京都大学 / 新制・課程博士 / 博士(工学) / 甲第23221号 / 工博第4865号 / 新制||工||1759(附属図書館) / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 水落 憲和, 教授 浜地 格, 教授 SIVANIAH Easan / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Les films magnétiques ultra-minces font partie intégrante des technologies d'aujourd'hui, comme l'illustre leur omniprésence dans de nombreuses applications courantes telles que les disques durs. A cause de leurs dimensions réduites, les propriétés magnétiques spécifiques à ces échelles conduisent à la formation de structures de spin exotiques et de taille nanométrique. Pour explorer ces matériaux en détail, nous utilisons un magnétomètre à balayage développé dans notre laboratoire et qui est basé sur un défaut de spin unique dans le diamant. Ce capteur non-invasif peut mesurer à l'échelle nanométrique à la fois le champ magnétique et la topographie, et fonctionne aux conditions ambiantes. En développant une méthode d'évaluation originale du champ magnétique, nous déterminons la structure interne de parois de domaines ferromagnétiques et quantifions la force de l'interaction Dzyaloshinskii-Moriya dans des hétérostructures à couches minces. Ensuite, nous mettons en évidence le rôle clé du désordre et de l'histoire magnétique sur la stabilisation des skyrmions dans un échantillon de bicouche magnétique. Enfin, nous visualisons dans l'espace réel une spirale de spin de 70 nm de période dans le matériau multiferroïque BiFeO3 et nous manipulons sa direction de propagation avec des champs électriques. Les connaissances tirées de ces études aideront à exploiter au maximum les capacités des matériaux magnétiques à couche ultra-mince et à les mettre en œuvre dans de nouveaux dispositifs de spintronique. / Thin film magnetic materials are an integral part of today’s technology and widespread applications like the magnetic hard drive disk mirror their potential. Due to their reduced dimensions, size-specific magnetic properties induce the formation of nanoscale, exotic spin structures. To explore such materials in detail, we utilize a home-built nitrogen vacancy scanning magnetometer, based on a single defect in diamond. This non-perturbative probe combines nanoscale magnetic field- and spatial resolution and works under ambient conditions. We develop a new way to determine the inner structure of magnetic domain walls and quantify the strength of the Dzyaloshinskii-Moriya interaction in thin film heterostructures. We reveal the key role of disorder and magnetic history on the stabilization of skyrmions in a magnetic bilayer sample. Finally, we reveal the 70nm-pitch spin spiral in the multiferroic bismuth ferrite in real space and manipulate its propagation direction with electric fields. The insight gained from these studies will help to exploit the full capacity of thin film magnetic materials for spintronic application.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19002号 / 工博第4044号 / 新制||工||1622(附属図書館) / 31953 / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 白川 昌宏, 教授 田中 庸裕, 教授 濵地 格 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

In recent years, the nitrogen-vacancy (NV) center has emerged as a promising magnetic sensor capable of measuring magnetic fields with high sensitivity and spatial resolution under ambient conditions. This combination of characteristics allows NV magnetometers to probe magnetic structures and systems that were previously inaccessible with alternative magnetic sensing technologies. This dissertation presents and discusses a number of the initial efforts to demonstrate and improve NV magnetometry. In particular, a wide-field CCD based NV magnetic field imager capable of micron-scale spatial resolution is demonstrated; and magnetic field alignment, preferential NV orientation, and multipulse dynamical decoupling techniques are explored for enhancing magnetic sensitivity. The further application of dynamical decoupling control sequences as a spectral probe to extract information about the dynamics of the NV spin environment is also discussed; such information may be useful for determining optimal diamond sample parameters for different applications. Finally, several proposed and recently demonstrated applications which take advantage of NV magnetometers' sensitivity and spatial resolution at room temperature are presented, with particular focus on bio-magnetic field imaging. / Engineering and Applied Sciences

Observing and controlling solid state quantum systems is an area of intense research in quantum science today. Such systems offer the natural advantage of being bound into a solid device, eliminating the need for laser cooling and trapping of atoms in free space. These solid state "atoms" can interface directly with photonic channels designed to efficiently couple into larger networks of interacting quantum systems. With all of the tools of semiconductor fabrication technology available, the idea of scalable, chip-based quantum networks is a tantalizing prospect. / Physics

<p>The enhancement of the emission from nitrogen vacancy color centers will help facilitate advancements in quantum information technology. To this end, the reduction of the excited state lifetimes of NVs as well as the design of devices which support electroluminescence of nitrogen vacancies, as well as the broadband enhancement of the emission from these centers is of great importance.</p> <p> </p> <p>In this study, we create diamond thin films containing nitrogen vacancy color centers using salt-assisted ultrasonic disaggregation techniques and electrophoretic deposition. These films are implanted with xenon atoms and the resulting structures are characterized optically. We report a reduction in the bulk emission lifetime of nitrogen vacancy color centers of two orders of magnitude. A coupled-mode theory approach is used to analyze the emission from the xenon-doped nanodiamond species. It is determined that the lifetime reduction occurs due to coupling between nitrogen vacancy color centers and xenon color centers within the diamond lattice.</p> <p> </p> <p>A diamond field effect transistor is investigated via simulations utilizing Sentaurus TCAD software. The device is scaled by three orders of magnitude from previous experiments involving the same structure. Transport characteristics are obtained from simulation results. We confirm the existence of a decreasing saturation voltage with a decrease in gate length in the diamond field effect transistor. Further investigation into the device’s viability as a quantum emitter is conducted. </p> <p> </p> <p>The design of a single photon source utilizing plasmonic structures to enhance emission from nitrogen vacancy color centers is proposed. The plasmonic structure is investigated to extract operating parameters and to quantify the optical coupling and propagation characteristics for various physical dimensions</p> <p> </p> The design of a plasmonic device which features both electroluminescence via nitrogen vacancy color centers and their enhancement via plasmonic effects is numerically simulated. The device features large Purcell enhancement factor and good photon emission rate. In summary, this work paves the way towards the advancement of the nitrogen vacancy color center as a stable source of room temperature photons for quantum information applications.

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To fully exploit the capability of NV centers in diamond as magnetic sensors and quantum bits, the optimum production recipe as well as the method to enhance its optical performance has been studied in this work. The NV centers in bulk diamond were prepared by ion implantation and electron irradiation, and the optimum dose and temperature are found by comparing its optical and magnetic performance both experimentally and theoretically. In addition, the enhancement of optical performance and size characterization of NV centers in nanodiamonds will be discussed in this work.

Orientadores: Gilberto Medeiros Ribeiro e Jose Antonio Brum / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-11T11:01:49Z (GMT). No. of bitstreams: 1 Alegre_ThiagoPedroMayer_D.pdf: 15787837 bytes, checksum: a41c0877b93a156734db9d614610e2f4 (MD5) Previous issue date: 2008 / Resumo: Esta tese consistiu na proposição e implementação de um sistema para processamento de informação quântica, focando a instrumentação necessária. Os aspectos físicos da computação, como a energia associada, entropia de Shannon, entre outros conceitos básicos observados na perspectiva de física, foram revistos. Pontos quânticos semicondutores de InAs:GaAs foram eleitos como candidatos para a implementação física do sistema; em particular, focou-se no grau de liberdade de spin do elétron. Conseqüentemente, investigaram-se as propriedades de tensor-g dos elétrons aprisionados em pontos quânticos e o grau de polarização de spin, como função do campo magnético e da temperatura. Naturalmente, as propriedades eletrônicas, como o potencial de confinamento e as transições ópticas, foram caracterizadas e modeladas através da teoria de massa efetiva, assumindo-se um potencial de confinamento lateral parabólico. Dado que o grau de liberdade de spin foi eleito, construiu-se um sistema de medidas de ressonância paramagnética de spins. Optou-se por não se utilizar sistemas comerciais padrão. Em lugar disto, foi projetada uma montagem conectorizada, onde o material semicondutor se encontra dentro de umchip desenhado para concentrar o campo magnético de microonda sobre o dispositivo, campo este necessário para a realização de ressonância paramagnética. O chip consistiu basicamente de uma cavidade de microfita de meia onda. Foi construída também uma cavidade com duas entradas, permitindo o controle arbitrário da polarização aplicada à amostra. Finalmente, a leitura de estados quânticos de spin em centros paramagnéticos é demonstrada através de detecção óptica. A alta sensibilidade desse tipo de detecção permite que um único defeito seja mapeado. A seletividade, tanto do ponto de vista das transições ópticas quanto das transições de spin, é estudada e manipulada, utilizando-se da montagem experimental de cavidades ressonantes. Adicionalmente, perspectivas de experimentos sobre a integração e utilidade do sistema são apresentados / Abstract: This thesis proposes and implements a system for quantum information processing, focusing primarily on the associated instrumentation. The basic physical aspects for computation, such as the associated energy and Shannon's entropy, were revisited. InAs:GaAs quantum dots were elected as the physical system of choice for this implementation; in particular, the spin degree of freedom of the trapped electrons was utilized. Therefore, the electronic properties of the quantum dots, as well the g-tensor and the polarization degree, were investigated as a function of the temperature and magnetic field. It was possible to describe the electronic properties within the effective mass formalism, assuming a parabolic lateral confinement. Since the spin degree of freedom was elected as the basis for the quantum computation, a system for spin paramagnetic resonance was devised. The choice for not using a commercial system was made. Instead, a connectorized setup was designed, permitting the semiconductor material to be within a chip, and additionally allowing for focusing the microwave magnetic field above the device. Basically, this chip consisted of a half-wavelength microstrip cavity. A second microstrip cavity with two input ports was also designed to allow the arbitrary control of microwave polarization delivered to the sample. Finally, the quantum state read-out was demonstrated through an optical technique on Nitrogen-Vacancy complexes in diamond. The high sensitivity of the system allows for single spin detection. The selectivity for the optical and spin transitions was characterized and manipulated, using the resonant cavity experimental setup. As a perspective, experiments exploring integration issues on the system are shown / Doutorado / Física da Matéria Condensada / Doutor em Ciências