Letteratura scientifica selezionata sul tema "Hole spin quantum bit"
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Articoli di riviste sul tema "Hole spin quantum bit"
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Mäkelä, Jarmo. "Wheeler’s it from bit proposal in loop quantum gravity". International Journal of Modern Physics D 28, n. 10 (luglio 2019): 1950129. http://dx.doi.org/10.1142/s0218271819501293.
Testo completoAbstract (sommario):
As an attempt to realize Wheeler’s “it-from-bit proposal” that physics should be reduced to simple yes–no questions, we consider a model of loop quantum gravity, where the only allowed values of the quantum numbers [Formula: see text] at the punctures [Formula: see text] of the spin network on the spacelike two surfaces of spacetime are [Formula: see text] and [Formula: see text]. When [Formula: see text], the puncture is in the vacuum, and it does not contribute to the area of the two surface, whereas when [Formula: see text], the puncture is in an excited state, and the allowed values of the associated quantum number [Formula: see text] are [Formula: see text] and [Formula: see text]. As a consequence, the spin network used as a model of spacetime is analogous to a system of particles with spin [Formula: see text], and every puncture carries exactly one bit of information. When applied to spacetimes with horizon, our model enables us to find an explicit expression for the partition function of spacetime. Using this partition function we may, among other things, obtain the Bekenstein–Hawking entropy law for black holes. When applied to cosmological models with horizon, the partition function predicts a cosmic phase transition in the early universe, where the cosmological constant went through a dramatic decrease and the matter of the universe was created out of the vacuum.
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Combescot, Monique, e Shiue-Yuan Shiau. "From spherical to periodic symmetry: the analog of orbital angular momentum for semiconductor crystals". Journal of Physics: Condensed Matter 34, n. 20 (4 aprile 2022): 205502. http://dx.doi.org/10.1088/1361-648x/ac5867.
Testo completoAbstract (sommario):
Abstract The angular momentum formalism provides a powerful way to classify atomic states. Yet, requiring a spherical symmetry from the very first line, this formalism cannot be used for periodic systems, even though cubic semiconductor states are commonly classified according to atomic notations. Although never noted, it is possible to define the analog of the orbital angular momentum, by only using the potential felt by the electrons. The spin–orbit interaction for crystals then takes the L ^ ⋅ S ^ form, with L ^ reducing to L ^ = r ^ × p ^ for spherical symmetry. This provides the long-missed support for using the eigenvalues of L ^ and J ^ = L ^ + S ^ , as quantum indices to label cubic semiconductor states. Importantly, these quantum indices also control the phase factor that relates valence electron to hole operators, in the same way as particle to antiparticle, in spite of the fact that the hole is definitely not the valence-electron antiparticle. Being associated with a broader definition, the ( L ^ , J ^ ) analogs of the ( L ^ , J ^ ) angular momenta, must be distinguished by names: we suggest ‘spatial momentum’ for L ^ that acts in the real space, and ‘hybrid momentum’ for J ^ that also acts on spin, the potential symmetry being specified as ‘cubic spatial momentum’. This would cast J ^ as a ‘spherical hybrid momentum’, a bit awkward for the concept is novel.
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Jiang, Ao, Shibo Xing, Haowei Lin, Qing Chen e Mingxuan Li. "Role of Pyramidal Low-Dimensional Semiconductors in Advancing the Field of Optoelectronics". Photonics 11, n. 4 (15 aprile 2024): 370. http://dx.doi.org/10.3390/photonics11040370.
Testo completoAbstract (sommario):
Numerous optoelectronic devices based on low-dimensional nanostructures have been developed in recent years. Among these, pyramidal low-dimensional semiconductors (zero- and one-dimensional nanomaterials) have been favored in the field of optoelectronics. In this review, we discuss in detail the structures, preparation methods, band structures, electronic properties, and optoelectronic applications (photocatalysis, photoelectric detection, solar cells, light-emitting diodes, lasers, and optical quantum information processing) of pyramidal low-dimensional semiconductors and demonstrate their excellent photoelectric performances. More specifically, pyramidal semiconductor quantum dots (PSQDs) possess higher mobilities and longer lifetimes, which would be more suitable for photovoltaic devices requiring fast carrier transport. In addition, the linear polarization direction of exciton emission is easily controlled via the direction of magnetic field in PSQDs with C3v symmetry, so that all-optical multi-qubit gates based on electron spin as a quantum bit could be realized. Therefore, the use of PSQDs (e.g., InAs, GaN, InGaAs, and InGaN) as effective candidates for constructing optical quantum devices is examined due to the growing interest in optical quantum information processing. Pyramidal semiconductor nanorods (PSNRs) and pyramidal semiconductor nanowires (PSNWRs) also exhibit the more efficient separation of electron-hole pairs and strong light absorption effects, which are expected to be widely utilized in light-receiving devices. Finally, this review concludes with a summary of the current problems and suggestions for potential future research directions in the context of pyramidal low-dimensional semiconductors.
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Hartmann, Jean-Michel, Nicolas Bernier, Francois Pierre, Jean-Paul Barnes, Vincent Mazzocchi, Julia Krawczyk, Gabriel Lima, Elyjah Kiyooka e Silvano De Franceschi. "Epitaxy of Group-IV Semiconductors for Quantum Electronics". ECS Meeting Abstracts MA2023-01, n. 29 (28 agosto 2023): 1792. http://dx.doi.org/10.1149/ma2023-01291792mtgabs.
Testo completoAbstract (sommario):
Epitaxy of group-IV semiconductors is a key enabler for quantum devices. Low temperature epitaxy can be used to deposit Si:B layers with boron concentrations so high that they are superconductive (ECS Transactions 98(5), 203 (2020)). Tensily strained Si layers sandwiched between relaxed Si0.7Ge0.3 layers behave as quantum wells for electrons, enabling electron spin quantum bit (qubit) fabrication. Purified 28Si without deleterious 29Si isotopes (with a nuclear spin) are ideal as the core of fully-depleted, multiple gate transistors for qubits. Compressively-strained Ge layers sandwiched between relaxed Si0.2Ge0.8 layers can confine a two-dimensional hole gas (2DHG) offering an emerging pathway to hole-spin qubits. In the following, we will focus on the latter two subjects. We will show how we succeeded in growing 28Si layers with the following concentrations: 28Si isotopes > 99,992%, 29Si isotopes < 0.006% and 30Si isotopes < 0.002% (Journal of Crystal Growth 509, 1 (2019)). Such values can instructively be compared to those in natural Si: 28Si: 92.223%, 29Si: 4.678% and 30Si: 3.092%. The availability and cost of isotopically enriched 28SiH4 is a major difficulty, however. We thus quantified the impact of growth temperature and HCl mass-flow on the Si growth rate. At high temperature, above 850°C, we reached a silane supply limited regime with a good decomposition efficiency, high growth rates (> 100 nm min.-1 for the SiH4 mass-flow selected) and almost no impact of the HCl flow. There was otherwise, below 850°C, a H- and Cl-surface desorption limited regime, with a lesser decomposition efficiency and Si growth rates which dropped as the temperature decreased and/or the HCl mass-flow increased. Thick 28Si layers should be grown at high temperature, while low temperature epitaxy should be limited to the deposition of thin 28Si layers on top of SiGe sacrificial layers (28SOI fabrication with a bonding-etch back approach) or the thickening of SOI substrates (to avoid elastic or plastic relaxation/dewetting). We otherwise fabricated c-Ge/SiGe heterostructures for hole spin qubits. We first grew at 850°C, 20 Torr and with a SiH2Cl2 + GeH4 chemistry, SiGe virtual substrates (VS), with a gradual ramping-up of the Ge concentration (to confine misfit dislocations) and a capping with 3 µm thick constant composition layers. Reciprocal Space Maps around the (004) and (224) X-Ray Diffraction (XRD) orders gave us the Ge concentration in those SiGe caps (73.8% and 78.7%) and their macroscopic degrees of strain relaxation (102.0 and 102.5%). The surface cross-hatch, e.g. the regular array of undulations with a 1-2 µm spatial wavelength because of a periodic strain field in VS, was suppressed using Chemical Mechanical Polishing (CMP). We then grew on top of the polished SiGe VS, at 500°C, 20 Torr and with a SiH2Cl2 + GeH4 chemistry, {100 nm thick SiGe 74% or 79% / 16 nm thick compressively-strained Ge / variable thickness SiGe 74% or 79% overlayer / Si 2nm cap} stacks. The parameter that changed was the SiGe overlayer, with 22, 33, 44 or 55 nm thicknesses probed. Compared to polished surfaces, a slight surface roughening was observed for the SiGe stacks, larger for the SiGe 74%/c-Ge than for 79%/c-Ge stacks. Thicker SiGe overlayers yielded smoother surfaces. We ascribe these surface undulations, with a ~ 100 nm wavelength, to an elastic relaxation of the compressive strain in the c-Ge layers. XRD showed that those stacks were pseudomorphic, with the same in-plane lattice parameter for the c-Ge layers than that of the SiGe VS underneath. Energy Dispersive X-ray spectroscopy (EDX) mapping of the whole structure showed that the Ge grading was rather linear with, as intended, a 10% Ge/µm grading. Cross-sectional Transmission Electron Microscopy (TEM) showed the presence of numerous misfit dislocations in the graded layer and none in the thick Si0.21Ge0.79 / c-Ge stack on top. A slight Ge concentration increase, by a few %, was measured by EDX at the CMP location, with a perfect crystallinity in the stack grown on top. The 16 nm thick c-Ge layer itself was perfectly monocrystalline, with a 1-2 bi-atomic layer roughness at c-Ge/SiGe interfaces, no in-plane deformation compared to the surrounding SiGe and an out-of-plane deformation of 1.5% from Precession Electron Diffraction. Magnetotransport measurements in Hall-bar devices were performed at 4.2 K to assess the electrical properties of the 2DHG in the grown SiGe/c-Ge heterostructures. At low magnetic field, a hole mobility of 1.2 x 105 cm2 V-1 s-1 was obtained for a hole density of n2DHG = 3.7x1011 cm-2 in the c-Ge/SiGe 79% 55nm sample, whereas quantum Hall effect plateaus and Shubnikov-De-Haas oscillations were observed at higher fields. Figure 1
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Marie, X., T. Amand, P. Le Jeune, M. Paillard, P. Renucci, L. E. Golub, V. D. Dymnikov e E. L. Ivchenko. "Hole spin quantum beats in quantum-well structures". Physical Review B 60, n. 8 (15 agosto 1999): 5811–17. http://dx.doi.org/10.1103/physrevb.60.5811.
Testo completo
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Oguri, A., K. Yamanaka, J. Inoue e S. Maekawa. "Quantum spin-liquid state with a hole". Physical Review B 43, n. 1 (1 gennaio 1991): 186–92. http://dx.doi.org/10.1103/physrevb.43.186.
Testo completo
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Ferreira, R., e G. Bastard. "Hole “Spin” Relaxation in Semiconductor Quantum Wells". Europhysics Letters (EPL) 23, n. 6 (20 agosto 1993): 439–44. http://dx.doi.org/10.1209/0295-5075/23/6/010.
Testo completo
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Zinov’eva, A. F., A. V. Nenashev e A. V. Dvurechenskii. "Hole spin relaxation in Ge quantum dots". Journal of Experimental and Theoretical Physics Letters 82, n. 5 (settembre 2005): 302–5. http://dx.doi.org/10.1134/1.2130917.
Testo completo
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Baylac, B., X. Marie, T. Amand, M. Brousseau, J. Barrau e Y. Shekun. "Hole spin relaxation in intrinsic quantum wells". Surface Science 326, n. 1-2 (marzo 1995): 161–66. http://dx.doi.org/10.1016/0039-6028(94)00743-8.
Testo completo
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LI, ZHONG-HENG. "QUANTUM ERGOSPHERE AND HAWKING PROCESS". Modern Physics Letters A 14, n. 28 (14 settembre 1999): 1951–60. http://dx.doi.org/10.1142/s0217732399002029.
Testo completoAbstract (sommario):
We study both spherically symmetric and rotating (Kerr) nonstationary black holes and discuss the radiation of these black holes via the Hawking process. We find that the thermal radiation spectrum of a nonstationary black hole is obviously dependent on the spin state of a particle and is different from the case of a stationary black hole. This effect originates from the quantum ergosphere. We also find that the field equations of spin s=0,1/2,1 and 2 can combine into a generalized Teukolsky-type master equation with sources for any spherically symmetric black hole.
Tesi sul tema "Hole spin quantum bit"
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Bassi, Marion. "Résilience ajustable d'un spin de trou au bruit de charge". Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALY018.
Testo completoAbstract (sommario):
Les bits quantiques de spin (qubits) établis dans des boîtes quantiques au sein de semiconducteurs du groupe IV constituent une plateforme prometteuse en vue de futurs processeurs quantiques à grande échelle, du fait de leur faible encombrement et de leur processus de fabrication compatibles avec l'industrie des semiconducteurs traditionnelle. En particulier, les particules de trous ont gagné en attention ces dernières années en vue de leur potentiel en tant que qubit de spin car elles permettent une manipulation rapide de l'orientation du spin, entièrement induites par des champs électriques grâce à leur couplage spin-orbite intrinsèquement important. Ce dernier est toutefois à double tranchant car il expose aussi le spin de trou à des fluctuations électriques indésirables provenant du milieu environnant, ce qui en somme, dégrade le temps de cohérence du qubit. Au cours des dernières années, de nombreux efforts ont été déployés pour réduire l'influence du bruit électrique provenant de l'environnement sur les qubits de spins, révélant ainsi l'existence de points préférentiels, appelés "sweetspots", où le temps de cohérence est grandement étendu dépendamment de l'orientation du champ magnétique.Dans ce manuscrit, l'accent est mis sur la caractérisation des contributions de bruit électrique ayant un impact sur un qubit de spin à trou unique en fonction de l'orientation du champ magnétique dans un échantillon de silicium naturel dopé P ayant une structure MOS. La particule de trou est confinée spatialement dans une boîte quantique définie électrostatiquement à l'intérieur du dispositif. L'orientation de son spin est lue par réflectométrie radio-fréquence basée sur une méthode de discrimination en énergie des états de spin. Nous démontrons expérimentalement que les "sweetspots" précédemment mentionnés appartiennent en fait à des lignes continues, dites "sweetlines" autour de la sphère angulaire du champ magnétique, en accord avec les prédictions théoriques. Nous montrons également qu'en plus d'un temps de cohérence étendu, le fonctionnement des sweetlines est compatible avec une manipulation efficace avec des fréquences de Rabi, f_R, dépassant confortablement 10 MHz, et un facteur de qualité défini comme Q = 2 f_R T_2^R s'élevant jusqu'à environ 690, rivalisant avec les estimations rapportées pour les électrons. En outre, cette étude met en évidence un contrôle accru de la position angulaire des sweetlines en fonction de la tension de grille. Ceci constitue un aspect particulièrement important dans le contexte d'une future implémentation à plus grande échelle. Enfin, l'étude expérimentale de ces points de fonctionnement optimaux est reproduite pour un système à deux qubits soulignant l'importance des sweetlines pour les systèmes de qubits de spinSpin quantum bits (qubits) established in group-IV semiconductor quantum dots structures (QD) embody a promising platform for large-scale quantum processors leveraging on small footprint and compatible fabrication processes with mainstream semiconductor industry. In particular, hole particles recently gained attention as spin qubit platform as they enable fast and all-electrical manipulation due to their intrinsically large spin-orbit coupling. The latter coupling however stands as a two-edged sword as it also exposes the hole spin to undesired interactions with the surrounding environment, which in turn degrade the qubit coherence time. Over the past years, many efforts have been conducted to mitigate electrical noise influence stemming from the environment thus revealing the existence of preferential points of enhanced coherence time, named ``sweetspots'', depending on magnetic field orientation.In this manuscript, the emphasis is laid on the characterization of electrical noise contributions impacting a single hole spin qubit with respect to magnetic field orientation on a P-doped natural silicon-MOS architecture. The hole particle is spatially confined in a QD defined electrostatically within the device. Spin orientation is readout by radio-frequency reflectometry based on energy-selective readout method. We experimentally demonstrate that the reported ``sweetspots'' belong in fact to continuous ``sweetlines'' wrapped around the sphere of magnetic-field polar-angle components, in agreement with theoretical predictions. We also show that, in addition to extended coherence time, sweetline operation is compatible with efficient electric-dipole spin resonance with Rabi frequencies, f_R, comfortably exceeding 10 MHz, and a qubit quality factor Q = 2 f_R T_2^R as high as 690, competing with reported values for electrons. Our study evidences ample gate-voltage control of the sweetlines position in magnetic field, an aspect particularly relevant in the purview of scalability. Finally, the experimental investigation of such optimal operation points is extended to a two qubit system as a proof of concept underscoring the importance of sweetlines tuning for spin qubit systems
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Pingenot, Joseph Albert Ferguson. "Electron and hole spins in quantum dots". Diss., University of Iowa, 2009. https://ir.uiowa.edu/etd/259.
Testo completoAbstract (sommario):
As the technology underlying modern electronics advances, it is unlikely that previous rates of power use and computational speed improvement can be maintained. Devices using the spin of an electron or hole, "spintronic" systems, can begin to address these problems, creating new devices which can be used as a continuation and augmentation of existing electronic systems. In addition, spintronic devices could make special use of coherent quantum states, making it feasible to address certain problems which are computationally intractable using classical electronic components. Unlike higher-dimensional nanostructures such as quantum wires and wells, quantum dots allow a single electron or hole to be confined to the dot. Through the spin-orbit effect, the electron and hole g-tensor can be influenced by quantum dot shape and applied electric fields, leading to the possibility of gating a single quantum dot and using a single electron or hole spin for quantum information storage or manipulation.
In this thesis, the spin of electrons and holes in isolated semiconductor quantum dots are investigated in the presence of electric and magnetic fields using realspace numerical 8-band strain-dependent k · p theory. The calculations of electron and hole g-tensors are then used to predict excitonic g-tensors as a function of electric field. These excitonic g-factors are then compared against existing experimental work, and show that in-plane excitonic g-factor dependence on electric field is dominated by the hole g-factor. The dependence of the electron and hole g-tensors on the applied electric field are then used to propose a class of novel quantum dot devices which manipulate the electron or hole spins in either a resonant or a non-resonant mode. Because of the highly parabolic dependence of some components of the hole g-tensor on the applied electric field, a shift in the Larmor frequency and an additional resonance are predicted, with additional shifts and resonances occurring for higher-order dependencies. Spin manipulation times down to 3.9ns for electrons and 180ps for holes are reported using these methods.
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Notbohm, Susanne. "Spin dynamics of quantum spin-ladders and chains". Thesis, St Andrews, 2007. http://hdl.handle.net/10023/403.
Testo completo
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Thiney, Vivien. "Detection of travelling electrons in the Quantum Hall effect regime with a singlet-triplet quantum bit detector". Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY069/document.
Testo completoAbstract (sommario):
L’optique quantique avec électron est un domaine de recherche en expansion depuis ses débuts au cours des années 90 prenant suite aux premières expériences d’interférence avec électrons réalisées dans les années 80. Ce domaine est dédié à la réalisation d’expérience d’optique quantique avec des électrons plutôt que des photons. Leur intérêt est double, d’une part les électrons étant des fermions de nouveaux phénomènes, en comparaison des photons qui sont des bosons, peuvent être observés. L’électron anti-bunching, en comparaison du bunching des photons obtenu dans des expériences de corrélations en est un exemple. Le deuxième avantage des électrons est le fait qu’ils peuvent être contrôlés et manipulés à l’aide de champ électrique, un tel contrôle n’est pas possible avec des photons. Alors que les composants de base pour la réalisation de ces expériences sont déjà existant comme la lame séparatrice, ou encore les sources cohérentes à électrons uniques, la détection immédiate d’un électron unique dans de telles expériences est toujours manquante. La difficulté étant le faible temps d’interaction entre l’électron en déplacement et le détecteur de charge qui est limité typiquement à moins de 1ns principalement à cause de la vitesse élevée de déplacement de l’électron qui est égale à la vitesse de Fermi soit 10-100km/s. Ce temps d’interaction est environ deux ordres de grandeurs plus petits que ce qui est nécessaire pour le meilleur détecteur de charge démontré jusqu’à présent.Dans ce manuscrit est présenté le développement d’un détecteur ultra-sensible pour la détection immédiate d’un électron se déplaçant à la vitesse de Fermi. Notre stratégie est de détecter un électron unique se déplaçant dans les canaux de bords (ECs) de l’effet Hall quantique à partir de la mesure d’une variation de phase d’un bit quantique singlet-triplet, appelé qubit détecteur par la suite. La détection immédiate de cet électron en déplacement n’étant possible que si l’interaction avec ce dernier induit une variation de phase de pi, avec une lecture immédiate de l’état de spin du qubit détecteur.Grâce au développement et à l’utilisation d’un RF-QPC, cette lecture immédiate de l’état de spin est tout d’abord démontrée. Par la suite le développement du qubit détecteur avec la réalisation d’oscillations cohérentes d’échange est décrit. Sa sensibilité en charge est démontrée avec l’observation d’une phase induite par l’interaction avec un courant d’électrons dans les ECs. Ce courant est imposé par l’application d’un biais de tension contrôlant le potentiel chimique de ces ECs.Après optimisation de ce qubit détecteur pour la détection d’un électron unique, il est calibré en utilisant le même procédé de courant imposé par application d’un biais de tension. Cette calibration nous fournie la variation de signal attendue pour l’interaction avec cette charge unique est indique que sa détection immédiate est impossible dans nos conditions expérimentales. Notre détecteur ayant une sensibilité de charge de l’ordre de 8.10-5 pour une bande passante allant de DC à 1THz. Cette sensibilité est environ deux ordres de grandeur trop petite que ce qui est nécessaire pour la détection immédiate de cette charge unique. Finalement, ce qubit détecteur est utilisé pour détecté, dans une expérience moyennée, ce qui est appelé un edge magneto plasmon composé par moins de 5 électrons. Néanmoins, atteindre la détection de la charge unique dans n’a pas été possible, la sensibilité en charge étant légèrement trop petite pour y arriver.Les différentes limites de notre détecteur sont listées et expliquées tout au long du manuscrit, avec une présentation de différents axes de développement qui devraient permettre de réussir cette détection d’un électron unique dans une nouvelle expérienceThe electron quantum optics field is a research topic with an interest growing over the years since the 80's and the first interference experiment with electrons. This field is dedicated to the implementation of quantum optics experiments with electrons instead of photon. The advantage is twofold, one is the fermion nature of the electrons which ensure the observation of phenomenon which cannot be observed with photon (boson), the anti-bunching of the electrons in correlation experiments contrary to the bunching for photons illustrates this point. The second advantage is the possibility to interact and control electrons with electric fields since they are charged particles. Such control does not exist with photon. In addition to these fundamental experiments, it has been recently demonstrated that this topic presents a possible candidate for quantum information with so called flying qubit. While the based components to mimic the quantum optics experiments are already demonstrated like the beam splitter, phase shifter or coherent single electron source, the single electron detection in a single shot manner in such system is still lacking. The difficulty being the short interaction time between the travelling charge and the charge detector, being of less than 1ns in such system where the electron propagate at the Fermi velocity 10-100km/s. This interaction is approximately two orders of magnitude shorter than what is required with the actual best on chip charge detector.In this thesis is presented the development of an ultra-sensitive detector for the single shot detection of an electron travelling at the Fermi velocity. Our strategy was to detect a single travelling electron propagating in the edge channels (ECs) of the quantum Hall effect by measuring the induced phase shift of a singlet-triplet qubit, referred as to the qubit detector. The single shot detection being only possible if the interaction with the travelling electron induces a complete π phase shift and the spin readout of the qubit detector being performed in a single shot manner.Thanks to the development and use of a RF-QPC the single shot spin readout of the qubit detector has been first demonstrated. Its development with the implementation of coherent exchange oscillations is then described. The charge sensitivity of the qubit detector is validated in an experiment consisting in recording a phase shift of these oscillations due to the interaction with an imposed flow of electrons in the ECs. This flow of electron was induced by a DC voltage bias applied on the ECs to tune their chemical potential.This qubit detector is then optimised for the single travelling charge detection. Its calibration has been implemented using the same imposed flow of electrons by application of a DC bias. This calibration provides the expected signal variation induced by the interaction with a single travelling electron, and indicates the impossibility to implement this detection in a single shot manner in our experimental conditions. Our detector exhibits a charge sensitivity estimated close to 8.10-5 e/Hz-1/2 for a detection bandwidth from DC to 1 THz. The sensitivity is close to two orders of magnitude smaller than required for a single shot detection. Finally this qubit detector has been employed to detect in average measurements an edge magneto plasmon composed by less than 5 electrons. However, the single electron level could not be reached in statistical measurement neither, the sensitivity of our qubit detector being too limited.The different limitations of our experiment are listed and explained with the presentation of different axes of development which could permit to succeed this detection in another experiment
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Huthmacher, Lukas. "Investigation of efficient spin-photon interfaces for the realisation of quantum networks". Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/277150.
Testo completoAbstract (sommario):
Quantum networks lie at the heart of distributed quantum computing and secure quantum communication - research areas that have seen a strong increase of interest over the last decade. Their basic architecture consist of stationary nodes composed of quantum processors which are linked via photonic channels. The key requirement, and at the same time the most demanding challenge, is the efficient distribution of entanglement between distant nodes. The two ground states of single spins confined in self-assembled InGaAs quantum dots provide an effective two-level system for the implementation of quantum bits. Moreover, they offer strong transition dipole moments with outstanding photonic properties allowing for the realisation of close to ideal, high-bandwidth spin-photon interfaces. These properties are combined with the benefits of working in the solid state, such as scalability and integrability of devices, to form a promising candidate for the implementation of fast entanglement distribution. In this dissertation we provide the first implementation of a unit cell of a quantum network based on single electron spins in InGaAs. We use a probabilistic scheme based on spin-photon entanglement and the erasure of which path information to project the two distant spins into a maximally entangled Bell state. The successful generation of entanglement is verified through a reconstruction of the final two-spin state and we achieve an average fidelity of $61.6\pm2.3\%$ at a record-high generation rate of $5.8\,\mathrm{kHz}$. One of the main constraints to the achieved fidelity is the limited coherence of the electron spin. We show that it can be extended by three orders of magnitude through decoupling techniques and develop a new measurement technique, allowing us to investigate the origins of the decoherence which has previously been obscured by nuclear feedback processes. Our results evidence that further extension of coherence is ultimately limited by intrinsic mechanisms closely related to local strain due to the growth method of self-assembled quantum dots. After establishing the intrinsic limits to the electron coherence we investigate the coherence properties of the single hole spin as an alternative two-level system with the potential for higher coherence times. We show that the hole spin coherence is indeed superior to the one of the electron and realise the first successful dynamic decoupling scheme implemented in these systems. We find that the decoherence at low external magnetic fields is still governed by coupling to the nuclear spins whereas it is dominated by electrical noise for fields exceeding a few Tesla. This noise source is extrinsic to the quantum dots and a better understanding offers the potential for further improvement of the coherence time. The findings of this work present a complete study of the coherence of the charge carriers in self-assembled quantum dots and provide the knowledge needed to improve the implementation of a quantum-dot based quantum network. In particular, the combination of spin-spin entanglement and the hole coherence times enable further research towards multidimensional photonic cluster states.
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Torresani, Patrick. "Hole quantum spintronics in strained germanium heterostructures". Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY040/document.
Testo completoAbstract (sommario):
Le travail exposé dans cette thèse de doctorat présente des expériences à basse température dans le domaine de la spintronique quantique sur des hétérostructures à base de germanium. Tout d’abord, les avantages attendus du germaniumpour la spintronique quantique sont exposés, en particulier la faible interaction hyperfine et le fort couplage spin-orbite théoriquement prédits dans le Ge. Dans un second chapitre, la théorie des boites quantiques et systèmes à double boite sont détaillés, en se focalisant sur les concepts nécessaires à la compréhension des expériences décrites plus tard, c’est-à-dire les effets de charge dans les boites quantiques et double boites, ainsi que le blocage de spin de Pauli. Le troisième chapitre s’intéresse à l’interaction spin-orbite. Son origine ainsi que ses effets sur les diagrammes d’énergie de bande sont discutés. Ce chapitre se concentre ensuite sur les conséquences de l’interaction spin-orbite spécifiques aux gaz bidimensionnels de trous dans des hétérostructures de germanium, c’est-à-dire l’interaction spin-orbite Rashba, le mécanisme de relaxation de spin D’Yakonov-Perel ainsi que l’antilocalisation faible.Le chapitre quatre présente des mesures effectuées sur des nanofils coeur coquillede Ge/Si. Dans ces nanofils une boite quantique se forme naturellement et celui-ci est étudié. Un système à double boite quantiques est ensuite formé par utilisation de grilles électrostatiques, révélant ainsi du blocage de spin de Pauli.Dans le cinquième chapitre sont détaillés des mesures demagneto-conductance de gas de trous bidimensionnels dans des hétérostructures de Ge/SiGe contraints dont le puit quantique se situe à la surface. Ces mesuresmontrent de l’antilocalisation faible. Les temps de transport caractéristiques sont extraits ainsi que l’énergie de séparation des trous 2D par ajustement de courbe de la correction à la conductivité due à l’antilocalisation. De plus, les mesures montrent une suppression de l’antilocalisation par un champ magnétique parallèle au puit quantique. Cet effet est attribué à la rugosité de surface ainsi qu’à l’occupation virtuelle de sous-bandes inoccupées.Finalement, le chapitre six présente des mesures de quantisation de la conductancedans des hétérostructures de Ge/SiGe contraints dont le puit quantique est enterré. Tout d’abord, l’hétérostructure est caractérisée grâce à des mesures de magneto-conductance dans une barre de Hall. Ensuite, un second échantillon dessiné spécialement pour la réalisation de points de contact quantiques est mesuré. Celui-ci montre des marches de conductance. La dépendance en champ magnétique de ces marches est mesurée, permettant ainsi une extraction du facteur gyromagnétique de trous lourds dans du germaniumThis thesis focuses on low temperature experiments in germaniumbased heterostructure in the scope of quantumspintronic. First, theoretical advantages of Ge for quantum spintronic are detailed, specifically the low hyperfine interaction and strong spin orbit coupling expected in Ge. In a second chapter, the theory behind quantum dots and double dots systems is explained, focusing on the aspects necessary to understand the experiments described thereafter, that is to say charging effects in quantum dots and double dots and Pauli spin blockade. The third chapter focuses on spin orbit interaction. Its origin and its effect on energy band diagrams are detailed. This chapter then focuses on consequences of the spin orbit interaction specific to two dimensional germaniumheterostructure, that is to say Rashba spin orbit interaction, D’Yakonov Perel spin relaxation mechanism and weak antilocalization.In the fourth chapter are depicted experiments in Ge/Si core shell nanowires. In these nanowire, a quantumdot formnaturally due to contact Schottky barriers and is studied. By the use of electrostatic gates, a double dot system is formed and Pauli spin blockade is revealed.The fifth chapter reports magneto-transport measurements of a two-dimensional holegas in a strained Ge/SiGe heterostructure with the quantum well laying at the surface, revealing weak antilocalization. By fitting quantumcorrection to magneto-conductivity characteristic transport times and spin splitting energy of 2D holes are extracted. Additionally, suppression of weak antilocalization by amagnetic field parallel to the quantum well is reported and this effect is attributed to surface roughness and virtual occupation of unoccupied subbands.Finally, chapter number six reportsmeasurements of quantization of conductance in strained Ge/SiGe heterostructure with a buried quantumwell. First the heterostructure is characterized by means ofmagneto-conductance measurements in a Hall bar device. Then another device engineered specifically as a quantum point contact is measured and displays steps of conductance. Magnetic field dependance of these steps is measured and an estimation of the g-factor for heavy holes in germanium is extracted
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Godden, Timothy Mark. "Coherent optical control of the spin of a single hole in a quantum dot". Thesis, University of Sheffield, 2012. http://etheses.whiterose.ac.uk/2190/.
Testo completoAbstract (sommario):
This thesis describes experiments on the initialisation, coherent control, and readout of a single hole spin trapped in a self assembled InGaAs semiconductor quantum dot. High fidelity initialisation of a hole spin state is achieved by the fast ionisation of a spin polarised neutral exciton under an applied electric field and in a Faraday geometry magnetic field. The preparation of a coherent superposition state is demonstrated by observing the precession of the hole spin about a Voigt geometry magnetic field. The hole spin dephasing time is deduced from the decay of the spin contrast. Coherent optical rotation of the hole spin state about the z-axis is demonstrated using the geometric phase shift induced by a picosecond laser pulse. By combining the precession of the spin about the x-axis, and optical rotations about the z-axis, full quantum control of a hole spin is demonstrated over the surface of the Bloch sphere. This is an important prerequisite for the use of a hole spin as a qubit for quantum information processing applications.
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Thiele, Stefan. "Read-out and coherent manipulation of an isolated nuclear spin using a single-molecule magnet spin-transistor". Phd thesis, Université de Grenoble, 2014. http://tel.archives-ouvertes.fr/tel-00984973.
Testo completoAbstract (sommario):
La réalisation d'un ordinateur quantique fonctionnel est l'un des objectifs tech- nologiques les plus ambitieux pour les scientifiques d'aujourd'hui. Sa brique de base est composée d'un système quantique à deux niveaux, appelé bit quantique (ou qubit). Parmi les différents concepts existants, les dispositifs à base de spin sont très attractifs car ils bénéficient de la progression constante des techniques de nanofabrication et permettent la lecture électrique de l'état du qubit. Dans ce contexte, les dispositifs à base de spins nucléaires offrent un temps de cohérence supérieur à celui des dispositifs à base de spin electronique en raison de leur meilleure isolation à l'environnement. Mais ce couplage faible a un prix: la détection et la manipulation des spins nucléaires individuels restent des tâches difficiles. De très bonnes conditions expérimentales étaient donc essentielles pour la réussite de ce projet. Outre des systèmes de filtrage des radiofréquences à très basses températures et des amplificateurs à très faible bruit, j'ai développé de nouveaux supports d'échantillons et des bobines de champ magnétique trois axes compacts avec l'appui des services techniques de l'Institut Néel. Chaque partie a été optimisée afin d'améliorer la qualité de l'installation et évaluée de manière quantitative. Le dispositif lui-même, un qubit réalisé grâce à un transistor de spin nucléaire, est composé d'un aimant à molécule unique couplé à des électrodes source, drain et grille. Il nous a permis de réaliser la lecture électrique de l'état d'un spin nucléaire unique, par un processus de mesure non destructif de son état quantique. Par conséquent, en sondant les états quantique de spin plus rapidement que le temps de relaxation caractéristique de celui-ci, nous avons réalisé la mesure de la trajectoire quantique d'un qubit nucléaire isolé. Cette expérience a mis en lumière le temps de relaxation T1 du spin nucléaire ainsi que son mécanisme de relaxation dominant. La manipulation cohérente du spin nucléaire a été réalisée en utilisant des champs électriques externes au lieu d'un champ magnétique. Cette idée originale a plusieurs avantages. Outre une réduction considérable du chauffage par effet Joule, les champs électriques permettent de contrôler et de manipuler le spin unique de façon très rapide. Cependant, pour coupler le spin à un champ électrique, un processus intermédiaire est nécessaire. Un tel procédé est l'interaction hyperfine, qui, si elle est modifiée par un champ électrique, est également désigné sous le nom d'effet Stark hyperfin. En utilisant cet effet, nous avons mis en évidence la manipulation cohérente d'un spin nucléaire unique et déterminé le temps de cohérence T2 . En outre, l'exploitation de l'effet Stark hyperfin statique nous avons permis de régler le qubit de spin nucléaire à et hors résonance par l'intermédiaire de la tension de grille. Cela pourrait être utilisé pour établir le contrôle de l'intrication entre les différents qubits nucléaires. En résumé, nous avons démontré pour la première fois la possibilité de réaliser et de manipuler un bit quantique basé sur un aimant à molécule unique, étendant ainsi le potentiel de la spintronique moléculaire au delà du stockage de données classique. De plus, la grande polyvalence des molécules aimants est très prometteuse pour une variété d'applications futures qui, peut-être un jour, parviendront à la réalisation d'un ordinateur quantique moléculaire.
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Hirsch, William H. "Quantum effects of the massless spin one-half field in static spherically symmetric black hole and wormhole spacetimes". Winston-Salem, NC : Wake Forest University, 2009. http://dspace.zsr.wfu.edu/jspui/handle/10339/44689.
Testo completo
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Varwig, Steffen [Verfasser], Manfred [Akademischer Betreuer] Bayer e Metin [Gutachter] Tolan. "Optical electron spin tomography and hole spin coherence studies in (In,Ga)As/GaAs quantum dots / Steffen Varwig. Betreuer: Manfred Bayer. Gutachter: Metin Tolan". Dortmund : Universitätsbibliothek Dortmund, 2014. http://d-nb.info/1100692487/34.
Testo completoCapitoli di libri sul tema "Hole spin quantum bit"
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Sorella, S., e Q. F. Zhong. "Spin-Charge Decoupling and the One-Hole Green’s Function in a Quantum Antiferromagnet". In Correlation Effects in Low-Dimensional Electron Systems, 185–89. Berlin, Heidelberg: Springer Berlin Heidelberg, 1994. http://dx.doi.org/10.1007/978-3-642-85129-2_20.
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Roussignol, Ph, P. Rolland, R. Ferreira, C. Delalande, G. Bastard, A. Vinattieri, J. Martinez-Pastor et al. "Evidence of Slow Hole Spin Relaxation in n-Modulation Doped GaAs/AlGaAs Quantum Well Structures". In Ultrafast Phenomena VIII, 446–47. Berlin, Heidelberg: Springer Berlin Heidelberg, 1993. http://dx.doi.org/10.1007/978-3-642-84910-7_143.
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Satija, Indubala I. "Pseudo-Spin-1/2 Models and Topological States of Matter". In The Wonder of Quantum Spin, 271–308. Oxford University PressOxford, 2024. http://dx.doi.org/10.1093/oso/9780198884859.003.0012.
Testo completoAbstract (sommario):
Abstract This chapter is a gateway to the exploration of the exotic states of matter—the topological insulators and superconductors within the framework of spin-1/2 models. The chapter introduces topological concepts and describes how topology manages to sneak into the description of the macroscopic states in view of energy gap underlying the spectral properties. Discussion includes models for quantum Hall, quantum spin Hall, and topological superconductors and the underlying topological invariant along with the central role played by the edge modes. Here is a description of Majorana fermions and zero Majorana modes exhibiting exotic properties, appearing as quasiparticles in condensed matter systems. Topics covered also include the ten-fold classification of topological states based on time reversal and particle-hole symmetries and the role of Clifford algebra in this classification.
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Schenkel, Thomas, Cheuk Lo, Christoph Weis, Jeffrey Bokor, Alexei Tyryshkin e Stephen Lyon. "A Spin Quantum Bit Architecture with Coupled Donors and Quantum Dots in Silicon". In Single-Atom Nanoelectronics. Pan Stanford Publishing, 2013. http://dx.doi.org/10.1201/b14792-12.
Testo completoAtti di convegni sul tema "Hole spin quantum bit"
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Oestreich, M., R. Dahbashi, F. Berski e J. Hübner. "Spin noise spectroscopy: hole spin dynamics in semiconductor quantum dots". In SPIE NanoScience + Engineering, a cura di Henri-Jean Drouhin, Jean-Eric Wegrowe e Manijeh Razeghi. SPIE, 2012. http://dx.doi.org/10.1117/12.930866.
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Saini, L. K., Mukesh G. Nayak e R. O. Sharma. "Correlation effects on spin-polarized electron-hole quantum bilayer". In INTERNATIONAL CONFERENCE ON CONDENSED MATTER AND APPLIED PHYSICS (ICC 2015): Proceeding of International Conference on Condensed Matter and Applied Physics. Author(s), 2016. http://dx.doi.org/10.1063/1.4946051.
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Godden, Timothy M., John H. Quilter, Andrew J. Ramsay, Stephen J. Boyle, Isaac J. Luxmoore, Jorge Puebla-Nunez, Mark Fox e Maurice S. Skolnick. "Coherent optical control a single hole spin in a quantum dot". In Quantum Electronics and Laser Science Conference. Washington, D.C.: OSA, 2012. http://dx.doi.org/10.1364/qels.2012.qm3g.1.
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Smirl, Arthur L., Eric J. Loren, Julien Rioux, J. E. Sipe e Henry M. van Driel. "Ultrafast Optical Measurement of Hole and Electron Spin Dynamics in Germanium". In Quantum Electronics and Laser Science Conference. Washington, D.C.: OSA, 2010. http://dx.doi.org/10.1364/qels.2010.qwc6.
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Ito, T., H. Gotoh, M. Ichida e H. Ando. "Dynamics of Hole-Spin Superposition in GaAs/AlGaAs Quantum Wells". In 2013 International Conference on Solid State Devices and Materials. The Japan Society of Applied Physics, 2013. http://dx.doi.org/10.7567/ssdm.2013.e-3-3.
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Akimoto, R., K. Ando, F. Sasaki, S. Kobayashi e T. Tani. "Femtosecond Carrier Spin Dynamics in CdTe/Cd0.6Mn0.4Te Quantum Wells". In International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 1996. http://dx.doi.org/10.1364/up.1996.tue.38.
Testo completoAbstract (sommario):
In recent years, many interests are focused on the spin relaxation in the semiconductor hetero structures such as the quantum wells, since the spin relaxation time is much faster than the carrier life time. In the quantum wells, the degeneracy between the heavy hole and the light hole excitons is lifted, so that the one spin state in the conduction- and valence-band state can be excited selectively by the circularly polarized light. In the previous study of the spin relaxation in the quantum wells, the pump-probe using the circular polarization where the wavelength of the pump and the prove are the same and resonant with the heavy hole exciton[1-4], or the time-resolved luminescence measurement where the heavy hole exciton is excited resonantly by the circularly polarized pulse, and the decay of the circular polarization in the luminescence is measured[5-9], have been employed. In both cases of the measurements for the undoped quantum wells, the spin relaxation of the heavy hole exciton is contributed to both the electron spin relaxation and the heavy hole spin relaxation, simultaneously. A possible way to isolate the electron spin relaxation from the heavy hole relaxation in GaAs/AlGaAs quantum wells, is to use the p-doped quantum wells for the electron spin relaxation and the n-doped one for the heavy hole spin relaxation[9]. However, the doped quantum wells may be quite different from undoped quantum wells in the spin relaxation mechanism such as carrier-impurity scattering, the Coulomb screening of the carriers and so on. Therefore, here, we present an approach to measure the electron spin relaxation separately from the heavy hole one in the undoped quantum wells by the measurement of the femtosecond time-resolved circular dichroic spectrum. The present pump-probe method has the unconventional configuration in the absorption saturation measured from unoccupied light hole (lh) spin state and occupied heavy hole (hh) spin state simultaneously using the circularly polarized probe pulse with the continuum spectrum. The sample used in our experiments is CdTe/Cd0.6Mn0.4Te quantum wells, where the sp-d exchange interaction between the carrier spin in the well and the Mn ion spin in the barrier can be controlled by the confinement degree of the carrier wave function and we can examine the effect of the sp-d exchange interaction on the carrier spin relaxation.
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Rühle, W. W., M. Oestreich, R. Hannak, A. P. Heberle, R. Nötzel, K. Ploog e Klaus Köhler. "Spin Quantum Beats in Quantum Wells and Wires". In Quantum Optoelectronics. Washington, D.C.: Optica Publishing Group, 1995. http://dx.doi.org/10.1364/qo.1995.qwb1.
Testo completoAbstract (sommario):
Recently, the observation of spin quantum beats in time-resolved photoluminescence after picosecond excitation of GaAs quantum wells (QWLs) was reported.[1] A semiclassical description of this novel experiment follows: The circularly polarized laser generates an electron spin polarization in z direction according to the transition rules (Fig. 1). The magnetic field in the perpendicular x-direction forces these spins into a Larmor precession around the x direction, i.e., the electron spin polarization changes periodically with the Larmor frequency between parallel and antiparallel to the z direction. As a consequence, light emitted in z direction periodically oscillates between the two circular polarizations. A typical example is shown in Fig. 2 for a high quality 25nm QWL with an inhomogeneous broadening of the heavy-hole exciton line of 300μeV. [1]
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Godden, Timothy M., Stephen J. Boyle, Andrew J. Ramsay, Mark Fox e Maurice Skolnick. "Fast high fidelity hole spin initialization in a single InGaAs quantum dot". In Quantum Electronics and Laser Science Conference. Washington, D.C.: OSA, 2011. http://dx.doi.org/10.1364/qels.2011.qthr5.
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Riblet, P., AR Cameron e A. Miller. "Spin-Gratings and In-Well Carrier Transport Measurements in GaAs/AlGaAs Multiple Quantum Wells". In Quantum Optoelectronics. Washington, D.C.: Optica Publishing Group, 1997. http://dx.doi.org/10.1364/qo.1997.qthe.3.
Testo completoAbstract (sommario):
We have recently demonstrated [1] that transient electron spin gratings created by cross-polarised excitation pulses at a wavelength resonant with the heavy hole exciton, can provide a new and unique way of measuring in-well electron drift mobilities in semiconductor multiple quantum well structures. This compares with the usual transient grating method in which only the ambipolar diffusion coefficient can be determined [2]. A comparison of concentration and spin grating decay rates allows the direct measurement of both the electron and hole drift mobilities in the same sample. In this work we extend these measurements to GaAs/AlGaAs multiple quantum wells with different well widths and compare results obtained under conditions of exciton saturation and broadening.
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Uehira, Kazutake, e Hiroshi Unno. "Image Recognition by Quantum Annealing Using Multi-bit Spin Variables". In ICGSP 2021: 2021 the 5th International Conference on Graphics and Signal Processing. New York, NY, USA: ACM, 2021. http://dx.doi.org/10.1145/3474906.3474911.
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