up-converted analogue signal. The carrier frequency is used in this case as a sampling signal.Each comparator, made with a SQUID loop, produces one bit at the carrier frequency: it codes the input signal by generating or not an RSFQ pulse (respectively "1” or “0"), and passes the residue (attenuated signal) in the following comparator.Here, we present steps for the comparator optimisation and mask design.Besides simulation results, we present the measurements at 30GHz carrier frequency of the comparator designed at low critical temperature (LTS). Finally, we suggest other tools to develop the optimised low critical temperature converter and we proposed the concept of the comparator operating at high critical temperature (HTS)

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Otto, Ernst. "Development of superconducting bolometer device technology for millimeter-wave cosmology instruments". Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:30a1103a-ea7a-4b08-ba92-665cbd9740e0.

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The Cold-Electron Bolometer (CEB) is a sensitive detector of millimeter-wave radiation, in which tunnel junctions are used as temperature sensors of a nanoscale normal metal strip absorber. The absorber is fed by an antenna via two Superconductor-Insulator-Normal metal (SIN) tunnel junctions, fabricated at both ends of the absorber. Incoming photons excite electrons, heating the whole electron system. The incoming RF power is determined by measuring the tunneling current through the SIN junctions. Since electrons at highest energy levels escape the absorber through the tunnel junctions, it causes cooling of the absorber. This electron cooling provides electro-thermal feedback that makes the saturation power of a CEB well above that of other types of millimeter-wave receivers. The key features of CEB detectors are high sensitivity, large dynamic range, fast response, easy integration in arrays on planar substrates, and simple readout. The high dynamic range allows the detector to operate under relatively high background levels. In this thesis, we present the development and successful operation of CEB, focusing on the fabrication technology and different implementations of the CEB for efficient detection of electromagnetic signals. We present the CEB detector integrated across a unilateral finline deposited on a planar substrate. We have measured the finline-integrated CEB performance at 280-315 mK using a calibrated black-body source mounted inside the cryostat. The results have demonstrated strong response to the incoming RF power and reasonable sensitivity. We also present CEB devices fabricated with advanced technologies and integrated in log-periodic, double-dipole and cross-slot antennas. The measured CEB performance satisfied the requirements of the balloon-borne experiment BOOMERANG and could be considered for future balloon-borne and ground-based instruments. In this thesis we also investigated a planar phase switch integrated in a back-to-back finline for modulating the polarization of weak electromagnetic signals. We examine the switching characteristics and demonstrate that the switching speed of the device is well above the speed required for phase modulation in astronomical instruments. We also investigated the combination of a detector and a superconducting phase switch for modulating the polarization of electromagnetic radiation.

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Berritta, Marco. "Coherent Nanostructures: Dynamics control and noise". Doctoral thesis, Università di Catania, 2013. http://hdl.handle.net/10761/1432.

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In the last three decades the scienti c community has been attracted by the possibility of controlling quantum system, for example for quantum computing or quantum simulators. Initially this idea was exploited only in microscopic quantum system as atoms and molecules. However these sys-tems present diffi culties on the large scale application due to the extreme laboratory condition that they need, for example ultra low temperature of the order of 1 microKelvin. On the other hand, great progress has been made with superconducting nanodevices, that can be more easily scaled. One of the most important problems that arise in quantum control is decoherence. We will study quantum control for coherent superconducting nanodevices. This devices are aff ected by a Broad Band Colored and Structured (BBCS) noise, which is qualitatively di fferent to what encountered in atomic physics, since it is chatacterized by a strong non-Markovian low-frequency component with a characteristic power spectrum S (f) proportional to 1/f. In this thesis we will present a roundup of physical situations, inolving both undriven and externally driven open quantum systems, which need to be analyzed in the perspective of quantum control. Promising applications to superconducting nanodevices, as the implementation of "Lambda" systems, possibly allowing control of microwawe photons, are discussed in detail. The thesis is structured as follows. Chapter 1 is an overview of the theoretical background of quantum control and quantum computation. In chapter 2 an archetypical problem for driven quantum systems, namely the Rabi problem, is studied in the presence of BBCS low-frequency noise which is not accounted for in standard Master Equation treatments based on the Markovian assumption. In chapter 3 a protocol named STImulated Raman Adiabatic Passage (STIRAP) is studied in the presence of BBCS noise, in view of its implementation in a class of superconducting nanode-vices named Cooper Pair Box. This is done in chapter where Design and control requirements to achieve large e fficiency are discussed, and a new figure of merit is introduced to characterize the tradeoff between effi cient coupling of the control and noise. Actually selection rules due to charge-parity simmetry make impossible operate STIRAP in these device in the regime of maximum protection from noise. Therefore in chapter 5 we propose a new implementation of STIRAP with superconductive device that allows us to circumvent selection rules, based on three-photon coherent processes and suitable crafted pulses compensating the Stark shifts. In chapter 6 we will study the problem of the tunneling of a quantum particle with strongly coupled environment in a bistable pontential. Finally in chapter 7 the study of the motion of a chiral quasiparticle in graphene a ffected by white noise will be presented.

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Fedortchenko, Sergueï. "The ultrastrong coupling regime as a resource for the generation of nonclassical states of light". Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCC279/document.

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Depuis l’avènement de la mécanique quantique, l’étude des interactions lumière-matière à l’échelle quantique s’est énormément développée en tant que domaine de recherche. Par exemple, grâce à des prédictions théoriques surprenantes, des interactions d’une force sans précédant ont été démontrées entre de la matière et des radiations terahertz et microonde. Ces résultats correspondent à un régime dit de couplage ultrafort, atteint lorsque l’énergie d’interaction devient comparable aux énergies propres de la lumière et de la matière lorsque celles-ci n’interagissent pas. Dans ce régime, des propriétés intrigantes peuvent subsister telles que la présence de photons même lors qu’aucune énergie n’est fournie au système. Cependant, ces photons ne peuvent, a priori, être émis du système vers l’extérieur de manière à pouvoir être mesurés et par conséquent démontrer ces propriétés.Dans cette thèse, nous avons étudié ces propriétés intrigantes et proposé plusieurs moyens permettant d’y accéder expérimentalement. Nous nous sommes appuyés sur plusieurs plate-formes physiques qui sont de bon candidats pour ces études, et pour chacun de ces systèmes nous avons mis au point un modèle mettant en évidence ces propriétés d’une manière ou d’une autre. De cette façon, nous avons exploré le lien entre le régime de couplage ultrafort et la génération d’états non-classiques de la lumière. En outre, dans une étude plus ouverte nous avons montré que les interactions lumière- matière dans l’une de ces plate-formes peuvent être utilisés pour concevoir des protocols de communication quantique. En plus de montrer un intérêt fondamental, nos résultats s’inscrivent dans une optique de développement d’applications pour les technologies quantiques en utilisant différents systèmes expérimentaux disponibles actuellement
Since the advent of quantum mechanics, the study of light-matter interactions at thequantum level has been greatly developed as a research field. For instance, surprisingtheoretical predictions gave rise to experiments with unprecedented interactionstrengths between matter, and terahertz and microwave radiations. These results correspondto the so-called ultrastrong coupling regime, that is reached when the interactionenergy becomes comparable to the typical energies of the light and matter when they arenot interacting. In this regime, intriguing properties can be found such as the presenceof photons even when no energy is given to the system. However, these photons cannot,a priori, be emitted from the system to the outside world in order to be measured andtherefore demonstrate these properties. In this thesis, we studied these intriguing properties and proposed several means toaccess them experimentally. We relied on several physical platforms which are goodcandidates for such studies, and for each one of these systems we devised a model thatcan evidence these properties one way or another. By doing so, we explored the linkbetween the ultrastrong coupling regime and the generation of nonclassical states oflight. Additionally, as an outlook we showed that the light-matter interactions in oneof these platforms could be used to design quantum communication protocols. On topof showing fundamental interest, our results fit in the line of developing applications forquantum technologies using different experimentally available systems

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Lochner, Emile Tobias. "Towards a global SQUID network through optimal monitoring station design". Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/96817.

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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.

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Ley, Li Yuan [Verfasser], i József [Akademischer Betreuer] Fortágh. "Coupling of Rydberg atoms to a superconducting coplanar waveguide resonator for a quantum memory device / Li Yuan Ley ; Betreuer: József Fortágh". Tübingen : Universitätsbibliothek Tübingen, 2018. http://d-nb.info/1169652417/34.

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Humphrey, Kevin P. "An actively shielded, adaptively balanced high temperature superconducting quantum interference device ( SQUID ) gradiometer capable of detecting moving targets from a mobile platform". Thesis, University of Strathclyde, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431813.

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Bovo, Laura. "Nanostructured Materials Based on ZnO for Cataltytic, Optical and Magnetic Applications". Doctoral thesis, Università degli studi di Padova, 2011. http://hdl.handle.net/11577/3423214.

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ZnO based materials, such as Zn1-xTMxO (TM = Mn, Co, Cu) nanopowders, were synthesised by a Sol gel route to investigate their properties in three fields: catalysis, optics and magnetism. These materials were characterised by complementary techniques such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and UV-Vis Spectroscopy. The fine structure and electronic properties of these nanomaterials were studied by X-ray Absorption Spectroscopy (XAS) and Electron Paramagnetic Resonance (EPR). These techniques give site, element and chemical specific measurements which allow a better understanding of the interplay and role of each element in the functionality of the system. The catalytic performance of undoped and Cu-doped ZnO nanosystems were tested with respect to the Methanol Steam Reforming (MSR) reaction. Contrary to what is generally accepted in literature, the results obtained in this study demonstrate that ZnO also plays a prominent role in this catalytic process. The structure–activity relationship of ZnO and copper-doped ZnO catalysts described in this work give an insight into the effective function of each component which is vital to enable the rational design of improved catalysts. The luminescence properties of the doped Zn1-xTMxO nanopowders were investigated with X-ray Excited Optical Luminescence (XEOL) techniques: these experiments provided a better understanding of the relationship between the electronic structure of the systems and their properties. Results showed how it is possible to manipulate the luminescence of ZnO grown by Sol gel by modifying synthesis conditions – i.e. the annealing temperature and the nature and concentration of the transition metal ion. Finally, preliminary results were presented on the materials' magnetic properties, obtained by SQUID (Superconducting Quantum Interference Devices) magnetometry, where the coexistence of different contributions has been detected. Even though further characterisation is still needed, this study is a step towards the determination of the nature of magnetic interactions in such systems, of which there has been considerable debate in the scientific community.
Materiali a base di ZnO, in particolare nano-polveri di Zn1-xTMxO (TM = Mn, Co, Cu), sono stati sintetizzati via Sol gel per studiarne le proprietà in tre diversi campi applicativi quali la catalisi, l’ottica ed il magnetismo. Tali materiali sono stati caratterizzati utilizzando diverse tecniche, complementari tra loro, quali X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) e UV-Vis Spectroscopy. X-ray Absorption Spectroscopy (XAS) ed Electron Paramagnetic Resonance (EPR) vengono invece impiegate per studiare le proprietà elettroniche e di struttura fine delle nano-polveri. Tali caratterizzazioni si sono dimostrate fondamentali per la comprensione delle proprietà del sistema ed, in particolare, per cercare di identificare le interazioni sussistenti tra struttura, composizione, morfologia dei materiali e la loro capacità di espletare una determinata funzionalità. Nano-polveri di ZnO tal quali e drogate con ioni rame vengono testate come catalizzatori nella reazione di Steam Reforming del metanolo. I risultati ottenuti in questo studio dimostrano il ruolo attivo dell’ossido di zinco nel processo catalitico, contrariamente a quanto solitamente accettato in letteratura. La relazione sussistente tra struttura-attività nei catalizzatori a base di ZnO permette di ottenere informazioni circa l’effettiva funzione di ogni componente, aspetto di estrema importanza per la progettazione razionale di catalizzatori con elevate performance. Le proprietà di luminescenza dei sistemi drogati Zn1-xTMxO vengono studiate mediante spettroscopia X-ray Excited Optical Luminescence (XEOL); tali esperimenti forniscono una migliore comprensione del rapporto che sussiste tra la struttura elettronica dei sistemi in esame e le loro proprietà di emissione. I risultati mostrano come sia possibile modulare la luminescenza di ZnO prodotto via Sol gel modificando le condizioni di sintesi – i.e. temperatura di trattamento, natura e concentrazione del metallo di transizione utilizzato come drogante. Infine, risultati preliminari sulle proprietà magnetiche dei materiali ottenuti mediante SQUID magnetometer (Superconducting Quantum Interference Devices) hanno rivelato la coesistenza di diversi contributi magnetici. Nonostante ulteriori caratterizzazioni siano sicuramente necessarie, questo studio si è rivelato un passo avanti verso una comprensione della natura delle interazioni magnetiche in tali sistemi, da tempo causa di vivace dibattito nella comunità scientifica.

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Malassis, Roger. "Thermometre a bruit fonctionnant entre 1 et 7 kelvins". Paris 6, 1987. http://www.theses.fr/1987PA066504.

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Labbe, Aimé. "Développement d'antennes supraconductrices basées sur les réseaux de SQUID pour la résonance magnétique nucléaire à champ faible". Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0166/document.

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L'imagerie par résonance magnétique (IRM) est une modalité qui offre de bons contrastes et une bonne résolution spatiale, mais qui souffre d'un important problème de sensibilité. Pour répondre à cette problématique, le paradigme actuel est d'accroitre le champ magnétique des aimants d'IRM. Ceci mène toutefois à une explosion des coûts et à des contraintes accrues vis-à-vis des patients. L'approche que nous présentons est radicalement différente~: il s'agit de travailler à champ faible. Les antennes classiques n'étant pas assez sensibles pour recueillir le signal, l'idée est d'utiliser des SQIF. Ces derniers sont une nouvelle technologie d'antennes supraconductrices ultra-sensibles basées sur les réseaux de SQUID. Le projet vise à optimiser les capteurs SQIF et à les adapter pour la première fois à la RMN afin de mesurer un signal sur un aimant à 0.2~T.Pour ce faire, nous avons développé et étudié les performances de nouvelles architectures d'antennes SQIF afin de définir la géométrie la plus adaptée à la RMN. Nous avons également cherché à mieux comprendre comment le contexte d'utilisation de ces nouvelles antennes pouvait influencer leurs performances. Le jeu d'antennes le plus performant réalisé avait un facteur de transfert de 8.4~kVperT et un seuil de détection de 190~fTperHz. Il fut également observé que la présence d'un champ magnétique pendant le refroidissement de ces capteurs supraconducteurs dégradait leur réponse, phénomène à prendre en compte en RMN.Un Démonstrateur Super-QIF intégrant un SQIF dans l'IRM à 0.2~T fut conçu en tenant compte des contraintes géométriques et de l'environnement magnétique. Après sa fabrication, la température du cryostat était de 50~K, donc suffisante pour le bon fonctionnement des SQIF. Les premiers tests ont montrés que la présence du système ne perturbait pas le signal de RMN.Le démonstrateur est toujours en cours de développement et devrait permettre de mesurer un de RMN dans les mois à venir. À long terme, ces travaux pavent la voie à des applications des SQIF en IRM à champ terrestre
Magnetic resonance imaging (MRI) is a modality that offers good contrasts and good spatial resolution, but suffers from a significant sensitivity problem. To address this issue, the current paradigm is to increase the magnetic field of MRI magnets. However, this leads to an explosion of costs and to increased constraints on patients. The approach we present is radically different: it involves working in a weak field. As conventional antennas are not sensitive enough to collect the signal, the idea is to use SQIF. These are a new ultra sensitive superconducting antenna technology based on SQUID networks. The project aims to optimize SQIF technology and adapt it to measure an NMR signal in a 0.2~T magnet.To do this, we developed and studied the performance of new SQIF antenna architectures in order to define the geometry most suitable for NMR. We also sought to better understand how the context of use of these new antennas could influence their performance. The best performing antennas set had a transfer factor of 8.4~kVperT and a detection threshold of 190~fTperHz. It was also observed that the presence of a magnetic field during the cooling of these superconducting sensors degraded their response, a phenomenon to be accounted for in NMR.The Super-QIF Demonstrator incorporating a SQIF in the 0.2~T MRI was designed considering the geometric constraints and the magnetic environment. After its assembly, the temperature of the cryostat was 50~K, therefore sufficient for the proper operation of SQIF. The first tests showed that the system presence did not disturb the NMR signal.The demonstrator is still under development and is expected to measure an NMR signal in the forthcoming months. In the long term, this work paves the way for applications of SQIF in Earth's field MRI

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Cyrille, Marie-Claire. "Étude et réalisation de SQUIDS à polarisation continue pour l'amplification radiofréquence à très faible température de bruit". Université Joseph Fourier (Grenoble ; 1971-2015), 1996. http://www.theses.fr/1996GRE10228.

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Le squid dc (superconducting quantum device direct current) est un capteur de flux extremement sensible. Associe a un circuit de couplage approprie, il est bien adapte pour l'amplification de tres faibles signaux dans la gamme de frequence 1-150mhz. Ce travail presente l'etude de l'optimisation de l'ensemble des parametres geometriques et electriques des amplificateurs a squid ; la mise en place des procedes technologiques necessaire a leur fabrication ainsi que la mesure de leurs performances. La fabrication de jonctions josephson nb/al-alox/nb de petite surface ( 4m#2), elements de base des squids a ete etudiee puis optimisee avec une bonne reproductibilite de leurs parametres electriques. Une premiere approche du probleme a consiste a realiser et caracteriser des squids en niobium non couples. Enfin, la geometrie des squids et de leurs structures de couplage est choisie avec un large choix de parametres qui permettra ulterieurement de definir ceux les mieux adaptes a l'amplification. Un procede technologique multi-couches complet est alors defini puis etudie pour la realisation des dispositifs. Leur caracterisation electrique met en evidence la modification du fonctionnement des squids en presence de leur structure de couplage

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Migliaccio, Claire. "Passifs fonctionnels en technologie supraconductrice HTc : applications aux SQUIDs couplés HF". Grenoble INPG, 1996. http://www.theses.fr/1996INPG0020.

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Les squids (superconducting quantum interference device) sont des dispositifs supraconducteurs utilises, entre autres, en capteur de flux magnetique. Grace a leur extreme sensibilite (possibilite de detecter des champs magnetiques de 10 ft/hz a 1 hz)) ce sont les detecteurs les plus performants a l'heure actuelle. Notre etude porte sur la possibilite d'utiliser les capteurs a squids pour des applications ou la frequence de fonctionnement est de l'ordre du ghz (compatibilite electromagnetique, amplificateur pour l'instrumentation tres haute performance). Neanmoins leurs performances aux frequences elevees sont conditionnees par les elements passifs necessaires a la realisation des dispositifs a squid par integration. Il s'agit essentiellement de boucles supraconductrices de grande dimension et d'inductances planaires possedant un nombre de tours eleve. Ces derniers sont constitues de lignes de transmission associant les effets fonctionnels (pour nous inductifs) aux effets parasites (pour nous capacitifs). Nous modelisons l'ensemble des elements passifs en utilisant un solveur electromagnetique base sur la resolution des equations integrales de maxwell a l'aide de la methode des moments. Apres avoir valide notre methodologie sur des lignes supraconductrices en technologie coplanaire jusqu'a 0,96 t#c et 30 ghz, et sur des inductances planaires conductrices, nous interpretons le comportement frequentiel du squid couple. Nous en deduisons des formules de conception assistee par ordinateur ainsi qu'une procedure d'optimisation generale qui nous permet d'atteindre les frequences de fonctionnement requises

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Ghohroodi, Ghamsari Behnood. "Guided-Wave Superconducting Quantum Optoelectronic Devices". Thesis, 2010. http://hdl.handle.net/10012/5252.

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This thesis investigates a novel optoelectronic platform based on the integration of superconductive structures, such as thin films and micro-constrictions, with optical waveguides for ultra-fast and ultra-sensitive devices with applications including high-speed optical communications, quantum optical information processing, and terahertz (THz) devices and systems. The kinetic-inductive photoresponse of superconducting thin films will be studied as the basic optoelectronic process underlying the operation of these novel devices. Analytical formulation for the non-bolometric response is presented, and experimental photodetection in YBCO meander-line structures will be demonstrated. A set of superconducting coplanar waveguides (CPW) are designed and characterized, which support the operation of the devices at microwave frequencies. Microwave-photonic devices comprising a microwave transmission line and a light-sensitive element, such as a meander-line structure, are designed and measured for implementation of optically tunable microwave components. In order to support low-loss and low-dispersion propagation of millimeter-wave and THz signals in ultra-fast and wideband kinetic-inductive devices, surface-wave transmission lines are proposed, incorporating long-wavelength Surface Plasmon Polariton (SPP) modes in planar metal-dielectric waveguides. The theory of superconducting optical waveguides, including analytical formulation and numerical methods, is developed in detail. The implementation of superconducting optical waveguides is discussed thoroughly, employing conventional dielectric-waveguide techniques as well as optical SPP modes. Superconductive traveling-wave photodetectors (STWPDs) are introduced as a viable means for ultra-fast and ultra-sensitive photodetection and photomixing. A modified transmission line formalism is developed to model STWPDs, where light is guided through an optical waveguide and photodetection is distributed along a transmission line. As an appendix, a systematic approach is developed for the analysis of carrier transport through superconducting heterostructures and micro-constrictions within the Bogoliubov-de Gennes (BdG) framework. The method is applied to study the role of Andreev reflection and Josephson-like phenomena in the current-voltage characteristics of inhomogeneous superconducting structures. I-V characteristics are experimentally demonstrated in YBCO micro-constrictions with potential applications in millimeter-wave and THz devices.

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Majumder, Sourav. "Superconducting qubit-based hybrid devices". Thesis, 2022. https://etd.iisc.ac.in/handle/2005/6074.

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Quantum technology has potential applications in many areas of science and engineering. Recently, there has been significant progress in developing hybrid quantum devices using a superconducting qubit platform. The hybrid devices in this category combine the advantage of superconducting qubits with other degrees of freedom. Many experimental realizations of such devices have demonstrated entanglement, state preparation, and readout between multiple modes. I will present a hybrid electromechanical device consisting of a transmon type qubit and a SiN-based mechanical resonator. The device shows a large coupling between electrical and mechanical degrees of freedom compared to the earlier demonstration in traditional optomechanics. The large coupling manifests itself in the form of LZS interference observed in the qubit spectroscopy. In addition, I will present a theoretical model to understand the three-mode hybrid system in the presence of the external drive. In such a tripartite system, we analyze the steady-state occupation of the mechanical mode to show that the sideband cooling of the mechanical mode to its ground state is achievable. The theoretical calculations here predict the experimental parameters for the optimal readout of the mechanical mode, which is also verified experimentally. In the second part of my talk, I will discuss a novel architecture to implement a fast frequency tunable qubit in a three-dimensional waveguide cavity. Control over the qubit frequency can be a valuable resource in the hybrid system consisting of superconducting qubits. We investigate the flux-dependent dynamic range, relaxation from unconfined states, and the bandwidth of the flux-line. We use the fast-flux line to tune the qubit frequency and demonstrate the swap of a single excitation between cavity and qubit mode. The circuit QED setup presented here provides an alternating method to design a modular hybrid system where the components can easily be modified, added, or removed as required for a design.

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Motzoi, Felix. "Controlling Quantum Information Devices". Thesis, 2012. http://hdl.handle.net/10012/6793.

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Quantum information and quantum computation are linked by a common mathematical and physical framework of quantum mechanics. The manipulation of the predicted dynamics and its optimization is known as quantum control. Many techniques, originating in the study of nuclear magnetic resonance, have found common usage in methods for processing quantum information and steering physical systems into desired states. This thesis expands on these techniques, with careful attention to the regime where competing effects in the dynamics are present, and no semi-classical picture exists where one effect dominates over the others. That is, the transition between the diabatic and adiabatic error regimes is examined, with the use of such techniques as time-dependent diagonalization, interaction frames, average-Hamiltonian expansion, and numerical optimization with multiple time-dependences. The results are applied specifically to superconducting systems, but are general and improve on existing methods with regard to selectivity and crosstalk problems, filtering of modulation of resonance between qubits, leakage to non-compuational states, multi-photon virtual transitions, and the strong driving limit.

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Konstadopoulou, Anastasia, Apostolos Vourdas, R. Migliore, Zukarnain Z. Ahmad i A. Messina. "Entanglement of distant superconducting quantum interference device rings". 2005. http://hdl.handle.net/10454/3339.

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No
We consider two distant mesoscopic SQUID rings, approximated with two-level systems, interacting with two-mode microwaves. The Hamiltonian of the system is used to calculate its time evolution. The cases with microwaves which at t = 0 are in separable states (classically correlated) or entangled states (quantum mechanically correlated) are studied. It is shown that the Josephson currents in the two SQUID rings are also correlated.

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Kitapli, Feyruz. "Fabrication of Nanoscale Josephson Junctions and Superconducting Quantum Interference Devices". Thesis, 2011. http://hdl.handle.net/10012/6304.

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Fabrication of nanoscale Josephson junctions and Superconducting Quantum Interference Devices (SQUID) is very promising but challenging topic in the superconducting electronics and device technology. In order to achieve best sensitivity of SQUIDs and to reproduce them easily with a straightforward method, new fabrication techniques for realization of nanoSQUIDs needs to be investigated. This study concentrates on investigation of new fabrication methodology for manufacturing nanoSQUIDs with High Temperature Bi-Crystal Grain Boundary Josephson Junctions fabricated onto SrTiO3 bi-crystal substrates using YBa2Cu3O7-δ (YBCO) thin-films. In this process nanoscale patterning of YBCO was realized by using electron beam patterning and physical dry etching of YBCO thin films on STO substrates. YBCO thin films were deposited using RF magnetron sputtering technique in the mixture of Ar and O2 gases and followed by annealing at high temperatures in O2 atmosphere. Structural characterization of YBCO thin films was done by Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). Superconducting properties of thin films was characterized by AC magnetic susceptibility measurements. Nanoscale structures on YBCO thin films were fabricated by one E-Beam Lithography (EBL) step followed by Reactive Ion Etching (RIE) and physical dry etching. First SiO2 thin film were deposited on YBCO by RF magnetron sputtering and it was patterned by EBL using Polystyrene (PS) as resist material and RIE. Then SiO2 was used as an etch mask for physical dry etching of YBCO and nanoscale structures on YBCO were formed.

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Kalaee, Mahmoud. "Superconducting Electromechanical and Nanophotonic Devices for Quantum Measurement and Conversion". Thesis, 2019. https://thesis.library.caltech.edu/11247/7/Kalaee_Mahmoud_Thesis.pdf.

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Microscale and nanoscale mechanical resonators have been used in advanced technological applications, from high precision time keeping and mass sensing, to processing high frequency signals in mobile communications. In the last few decades, they have been an important part of progress in the field of quantum information and metrology and have been proposed as quantum memories or transducers for measuring or connecting different types of quantum systems.

The field of cavity optomechanics and electromechanics is concerned with coupling the electromagnetic field of a resonant optical cavity or electrical circuit to mechanical motion. These systems provide potential means to control and engineer the state of a mechanical object at the quantum level. This thesis contains the description of mechanical systems in megahertz to a few hundred megahertz frequency range formed by nano-fabricating photonic, phononic, and electrical circuits on a chip. These structures are designed to provide a large radiation pressure coupling between mechanical motion and electromagnetic fields to address and manipulate motional degrees of freedom. Qualitatively novel quantum effects are expected when one takes a step beyond linear coupling and exploits higher order interactions. To that end, we integrate electrical, mechanical and photonic structures in a multimode photonic crystal structure to observe "x²-coupling", where the optical cavity frequency is coupled to the square of the mechanical displacement. Moreover, we have developed two integrated on-chip platforms based on Si₃N₄ and Si nanomembranes capable of interfacing superconducting qubits and optical photons and realizing reversible microwave-to-optical conversion. We employ radiation pressure to cool these mechanical resonators to their quantum ground state. Finally, we demonstrate a form of electromechanical crystal for coupling microwave photons and hypersonic phonons of frequency ω_m/2π = 0.425 GHz by capacitively coupling a phononic crystal acoustic cavity to a superconducting microwave resonator. Moving to higher frequency acoustic cavities not only facilitates the integration of electromechanical circuits and nanophotonic systems capable of operation in the resolved sideband limit of optomechanics for noise-free quantum signal conversion, but it opens up the possibility of using phonons as information carriers via phononic circuits. Utilizing a two-photon resonance condition for efficient microwave pumping and phononic bandgap shield to eliminate acoustic radiation, we achieve large cooperative electromechanical coupling (C ≈ 30) and intrinsic decay time of 2.3 ms. Moreover, electrical read-out of the phonon occupancy shows that the acoustic mode thermalizes close to its quantum ground-state of motion (phonon occupancy n_m=1.5) at a fridge temperature of T_f = 10 mK. We conclude by considering several designs and fabrication improvements to the hypersonic electromechanical crystals that would enable them to perform quantum conversion between the electrical and acoustic domain.

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