17 research outputs found
Diamond Integrated Quantum Photonics: A Review
Integrated quantum photonics devices in diamond have tremendous potential for
many quantum applications, including long-distance quantum communication,
quantum information processing, and quantum sensing. These devices benefit from
diamond's combination of exceptional thermal, optical, and mechanical
properties. Its wide electronic bandgap makes diamond an ideal host for a
variety of optical active spin qubits that are key building blocks for quantum
technologies. In landmark experiments, diamond spin qubits have enabled
demonstrations of remote entanglement, memory-enhanced quantum communication,
and multi-qubit spin registers with fault-tolerant quantum error correction,
leading to the realization of multinode quantum networks. These advancements
put diamond at the forefront of solid-state material platforms for quantum
information processing. Recent developments in diamond nanofabrication
techniques provide a promising route to further scaling of these landmark
experiments towards real-life quantum technologies. In this paper, we focus on
the recent progress in creating integrated diamond quantum photonic devices,
with particular emphasis on spin-photon interfaces, cavity optomechanical
devices, and spin-phonon transduction. Finally, we discuss prospects and
remaining challenges for the use of diamond in scalable quantum technologies.Comment: 31 pages, 8 figure
Desing and Simulation of Advanced Fiber Optic Sensors for High Energy Physics Application
In the last two decades, Fiber Bragg Grating (FBG) sensor were been widely studied and employed in temperature and strain sensing application. Due to their high potentiality in term of radiation hardness and EMI insensitivity, they constitute the ideal device to operate in harsh environments, under ionizing radiation and strong magnetic fields. This thesis work is focused on the research, development and simulation of novel sensors and monitoring systems suitable to operete in these environmental conditions.In particular, the monitoring applications regards room temperature of Compact Muon Solenoid (CERN), cryogenic temperature (up to 4.2 K) of the powerful cooling system of the LHC's superconducting magnets, and magnetic field with magnetostrictive and magneto-optic approaches
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The silicon-vacancy centre in diamond for quantum information processing
Atomic defects in solids offer access to atom-like quantum properties without complex trapping methods while displaying a rich physics due to interactions with their solid-state environment. Such properties have made them an advantageous building block for quantum information processing, in particular to construct a quantum network, where information would be encoded in spins and transferred between nodes through photons. Among defects in solids, the negatively charged silicon-vacancy centre in diamond (SiV) has attracted attention for its very promising optical properties for such a network.
In this thesis, we investigate the spin properties of the silicon-vacancy centre as a potential spin-photon interface. First, we use resonant excitation of an SiV centre in an external magnetic field to selectively address different electronic states and analyse the resulting fluorescence. We find evidence of selection rules in the optical transitions revealing that the centre possesses an electronic spin S = 1/2. Making use of the dependence of such selection rules on the applied magnetic field orientation, we resonantly drive two optical transitions forming a -scheme. In the double resonance condition, we achieve coherent population trapping, whereby the SiV is pumped into a dark state corresponding to a superposition of the two addressed ground states of opposite spin. This technique allows us to evaluate the coherence time of the dark state and hence of the spin, while demonstrating the possibility of all-optical control of the spin when a -scheme is available. We then use resonant optical pulses to initialise and read out the spin state of a single SiV. By tuning a microwave pulse into resonance between two ground states of opposite spin, we demonstrate optically detected magnetic resonance. Subsequently, by varying the duration of a resonant microwave pulse, we achieve coherent control of a single SiV electronic spin. Through Ramsey interferometry, we measure a spin dephasing time of 115 9 ns. We then investigate interactions of the SiV with its environment. We analyse the hyperfine interaction of the SiV spin with the nuclear spin of Si, with a view to taking advantage of the long-lived nuclear spin in the future. We show that single-phonon-mediated excitations between electronic states of the SiV are the dominant spin dephasing and population decay mechanism and evaluate how external strain alters optical selection rules and can be used to improve the coherence time of the spin
High energy radiation effects in optical elements.
The detrimental effect of radiation has been a noted problem since its discovery by Becquerel. This thesis has studied the effect of radiation on components used in optical systems that have, or may be used, in instrumentation lofted on satellite platforms. Particular emphasis has been placed on the effects of radiation observed in materials associated with vacuum ultraviolet observations. The main parameter studied is transmission, though reference is made to methods of studying changes in dispersion. The results have been analysed and show that a number of factors can affect the influence of ionising radiation on a chosen medium. These results are used to see if these effects can be approximated by simple mathematical functions
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Radiation Damage in CMOS Image Sensors for Space Applications
The space radiation environment is damaging to silicon devices, such as Complementary Metal Oxide Semiconductor (CMOS) image sensors, affecting their performance over time or causing total failure.
The first part of this work investigates a Charge Coupled Device (CCD) style CMOS image sensor designed for TDI (Time Delay and Integration) mode imaging, a mode commonly used for Earth observation. Damage from high energy protons in the space environment decreases the Charge Transfer Efficiency (CTE) and increases the dark current of such devices. Experimental work on proton damaged devices is presented, showing the effects on CTE and dark current. The results are compared to a standard CCD by a simulation to take into account the different dimensions and operating conditions of the two devices.
The second part of this work describes an experimental campaign to determine the effects of process variations (namely the introduction of deep doping wells and the variation of epitaxial silicon thickness) on the rate of Single Event Latchup (SEL) in CMOS Active Pixel Sensor (APS) devices. SEL is a potentially destructive phenomenon which occurs in CMOS technology but not in CCDs. Test devices were subjected to heavy ion bombardement and SEL rates recorded for a range of heavy ions causing varying amounts of ionisation. A simulation using Technology Computer Aided Design (TCAD) was developed to predict the SEL rates due to heavy ions and to understand the characteristic shape of the SEL cross section vs. Linear Energy Transfer (LET) curves produced by SEL experiments. The simuation was carried out for structures representative of each of the design variants
Spectroscopic investigations at the diamond-water interface
Artificial Photosynthesis is a promising approach to tackle the increasing challenges of global warming. However, the direct conversion of CO2 to other chemicals presents major kinetic challenges, evoking exploration of abundant, cost effective and sustainable photocatalysts.
Diamonds are promising candidates as H-terminated diamond surfaces exhibit excellent electron emission characteristics in water because of their negative electron affinity. However, due to their wide band gap of 5.4 eV, the generation of solvated electrons, requires the photoactivation of diamond using deep UV radiation which is scarcely available in the solar spectrum. In this thesis two strategies are investi- gated to enable visible light absorption and enhance electron emission from diamonds. Specifically, the effect of B, N and P doping on the electronic structure of diamonds were investigated using soft X-ray ab- sorption spectroscopy at C K edge. The results of our study revealed that combining nanostructuration with B-doping leads to introduction of new electronic states close to both the valence band maximum and the conduction band minimum in B-doped diamonds. As an alternative strategy, the electronic structure of nanodiamonds sensitized with Ru(bpy)3 was probed. These studies presented evidence of electronic coupling between the Ru complex and the nanodiamonds with the HOMO of Ru(bpy)3 lying above the valence band minimum of the diamonds. As a result of this band alignment, the dye acts as an electron donor and can potentially refill the photogenerated holes in the valence band of diamonds.
Since photoactivation of diamonds generates solvated electrons in water, it is also important to un- derstand the diamond-water interface. To this aim, infrared spectroscopy was used to elucidate the influence of different pH conditions on the surface interactions of ND-OH surfaces at the diamond- water interface. This study provided insights that could help to determine the optimal environment that would enhance electron emission from these surfaces. Based on the results, a possible forma- tion of oxonium ions on an ND-OH surface in acidic conditions could be deduced. These oxonium ions could potentially form a charge stabilization layer with water molecules, thereby enhancing electron emission which could be advantageous for photocatalytic reductions. The results further suggested a possible aging mechanism of ND-H surfaces under long term UV irradiation. For efficient photoelectro- catalytic CO2 reduction, diamonds were also co-promoted by Cu2O to form a hybrid photocatalyst. The electronic structure of this hybrid material was probed at the Cu L edge to explain the role of diamond in this hybrid material. It was found out that diamond indeed acts as a very stable support for Cu2O thereby decelerating the process of aging and subsequent deactivation of the catalyst.
With this work, we thus, aim to highlight some of the characteristics of diamonds that would enable the development of diamond based photocatalysts in the future.Die künstliche Photosynthese ist ein vielversprechender Ansatz, um den wachsenden Herausforderungen der globalen Erwärmung zu begegnen. Die direkte Umwandlung von CO2 in andere Chemikalien stellt jedoch eine große Herausforderung dar, die zur Erforschung zahlreicher, kostengünstiger und nachhaltiger Photokatalysatoren führt.
Aufgrund ihrer großen Bandlücke von 5,4 eV sind Diamanten vielversprechende Kandidaten. Denn H- terminierte Diamantoberflächen weisen aufgrund ihrer negativen Elektronenaffinität in Wasser hervorragende Elektronenemissionseigenschaften auf. Die Erzeugung von solvatisierten Elektronen erfordert jedoch die Photoaktivierung von Diamanten mit tiefer UV-Strahlung, die im Sonnenspektrum kaum verfügbar ist. In der vorliegenden Arbeit wurden zwei Strategien untersucht, um die Absorption des sichtbaren Lichts zu ermöglichen und die Elektronenemission von Diamanten zu verbessern. Insbesondere wurden die elektronischen Strukturen von p- und n-Diamanten mit B-, N- bzw. P-Dotierung mittels weicher Röntgenabsorptionsspektroskopie an der C-K-Kante untersucht. Diese Untersuchungen zeigten, dass die Kombination von Nanostrukturierung mit B-Dotierung neue elektronische Zustände erzeugt, die sowohl dem Valenzbandmaximum als auch dem Leitungsbandminimum in B-dotierten Diamanten nahe kommen. Als alternative Strategie wurde die elektronische Struktur von Nanodiamanten untersucht, die mit Ru(bpy)3 sensibilisiert sind. Diese Studien zeigten eine elektronische Kopplung zwischen dem Ru-Komplex und den Nanodiamanten, wobei das HOMO von Ru(bpy)3 über dem Valenzband Minimum der Diamanten lag. Durch diese Bandausrichtung wirkt der Farbstoff als Elektronendonor und kann die photogenerierten Löcher im Valenzband der Diamanten potenziell wieder auffüllen.
Da die Photoaktivierung von Diamanten im Wasser solvatisierte Elektronen erzeugt, ist es auch wichtig, die Grenzfläche zwischen Diamant und Wasser zu verstehen. Wir untersuchten die Interaktion von OH- terminierten Diamant-Oberflächen mit Wasser bei unterschiedlichen pH-Werten, um die Elektronenemission von diesen Oberflächen zu verbessern. Es stellte sich heraus, dass unter sauren Bedingungen auf einer ND-OH-Oberfläche möglicherweise Oxoniumionen gebildet werden, die mit Wassermolekülen eine ladungsstabilisierende Schicht bilden könnten. Diese wiederum könnte die Elektronenemission er- höhen und die photokatalytische Reduktion von CO2 begünstigen.
Einen hybriden Photokatalysator mit Cu2O Schichten auf der Diamantenoberfläche wurde auch gebildet, als alternativen Weg für eine effiziente CO2-Photoreduktion. Die elektronische Struktur dieses Hybridmaterials wurde an der Cu-L-Kante untersucht, um die Rolle des Diamanten in diesem Hybridmaterial zu erklären. Es wurde herausgefunden, dass Diamant tatsächlich als sehr stabiler Träger für Cu2O wirkt, wodurch der Alterungsprozess und die daraus folgende Deaktivierung des Katalysators verzögert werden.
Mit dieser Arbeit wollen wir daher die Eigenschaften von Diamanten beleuchten, um künftig die Entwicklung von einem diamantbasierten Photokatalysator zu ermöglichen
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Measurement of Creep Deformation in Weldments
This PhD project has developed a new high temperature strain measurement system using Digital Image Correlation (DIC) in order to investigate spatially varying and time dependent deformation during high temperature creep tests of engineering materials. Several challenges associated with measuring creep deformation at elevated temperature have been overcome including the choice of specimen design, specimen oxidation, furnace temperature uniformity, image distortion caused by thermal currents and sufficient illumination. It is demonstrated that the system created can produce reliable measurement data over a period of several months with a spatial resolution of 0.6 mm for temperatures up to 650°C, but in principle higher resolution and temperatures should be achievable.
The research aim of this project, funded by EDF Energy (formerly British Energy), was to attempt to measure spatially varying creep deformation properties across thick and thin section weldments that operate at high temperatures in UK advanced gas cooled reactor power plant (AGR). The new measurement system is applied to examine the creep behaviour of a thick section multi-pass welded joint made from Type 316H austenitic stainless steel which was supplied by EDF Energy. Specifically the local creep deformation properties across the weldment in the parent material, heat affected zone (HAZ) and multipass weld layers are investigated in medium term creep tests (>2300 hours). This is achieved by cutting samples from three different locations of the thick section joint, that is from top, middle and bottom positions, and subjecting them to tensile and creep testing at a temperature of 545°C. Spatially resolved stress-strain (tensile) and strain-time (creep) results were obtained transversely across the whole section of the multi-pass weldment and across the thickness direction. The DIC in-situ measurements also provided strain information in the transverse to loading direction from which the reduction of area of the specimen and true stress and strain distribution were calculated. The weld metal showed faster creep rates than HAZ and parent materials and this is attributed to the observed introduction of substantial plastic strain in the parent material on initial loading. Locally the creep strain distribution in the weld metal appears to correlate with individual weld passes. The full-field measurement results allowed the development of creep deformation leading to ultimate rupture to be observed.
The high temperature tensile and creep results presented in this thesis demonstrate the capability of the new DIC based system created for full field measurements of displacement and strain at high temperature during creep tests enduring several thousand hours. The system opens a new horizon for studying deformation and rupture behaviour of complex structures at elevated temperature
Nanostructured nickel oxide thin films grown by reactive RF Magnetron Sputtering
Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Aplicada: Fecha de lectura:16-06-201