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1
Plant, Simon Richard. "Molecular engineering with endohedral fullerenes : towards solid-state molecular qubits." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:84f12a03-5b1d-4e04-82d5-5b28ca92e56c.
Full textAbstract:
Information processors that harness quantum mechanics may be able to outperform their classical counterparts at certain tasks. Quantum information processing (QIP) can utilize the quantum mechanical phenomenon of entanglement to implement quantum algorithms. Endohedral fullerenes, where atoms, ions or clusters are trapped in a carbon cage, are a class of nanomaterials that show great promise as the basis for a solid-state QIP architecture. Some endohedral fullerenes are spin–active, and offer the potential to encode information in their spin-states. This thesis addresses the challenges of how to engineer the components of a scalable QIP architecture based on endohedral fullerenes. It focuses on the synthesis and characterization of molecules which may, in the future, permit the demonstration of entanglement; the optical read-out of quantum states; and the creation of quasi-one-dimensional molecular arrays. Due to its long spin decoherence time, N@C<sub>60</sub> is the selected as the basic molecular unit for ‘coupled’ fullerene pairs, molecular systems for which it may be possible to demonstrate entanglement. To this end, isolated fullerene pairs, in the form of spin-bearing fullerene dimers, are created. This begins with the processing of N@C<sub>60</sub> at the macroscale and leads towards the synthesis of <sup>15</sup>N@C<sub>60</sub>-<sup>15</sup>N@C<sub>60</sub> dimers at the microscale. High throughput processing is introduced as the most efficient technique to obtain high purity N@C<sub>60</sub> on a reasonable timescale. A scheme to produce symmetric and asymmetric fullerene dimers is also demonstrated. EPR spectroscopy of the dimers in the solid-state confirms derivatization, whilst permitting the modelling of spin–spin interactions for 'coupled' fullerene pairs. This suggests that the optimum inter–spin separation for which to observe spin–spin coupling in powders is circa 3 nm. Motivated by the properties of the trivalent erbium ion for the optical detection of quantum states, optically–active erbium–doped fullerenes are also investigated. These erbium metallofullerenes are synthesized and isolated as individual isomers. They are characterized by low temperature photoluminescence spectroscopy, emitting in the infra- red at a wavelength of 1.5 μm. The luminescence is markedly different where a C<sub>2</sub> cluster is trapped alongside the erbium ions in the fullerene cage. Er<sub>2</sub>C<sub>2</sub>@C<sub>82</sub> (isomer I) exhibits emission linewidths that are comparable to those observed for Er<sup>3+</sup> in crystals. Finally, the discovery of a novel praseodymium-doped fullerene is reported. The balance of evidence favours the structure being assigned as Pr<sub>2</sub>@C<sub>72</sub>. This novel endohedral fullerene forms quasi-one-dimensional arrays in carbon nanotubes, which is a useful proof-of-principle of how a scaled fullerene-based architecture may be achieved.
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Fraval, Elliot, and elliot fraval@gmail com. "Minimising the Decoherence of Rare Earth Ion Solid State Spin Qubits." The Australian National University. Research School of Physical Sciences and Engineering, 2006. http://thesis.anu.edu.au./public/adt-ANU20061010.124211.
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[Mathematical symbols can be only approximated here. For the correct
display see the Abstract in the PDF files linked below] This work has
demonstrated that hyperfine decoherence times sufficiently long for
QIP and quantum optics applications are achievable in rare earth ion
centres. Prior to this work there were several QIP proposals using
rare earth hyperfine states for long term coherent storage of optical
interactions [1, 2, 3]. The very long T_1 (~weeks [4]) observed for
rare-earth hyperfine transitions appears promising but hyperfine T_2s
were only a few ms, comparable to rare earth optical transitions and
therefore the usefulness of such proposals was doubtful.
¶
This work demonstrated an increase in hyperfine T_2 by a factor of 7 ×
10^4 compared to the previously reported hyperfine T_2 for
Pr^[3+]:Y_2SiO_5 through the application of static and dynamic
magnetic field techniques. This increase in T_2 makes previous QIP
proposals useful and provides the first solid state optically active
Lamda system with very long hyperfine T_2 for quantum optics
applications.
¶
The first technique employed the conventional wisdom of applying a
small static magnetic field to minimise the superhyperfine interaction
[5, 6, 7], as studied in chapter 4. This resulted in hyperfine
transition T_2 an order of magnitude larger than the T_2 of optical
transitions, ranging fro 5 to 10 ms. The increase in T_2 was not
sufficient and consequently other approaches were required.
¶
Development of the critical point technique during this work was
crucial to achieving further gains in T_2. The critical point
technique is the application of a static magnetic field such that the
Zeeman shift of the hyperfine transition of interest has no first
order component, thereby nulling decohering magnetic interactions to
first order. This technique also represents a global minimum for back
action of the Y spin bath due to a change in the Pr spin state,
allowing the assumption that the Pr ion is surrounded by a thermal
bath. The critical point technique resulted in a dramatic increase of
the hyperfine transition T_2 from ~10 ms to 860 ms.
¶
Satisfied that the optimal static magnetic field configuration for
increasing T_2 had been achieved, dynamic magnetic field techniques,
driving either the system of interest or spin bath were investigated.
These techniques are broadly classed as Dynamic Decoherence Control
(DDC) in the QIP community. The first DDC technique investigated was
driving the Pr ion using a CPMG or Bang Bang decoupling pulse
sequence. This significantly extended T_2 from 0.86 s to 70 s. This
decoupling strategy has been extensively discussed for correcting
phase errors in quantum computers [8, 9, 10, 11, 12, 13, 14, 15], with
this work being the first application to solid state systems.
¶
Magic Angle Line Narrowing was used to investigate driving the spin
bath to increase T_2. This experiment resulted in T_2 increasing from
0.84 s to 1.12 s. Both dynamic techniques introduce a periodic
condition on when QIP operation can be performed without the qubits
participating in the operation accumulating phase errors relative to
the qubits not involved in the operation.
¶
Without using the critical point technique Dynamic Decoherence Control
techniques such as the Bang Bang decoupling sequence and MALN are not
useful due to the sensitivity of the Pr ion to magnetic field
fluctuations. Critical point and DDC techniques are mutually
beneficial since the critical point is most effective at removing high
frequency perturbations while DDC techniques remove the low frequency
perturbations. A further benefit of using the critical point technique
is it allows changing the coupling to the spin bath without changing
the spin bath dynamics. This was useful for discerning whether the
limits are inherent to the DDC technique or are due to experimental
limitations.
¶
Solid state systems exhibiting long T_2 are typically very specialised
systems, such as 29Si dopants in an isotopically pure 28Si and
therefore spin free host lattice [16]. These systems rely on on the
purity of their environment to achieve long T_2. Despite possessing a
long T_2, the spin system remain inherently sensitive to magnetic
field fluctuations. In contrast, this work has demonstrated that
decoherence times, sufficiently long to rival any solid state system
[16], are achievable when the spin of interest is surrounded by a
concentrated spin bath. Using the critical point technique results in
a hyperfine state that is inherently insensitive to small magnetic
field perturbations and therefore more robust for QIP applications.
3
Lo, Nardo Roberto. "Charge state manipulation of silicon-based donor spin qubits." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:29a0f336-82ce-4794-82fe-d7db2802ffc1.
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Spin properties of donor impurities in silicon have been investigated by electron spin resonance (ESR) techniques for more than sixty years. These studies gave us a contribution towards understanding some of the physics of doped semiconductor materials in general, which is the platform for much of our current technology. Despite the fact that donor electron and nuclear spins have been researched for so long, ESR studies of their properties are still giving us interesting insights. With the introduction of the concept of quantum information in the 1980s, some properties of donor spins in silicon, that were known from the fifties (such as long relaxations), have been reinterpreted for their potential application in this field. Since then, incredible experimental results have been achieved with magnetic resonance control, including manipulation and read-out of individual spins. However, some open questions are still to be answered before the realisation of a spin-based silicon quantum architecture will be achieved. Currently, ESR studies still contribute to help answering some of those questions. In this thesis, we demonstrate electrical and optical methods for donor charge state manipulation measured by ESR. Recent experiments have demonstrated that coherence time of nuclear spins may be enhanced by manipulating the state of donors from neutral to singly charged. We investigate electric field ionisation/neutralisation of arsenic donors in a silicon SOI device measured by ESR. Below ionisation threshold, we also measure the hyperfine Stark shift of arsenic donors spins in silicon. These results have, for instance, implications on how fast individual addressability of donor spins may be achieved in certain quantum computer architectures. Here, we also study optical-driven charge state manipulation of selenium impurities in silicon. Selenium has two additional electrons when it replaces an atom in the silicon crystal (i.e. double donor). The electronic properties of singly-ionised selenium make it potentially advantageous as spin qubit, compared to the more commonly studied group-V donors. For instance, we find here that the electron spin relaxation and coherence times of selenium are up to two orders of magnitude longer than phosphorus at the same temperature. Finally, we demonstrate that it is possible to bring selenium impurity in singly-charged state and subsequently re-neutralise them leaving a potential long-lived <sup>77</sup>Se nuclear spin.
4
Gündoğan, Mustafa. "Solid-state quantum memory for photonic qubits." Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/322551.
Full textAbstract:
Optical quantum memories (QMs) are one of the fundamental building blocks in quantum information science (QIS). They might find important use in quantum communication and computation applications.
Rare-earth ions (REIs) have been investigated for decades for their optical properties. They exhibit excellent coherence properties when cooled down to cryogenic temperatures. Not surprisingly, they emerged as a promising candidate for use in QIS as QMs.
In this thesis, we investigated the quantum storage of photonic qubits in a Pr3+ :Y2SiO5 (PrYSO) crystal for potential use in quantum communication
and networking applications.
We started by constructing the experimental setup and the laser system from scratch as our research group had just been established at the beginning of this PhD study. First experiments included spectroscopy of the PrYSO system in order to identify the electronic transitions that are
suitable for the QM experiments. We used the atomic frequency comb (AFC) memory protocol in all the experiments presented in this thesis.
We also developed complex pulse sequences that are necessary for the optical preparation of an AFC.
As a first experiment, we demonstrated the storage of photonic polarization qubits encoded in weak coherent states in the excited states of Pr3+ ions for a predetermined storage time of 500 ns. This had not been achieved previously due to the polarization dependent absorption of the material.
We achieved average storage fidelities of ~95% which surpass the best achievable value with a measure and prepare strategy, thus proving the
quantum character of our interface.
Nevertheless, in order to be implemented in realistic quantum networking architectures, a QM should have the capability of on-demand retrieval of
the stored information. As a first step towards this goal, our next experiment concerned the transfer of the input pulses to and from the long-lived
hyperfine ground levels of Pr3+ ions, albeit with bright pulses. Furthermore, by performing time-bin interference experiments, we demonstrated
that the coherence is preserved during the storage, transfer and retrieval processes. Temporal multimode storage in the spin-states up to 5 modes
was also shown.
Finally, in the last part of this thesis we demonstrated a solid-state spinwave quantum memory, with qubits encoded in weak coherent states at the single photon level. Storing and retrieving single-photon level fields in the ground levels of the PrYSO system is challenging as the strong control pulses and the weak input pulse to be stored in the memory are separated by only 10:2 MHz. The control pulses create noise, mostly as free-induction decay, fluorescence and scattering off the optical surfaces. In order to circumvent this problem we employed narrow-band spectral, temporal and spatial filtering. By using spectral-hole burning based narrow band filter created in a second PrYSO crystal, we could achieve signal-to-noise ratio (SNR) > 10 for input pulses with mean photon number of around 1. The high SNR we achieved allowed us to store and recall time-bin qubits with conditional fidelities again higher than that is possible with a measure and prepare strategy. This experiments also represents the first demonstration of a quantum memory for time-bin qubits with on demand read-out of the stored quantum information.
The results presented in this thesis fill an important gap in the field of solid-state quantum memories and open the way for the long-lived storage of non-classical states of light. They further strengthen the position of REI based systems in QIS, specifically as nodes in scalable quantum network architectures.<br>Les memòries quàntiques òptiques (MQs) son un dels elements fonamentals en la ciència de la informació quàntica (CIQ). El seu ús podria ser important en aplicacions relacionades amb la comunicació i la computació quàntiques. Els ions de terres rares (ITRs) han sigut investigats durant dècades per les seves propietats òptiques. Exhibeixen excel·lents propietats de coherència quan es refreden a temperatures criogèniques. Per tant, no es sorprenent que hagin emergit com a candidats per ser usats en la CIQ com a MQs. En aquesta tesis, hem investigat l'emmagatzematge quàntic de qubits fotònics en un cristall de Pr3+:Y2SiO5 (PrYSO) per al seu possible ús en aplicacions relacionades amb xarxes d'informació quàntiques. Vam començar construint el dispositiu experimental i sistemes làser des de zero, ja que el nostre grup de recerca acabava de néixer. Els primers experiments van incloure espectroscòpia del sistema de PrYSO per identificar les transicions electròniques més apropiades per als següents experiments de MQs. En tots els experiments vam utilitzar el protocol de memòria basat en una pinta de freqüències atòmiques (PFA). També vam desenvolupar complexes seqüències de polsos, necessàries per a la preparació òptica d'una PFA. En el primer experiment vam demostrar l'emmagatzematge de qubits fotònics de polarització codificats en estats coherents febles. Aquest emmagatzematge es va dur a terme en els estats excitats dels ions Pr3+ durant un temps d'emmagatzematge predeterminat de 500 ns. Aquesta fita no s'havia assolit abans degut a que l'absorció òptica del material depèn de la polarització llum. Vam aconseguir fidelitats d'emmagatzematge d'un 95% de mitjana les quals sobrepassen el millor valor que es pot aconseguir amb una estratègia de mesura i preparació provant per tant el caràcter quàntic de la nostra interfície. Per poder-se implementar de manera realista en xarxes quàntiques, una MQ hauria de tenir la capacitat de recuperar la informació en-demanda (en el moment que es desitgi). Com a primer pas, el nostre següent experiment va involucrar la transferència dels polsos d'entrada cap a i des de els nivells fonamentals hiperfins i longeus dels ions Pr3+, mitjançant polsos brillants. A més, duent a terme experiments d'interferència, vam demostrar que la coherència es preserva durant els processos d'emmagatzematge, transferència i recuperació. També vam demostrar l'emmagatzematge temporalment multimodal en els estats d'espín, de fins a 5 modes. En l'última part d'aquesta tesis vam demostrar una memòria quàntica d'estat sòlid basada en ones d'espín, amb qubits codificats en estats coherents febles al nivell d'intensitat de fotons individuals. Emmagatzemar i recuperar camps òptics al nivell de fotons individuals en estats fonamentals del sistema PrYSO és exigent perquè els potents polsos de control i el polsos dèbils d'entrada que s'emmagatzemen a la memòria estan separats per només 10.2 MHz. Els polsos de control creen soroll, la majoria consistent en decaïment de lliure inducció, fluorescència i dispersió en les superfícies òptiques. Per resoldre aquest problema vam utilitzar filtratge estret de banda en freqüència i també filtratges temporal i espacial. Utilitzant un filtre estret de banda basat el la crema de forats espectrals en un segon cristall de PrYSO, vam poder aconseguir una relació senyal soroll (RSS) > 10 per a polsos d'entrada amb un número mitjà de fotons al voltant de 1. L'alta RSS que vam aconseguir ens va permetre emmagatzemar i recuperar qubits de inteval-de-temps amb fidelitats condicionals més altes una altra vegada que el que és possible amb l'estratègia de mesura i preparació. Els resultats presentats omplen un buit important en el camp de les memòries quàntiques d'estat sòlid i obren la porta a l'emmagatzematge de llarga durada d'estats de llum no-clàssics. A més, enforteixen la posició dels sistemes de IQ basats en ITR, específicament com a nodes en arquitectures de xarxes quàntiques.
5
Smith, Thomas Benjamin. "Entanglement and measurement of solid-state qubits." Thesis, The University of Sydney, 2020. https://hdl.handle.net/2123/24894.
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A full-scale quantum computer requires physical qubits that can be controlled with high precision and accuracy. Unfortunately, few state-of-the-art qubits can perform all their elementary operations (preparation, measurement, single-qubit gates and two-qubit gates) with sufficient fidelity. In this thesis, we investigate alternative schemes for such operations in solid-state qubits. Specifically, two-qubit gates and measurements, which are often the noisiest of the four.
We first provide a preliminary introduction to quantum computing, and describe how quantum information can be encoded and manipulated in quantum systems. We include background information for the three different solid-state qubit architectures that feature in this thesis: spin qubits, superconducting qubits and Majorana qubits.
Following this, we investigate a scheme for mediating a two-qubit interaction between spin qubits via a multielectron quantum dot. We study a multielectron dot in detail, and characterise its exchange interaction with a single spin. With the aid of a theoretical model, we show that the multielectron dot possesses an irregular triplet-preferring ground state, analogous to Hund's rule from atomic physics. Using these findings, we then demonstrate that the multielectron dot can be used to mediate a fast, long-range exchange interaction between two spin qubits.
Subsequently, we examine two resonator-based measurement schemes for Majorana qubits. We first propose a readout technique based on a longitudinal qubit-resonator interaction. This leads to a measurement that is fast, high-fidelity and quantum non-demolition (QND). We then investigate a more conventional dispersive readout scheme. Not only does this yield a high quality measurement, but it can also offers a more protected readout mechanism in comparison to the dispersive readout of conventional superconducting qubits.
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Fraval, Elliot. "Minimising the decoherence of rare earth ion solid state spin qubits /." View thesis entry in Australian Digital Theses Program, 2005. http://thesis.anu.edu.au/public/adt-ANU20061010.124211/index.html.
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Hornibrook, John Murray. "Readout and Control Beyond a Few Qubits: Scaling-up Solid State Quantum Systems." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/14448.
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Quantum entanglement and superposition, in addition to revealing interesting physics in their own right, can be harnessed as computational resources in a machine, enabling a range of algorithms for classically intractable problems. In recent years, experiments with small numbers of qubits have been demonstrated in a range of solid-state systems, but this is far from the numbers required to realise a useful quantum computer. In addition to the qubits themselves, quantum operation requires a host of classical electronics for control and readout, and current techniques used in few-qubit systems are not scalable. This thesis presents a series of techniques for control and readout of solid-state qubits, working towards scalability by integrating classical control with the quantum technology. Two techniques for reducing the footprint associated with readout of gallium arsenide spin qubits are demonstrated. Gate electrodes, used to define the quantum dot, are also shown to be sensitive state detectors. These gate-sensors, and the more conventional Quantum Point Contacts, are then multiplexed in the frequency domain, where three-channel qubit readout and ten-channel QPC readout are demonstrated. Two types of superconducting devices are also explored. The loss in superconducting coplanar waveguide resonators is measured, and a suppression of coupling to the parasitic electromagnetic environment is demonstrated. The thesis also details software for the simulation of Josephson-junction based circuits including features beyond what is available in commercial products. Finally, an architecture for managing control of a scalable machine is proposed where classical components are distributed throughout a cryostat and cryogenic switches route control pulses to the appropriate qubits. A simple implementation of the architecture is demonstrated that incorporates a double quantum dot, a gallium arsenide switch matrix, frequency multiplexed readout, and cryogenic classical computation.
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Del, Duce A. "Quantum Logic circuits for solid-state quantum information processing." Thesis, University College London (University of London), 2010. http://discovery.ucl.ac.uk/20166/.
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This thesis describes research on the design of quantum logic circuits suitable for the experimental demonstration of a three-qubit quantum computation prototype. The design is based on a proposal for optically controlled, solid-state quantum logic gates. In this proposal, typically referred to as SFG model, the qubits are stored in the electron spin of donors in a solid-state substrate while the interactions between them are mediated through the optical excitation of control particles placed in their proximity. After a brief introduction to the area of quantum information processing, the basics of quantum information theory required for the understanding of the thesis work are introduced. Then, the literature on existing quantum computation proposals and experimental implementations of quantum computational systems is analysed to identify the main challenges of experimental quantum computation and typical system parameters of quantum computation prototypes. The details of the SFG model are subsequently described and the entangling characteristics of SFG two-qubit quantum gates are analysed by means of a geometrical approach, in order to understand what entangling gates would be available when designing circuits based on this proposal. Two numerical tools have been developed in the course of the research. These are a quantum logic simulator and an automated quantum circuit design algorithm based on a genetic programming approach. Both of these are used to design quantum logic circuits compatible with the SFG model for a three-qubit Deutsch-Jozsa algorithm. One of the design aims is to realise the shortest possible circuits in order to reduce the possibility of errors accumulating during computation, and different design procedures which have been tested are presented. The tolerance to perturbations of one of the designed circuits is then analysed by evaluating its performance under increasing fluctuations on some of the parameters relevant in the dynamics of SFG gates. Because interactions in SFG two-qubit quantum gates are mediated by the optical excitation of the control particles, the solutions for the generation of the optical control signal required for the proposed quantum circuits are discussed. Finally, the conclusions of this work are presented and areas for further research are identified.
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Young, Andrew Buchanan. "Cavity quantum electrodynamics : applications to solid state quantum information." Thesis, University of Bristol, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.720859.
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Stace, Thomas Michael. "Quantum information transfer in solid state devices." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615715.
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GIORGI, Gian Luca. "Quantum information processing in solid state and optical devices." Doctoral thesis, La Sapienza, 2006. http://hdl.handle.net/11573/917133.
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Bourdet, Léo. "Modeling of electrical manipulation in silicon spin qubits." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY058/document.
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Dans la course à l’ordinateur quantique, le silicium est devenu ces dernières années un matériau de choix pour l'implémentation des qubits de spin. De tels dispositifs sont fabriqués au CEA en utilisant les technologies CMOS, afin de faciliter leur intégration à grande échelle. Cette thèse porte sur la modélisation de ces qubits, et en particulier sur la manipulation de l’état de spin par un champ électrique. Pour cela nous utilisons un ensemble de techniques numériques avancées pour calculer le potentiel et la structure électronique des qubits (notamment les méthodes de liaisons fortes et k.p), afin d’être le plus proche possible des dispositifs expérimentaux. Ces simulations nous ont permis d’étudier deux résultats expérimentaux d’importance : l’observation de la manipulation par champ électrique du spin d’un électron d’une part, et la caractérisation de l’anisotropie de la fréquence de Rabi d’un qubit de trou d’autre part. Le premier résultat était plutôt inattendu, étant donné; le très faible couplage spin-orbite dans la bande de conduction du silicium. Nous développons un modèle, validé par les simulations et certains résultats expérimentaux, qui met en évidence le rôle essentiel du couplage spin-orbite inter-vallée, exacerbé par la faible symétrie du système. Nous utilisons ces résultats pour proposer et tester numériquement un schéma de manipulation électrique consistant à passer réversiblement d’un qubit de spin à un qubit de vallée. Concernant les qubits de trous, le couplage spin-orbite relativement élevé autorise la manipulation du spin par champ électrique, toutefois les mesures expérimentales d’anisotropie donnent à voir une physique complexe, insuffisamment bien décrite par les modèles actuels. Nous développons donc un formalisme permettant de caractériser simplement la fréquence de Rabi en fonction du champ magnétique, et qui peut s’appliquer à d’autre type de qubit spin-orbite. Les simulations permettent de reproduire les résultats expérimentaux, et de souligner le rôle important de la contrainte<br>In the race for quantum computing, these last years silicon has become a material of choice for the implementation of spin qubits. Such devices are fabricated in CEA using CMOS technologies, in order to facilitate their large-scale integration. This thesis covers the modeling of these qubits andin particular the manipulation of the spin state with an electric field. To that end, we use a set numerical tools to compute the potential and electronic structure in the qubits (in particular tightbinding and k.p methods), in order to be as close as possible to the experimental devices. These simulations allowed us to study two important experimental results: on one hand the observation of the electrical manipulation of an electron spin, and on the other hand the characterization of the anisotropy of the Rabi frequency of a hole spin qubit. The first one was rather unexpected, since the spin-orbit coupling is very low in the silicon conduction band. We develop a model, confirmed by thesimulations and some experimental results, that highlights the essential role of the intervalley spinorbit coupling, enhanced by the low symmetry of the system. We use these results to propose and test numerically a scheme for electrical manipulation which consists in switching reversibly betweena spin qubit and a valley qubit. Concerning the hole qubits, the relatively large spin-orbit coupling allows for electrical spin manipulation. However the experimental measurements of Rabi frequency anisotropy show a complex physics, insufficiently described by the usual models. Therefore we developa formalism which allows to characterize simply the Rabi frequency as a function of the magnetic field, and that can be applied to other types of spin-orbit qubits. The simulations reproduce the experimental features, underline the important role of strain
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Gullans, Michael John. "Controlling Atomic, Solid-State and Hybrid Systems for Quantum Information Processing." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:11146.
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Quantum information science involves the use of precise control over quantum systems to explore new technologies. However, as quantum systems are scaled up they require an ever deeper understanding of many-body physics to achieve the required degree of control. Current experiments are entering a regime which requires active control of a mesoscopic number of coupled quantum systems or quantum bits (qubits). This thesis describes several approaches to this goal and shows how mesoscopic quantum systems can be controlled and utilized for quantum information tasks.<br>Physics
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Ping, Yuting. "Collective dynamics of solid-state spin chains and ensembles in quantum information processing." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:dc9bed87-0436-48c4-b116-0895a25560b6.
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This thesis is concerned with the collective dynamics in different spin chains and spin ensembles in solid-state materials. The focus is on the manipulation of electron spins, through spin-spin and spin-photon couplings controlled by voltage potentials or electromagnetic fields. A brief review of various systems is provided to describe the possible physical implementation of the ideas, and also outlines the basis of the adopted effective interaction models. The first two ideas presented explore the collective behaviour of non-interacting spin chains with external couplings. One focuses on mapping the identical state of spin-singlet pairs in two currents onto two distant, static spins downstream, creating distributed entanglement that may be accessed. The other studies a quantum memory consisting of an array of non-interacting, static spins, which may encode and decode multiple flying spins. Both chains could effectively `enhance' weak couplings in a cumulative fashion, and neither scheme requires active quantum control. Moreover, the distributed entanglement generated can offer larger separation between the qubits than more conventional protocols that only exploit the tunnelling effects between quantum dots. The quantum memory can also `smooth' the statistical fluctuations in the effects of local errors when the stored information is spread. Next, an interacting chain of static spins with nearest-neighbour interactions is introduced to connect distant end spins. Previously, it has been shown that this approach provides a cubic speed-up when compared with the direct coupling between the target spins. The practicality of this scheme is investigated by analysing realistic error effects via numerical simulations, and from that perspective relaxation of the nearest-neighbour assumption is proposed. Finally, a non-interacting electron spin ensemble is reviewed as a quantum memory to store single photons from an on-chip stripline cavity. It is then promoted to a full quantum processor, with major error effects analysed.
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Devitt, Simon John. "Quantum information engineering : concepts to quantum technologies /." Connect to thesis, 2007. http://eprints.unimelb.edu.au/archive/00003925.
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Wan, Noel H. (Noel Heng Loon). "Scalable creation of spin-photon interfaces for solid-state quantum information processing." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/108979.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 61-64).<br>The negatively charged nitrogen vacancy (NV) defect center in diamond is a promising solid-state qubit due to its exceptional spin and optical properties. In this thesis, we develop high-yield, efficient spin-photon interfaces in diamond. In particular, we demonstrate a process that produces dielectic reflectors and photonic crystal nanobeam cavities directly on the surface of bulk diamond. Our results pave the way towards a scalable network of entangled quantum registers based on spin qubits in diamond.<br>by Noel H. Wan.<br>S.M.
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Newman, Timothy Geoffrey Meadows. "Hardware and Methods for Scaling Up Quantum Information Experiments." Thesis, The University of Sydney, 2019. https://hdl.handle.net/2123/21719.
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Quantum computation promises to solve presently intractable problems, with hopes of yielding solutions to pressing issues to society. Despite this, current machines are limited to tens of qubits. The field is in a state of continuous scaling, with groups around the world working on all aspects of this problem. The work of this thesis aims to contribute to this effort. It is motivated by the goal of increasing both the speed and bandwidth of experiments conducted within our laboratory. Low-loss radio-frequency multiplexers were characterised at cryogenic temperatures, with some shown to operate at below 7mK. The Analog Devices ADG904 was one of these, and its insertion loss was measured at <0.5dB up to 2GHz. Their heat load was measured, and it was found that a switching speed of 10 MHz with an RF signal power of -30dB dissipates 43uW. Installing these switches yields a benefit over installing extra cabling in our cryostat for a switching speed of up to 2MHz and RF power of -30dBm. A switch matrix was prototyped for cryogenic operation, enabling re-routing of wiring inside a cryostat with a minimally increased thermal load. This could be used to significantly increase the scale of high frequency experiments. This switch has also been embedded within a calibration routine, facilitating measurement of a specific feature of interest at millikelvin temperatures. As the field of quantum engineering scales, such measurements will be crucial to close the loop, providing feedback to fabrication and semiconductor growth efforts. Finally, a rapid-turnaround test rig has been developed which has 32 high frequency and 100 DC lines, enabling tests of significant scale in liquid helium. This reduces the time per experiment at 4.2 K to hours rather than days, enabling tests such as thermal cycling, as well as the evaluation of on-chip structures or active electronics and classical computing hardware; which are all necessary elements of any solid state quantum computing architecture.
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Manousakis, Jan [Verfasser], Alexander [Gutachter] Altland, and Simon [Gutachter] Trebst. "New approaches to the realization and identifcation of Majorana qubits in solid state quantum devices / Jan Manousakis ; Gutachter: Alexander Altland, Simon Trebst." Köln : Universitäts- und Stadtbibliothek Köln, 2020. http://d-nb.info/1219652369/34.
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TOLIOPOULOS, DIMOSTHENIS. "Single photon sources integrated on Ge Mie resonator fabricated by solid state dewetting." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2021. http://hdl.handle.net/10281/311361.
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-<br>The following Ph.D. thesis summarizes the work that has been made aiming at the fabrication and characterization of quantum emitters integrated inside Ge nanoisland on Si substrates.
We choose to induce localized Ge impurities centers inside a thin layer of Al0.25Ga0.75As epitaxially grown on Ge islands acting as dielectric Mie Resonators (MR’s). These centers are working as light sources, capable of single photon emission and quantum entanglement properties. Fabrication of the Ge islands was done by solid state dewetting in an ultra-high vacuum environment, obtaining both amorphous and monocrystalline islands, with sizes ranging from 50 to 500 nm. These islands are also photonic Mie-resonators enhancing light-matter interaction and steering the localized defects emission, acting as dielectric nanoantennas.
This thesis exploits molecular beam epitaxy, solid state dewetting and electron assisted lithography for realizing patterned samples. Many different characterization methods have been used to assess the quality of the fabricated samples. We use morphological characterization via scanning electron microscopy (SEM) and atomic force microscopy (AFM). Optically, we characterized the Mie resonators by dark field (DF) spectroscopy to ensure their photonic mode appearance. Also, the crystallinity of the Ge seeds was investigated by RAMAN spectroscopy. In the end, the optical response of the samples will be tested by micro and macro Photoluminescence, time-resolved measurements, and auto-correlation measurements to assess the quantum nature of the emission at low temperatures. Towards our goal we faced three main different topics: i) the growth of Ge nanoisland via solid state dewetting, ii) the optimization of the photonic response of semiconductor Mie resonators by engineering the geometry of the substrates, iii) the integration of III-V layers on Ge islands and the observation of interesting associated defects. Each of these aspects is described in detail in chapters 3,4 and 5. During my secondments at UNIFI, I had also been involved in a quite different approach towards the deterministic realization of quantum emitters integrated beneath a glass nanoantenna, an activity which led to article submission, but it is not reported in this thesis.
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Rolon, Soto Juan Enrique. "Coherent Exciton Phenomena in Quantum Dot Molecules." Ohio University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1314742055.
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Hughes, Marcus. "The development of microfabricated ion traps towards quantum information and simulation." Thesis, University of Sussex, 2013. http://sro.sussex.ac.uk/id/eprint/45142/.
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Trapped ions within Paul traps have shown to be a promising architecture in the realisation of a quantum information processor together with the ability of providing quantum simulations. Linear Paul traps have demonstrated long coherence times with ions being well isolated from the environment, single and multi-qubit gates and the high fidelity detection of states. The scalability to large number of qubits, incorporating all the previous achievements requires an array of linear ion traps. Microfabrication techniques allow for fabrication and micron level accuracy of the trap electrode dimensions through photolithography techniques. The first part of this thesis presents the experiential setup and trapping of Yb+ ions needed to test large ion trap arrays. This include vacuum systems that can host advanced symmetric and asymmetric ion traps with up to 90 static voltage control electrodes. Demonstration of a single trapped Yb+ ion within a two-layer macroscopic ion trap is presented. with an ion-electrode distance of 310(10) μm. The anomalous heating rate and spectral noise density of the trap was measured, a main form of decoherence within ion traps. The second half of this thesis presents the design and fabrication of multi-layer asymmetric ion traps. This allows for isolated electrodes that cannot be accessed via surface pathways, allowing for higher density of electrodes as well as creating novel trap designs that allow for the potential of quantum simulations to be demonstrated. These include two-dimensional lattices and ring trap designs in which the isolated electrodes provide more control in the ion position. For the microfabrication of these traps I present a novel high-aspect ratio electroplated electrode design that provides shielding of the dielectric layer. This provides a means to mitigate stray electric field due to charge build up on the dielectric surfaces. Electrical testing of the trap structures was performed to test bulk breakdown and surface flashover of the ion trap architectures. Results showed sufficient isolation between electrodes for both radio frequency and static breakdown. Surface flashover voltage measurements over the dielectric layer showed an improvement of more than double over previous results using a new fabrication technique. This will allow for more powerful ion trap chips needed for the next generation of microfabricated ion trap arrays for scalable quantum technologies.
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Mhibik, Oussama. "Développement des sources lasers solides continues, visibles et stabilisées en fréquence : une alternative aux lasers à colorants." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00656426.
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Le traitement de l'information quantique, en particulier celui utilisant les centres colorés du diamant et la manipulation cohérente des ions de terre rare incorporés dans des matrices solides (Pr3+, Eu3+) et la spectroscopie à ultra-haute résolution, nécessitent des sources accordables ayant une faible largeur de raie. Or, dans la gamme rouge-orange (570-635 nm) où les diodes lasers font défaut et les lasers solides restent très peu développés, les lasers à colorants sont actuellement les seules sources de rayonnement cohérent disponibles. En revanche, ce type de laser est assez complexe et difficile à stabiliser au niveau du kHz à cause des bruits à haute fréquence générés par le jet de colorant.Pour répondre aux besoins des expériences citées ci-dessus, cette thèse vise à proposer une alternative "tout solide" aux lasers à colorants en explorant différentes possibilités pour la construction d'une source stable émettant dans l'orange-rouge. Dans ce but, nous avons proposé deux solutions:1. La première consiste à développer des oscillateurs paramétriques optiques. Dans cette voie, nous avons développé un OPO simplement résonant à doublage de fréquence intra-cavité et stabilisé en frequence au niveau du kHz.2. La deuxième consiste en un laser à base de fluorures dopés au Pr3+pompé par diode.
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Fraval, Elliot. "Minimising the Decoherence of Rare Earth Ion Solid State Spin Qubits." Phd thesis, 2005. http://hdl.handle.net/1885/47058.
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This work has demonstrated that hyperfine decoherence times sufficiently long for QIP and quantum optics applications are achievable in rare earth ion centres. Prior to this work there were several QIP proposals using rare earth hyperfine states for long term coherent storage of optical interactions. The very long T_1 (~weeks ) observed for rare-earth hyperfine transitions appears promising but hyperfine T_2s were only a few ms, comparable to rare earth optical transitions and therefore the usefulness of such proposals was doubtful. ¶ This work demonstrated an increase in hyperfine T_2 by a factor of 7 × 10^4 compared to the previously reported hyperfine T_2 for Pr^[3+]:Y_2SiO_5 through the application of static and dynamic magnetic field techniques. This increase in T_2 makes previous QIP proposals useful and provides the first solid state optically active Lamda system with very long hyperfine T_2 for quantum optics applications. ¶ ...
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Chirolli, Luca [Verfasser]. "Quantum control and quantum measurement in solid state qubits / vorgelegt von Luca Chirolli." 2010. http://d-nb.info/1008382876/34.
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Gupta, Santosh Kumar. "Superconducting qubits : survey and theoretical investigations for solid state quantum computing." Thesis, 2006. http://hdl.handle.net/2429/17965.
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Superconducting qubits have in recent years become a promising candidate for the implementation of a quantum computer due to their design flexibility, good protection from decohering elementary excitations, and availability of well developed fabrication and measurement techniques. Superconducting flux qubits, for which the effect of offset charge noise is reduced due to the fact that the Josephson energy dominates over the charging energy, correspond to one of the proposed means of designing a superconducting qubit. A nonlinear dispersive readout scheme of flux qubits involving a DC SQUID magnetometer that avoids the effects of on-chip dissipation can be readily implemented, yielding high contrast output for single qubit readout. Coupling schemes via nonlinear Josephson elements have also been realized. On the other hand, while the means of isolating superconducting qubits from external noise sources has been found, the mechanisms by which they undergo relaxation and decoherence due to intrinsic noise sources in the junctions themselves are not very well understood, and the question of how to deal with these noise sources remains unanswered in the general case. Other questions deal with the problem of experimentally observing entanglement in an array of coupled superconducting qubits, and finding the means by which the existence of entanglement in a typical laboratory setup may to some extent be verified by measurements on a global scale. Following a brief introductory review, we will first investigate the influence of a Two-Level Fluctuator on a DC SQUID driven by a finite current bias. Then we introduce a directly measurable signature of multiqubit entanglement for a large system of qubits and show that it is compatible to a recently introduced measure of global entanglement.<br>Science, Faculty of<br>Physics and Astronomy, Department of<br>Graduate
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Janitz, Erika. "Low Temperature Spectroscopy of Solid State Quantum Systems." Thesis, 2013. http://hdl.handle.net/10012/7813.
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Control and coupling of individual quantum systems remains an important research area in experimental quantum information. Single quantum systems in the solid state offer many attractive properties in terms of isolation and control: strong interaction due to close proximity, and scalability using mature fabrication techniques. Similar to atoms, many solid state quantum systems can couple to photons, offering potential for long-range interaction. Two such candidate systems are the nitrogen vacancy center in diamond, and the nanowire semiconductor quantum dot. These systems can act like isolated atoms in a solid state system, and can serve as sources of indistinguishable photons. This report discusses low temperature excitation of these systems, a regime in which the spectral properties are desirable for applications in quantum information, such as long-distance entanglement.
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Liou, Saxon, and 劉少勳. "Solid-state devices for quantum information amplification and detection." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/17616108932131557598.
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博士<br>國立中興大學<br>物理學系所<br>100<br>Our research has experimentally demonstrated that the dc response of one dimensional superconductor/insulator/superconductor junctions array (1D SIS array) can be used to gauge the affected radio-frequency (rf) power. The results suggest a primary and direct rf detection scheme using 1D SIS junction arrays. Using 1D array as an rf detecting gauge, we studied the rf coupling strength as tuning impedance of 1D array. According to many experimental evidences, we deduced that the screening effect plays an important role as studying coupling strength.
As a candidate of quantum bit readout, charge sensitivity of the rf single-electron transistor are experimentally studied by probing reflected rf signals in amplitude detection (AD) and phase-shift detection (PSD). Interestingly, sensitivities in AD and PSD have different dependences with tuning carrier frequency: for AD, the resonant frequency is the most sensitive operating point while for the PSD, the most sensitive point is slightly off the resonance. The best charge sensitivity using PSD is better than that using AD when the quality factor, Q-value of the tank circuit is higher than 10. The higher Q-value is, the superior PSD. The Coulomb oscillations for AD and PSD in the bias region which shows negative differential resistance are also analyzed
Recently, the promising nanoelectromechanical systems (NEMS) are also involved in this thesis. For understanding dynamics of NEMS, giant piezoresistance (PZR) was pointed out as a suitable direction to study its dc electrical properties. Here, giant PZR of top down fabricated silicon nanowire was measured in two crystallographic directions. The PZR has been investigated under electrical modulation and mechanical strain, and a transition from linear to nonlinear PZR was observed as the carrier concentration modulated by the back gate. The fully depleted silicon nanowires show a giant PZR which is a factor of 27 times larger than it in bulk silicon. Our study shows that the PZR is controlled by the conducting state of interface.
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Moussa, Osama. "On single-crystal solid-state NMR based quantum information processing." Thesis, 2010. http://hdl.handle.net/10012/5195.
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Quantum information processing devices promise to solve some problems more efficiently than their classical counterparts. The source of the speedup is the structure of quantum theory itself. In that sense, the physical units that are the building blocks of such devices are its power. The quest then is to find or manufacture a system that behaves according to quantum theory, and yet is controllable in such a way that the desired algorithms can be implemented. Candidate systems are benchmarked against general criteria to evaluate their success. In this thesis, I advance a particular system and present the progress made towards each of these criteria. The system is a three-qubit 13C solid-state nuclear magnetic resonance (NMR) based quantum processor. I report results concerning system characterization and control, pseudopure state preparation, and quantum error correction. I also report on using the system to test a central question in the foundation of quantum mechanics.
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Seidelin, Signe. "Towards Quantum Information Processing with Atomic and Solid State Systems." Habilitation à diriger des recherches, 2011. http://tel.archives-ouvertes.fr/tel-00579308.
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La partie I décrit une série d'expériences en information quantique avec des ions piégés. Ces résultats ont été obtenus au NIST, Boulder, Colorado (USA). La partie II présente des expériences sur des boites quantiques insérées dans des microcavités. Ces expériences ont eu lieu à l'Institut Néel - Université Joseph Fourier Grenoble I.
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Ferguson, Katherine Rose. "Generation and storage of optical entanglement in a solid state spin-wave quantum memory." Phd thesis, 2016. http://hdl.handle.net/1885/109193.
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This thesis investigates an entangled light source with an
in-built quantum memory based on the protocol of rephased
amplified spontaneous emission (RASE). RASE has promising
applications as a building-block of a quantum repeater: a device
essential for extending the range of current quantum
communication links. To be useful RASE must be able to produce
high fidelity non-classical light with high efficiency, and be
able to store multimode entanglement for long times. This thesis
characterises the RASE source and determines to what degree these
requirements can be met.
The experimental RASE demonstration was conducted in a rare-earth
ion doped crystal. Rare-earth ions provide a particularly
promising platform for developing quantum technologies as they
possess long coherence times on both the optical and hyperfine
transitions.
In the RASE protocol an inverted ensemble of two-level atoms
amplifies the vacuum fluctuations resulting in amplified
spontaneous emission (ASE). This results in entanglement between
the output optical field and the collective modes of the
amplifying ensemble. The collective atomic state dephases due to
the inhomogeneous broadening of the ensemble but this can be
rephased using photon echo techniques. When the ensemble
rephases, a second optical field, the rephased amplified
spontaneous emission (RASE), is emitted and is entangled with the
ASE. In this thesis, a modified four-level rephasing scheme is
used that allows the single photon signals to be spectrally
resolved from any coherent background emission associated with
the bright driving fields. In addition, four-level RASE
incorporates storage on the long-lived hyperfine ground states.
Two experiments are described in this thesis. First, a free-space
four-level RASE demonstration using continuous-variable
detection. In this experiment the different sources of noise were
characterised and low noise operation was shown to be possible.
Entanglement of the ASE and RASE was confirmed by violating the
inseparability criterion with 98.6% confidence. In addition,
entanglement was demonstrated after storage of the collective
atomic state on the spin states and RASE was shown to be
temporally multimode, with almost perfect distinguishability
between two temporal modes demonstrated. The degree of
entanglement between the ASE and RASE was limited by the
rephasing efficiency, which saturated at 3%. It was determined
that distortion of the rephasing pulses as they propagate through
the optically thick ensemble was the probable cause of the low
efficiency.
The second experiment was a preliminary cavity-enhanced RASE
demonstration. Theoretically perfect rephasing efficiency can be
obtained by placing the crystal in an impedance-matched optical
cavity. The initial cavity design showed encouraging evidence of
an enhancement in the rephasing efficiency, with a 4-fold
improvement over the free-space experiment. Improvements to the
cavity design were proposed to allow a further increase in the
rephasing efficiency of RASE.
In summary, this thesis provides an extensive characterisation of
an entangled light source with an in-built quantum memory based
on rephasing spontaneous emission from an ensemble of ions.
Importantly, the RASE scheme allows generation and storage of
entanglement in a single protocol, which holds great promise for
the development of integrated quantum networks.
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Zheng, Jiabao. "Efficient spin-photon interface for solid-state-based spin systems for quantum information processing and enhanced metrology." Thesis, 2017. https://doi.org/10.7916/D8N87PB3.
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The holy grail for quantum engineers and scientists is to build the quantum internet that spans over the entire globe. This information infrastructure holds the promise for transmitting information securely, scaling up computing power exponentially and setting the standards for precision measurement at the ultimate limit. Solid-state-based spin systems recently emerge as promising building blocks for the quantum internet. Among these candidates, the negatively charged nitrogen vacancy (NV) center in diamond attracted much attention thanks to its optical addressability, long spin coherence times, and well-controlled electronic orbitals and spin states. However, the non-ideal optical properties of NV poses a challenge to its implementation in quantum technologies. This calls for building photonic structures as efficient spin-photon interfaces for realizing strong interactions with photon modes or efficient out-coupling of its fluorescence. Such interfacing structures are also of great importance for other optically active spin-systems newly found.
In this dissertation, chirped dielectric cavities are designed for building NV as fast single photon sources via broadband Purcell enhancement, using an inverse simulation approach to maximize the broadband absorption of the atomically thin absorbers. Simulated NV-cavity coupling indicates broadband Purcell factor of ∼> 100. Next, to realize coupled NV-cavity systems over large scale, a self-aligned nano-implantation technique is investigated using a lithographically defined hybrid mask for both precision pattern transfer and nitrogen implantation. Measured results show single-NV per cavity yield of ∼ 26±1% and 5-fold Purcell induced intensity enhancement. Finally, chirped circular gratings are designed for efficient collection from the NV for remote entanglement and precision sensing. Simulated grating structures present near-unity collection efficiencies. These demonstrated techniques and structures are also applicable to other solid-state-based spin systems.