Cette thèse porte sur la réalisation d'un processeur quantique hybride, dans lequel les degrés de liberté collectifs d'un ensemble de spins sont utilisés comme une mémoire quantique multimode pour les qubits supraconducteurs. Nous concevons un protocole capable de stocker et de récupérer à la demande les états d'un grand nombre de qubits dans un ensemble de spin et nous démontrons les briques de bases des opérations mémoires avec des centres NV dans le diamant. Le protocole repose sur le couplage des spins à un résonateur à fréquence et facteur de qualité accordable. Les états quantiques sont écrits par absorption résonante d'un photon micro-ondes dans l'ensemble de spins, et lus par application d'une séquence d'impulsions aux spins. L'étape d'écriture du protocole est démontrée dans une première expérience dans laquelle sont intégrés sur la même puce un qubit supraconducteur, un résonateur à fréquence accordable, et l'ensemble de spins. Les états du qubit sont stockés dans les spins via le résonateur. Après le stockage, l'état quantique collectif qui en résulte est rapidement déphasé en raison de l'élargissement inhomogène de l'ensemble et une séquence de refocalisation doit être appliquée sur les spins pour déclencher la réémission collective comme un écho de l'état quantique initialement absorbé. Dans une seconde expérience, nous démontrons une brique de base importante de cette opération de lecture, qui consiste à récupérer de multiples impulsions micro-ondes classiques au niveau du photon unique en utilisant des techniques d’écho de Hahn. Enfin, le repompage optique des spins est implémenté afin de réinitialiser la mémoire entre deux séquences successives. / This 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.

Quantum sensing, a protocol that takes advantage of the extreme sensitivity of quantum systems to their environment, enables many applications of quantum systems for sensing. Inspired by direct electric field sensing using the Stark effect of a nitrogen-vacancy(NV) center, this work implements an NV-magnet hybrid way to explore the possibilities of overcoming NV’s relatively weak coupling strength to electric fields. The magnetic-noise-induced population relaxation of the NV center serves as the mechanism for sensing. Within this scheme, the magnetic noise spectrum is tuned by modulating the magnetic properties via voltage-controlled magnetic anisotropy (VCMA) or electric-field-induced magnetoelastic effect. In this way, the noise carrying the information of the electric field is taken as a signal - the shift of the noise spectrum leads to a population difference of NV energy levels, which is used for evaluating electric fields. The investigation of the relation between sensitivities and operation points reveals that lower operation frequency is desirable for better performance. The comparison between VCMA and electric-field-induced magnetoelastic effect indicates that the efficiency of converting electric field into magnetic property modulation is a critical parameter for sensitivity enhancement.

In der vorliegenden Arbeit ist es in Kombination von Simulation und Experiment gelungen 13-C-Spins mithilfe von Stickstoff-Fehlstellen-(NV)-Zentren im Diamanten weit über das thermische Gleichgewicht hinaus zu polarisieren. Zu diesem Zweck wurde ein neues Mess-Setup entwickelt, welches eine optische Bestrahlung der Probe in einem niedrigen Magnetfeld und einen anschließenden Transfer der Probe innerhalb eines spuraleitenden Solenoiden ermöglicht. Somit ist bereits etwa eine Sekunde nach der optischen Bestrahlung eine NMR-Messung durchführbar. Auf diese Weise konnte erstmals der grundlegende Mechanismus für Hyperpolarisation einer Kreuz-Relaxation zwischen NV- und substitutionellen Stickstoff-(P1)-Zentren zugeordnet werden. Dabei ist die P1-intrinsische Hyperfeinaufspaltung der elektronischen Spin-Energie-Niveaus durch die Wechselwirkung mit dem nuklearen Stickstoffspin zu berücksichtigen und die aus einem statischen Jahn-Teller-Effekt resultierende Anisotrope dieser Hyperfeinwechselwirkung. Neben Hyperpolarisation durch 'erlaubte' Quantenübergänge im P1-Zentrum, konnten auch durch 'verbotene' Übergänge verursachte Hyperpolarisationen nachgewiesen werden. Der Vergleich der hyperpolarisierten NMR-Spektren und denen im thermischen Gleichgewicht weist eine fast drei Mal schmalere 13-C-Linie für den ersteren Fall auf. Dies deutet auf unterschiedliche Spin-Umgebung der gemessenen 13-C-Spins in beiden Fällen hin.

With the unique advantage of great isolation from the thermal environment, levitated optomechanics has emerged as a powerful platform for various fields of physics including microscopic thermodynamics, precision measurements, and quantum mechanics. Experiments with optically levitated micro- and nanoparticles have already obtained remarkable feats of zeptonewton force sensing and ground-state cooling. The novel system has also been proposed to assess various theories including the objective collapse models and macroscopic quantum mechanics. <br><div><br></div><div>This thesis reports experimental results on a levitated Cavendish torsion balance, a GHz nanomechanical rotor, and a torque sensor with unprecedented sensitivity realized with optically levitated nanoparticles in a vacuum environment. The system at room temperature achieves a sensitivity of (4.2±1.2)×10−27Nm/ √ Hz surpassing the sensitivity of most advanced nanofabricated torque sensors at cryogenic environments. Calculations suggest potential detection of Casimir torque and vacuum friction under realistic conditions. Moreover, the nanoparticles are driven into ultrafast rotations exceeding 5 GHz, which achieves the fastest humanmade nanomechanical rotor. Such fast rotations allow studies on the ultimate tensile strength of the nanoparticles as well. <br></div><div><br></div><div>Subsequently, the electron spin control of nitrogen vacancies (NV) in optically trapped diamond naoparticles is demonstrated in low vacuum. The configuration is analogous to trapped atoms and ions which serve as a quantum system with internal states. The effect of the air pressure, surrounding gas, and laser power on the electron spin resonance (ESR) are studied, and the temperature of the diamond is also measured with the ESR. The levitated nanodiamonds will provide the means to implement a hybrid spin-optomechanical system.<br></div>

Les défauts ponctuels dans les matériaux à grande bande interdite font l’objet de nombreuses recherches, compte tenu des perspectives d’applications en technologie quantique. La réalisation de qubits et de capteurs quantiques a échelle nanomètres à l’aide du centre NV– a suscité la recherche de défauts ayant des propriétés magnéto-optiques similaires, mais dans un matériau technologiquement plus mûr tel que le carbure de silicium (SiC). Le SiC se présente sous différentes structures cristallographiques, notamment cubique (3C) et hexagonales (4H et 6H). Cette propriété permet d’obtenir une plus grande variété de défauts ponctuels profonds. Dans cette thèse, j'ai établi présence du défaut azote-lacune (NCVSi) de spin S=1 dans un échantillon de 4H-SiC irradié par des protons, en réalisant la spectroscopie d'excitation de la photoluminescence à la température cryogénique et en comparant les résultats à des calculs ab initio. J'ai également développé un dispositif qui m'a permis de détecter optiquement la résonance magnétique de spin S=1 (ODMR) de la bilacune (VCVSi) dans un échantillon de 3C-SiC et d'étudier son interaction hyperfine avec des spins nucléaires d’atome de carbone et de silicium voisins. / Point-like defects in wide-bandgap materials are attracting intensive research attention owing to prospective applications in quantum technologies. Inspired by the achievements obtained with the NV– center in diamond for which qubit and nanoscale quantum sensors have been demonstrated, the search for high spin color centers with similar magneto-optical properties in a more technological mature material such as silicon carbide (SiC) had a renewed interest. Indeed, SiC exhibits polymorphism, existing for instance with cubic (3C polytype) or hexagonal (4H and 6H polytypes) crystalline structures. Such property provides a degree of freedom for engineering a rich assortment of intrinsic and extrinsic atomic-like deep defects. In this thesis using photoluminescence excitation spectroscopy at cryogenic temperature and a comparison to ab initio calculations I have evidence the presence of nitrogen-vacancy spin S=1 (NCVSi) defect in proton irradiated 4H-SiC. I have also developed a setup that allowed me to detect optically the S=1 spin magnetic resonance (ODMR) of the divacancy (VCVSi) in 3C-SiC, and study its hyperfine interaction with nearby carbon and silicon nuclear spins.

anks to their unique properties and high biocompatibilities, fluorescent nanodiamonds are promising representatives of modern carbon nanomaterials with a broad range of applications. Nevertheless, their wider use is limited because of weak fluorescence intensity and low colloidal stability in the biological environment. e optimization of treatment procedures and development of new suitable surface designs is therefore critically needed. In this study, several key steps for fluorescent nanodiamond treatment have been optimized, leading to both a substantial increase in fluorescence intensity and to significantly lower surface damage caused by graphitization. Further, a new high-throughput irradiation technique was developed. e influence of surface chemistry on the fluorescence parameters was studied using partial fluorination of the functional groups on the nanodiamond surface. A novel method which significantly affects the interaction of nanodiamonds with biological systems by increasing of the homogeneity and circularity was developed. e potential of nanodiamonds for future medical and biological research was demonstrated on particles with complex surface architectures that enabled targeting and therapy of tumor cells. Moreover, a strong and highly selective affinity of fibroblast growth factors to diamond...

<p>In recent years, correlated magnetic phenomena have emerged as a unique resource for enabling alternative computing, memory, and sensing applications. This has led to the exploration of novel magnetic hybrid platforms with the promise of improved figures of merit over the state-of-the-art. In this dissertation, we delve into several example platforms where magnets interact with various other degrees of freedom, resulting in enhanced figures of merit and/or the emergence of novel functionalities.</p><p>First, we investigate the possibility of utilizing the collective resonant mode of nanomagnets to enhance the electric field sensitivity of quantum spin defects. While quantum systems have garnered significant attention in recent years for their extraordinary potential in information processing, their potential in the field of quantum sensing remains yet to be fully explored. Quantum systems, with their inherent fragility to external signals, can be harnessed as powerful tools to develop highly efficient sensors. In this dissertation, we explore the potential of a specific type of quantum sensor, namely the quantum spin defects as an electric field sensor, when integrated with a nanomagnet/piezoelectric composite multiferroic. This integration yields at least an order of magnitude enhancement in sensitivity, presenting a promising avenue for quantum sensing applications.</p><p>Next, we shift our focus towards harnessing magnetic correlation in the emerging class of atomically thin magnets known as van der Waals magnets. These magnets provide distinctive opportunities for controlling and exploiting magnetic correlations. Specifically, these platforms allow for tunable magnetic interactions by twisting two vertically adjacent layers of the magnet, features that are unique to van der Waals materials. By capitalizing on such twist degrees of freedom, we demonstrate the creation of twist-tunable nanoscale magnetic ground states. This capability opens up avenues for applications such as high-density memories and magnon crystals.</p><p>Interestingly, the same material platform also allows for exploiting magnetic correlation by controlling the local electrical environment. We uncover the symmetry-allowed spin-charge coupling mechanisms in the heterostructures of such magnets, a prediction that has received experimental support. Utilizing such an understanding, we propose a setup for the electrical generation of magnons. Magnons—the elementary excitation of spin waves—have garnered a lot of attention these days due to their potential to couple various diverse physical systems and in the field of low dissipation computing. Our findings offer a potential pathway towards the realization of magnon-based spintronic devices.</p>