Dissertations / Theses on the topic 'Spin qubit'
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Wernz, Johannes. "Dekohärenz gekoppelter Spin- und Qubit-Systeme." [S.l. : s.n.], 2003. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB10761312.
Full textJadot, Baptiste. "Coherent long-range transport of entangled electron spins." Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALY007.
Full textQuantum computing is a field of growing interest, especially in Grenoble with an exceptional concentration of both research and industrials groups implicated in this field. The global aim is to develop a new kind of nano-processors, based on quantum properties. Its building brick is a two-level quantum system, in our case the spin of electrons trapped in a quantum dot.In this quest for a large-scale architecture, networked quantum computers offer a natural path towards scalability. Indeed, separating the computational task among quantum core units interconnected via a coherent quantum mediator would greatly simplify the addressability challenges. These quantum links should be able to coherently couple arbitrary nodes on fast timescales, in order to share entanglement across the whole quantum circuit. In semiconductor quantum circuits, nearest neighbor entanglement has already been demonstrated, and several schemes exist to realize long-range coupling. Among them, a possible implementation of this quantum mediator would be to prepare an entangled state and shuttle individual electron spins across the structure, provided that this transport preserves the entanglement.In this work, we demonstrate the fast and coherent transport of electron spin qubits across a 6.5 μm long channel, in a GaAs/AlGaAs laterally defined nanostructure. Using the moving potential induced by a propagating surface acoustic wave, we send sequentially two electron spins initially prepared in a spin singlet state. During its displacement, each spin experiences a coherent rotation due to spin-orbit interaction, over timescales shorter than any decoherence process. By varying the electron separation time and the external magnetic field, we observe quantum interferences which prove the coherent nature of both the initial spin state and the transfer procedure.We show that this experiment is analogous to a Bell measurement, allowing us to quantify the entanglement between the two electron spins when they are separated, and proving this fast and long-range qubit displacement is an efficient procedure to share entanglement across future large-scale structures
Conway, Lamb Ian. "Cryogenic Control Beyond 100 Qubits." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/17046.
Full textGe, Ling. "Theory and Modelling of Spin-qubit Interactions in Nanotubes and Fullerenes." Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504351.
Full textPerez, Barraza Julia Isabel. "Ultrasmall silicon quantum dots for the realization of a spin qubit." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708003.
Full textSchauer, Floyd [Verfasser], and Dominique [Akademischer Betreuer] Bougeard. "Realizing spin qubits in 28Si/SiGe: heterostructure gating, qubit decoherence and asymmetric charge sensing / Floyd Schauer ; Betreuer: Dominique Bougeard." Regensburg : Universitätsbibliothek Regensburg, 2021. http://d-nb.info/1225935849/34.
Full textHabgood, Matthew. "Correlated electron models for spin-qubit interactions in fullerenes, nanotubes and nanowires." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.496903.
Full textCerfontaine, Pascal [Verfasser], Jörg Hendrik [Akademischer Betreuer] Bluhm, and David P. [Akademischer Betreuer] DiVincenzo. "High-fidelity single- and two-qubit gates for two-electron spin qubits / Pascal Cerfontaine ; Jörg Hendrik Bluhm, David P. DiVincenzo." Aachen : Universitätsbibliothek der RWTH Aachen, 2019. http://d-nb.info/1211487806/34.
Full textMedford, James Redding. "Spin Qubits in Double and Triple Quantum Dots." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:10766.
Full textPhysics
Kuhlen, Sebastian [Verfasser]. "Spinkohärenz und Spindynamik in Zinkoxid : vom donatorgebundenen Exziton zum Spin-Qubit / Sebastian Kuhlen." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2014. http://d-nb.info/1056993995/34.
Full textAres, Natalia. "Electronic transport and spin control in SiGe self-assembled quantum dots." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENY060/document.
Full textQuantum mechanics displays all its exciting strangeness already by considering the Schrödingerequation in a one-dimensional square well potential; tunnelling events put this statement in evidence.To recreate this situation in a given material system is an inspiring playground and a big step towardstaking control of quantum mechanisms. For instance, it is now possible to confine electrons in solidstatedevices enabling amore efficient solar-cell technology. Confining individual electron spins has infact been suggested as a possible approach to the realization of a quantum computer. Each electronspin forms a natural two-level systems encoding an elementary bit of quantum information (a socalledspin qubit). This proposal, by Loss and DiVincenzo, has contributed to the opening of an activeresearch field referred to as quantum spintronics. Spin qubits rely on the fact that spin states canpreserve their coherence on much longer time scales than charge (i.e. orbital) states.A confinement potential can be created artificially in many different ways; producing constantmagnetic fields and spatially inhomogeneous electric fields, applying oscillating electric fields, usingconductive oxide layers, etc. To take advantage of the band-alignment of different semiconductors isamong these. The relevant dimensions of the considered system should still be smaller than the phasecoherence length of the confined particles in order that their quantum behaviour is preserved.So far, most of the progress has been achieved using GaAs-based semiconductor heterostructures. Insuch layered systems themotion of carriers is confined to a plane and further confinement is achievedbymeans of lithographic techniques, which allow lateral confinement to be achieved on a sub-100 nmlength scale. In this way, quasi-zero-dimensional systems whose electronic states are completelyquantized, i.e. quantum dots (QDs), can be devised.Various time-resolved techniques involving high-frequency electrical signals have been developed tomanipulate and read-out the spin state of confined electrons in GaAs QDs, and several years ago thefirst spin qubits were reported. In GaAs-based QDs, however, the quantum coherence of electronspins is lost on relatively short time scales due to the hyperfine interactionwith the nuclear spins (bothGa and As have non-zero nuclear spin moments). In spite of significant advances on controlling thenuclear polarization [3, 4], this problem remains unsolved.In the past few years an increasing effort is concentrating on alternative material systems in whichhyperfine interaction is naturally absent or at least very weak and, in principle, controllable by isotopepurification. While Si fulfils this requirement and it is the dominant material in modernmicroelectronics, it suffers from low mobility compared to III-V semiconductors, which obstructs itsapplication for quantum spintronics. SiGe structures offer a way to circumvent this problem that isstill compatible with standard silicon processes.I have focused mainly on the study of the electronic properties of SiGe self-assembled islands, alsocalled SiGe nanocrystals. This work, which condensates the main points of this study, is organized insix chapters. In the first chapter, I describe the basics of the growth of SiGe self-assembled islands andthe properties of the quasi-zero-dimensional confinement potential that they define. Chapter 2 isdevoted to the basics of electronic transport in these structures. Chapter 3 deals with the electricmodulation of the hole g-factor in SiGe islands, which would enable a fast manipulation of the spinstates. In Chapter 4 I present theoretical and experimental findings related to spin selectivity in SiGeQDs and Chapter 5 is dedicated to the realization of an electron pump in InAs nanowires based on thiseffect. Finally, Chapter 6 exhibits our progress towards the study of coupled SiGe QD devices
Hakimi, Shirin. "Theory and Modeling of Electrical Control of Chiral Qubit in Spin-Frustrated Molecular Triangle." Thesis, Linnéuniversitetet, Institutionen för fysik och elektroteknik (IFE), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-84587.
Full textEl, Homsy Victor. "Apprivoiser le bruit pour les qubits de spin d'électrons en CMOS." Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALY007.
Full textWhile being a bit more than a century old, quantum physics have become technological. The most ubiquitous instance of the use of quantum physics is the transistor, as the building block of modern computing devices. Progress in nanoscale fabrication has fostered an exponential increase of transistor density In microelectronics circuits. Once in the nanometer range, unavoidable quantum effects tamper further miniaturization. Alternative transistor designs are being developed to mitigate this showstopper. The complementary metal-oxide-semiconductor (CMOS) fully-depleted silicon-on-insulator (FD-SOI) platform is one of them.In parallel to these developments, quantum physics spawned a new generation of technological innovation, thanks to the ability to control matter at the single particle level. Isolating elementary particles in a quiet environment gives access to their superposition and entanglement properties. Using these to process information would realize the quantum computing paradigm shift, where classically intractable problems are promised to come at reach. Many candidates are racing for the best implementation of a quantum bit (or “qubit”) and all of them are facing the challenge to up-scale their architecture from a few lab qubits to an industrial processor. Among them, electrons trapped in silicon structures offer promising prospects thanks to their reduced exposure to magnetic nuclei and spin-orbit interaction, and to the possibility to purify away non-zero nuclear spins. Moreover, the expected compatibility of silicon structures with microelectronics know-how gives hopes for scalability. In this thesis, we study single electrons trapped in gate-defined quantum dots formed in CMOS FD-SOI transistors. We investigate on how to improve their use as qubits, focusing on experimental noise aspects.First, we demonstrate coherent manipulation of a single CMOS electron spin with electrically driven spin resonance. A micromagnet is patterned directly on top of the CMOS chip, creating an inhomogeneous magnetic field. Driving the electron motion inside this gradient with the available electric gates makes it feel an effective oscillating magnetic field, and enables single qubit operations, with a relatively low 1 MHz Rabi frequency and short 500 ns dephasing time. This limited performance is attributed to a finite number of two-level fluctuators and smaller quantum dot sizes compared to other silicon architectures. The shape of the Rabi decay and the sub-µs dephasing time are characteristic of hyperfine interaction with spinful nuclei. However, dynamically decoupling the electron spin from this frequency range showed state-of-the-art coherence times and performance limited by charge noise, in accordance with simple charge sensor measurements at low frequencies. These results point towards the relevance of isotopic purification to avoid hyperfine-induced dephasing in CMOS FD-SOI devices.After focusing on qubit control, a second part of this thesis deals with readout noise. The objective was to demonstrate the use of a traveling-wave parametric amplifier (TWPA) in the amplification chain of radio-frequency readout of CMOS devices. Patterning inductors on the CMOS chip reduced the parasitic capacitance of our resonators and enabled to perform lumped-element reflectometry in the 3-4 GHz range, closer to usual TWPA operating regimes. Even when being pumped far from its gap, the TWPA shows nominal figures of merit, and a resilience to magnetic fields typical for spin qubit experiments. Its high -100dBm compression point, wide and tunable 2 GHz bandwidth and quantum-limited added noise enabled to get more than 10dB signal-to-noise ratio improvement on interdot charge transitions in our devices, and to multiplex interdot readout in a 6-gate device. This compatibility between a large bandwidth superconducting amplifier and multi-gate CMOS FD-SOI quantum devices is promising towards CMOS electron spin qubit experiments at larger scale
Gheeraert, Nicolas. "Non-linéarités quantiques d'un qubit en couplage ultra-fort avec un guide d'ondes." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY034/document.
Full textIn the recent years, the field of light-matter interaction has made a further stride forward with the advent of superconducting qubits ultra-strongly coupled to open waveguides. In this setting, the qubit becomes simultaneously coupled to many different modes of the waveguide, thus turning into a highly intricate light-matter object. Investigating the wealth of new dynamical phenomena that emerge from the high complexity of these engineered quantum many-body systems is the main objective of this thesis.As a first crucial step, we tackle the time-evolution of such a non-trivial system using a novel numerical technique based on an expansion of the full state vector in terms of multi-mode coherent states. Inspired by earlier semi-classical approaches, this numerically exact method provides an important advance compared to the state-of-the-art techniques that have been used so far to study the many-mode ultra-strong coupling regime. Crucially, it also keeps track of every detail of the dynamics of the complete qubit-waveguide system, allowing both to perform the tomography and to extract multi-particle scattering of the waveguide degrees of freedom.An exploration of the many-mode ultra-strong coupling regime using this new technique led to the two core theoretical predictions of this thesis. The first demonstrates that the radiation spontaneously emitted by an excited qubit takes the form of a Schrödinger cat state of light, a result strikingly different from the usual single-photon emission known from standard quantum optics. The second prediction concerns the scattering of low-power coherent signals on a qubit, a very common experimental protocol performed routinely in laboratories. Most remarkably, it is shown that the qubit non-linearity, transferred to the waveguide through the ultra-strong light-matter interaction, is able to split photons from the incoming beam into several lower-energy photons, leading to the emergence of a low-frequency continuum in the scattered power spectrum that dominates the inelastic signal. By studying the second-order correlation function of the radiated field, it is also shown that emission at ultra-strong coupling displays characteristic signatures of particle production.In the final part of the thesis, the second-order correlation function is investigated again, but this time experimentally, and in the regime of moderate coupling. Although the results are still preliminary, this part of the thesis will provide an instructive account of signal measurement theory and will allow to understanding in-depth the experimental procedure involved in measuring quantum microwave signals. Moreover, the experimental developments and microwave simulations tools described in this section could be applied in the future to signals emitted by ultra-strongly coupled qubits, in order to observe the signatures of particle production revealed by the second-order correlation function
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.
Full textGrezes, Cécile. "Towards a spin ensemble quantum memory for superconducting qubits." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066635.
Full textThis thesis work discusses the development of a hybrid quantum processor, in which collective degrees of freedom of an ensemble of spins are used as a multimode quantum memory for superconducting qubits. We design a memory protocol able to store and retrieve on demand the state of a large number of qubits in a spin ensemble and we demonstrate building blocks of its operations with NV centers in diamond. The protocol relies on the coupling of the NV ensemble to a resonator with tunable frequency and quality factor. Incoming quantum states are written by resonant absorption of a microwave photon in the spin ensemble, and then read out of the memory by applying a sequence of control pulses to the spins and to the resonator. The write step of the protocol is demonstrated in a first experiment by integrating on the same chip a superconducting qubit, a resonator with tunable frequency, and the NV ensemble. Arbitrary qubit states are stored into the spin ensemble via the resonator. After storage, the resulting collective quantum state is rapidly dephased due to inhomogeneous broadening of the ensemble and a refocusing sequence must be applied on the spins to bring them to return in phase and to re-emit collectively the quantum state initially absorbed as an echo. In a second experiment, we demonstrate an important building block of this read-out operation, which consists in retrieving multiple classical microwave pulses down to the single photon level using Hahn echo refocusing techniques. Finally, optical repumping of the spin ensemble is implemented in order to reset the memory in-between two successive sequences
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.
Full textPoulin-Lamarre, Gabriel. "La boîte quantique triple : nouvelles oscillations et incorporation de microaimants." Mémoire, Université de Sherbrooke, 2014. http://hdl.handle.net/11143/5989.
Full textCandoli, Davide. "Simulation of NMR/NQR observables and spin control for applications in Quantum Science." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
Find full textRochette, Sophie. "Étude en transport électrique d'une double boîte quantique latérale en silicium." Mémoire, Université de Sherbrooke, 2014. http://hdl.handle.net/11143/5913.
Full textRoy, Anne-Marie. "Détection de charge rapide radiofréquence." Mémoire, Université de Sherbrooke, 2015. http://hdl.handle.net/11143/8155.
Full textHollmann, Arne [Verfasser], Hendrik [Akademischer Betreuer] Bluhm, and Dominique [Akademischer Betreuer] Bougeard. "Relaxation and decoherence of a 28Si/SiGe spin qubit with large valley splitting / Arne Hollmann ; Hendrik Bluhm, Dominique Bougeard." Aachen : Universitätsbibliothek der RWTH Aachen, 2019. http://d-nb.info/122008252X/34.
Full textBrown, Richard Matthew. "Coherent transfer between electron and nuclear spin qubits and their decoherence properties." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:21e043b7-3b72-44d7-8095-74308a6827dd.
Full textGRIMAUDO, Roberto. "Exact quantum dynamics of interacting spin systems subjected to controllable time dependent magnetic fields." Doctoral thesis, Università degli Studi di Palermo, 2020. http://hdl.handle.net/10447/401920.
Full textCubaynes, Tino. "Shaping the spectrum of carbon nanotube quantum dots with superconductivity and ferromagnetism for mesoscopic quantum electrodynamics." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS195/document.
Full textIn this thesis, we study carbon nanotubes based quantum dot circuits embedded in a microwave cavity. This general architecture allows one to simultaneously probe the circuit via quantum transport measurements and using circuit quantum electrodynamics techniques. The two experiments realized in this thesis use metallic contacts of the circuit as a resource to engineer a spin sensitive spectrum in the quantum dots. The first one is a Cooper pair splitter which was originally proposed as a source of non local entangled electrons. By using cavity photons as a probe of the circuit internal dynamics, we observed a charge transition dressed by coherent Cooper pair splitting. Strong charge-photon coupling in a quantum dot circuit was demonstrated for the first time in such a circuit. A new fabrication technique has also been developed to integrate pristine carbon nanotubes inside quantum dot circuits. The purity and tunability of this new generation of devices has made possible the realization of the second experiment. In the latter, we uses two non-collinear spin-valves to create a coherent interface between an electronic spin in a double quantum dot and a photon in a cavity. Highly coherent spin transitions have been observed. We provide a model for the decoherence based on charge noise and nuclear spin fluctuations
Santos, Marcelo Meireles dos. "Soluções exatas e medidas de emaranhamento em sistemas de spins." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-23032018-210425/.
Full textRecently, an implementation of a universal set of one- and two-qubit logic gates for quantum computing using spin states of single-electron quantum dots was proposed. These results motivated us to develop a formal theoretical study of the corresponding model of two spins placed in an external magnetic field and coupled by a time-dependent mutual interaction of Heisenberg. We then consider the so-called two-spin equation, which describes four-level quantum systems. A useful property of this equation is that the corresponding problem for the case of parallel external magnetic fields can be reduced to the problem of a single spin in an effective external field. This allows us to generate a series of exact solutions for the two-spin equation from the already known exact solutions of the one-spin equation. Based on this fact, we construct and present in this study a list of new exact solutions for the two-spin equation for different configurations of external fields and interaction between particles. Using some of these solutions obtained, we study the dynamics of the entropy of entanglement of the respective systems considering different initially separable spins states.
Weichselbaum, Andreas. "Nanoscale Quantum Dynamics and Electrostatic Coupling." Ohio University / OhioLINK, 2004. http://www.ohiolink.edu/etd/view.cgi?ohiou1091115085.
Full textLaird, E. A. "Electrical control of quantum dot spin qubits." Thesis, Lancaster University, 2009. http://eprints.lancs.ac.uk/124373/.
Full textBrooks, Matthew [Verfasser]. "Spin Qubits in Two-Dimensional Semiconductors / Matthew Brooks." Konstanz : KOPS Universität Konstanz, 2019. http://d-nb.info/1204829217/34.
Full textBourdet, Léo. "Modeling of electrical manipulation in silicon spin qubits." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY058/document.
Full textIn 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
Stano, Peter. "Controlling electron quantum dot qubits by spin-orbit interactions." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=983802254.
Full textWitzel, Wayne Martin. "Decoherence and dynamical decoupling in solid-state spin qubits." College Park, Md. : University of Maryland, 2007. http://hdl.handle.net/1903/6889.
Full textThesis research directed by: Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
Balian, S. J. "Quantum-bath decoherence of hybrid electron-nuclear spin qubits." Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1470543/.
Full textSmith, Thomas Benjamin. "Entanglement and measurement of solid-state qubits." Thesis, The University of Sydney, 2020. https://hdl.handle.net/2123/24894.
Full textMorton, John J. L. "Electron spins in fullerenes as prospective qubits." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425947.
Full textGrajales, Julián Andrés Vargas. "Caracterização da evolução adiabática em cadeias de spin." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-05062018-151545/.
Full textAdiabatic quantum computation has its cornerstone in the adiabatic theorem, whose efficiency is traditionally related to the ratio of the Hamiltonian temporal variation that describes the system and the minimum gap between the ground state and the first excited state. Usually, this gap tends to decrease when the number of quantum resources (quantum bit: qubit) of a quantum processor increases, thus it requires slow variations of the Hamiltonian to ensure an adiabatic dynamic. Among the candidates for its physical implementation are the qubits superconducting circuit-based which have great potential because of their high control and promising scalability. However, when these qubits are implemented, they have an intrinsic source of noise due to manufacturing errors that can not be despised. Therefore, in this thesis we study how the effects caused by the fluctuations of the physical parameters of the qubit affect the behavior of the fidelity of the computation, accomplishing with this purpose the simulation of the dynamics of small disordered spin chains. From the exhaustive analysis of this studio, it was possible to propose a strategy that allows to increase the fidelity considering a noisy system. On the other hand, motivated by the interest of obtaining sufficient and necessary criteria to satisfy an adiabatic quantum computation and the fact that there is still no general adiabaticity condition despite there being numerous proposals, we present a new criterion that manifests sufficiency for more general systems and we finally presented evidence that such a condition would be a consistent quantifier.
Mehl, Sebastian Johannes [Verfasser]. "Achieving quantum computation with quantum dot spin qubits / Sebastian Johannes Mehl." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2014. http://d-nb.info/1065974485/34.
Full textCamirand, Lemyre Julien. "Nanofabrication de boîtes quantiques latérales pour l'optimisation de qubits de spin." Mémoire, Université de Sherbrooke, 2012. http://hdl.handle.net/11143/5771.
Full textGaudreau, Louis. "Manipulation cohérente de qubits de spin dans une boîte quantique triple." Thèse, Université de Sherbrooke, 2011. http://savoirs.usherbrooke.ca/handle/11143/5157.
Full textGodfrin, Clément. "Quantum information processing using a molecular magnet single nuclear spin qudit." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY015/document.
Full textThe application of quantum physics to the information theory turns out to be full of promises for our information society. Aware of this potential, groups of scientists all around the world have this common goal to create the quantum version of the computer. The first step of this ambitious project is the realization of the basic block that encodes the quantum information, the qubit. Among all existing qubits, spin based devices are very attractive since they reveal electrical read-out and coherent manipulation. Beyond this, the more isolated a system is, the longer its quantum behaviour remains, making of the nuclear spin a serious candidate for exhibiting long coherence time and consequently high numbers of quantum operation.In this context I worked on a molecular spin transistor consisting of a TbPc2 singlemolecule magnet coupled to electrodes (source, drain and gate) and a microwave antenna. This setup enabled us to read-out electrically both the electronic and the nuclear spin states and to coherently manipulate the nuclear spin of the Terbium ion. I focus during my Ph.D. on the study of the spins dynamic and mainly the 3/2 nuclear spin under the influence of a microwave pulse. The first step was to measure the energy difference between these statesleading in a second time to the coherent manipulation of the three nuclear spin transitions using only a microwave electric field. To further characterize the decoherence processes that break the phase of the nuclear spin states, I performed Ramsey and Hahn-echo measurements. These preliminary results show that we were in presence of three qubits with figure of merit higher than two thousands, thus meeting the expectations aroused by the use of a nuclearspin as the basic block of quantum information.More than demonstrating the qubit dynamic, I demonstrated that a nuclear spin embedded in the molecular magnet transistor is a four quantum states system that can be fully controlled, a qudit. Theoretical proposal demonstrated that quantum information processing such as quantum gates and algorithms could be implemented using a 3/2 spin. I focused on a research algorithm which is a succession of an Hadamard gate, that creates a coherent superposition of all the nuclear spin sates, and an unitary evolution, that amplified the amplitude of a desired state. It allows a quadratic speed-up to find an element in an unordered list compared to classical algorithm. During my Ph.D., I demonstrated the experimental proof of feasibility of this Grover like algorithm applied to a multi-levels system. The first step was to experimentally create coherent superposition of 2, 3 and 4 states. Then I measured coherent oscillations inbetween a 3 state superposition and a selected state which is the signature of the research algorithm implementation.In summary, this Ph.D. exposed the first quantum search algorithm on a single-molecule magnet based qudit. These results combined to the great versatility of molecular magnet holds a lot of promises for the next challenge: building up a scalable molecular based quantum computer
Elman, Samuel. "Long-range entanglement for spin qubits via quantum Hall edge modes." Thesis, The University of Sydney, 2017. http://hdl.handle.net/2123/17165.
Full textFraval, 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.
Full textVenitucci, Benjamin. "Modélisation de la manipulation électrique des qubits de trou dans le silicium." Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALY059.
Full textSpin quantum bits (qubits) are devices in which information is stored as a coherent superposition of two spin states of a particle. One of the perspectives of these devices is to exploit a massive parallelism allowed by such a superposition of solutions. The CEA Grenoble is studying in particular hole spin qubits in silicon, because their electrical manipulation is easier than electron qubits thanks to the strong spin-orbit coupling of the valence bands. This thesis thus focuses on the modeling of the electrical manipulation of these hole qubits. First of all, we introduce the k.p methods that describe the valence bands structure of silicon, and which allow to build numerical and analytical models. Then we present the experiments carried out by CEA Grenoble on these qubits derived from CMOS technologies. These experiments reveal the strong magnetic anisotropy of the Larmor and Rabi frequency, which respectively characterise the dynamic and the manipulation of the qubit. We introduce a gyromagnetic matrix formalism that completely describe these two frequencies.In addition, we show how symmetries impact the shape of this matrix, and how they explain the magnetic anisotropy of qubits. Next, we identify through numerical simulation, the microscopic mechanisms underlying the electrical manipulation of spin, which then allow us to build a minimal model for hole qubits. This model demonstrates that silicon is an ideal host material for a such qubit thanks to the strong anisotropy of its valence bands. Finally, we study numerically the impact of phonons on the lifetime of hole qubits. We show that the relaxation time is large enough to perform tens of thousand of operations despite the strong spin-orbit coupling
Rohling, Niklas [Verfasser]. "Quantum Computing with Spin and Valley Qubits in Quantum Dots / Niklas Rohling." Konstanz : Bibliothek der Universität Konstanz, 2015. http://d-nb.info/1095134507/34.
Full textHadden, J. P. "Photonic structures and techniques for enhanced measurement of spin qubits in diamond." Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.664971.
Full textFilidou, Vasileia. "Entangling nuclear spins using photoexcited triplet states." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:7c30ec89-f638-4cc0-9404-7300b93c6cd6.
Full textThalineau, Romain. "Qubits de spin : de la manipulation et déplacement d'un spin électronique unique à son utilisation comme détecteur ultra sensible." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00875970.
Full textTiwari, Rakesh P. "Topics in the theory of excitations in granular matter." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1259970038.
Full textWalsh, Michael P. Ph D. Massachusetts Institute of Technology. "Microwave and optical control of sub-diffraction spin qubits in diamond at cryogenic temperatures." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/101591.
Full textCataloged from PDF version of thesis.
Includes bibliographical references (pages 87-91).
Efficient entanglement of negative nitrogen vacancy (NV) centers in diamond will bring us significantly closer to realizing a large scale quantum network, including the design and development of quantum computers. A central requirement for generating large-scale entanglement is a system that can be entangled at a rate faster than it decoheres. There are a variety of proposed protocols to implement entanglement, however, thus far implementation of a system that performs efficiently enough in practice to overcome decoherence has been unsuccessful. In this thesis, I laid the ground work to entangle two NVs using a dipole coupling protocol, a protocol that has the advantageous property of not requiring use of identical photons, making this experimental approach highly feasible. The actual experiment will be done at cryogenic temperatures, a condition that provides an advantage over room temperature realizations of the protocol by extending coherence time and improving readout speed and fidelity. The ultimate goal of this work is to determine if this is achievable in a scalable architecture that will establish a foundation for future experiments in this research and development area.
by Michael P. Walsh.
S.M.
Russ, Maximilian [Verfasser]. "Quantum information processing in semiconductor quantum dots using single and multi-spin qubits / Maximilian Russ." Konstanz : KOPS Universität Konstanz, 2019. http://d-nb.info/1191693406/34.
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