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When strongly pumped at twice their resonant frequency, nonlinear resonators develop a high-amplitude intracavity field, a phenomenon known as parametric self-oscillations. The boundary over which this instability occurs can be extremely sharp and thereby presents an opportunity for realizing a detector. Here, we operate such a device based on a superconducting microwave resonator whose nonlinearity is engineered from kinetic inductance. The device indicates the absorption of low-power microwave wavepackets by transitioning to a self-oscillating state. Using calibrated pulses, we measure the detection efficiency to zeptojoule energy wavepackets. We then apply it to measurements of electron spin resonance, using an ensemble of 209Bi donors in silicon that are inductively coupled to the resonator. We achieve a latched readout of the spin signal with an amplitude that is five hundred times greater than the underlying spin echoes.

El Referencial Técnico para la Gestión Turística del Patrimonio Cultural (en adelante RETURPAC) es un documento técnico que establece una serie de requisitos para facilitar la articulación entre los procesos culturales y turísticos en el ámbito de los gobiernos municipales. Fue concebido como un texto abierto, construido colectiva y participativamente para la orientación de las políticas públicas de gestión turística del patrimonio cultural en los municipios bonaerenses. El referencial determina buenas prácticas establecidas por el Ministerio de Producción, Ciencia e Innovación Tecnológica, de aplicación voluntaria y no vinculante. El presente documento cobra sentido en función del abordaje de las problemáticas y de las particularidades locales, promoviendo la articulación entre las comunidades relacionadas al patrimonio, los representantes de la actividad turística y los gobiernos locales. En particular, se lo propone a los efectos de diseñar e implementar políticas de turismo cultural que favorezcan un desarrollo humano sostenible y socialmente justo. Es aplicable a todos los municipios bonaerenses que hubieran establecido en sus estructuras orgánicas áreas de gestión o articulación de procesos turísticos y culturales, independientemente de sus características, tamaño, ubicación u otras particularidades territoriales.

The use of superconducting microresonators together with quantum-limited Josephson parametric amplifiers has enhanced the sensitivity of pulsed electron spin resonance (ESR) measurements by more than four orders of magnitude. So far, the microwave resonators and amplifiers have been designed as separate components due to the incompatibility of Josephson junction-based devices with magnetic fields. This has produced complex spectrometers and raised technical barriers toward adoption of the technique. Here, we circumvent this issue by coupling an ensemble of spins directly to a weakly nonlinear and magnetic field-resilient superconducting microwave resonator. We perform pulsed ESR measurements with a 1-pL mode volume containing 6 × 107 spins and amplify the resulting signals within the device. When considering only those spins that contribute to the detected signals, we find a sensitivity of [Formula: see text] for a Hahn echo sequence at a temperature of 400 mK. In situ amplification is demonstrated at fields up to 254 mT, highlighting the technique's potential for application under conventional ESR operating conditions.

The use of superconducting microresonators together with quantum-limited Josephson parametric amplifiers has enhanced the sensitivity of pulsed electron spin resonance (ESR) measurements by more than four orders of magnitude. So far, the microwave resonators and amplifiers have been designed as separate components due to the incompatibility of Josephson junction-based devices with magnetic fields. This has produced complex spectrometers and raised technical barriers toward adoption of the technique. Here, we circumvent this issue by coupling an ensemble of spins directly to a weakly nonlinear and magnetic field-resilient superconducting microwave resonator. We perform pulsed ESR measurements with a 1-pL mode volume containing 6 x 10(7) spins and amplify the resulting signals within the device. When considering only those spins that contribute to the detected signals, we find a sensitivity of 2.8 x10(3)spins/root Hz for a Hahn echo sequence at a temperature of 400 mK. In situ amplification is demonstrated at fields up to 254 mT, highlighting the technique's potential for application under conventional ESR operating conditions.

The use of superconducting microresonators together with quantum-limited Josephson parametric amplifiers has enhanced the sensitivity of pulsed electron spin resonance (ESR) measurements by more than four orders of magnitude. So far, the microwave resonators and amplifiers have been designed as separate components due to the incompatibility of Josephson junction-based devices with magnetic fields. This has produced complex spectrometers and raised technical barriers toward adoption of the technique. Here, we circumvent this issue by coupling an ensemble of spins directly to a weakly nonlinear and magnetic field-resilient superconducting microwave resonator. We perform pulsed ESR measurements with a 1-pL mode volume containing 6 x 10(7) spins and amplify the resulting signals within the device. When considering only those spins that contribute to the detected signals, we find a sensitivity of 2.8 x10(3)spins/root Hz for a Hahn echo sequence at a temperature of 400 mK. In situ amplification is demonstrated at fields up to 254 mT, highlighting the technique's potential for application under conventional ESR operating conditions.

Out-of-time-ordered correlation functions (OTOCs) play a crucial role in the study of thermalization, entanglement, and quantum chaos, as they quantify the scrambling of quantum information due to complex interactions. As a consequence of their out-of-time-ordered nature, OTOCs are difficult to measure experimentally. Here we propose an OTOC measurement protocol that does not rely on the reversal of time evolution and is easy to implement in a range of experimental settings. The protocol accounts for both pure and mixed initial states, and is applicable to systems that interact with environmental degrees of freedom. We demonstrate the application of our protocol by the characterization of scrambling in a periodically driven spin that exhibits quantum chaos.

For the past three decades, nanoscience has widely affected many areas in physics, chemistry, and engineering, and has led to numerous fundamental discoveries as well as applications and products. Concurrently, quantum science and technology has developed into a cross-disciplinary research endeavour connecting these same areas and holds a burgeoning commercial promise. Although quantum physics dictates the behaviour of nanoscale objects, quantum coherence, which is central to quantum information, communication and sensing has not played an explicit role in much of nanoscience. This Review describes fundamental principles and practical applications of quantum coherence in nanoscale systems, a research area we call quantum-coherent nanoscience. We structure this manuscript according to specific degrees of freedom that can be quantum-coherently controlled in a given nanoscale system such as charge, spin, mechanical motion, and photons. We review the current state of the art and focus on outstanding challenges and opportunities unlocked by the merging of nanoscience and coherent quantum operations.

Nuclear spins were among the first physical platforms to be considered for quantum information processing1,2, because of their exceptional quantum coherence3 and atomic-scale footprint. However, their full potential for quantum computing has not yet been realized, owing to the lack of methods with which to link nuclear qubits within a scalable device combined with multi-qubit operations with sufficient fidelity to sustain fault-tolerant quantum computation. Here we demonstrate universal quantum logic operations using a pair of ion-implanted 31P donor nuclei in a silicon nanoelectronic device. A nuclear two-qubit controlled-Z gate is obtained by imparting a geometric phase to a shared electron spin4, and used to prepare entangled Bell states with fidelities up to 94.2(2.7)%. The quantum operations are precisely characterized using gate set tomography (GST)5, yielding one-qubit average gate fidelities up to 99.95(2)%, two-qubit average gate fidelity of 99.37(11)% and two-qubit preparation/measurement fidelities of 98.95(4)%. These three metrics indicate that nuclear spins in silicon are approaching the performance demanded in fault-tolerant quantum processors6. We then demonstrate entanglement between the two nuclei and the shared electron by producing a Greenberger–Horne–Zeilinger three-qubit state with 92.5(1.0)% fidelity. Because electron spin qubits in semiconductors can be further coupled to other electrons7–9 or physically shuttled across different locations10,11, these results establish a viable route for scalable quantum information processing using donor nuclear and electron spins.

Circuit quantum electrodynamics (cQED) provides a modern test bed for exploring the well-established physics of cavity quantum electrodynamics. cQED exploits circuit-based cavities that are fabricated on a chip and interfaced with real or artificial atoms to examine a range of light-matter interactions. It has gained considerable popularity and became one of the most powerful platforms to experimentally explore quantum mechanical effects in the solid state. cQED offers a simple way to couple together distinct quantized degrees of freedom, and this has instigated a new sub-field often referred to as “hybrid quantum systems”. Through combining different quantum systems with superconducting circuits, one can deploy the cQED toolbox to deliver advantages in other fields. Recently, superconducting micro-resonators have been used in conjunction with microwave parametric amplifiers to push the detection sensitivity in Electron Spin Resonance (ESR) spectroscopy to the quantum noise limit. ESR spectroscopy is an important technique for studying the structure and function of materials, broadly utilized throughout chemistry, physics and biology and sensitive enhancement is often a highly prized goal. The superconducting parametric amplifier circuits employed in previous quantum-limited ESR experiments have all been based on Josephson junction technology -- a lossless nonlinear element that enables many important cQED devices -- and are incompatible with the high magnetic fields often required by spins. Spin signals are collected using a linear resonator and must be routed to the amplifier (housed away from any magnetic fields) through various microwave components and cables, which introduce loss and complexity. In this thesis we develop a new type of superconducting parametric amplifier that utilizes a nonlinear kinetic inductance, called the KIPA. The amplifier contains no Josephson junctions and is compatible with the large magnetic fields relevant for ESR spectroscopy. We a

A common thread in the realization of quantum computers, quantum networks, and quantum sensors is the search for promising physical platforms. The dislocations of atoms in the solid state, referred to as defects, have historically been deemed undesirable as they can be deleterious to the operation of electronic and optoelectronic devices. In 1997, it was demonstrated that a single nitrogen-vacancy (NV) center defect in diamond could act as a stable single photon source [1]. In the same study, the electronic spin of the same defect was optically initialized and read out. Remarkably, both of these achievements occurred under ambient conditions. In the decades that have followed, the study of optically active defects in the solid state have garnered significant interest for quantum applications. Motivated by this, in this thesis we demonstrate experimental progress in defects in three materials: silicon carbide, diamond, and sapphire.Silicon carbide is a wide band-gap semiconductor with a mature manufacturing industry. In this material, we show the integration of surface defects (formed at the SiC/SiO2 interface) into microdisk resonators, showing an enhancement in single photon emission. Additionally, we construct a confocal microscopy apparatus and demonstrate room-temperature optically-detected magnetic resonance of silicon-vacancy defects in ~50 nm diameter SiC nanoparticles, further motivating their application for quantum sensing and nanophotonics.While NV-centers have been widely studied, we demonstrate coherent control of the electronic spin states, and coupling to their neighboring nuclear spins, using an apparatus that operates in ambient conditions, outside an otherwise carefully controlled environment of a research laboratory, and which can be constructed for ~USD 20k. This has enabled the development of a teaching lab that has been incorporated into a quantum engineering course for three consecutive years.Lastly, we upgrade a dilution refrigerator for opti

Donor-based nano devices in silicon offer a unique gateway into the quantum control of atomic-scale objects within a manufacturable solid-state hardware, and may be adopted for the construction of a large-scale quantum computer. Furthermore, the high level of control and exceptional coherence times of donor spins make these devices an ideal platform for exploring fundamental quantum phenomena. Designing and modelling the most groundbreaking experiments requires the use of advanced theoretical and computational tools. Here, we developed efficient tools to simulate the multi-electron wave-function of donor molecules in silicon. We implemented a quantum chemistry suite, in the framework of an established multi-valley effective mass theory implementation, including Hartree-Fock, full configuration interaction and mean-field solvers. We applied these tools to two phosphorus donors positioned along different lattice orientations to investigate the exchange interaction, valley population and electron densities. We performed exhaustive iterations over all physically relevant relative donor placements and studied electric field dependency to find the best configurations for two-qubit gates. A hyperfine-coupled three-electron two-phosphorus cluster was studied in a mean-field approach. High-spin donors, like antimony, have a non-zero nuclear quadrupole moment. This feature allowed us to electrically drive the ionized antimony nuclei and for the first time observe nuclear electric resonance (NER) in a single atom. Here, we combined finite element simulation with Density Functional Theory results. I was able to accurately triangulate the nuclei and reproduce the strain induced quadrupole splitting at this position. We could rule out a piezo-electric quartz monolayer as a source of NER. With electric field simulations, we could quantify that the microscopic source of NER is the polarization of the covalent bonding orbitals.

Recent results in quantum computing, such as Google achieving quantum supremacy, have made it clear that we are well within the noisy intermediate scale quantum (NISQ) computing regime. Whilst this enables the probing of quantum phenomena and the development of simple quantum algorithms, practical large-scale quantum computing is going to require millions of physical qubits to be constructed on an industrial scale.Silicon donor qubits are one of the most promising candidates for realising this immense technical challenge. Their long coherence times, well established read-out and control mechanisms make each qubit an excellent candidate to form the needed physical qubits. Combining this with architectures to couple these qubits with each other, compatibility with CMOS semiconductor fabrication processes and small physical size means that silicon donor qubits are perfectly placed to become the qubit system of the future.One crucial factor still needed for the large-scale development of donor qubits is a system that enables the deterministic placement of individual donors in the silicon lattice. Developed in the field of high-energy physics, semiconductor detectors can detect ionising radiation impacting the chip. In this thesis we present the progress that has been made in developing custom silicon detectors that can detect the implantation of a single ion for the purposes of quantum computing. We study different process steps and their impact on detector performance, paving a way for more sophisticated and reliable detectors. Also presented are several proposed experiments and design changes predicted to improve detector performance or the ease of integration with donor qubit devices. These improvements are crucial elements in forming functional silicon detectors that can be integrated with existing qubit architectures to build future large-scale quantum computers.Ion implantation allows the introduction of any group-V donor into the silicon crystal, giving us the ch

For the past three decades nanoscience has widely affected many areas in physics, chemistry and engineering, and has led to numerous fundamental discoveries, as well as applications and products. Concurrently, quantum science and technology has developed into a cross-disciplinary research endeavour connecting these same areas and holds burgeoning commercial promise. Although quantum physics dictates the behaviour of nanoscale objects, quantum coherence, which is central to quantum information, communication and sensing, has not played an explicit role in much of nanoscience. This Review describes fundamental principles and practical applications of quantum coherence in nanoscale systems, a research area we call quantum-coherent nanoscience. We structure this Review according to specific degrees of freedom that can be quantum-coherently controlled in a given nanoscale system, such as charge, spin, mechanical motion and photons. We review the current state of the art and focus on outstanding challenges and opportunities unlocked by the merging of nanoscience and coherent quantum operations., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., QuTech, QN/Vandersypen Lab, X-TU Delft

For the past three decades nanoscience has widely affected many areas in physics, chemistry and engineering, and has led to numerous fundamental discoveries, as well as applications and products. Concurrently, quantum science and technology has developed into a cross-disciplinary research endeavour connecting these same areas and holds burgeoning commercial promise. Although quantum physics dictates the behaviour of nanoscale objects, quantum coherence, which is central to quantum information, communication and sensing, has not played an explicit role in much of nanoscience. This Review describes fundamental principles and practical applications of quantum coherence in nanoscale systems, a research area we call quantum-coherent nanoscience. We structure this Review according to specific degrees of freedom that can be quantum-coherently controlled in a given nanoscale system, such as charge, spin, mechanical motion and photons. We review the current state of the art and focus on outstanding challenges and opportunities unlocked by the merging of nanoscience and coherent quantum operations.

For the past three decades nanoscience has widely affected many areas in physics, chemistry and engineering, and has led to numerous fundamental discoveries, as well as applications and products. Concurrently, quantum science and technology has developed into a cross-disciplinary research endeavour connecting these same areas and holds burgeoning commercial promise. Although quantum physics dictates the behaviour of nanoscale objects, quantum coherence, which is central to quantum information, communication and sensing, has not played an explicit role in much of nanoscience. This Review describes fundamental principles and practical applications of quantum coherence in nanoscale systems, a research area we call quantum-coherent nanoscience. We structure this Review according to specific degrees of freedom that can be quantum-coherently controlled in a given nanoscale system, such as charge, spin, mechanical motion and photons. We review the current state of the art and focus on outstanding challenges and opportunities unlocked by the merging of nanoscience and coherent quantum operations.

For the past three decades nanoscience has widely affected many areas in physics, chemistry and engineering, and has led to numerous fundamental discoveries, as well as applications and products. Concurrently, quantum science and technology has developed into a cross-disciplinary research endeavour connecting these same areas and holds burgeoning commercial promise. Although quantum physics dictates the behaviour of nanoscale objects, quantum coherence, which is central to quantum information, communication and sensing, has not played an explicit role in much of nanoscience. This Review describes fundamental principles and practical applications of quantum coherence in nanoscale systems, a research area we call quantum-coherent nanoscience. We structure this Review according to specific degrees of freedom that can be quantum-coherently controlled in a given nanoscale system, such as charge, spin, mechanical motion and photons. We review the current state of the art and focus on outstanding challenges and opportunities unlocked by the merging of nanoscience and coherent quantum operations., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., QN/Vandersypen Lab, Communication X-TU Delft

Semiconductor qubits are expected to have diverse future quantum applications. This Review discusses semiconductor qubit implementations from the perspective of an ecosystem of applications, such as quantum simulation, sensing, computation and communication.In the past decade, semiconducting qubits have made great strides in overcoming decoherence, improving the prospects for scalability and have become one of the leading contenders for the development of large-scale quantum circuits. In this Review, we describe the current state of the art in semiconductor charge and spin qubits based on gate-controlled semiconductor quantum dots, shallow dopants and colour centres in wide-bandgap materials. We frame the relative strengths of the different semiconductor qubit implementations in the context of applications such as quantum simulation, computing, sensing and networks. By highlighting the status and future perspectives of the basic types of semiconductor qubits, this Review aims to serve as a technical introduction for non-specialists and a forward-looking reference for scientists intending to work in this field.

Nuclear spins are highly coherent quantum objects. In large ensembles, their control and detection via magnetic resonance is widely exploited, e.g. in chemistry, medicine, materials science, and mining. Nuclear spins also prominently featured in early ideas and demonstrations of quantum information processing. In silicon, the high-fidelity coherent control of a single phosphorus (31-P) nuclear spin has led to record-breaking coherence times, as well as entanglement and weak measurements.Replacing 31-P by a high-spin donor leverages all of these features, and unlocks a rich variety of experiments that probe quantum physics at a fundamental level.In this thesis, we demonstrate the coherent quantum control of a single antimony (123-Sb) donor atom, whose higher nuclear spin has eight nuclear spin states.However, rather than conventional nuclear magnetic resonance (NMR), we employ nuclear electric resonance (NER) to drive nuclear spin transitions using localized electric fields produced within a silicon nanoelectronic device. This method exploits an idea first proposed in 1961 but never realized experimentally with a single nucleus, nor in a non-polar crystal such as silicon. Our results are quantitatively supported by a microscopic theoretical model that reveals how the purely electrical modulation of the nuclear electric quadrupole interaction results in coherent nuclear spin transitions. The spin dephasing time, 0.1 seconds, surpasses by orders of magnitude those obtained via methods that require a coupled electron spin for electrical drive. The coherent control of an 123-Sb nucleus opens up the door to experiments on the foundations of quantum mechanics, such as the emergence of chaos in the quantum-classical transition.We present here a realistic proposal to construct a chaotic driven top from the 123-Sb nuclear spin. We show that signatures of chaos are expected to arise for experimentally realizable system parameters, allowing the study of the relation between qua

Donor spins in silicon allow for extremely long storage of quantum information and provide accurate single spin control. While these properties make them attractive for quantum computation, to build a large-scale quantum computer some major challenges still need to be addressed.One key issue is coupling two donor quantum bits (qubits) with high fidelity, in a scalable manner, without requiring extremely accurate donor placement. In this thesis, we propose a new type of qubit, the flip-flop qubit, a combination of the electron-nuclear spin states of the phosphorus donor, that can be controlled by microwave electric fields. A dipole is created when separating the donor electron from the nucleus, allowing two-qubit gates mediated by electric dipole-dipole interaction at donor distances of several hundred nanometres. Gate fidelities are predicted to be within fault-tolerance thresholds for quantum error correction codes, using realistic charge noise values. Strong coupling of the qubit to superconducting resonators can also be achieved. This idea can be extended to couple nuclear spins to electric fields by adding a magnetic drive, applied simultaneously with the electric drive in a Raman-like configuration. Both qubits can be incorporated in a large scale quantum processor. Two types of flip-flop qubit prototypes, one suited for direct dipole-dipole coupling and one for coupling to a resonator, have been designed, fabricated and measured. Fundamental functionalities have been established and the coupling of a charge qubit to a resonator has been observed. When building a large scale quantum computer, precise knowledge of the fundamental physics of the donor system is of key importance. To this end, we analyse the electron spin relaxation. We find that the spin relaxation is caused by phonon emission at high magnetic fields (>3 T), but becomes dominated by evanescent-wave Johnson noise at lower fields. We also find evidence of spurious spin relaxation caused by electron

Nuclear spins of ionized donors in silicon have received considerable attention in the context of quantum computing because of their extraordinarily long coherence times. In this thesis, we study the properties of these quantum systems using electrically detected electron nuclear double resonance. We in particular focus on the heavier dopants arsenic and antimony and the peculiarities that come with a larger nuclear spin, such as the quadrupolar interaction with the crystal field in strained silicon and the generation of multi-quantum coherences., Aufgrund ihrer langen Kohärenzzeiten sind die Kernspins der ionisierten Donatoren in Silizium von großem Interesse für Quantenanwendungen. In dieser Arbeit charakterisieren wir die Eigenschaften dieser Quantensysteme mittels elektrisch detektierter Kern-Elektron Doppelresonanz und untersuchen dabei insbesondere die schwereren Donatoren Arsen und Antimon, welche aufgrund ihres größeren Kernspins über die Quadrupolwechselwirkung auf Kristallfelder in verspanntem Silizium reagieren und in denen Kohärenzen höherer Ordnung erzeugt werden können.

We identify the presence of monatomic steps at the Si/SiGe or Si/SiO2 interface as a dominant source of variations in the dephasing time of silicon (Si) quantum dot (QD) spin qubits. First, using atomistic tight-binding calculations we show that the g-factors and their Stark shifts undergo variations due to these steps. We compare our theoretical predictions with experiments on QDs at a Si/SiO2 interface, in which we observe significant differences in Stark shifts between QDs in two different samples. We also experimentally observe variations in the g-factors of one-electron and three-electron spin qubits realized in three neighboring QDs on the same sample, at a level consistent with our calculations. The dephasing times of these qubits also vary, most likely due to their varying sensitivity to charge noise, resulting from different interface conditions. More importantly, from our calculations we show that by employing the anisotropic nature of the spin-orbit interaction (SOI) in a Si QD, we can minimize and control these variations. Ultimately, we predict that the dephasing times of the Si QD spin qubits will be anisotropic and can be improved by at least an order of magnitude, by aligning the external dc magnetic field towards specific crystal directions, given other decoherence mechanisms do not dominate over charge noise., QCD/Veldhorst Lab

Nuclear spins of ionized donors in silicon have received considerable attention in the context of quantum computing because of their extraordinarily long coherence times. In this thesis, we study the properties of these quantum systems using electrically detected electron nuclear double resonance. We in particular focus on the heavier dopants arsenic and antimony and the peculiarities that come with a larger nuclear spin, such as the quadrupolar interaction with the crystal field in strained silicon and the generation of multi-quantum coherences., Aufgrund ihrer langen Kohärenzzeiten sind die Kernspins der ionisierten Donatoren in Silizium von großem Interesse für Quantenanwendungen. In dieser Arbeit charakterisieren wir die Eigenschaften dieser Quantensysteme mittels elektrisch detektierter Kern-Elektron Doppelresonanz und untersuchen dabei insbesondere die schwereren Donatoren Arsen und Antimon, welche aufgrund ihres größeren Kernspins über die Quadrupolwechselwirkung auf Kristallfelder in verspanntem Silizium reagieren und in denen Kohärenzen höherer Ordnung erzeugt werden können.

We identify the presence of monatomic steps at the Si/SiGe or Si/SiO2 interface as a dominant source of variations in the dephasing time of silicon (Si) quantum dot (QD) spin qubits. First, using atomistic tight-binding calculations we show that the g-factors and their Stark shifts undergo variations due to these steps. We compare our theoretical predictions with experiments on QDs at a Si/SiO2 interface, in which we observe significant differences in Stark shifts between QDs in two different samples. We also experimentally observe variations in the g-factors of one-electron and three-electron spin qubits realized in three neighboring QDs on the same sample, at a level consistent with our calculations. The dephasing times of these qubits also vary, most likely due to their varying sensitivity to charge noise, resulting from different interface conditions. More importantly, from our calculations we show that by employing the anisotropic nature of the spin-orbit interaction (SOI) in a Si QD, we can minimize and control these variations. Ultimately, we predict that the dephasing times of the Si QD spin qubits will be anisotropic and can be improved by at least an order of magnitude, by aligning the external dc magnetic field towards specific crystal directions, given other decoherence mechanisms do not dominate over charge noise., QCD/Veldhorst Lab

The control and measurement of the quantum state of single phosphorus atoms in silicon has opened up vast newavenues for exploration of quantum effects. The work outlined in this thesis describes the development of several ofthese avenues, extending the applications of the system for quantum science. The electron and nuclear states of thephosphorus donor have been utilised as a quantum memory, experimental means have been developed to opticallyaddress these quantum states, and experiments were developed to probe the nature of causality and time-symmetryin quantum systems.

A computer with quantum mechanical building blocks, or qubits, promises a new class of computational capability and is a natural platform on which to simulate microscopic systems. Building a quantum computer, however, is a formidable challenge. The system chosen must be engineered to balance contradicting requirements. The fragile quantum states must be sufficiently protected from noise in the environment, while being accessible for accurate measurement and control. Moreover, the system must be scalable to millions of qubits that can be made to interact in complex sequences. Recent experimental breakthroughs have highlighted spin qubits in silicon as a promising platform. Firstly, fabrication of these semiconductor devices would capitalize on the expertise developed by the microelectronics industry. Secondly, and more fundamentally, silicon can provide a virtually noiseless environment for spin qubits while maintaining qubit addressability. This thesis builds upon the foundational work on phosphorus donor electron spin qubits in silicon. We achieve dramatic improvements in the fundamental single qubit operations: the fidelities of readout, initialization and control of the electron spin are all enhanced to 99.9% simultaneously and we report a new record coherence time of 0.98 seconds. Furthermore, we provide novel theoretical proposals for the next steps in scaling this technology. We present a two-qubit operation that can be performed with fidelity exceeding 99%, robust to variability in donor positioning, and we devise a scheme for high-fidelity short-range qubit transport that may prove invaluable in the design of a quantum processor. The experimental setup required for scale-up is also addressed, as we report the first measurement of the silicon spin qubit device in a cryogen-free dilution refrigerator and present techniques to mitigate the noise induced by mechanical vibrations. Our work has solved several crucial problems on the road-map towards a full-scale p

Quantum computers have gained great attention in the recent past, with their promise for solving exceptionally difficult problems in short timescales. Spins associated with impurities and quantum dots in silicon are an ideal physical platform for quantum bits (qubits) - the fundamental element of a quantum computer - due to (i) their potential for scalability and (ii) long coherence times. There are three crucial elements of a spin based quantum computer: (i) a well defined spin qubit, that can be read out and controlled in a gated device, (ii) precise control and tunability of exchange interaction between two spins, and (iii) a robust spin transport mechanism for transferring the spin state to different parts of the quantum computer. This thesis presents detailed electrostatic and quantum mechanical modeling of several spin-hosting nanostructures that can demonstrate the above building blocks. The achievements of this thesis are enumerated below.(i) We demonstrate a metrology technique that locates impurity spin qubits to a precision several thousand times smaller than the experiment. (ii) With a numerically accurate technique, we investigate a particular scheme for tuning the exchange interaction between two impurity spins, and reveal exchange tunabilities much larger than current predictions.(iii) We then quantify the necessary experimental conditions for achieving high fidelity spin transport via two promising techniques - impurity chains and superconducting resonators.(iv) Finally, we model a crucial parameter ("valley splitting tunability") for implementing qubits with electrons in a silicon quantum dot, and report an excellent agreement with experiment.With the above, our modeling provides a deep insight into the required device topologies, qubit positions and electric fields - for high fidelity readout, control, exchange and transport of quantum spin information. Our results thereby offer a range of design considerations to experimentalists, who are in a glo

As classical computers begin to reach their fundamental performance limits, quantum computers will be an invaluable tool for the advance of science and technology. The trillion dollar silicon electronics industry sets the perfect stage for the evolution of quantum computation, yet it has so far proved to be a tough challenge to implement all the elements needed to build a scalable quantum computer in silicon.This thesis presents the first experimental demonstration of the full operation of single-spin qubits in Si. Our qubits consist of the electron and nuclear spins of a single phosphorus atom, implanted in a Si substrate, and controlled by a gated nanostructure. We describe an experimental setup tailored to minimise electron temperature and perform real-time data acquisition, analysis and instrument control. We present modeling, simulation and characterisation of a novel nanoscale coplanar antenna for spin control, designed to work at frequencies up to 50 GHz. These tools have allowed us to demonstrate the first ever single-atom spin-qubits in natural silicon, leading the way to demonstrating record qubit performances in isotopically purified 28Si: an electron spin qubit with measurement and control fidelities > 97% and coherence times of 0.5 seconds; and a nuclear spin qubit with fidelities > 99.99% and a record single-spin coherence of 30 s. We have performed noise spectroscopy in our system and concluded that decoherence is currently limited by magnetic noise originating from our broadband antenna. We also describe a methodology towards the demonstration of electron-nuclear entanglement in a single atom, through density matrix tomography. Finally, we present the experimental demonstration of one of the key milestones towards implementing two-qubit gates in our system: single-shot readout and relaxation measurements of the singlet-triplet states of coupled electrons from a P donor pair in natural Si; finding agreement of our observed exchange coupling and relaxa

Spin is a quantum mechanical property that describes the magnetic orientation of elementary and composite particles such as electrons and nuclei. For “spin-half” particles placed in a magnetic field, two states with differing energies are defined. Proposals exist for developing a revolutionary kind of computer that encodes bits of information on the states of a simple quantum two-level system - like those of a spin in a magnetic field. These “quantum computers” exploit the fundamental principles of quantum mechanics in order to perform certain calculations exponentially faster than their classical counterparts. Key to the development of such a device is the identification of potential systems that are suitable for employment as a quantum bit (qubit). This thesis explores quantum bits constructed from the spin states of single atoms hosted in silicon semiconductor devices. Silicon is an exceptional platform for spin-based quantum computing - in addition to being the dominant material in the microelectronic industry, it is also predominantly composed of nuclear spin-zero isotopes, providing very little background magnetic disturbance. The donor-atom phosphorus (31P) is investigated here. It possesses a nucleus that binds an additional electron to its positive charge, providing two distinct spin qubits.Here, several world-first experimental milestones in spin-based quantum information processing are reported. First, the readout of the electron spin is demonstrated in single-shot, using a silicon device which combines implanted phosphorus donors with a sensitive nanoscale electrometer. Then, the electron spin is coherently operated as a qubit by delivering on-chip microwave excitations. Combining the electron spin detection and control capabilities enables a quantum non-demolition measurement of the single 31P nuclear spin. Experiments yield exceptional nuclear readout fidelities - the highest for any solid-state qubit. Through an application of nuclear magnetic resonan

The exact location of a single dopant atom in a nanostructure can influence or fully determine the functionality of highly scaled transistors or spin-based devices. We demonstrate here a noninvasive spatial metrology technique, based on the microscopic modeling of three electrical measurements on a single-atom (phosphorus in silicon) spin qubit device: hyperfine coupling, ground state energy, and capacitive coupling to nearby gates. This technique allows us to locate the qubit atom with a precision of +/- 2.5 nm in two directions and +/- 15 nm in the third direction, which represents a 1500-fold improvement with respect to the prefabrication statistics obtainable from the ion implantation parameters.

The exact location of a single dopant atom in a nanostructure can influence or fully determine the functionality of highly scaled transistors or spin-based devices. We demonstrate here a noninvasive spatial metrology technique, based on the microscopic modeling of three electrical measurements on a single-atom (phosphorus in silicon) spin qubit device: hyperfine coupling, ground state energy, and capacitive coupling to nearby gates. This technique allows us to locate the qubit atom with a precision of +/- 2.5 nm in two directions and +/- 15 nm in the third direction, which represents a 1500-fold improvement with respect to the prefabrication statistics obtainable from the ion implantation parameters.

This review describes recent groundbreaking results in Si, Si/SiGe, and dopant-based quantum dots, and it highlights the remarkable advances in Si-based quantum physics that have occurred in the past few years. This progress has been possible thanks to materials development of Si quantum devices, and the physical understanding of quantum effects in silicon. Recent critical steps include the isolation of single electrons, the observation of spin blockade, and single-shot readout of individual electron spins in both dopants and gated quantum dots in Si. Each of these results has come with physics that was not anticipated from previous work in other material systems. These advances underline the significant progress toward the realization of spin quantum bits in a material with a long spin coherence time, crucial for quantum computation and spintronics.

This review describes recent groundbreaking results in Si, Si/SiGe, and dopant-based quantum dots, and it highlights the remarkable advances in Si-based quantum physics that have occurred in the past few years. This progress has been possible thanks to materials development of Si quantum devices, and the physical understanding of quantum effects in silicon. Recent critical steps include the isolation of single electrons, the observation of spin blockade, and single-shot readout of individual electron spins in both dopants and gated quantum dots in Si. Each of these results has come with physics that was not anticipated from previous work in other material systems. These advances underline the significant progress toward the realization of spin quantum bits in a material with a long spin coherence time, crucial for quantum computation and spintronics.

We demonstrate radio frequency (RF) readout of electrically detectedmagnetic resonance in phosphorus-doped silicon metal-oxide field-effecttransistors (MOSFETs), operated at liquid helium temperatures. For the first time, the Si:P hyperfine lines have been observed using radio frequency reflectometry, which is promising for high-bandwidth operation and possibly time-resolved detection of spin resonance in donor-basedsemiconductor devices. Here we present the effect of microwave (MW) power and MOSFET biasing conditions on the EDMR signals.