Advancement Of Silicon Based Spin Qubits

"Electron spins in gate-defined quantum dots have emerged as a leading candidate for quantum-information-processing applications, including quantum computation. Long coherence times and compatibility with conventional semiconductor-manufacturing techniques contribute to the appeal of implementing these devices as quantum bits, or qubits. Recent research efforts have demonstrated many of the fundamental requirements for their utilization in a future quantum processor. Despite this, further development in the performance of these devices is necessary if the goal is truly to realize a universal quantum computer. Improvements will likely come in the form of both device-engineering advancements as well as novel qubit-operation and qubit-measurement schemes. This thesis describes a number of experiments carried out in gate-defined quantum dots in Si/SiGe, including demonstrations of high-fidelity spin-measurement, multiple studies of environmental noise, and coherent control of electron-spin qubits. This work represents the first realization of such devices in the Nichol Group at the University of Rochester. Together, the results represent the advancement of our understanding of silicon-based quantum dots and spin qubits"--Page xii.

The project goals are to fabricate qubits in quantum dots in Si/SiGe modulation-doped heterostructures, to characterize and understand those structures, and to develop the technology necessary for a Si/SiGe quantum dot quantum computer. The physical qubit in our approach is the spin of an electron confined in a top-gated silicon quantum dot in a Si/SiGe modulation-doped heterostructure. Operations on such a qubit may be performed by controlling the voltages on gates in-between neighboring quantum dots. A quantum computer and qubits in silicon offer potential advantages, both fundamental and practical. Electron spins in silicon quantum dots are expected to have long coherence times. Silicon has an isotope, Si, which has zero nuclear spin and thus no nuclear magnetic moment. As a result, electron spins in silicon have longer coherence times than they would in the presence of a fluctuating nuclear spin background. From a practical perspective, modern classical computers are made in silicon, and one hopes that this will lead to synergy in the future with a silicon quantum computer. This QCCM includes both theory and experiment focusing on (i) the development of qubits in the form of electron spins in silicon quantum dots, (ii) the measurement and manipulation of those qubits, and (iii) the science essential for understanding the properties of such qubits.

Quantum mechanics, the subfield of physics that describes the behavior of very small (quantum) particles, provides the basis for a new paradigm of computing. First proposed in the 1980s as a way to improve computational modeling of quantum systems, the field of quantum computing has recently garnered significant attention due to progress in building small-scale devices. However, significant technical advances will be required before a large-scale, practical quantum computer can be achieved. Quantum Computing: Progress and Prospects provides an introduction to the field, including the unique characteristics and constraints of the technology, and assesses the feasibility and implications of creating a functional quantum computer capable of addressing real-world problems. This report considers hardware and software requirements, quantum algorithms, drivers of advances in quantum computing and quantum devices, benchmarks associated with relevant use cases, the time and resources required, and how to assess the probability of success.

Quantum information processing (QIP) is one of the most promising and exciting areas of nanoscience and nanotechnology. Silicon-based quantum computers have become popular candidates for QIP partly because the needed nanoscale manufacturing techniques are well-established for modern silicon electronics. Furthermore, electron spins bound to donors in Si have proven to be some of the most, if not the most, coherent quantum structures among proposed solid state QIP systems to date. Unfortunately, a serious obstacle impeding the physical implementation of quantum computing technology is the ability to readily control quantum bits (qubits). The unique inverted electronic structure of the lithium donor in silicon makes these quantum structures not only strongly coherent, but also readily manipulable. The goal of this work is the development of a complete quantum computing scheme allowing for electrical and piezoelastic control of lithium spin qubits in silicon. To achieve our goal and to enable electrical control of lithium spin qubits, we study the effect of a static electric field on lithium donor spins in silicon. We demonstrate that the anisotropy of the effective mass leads to the anisotropy of the quadratic Stark susceptibility. Using the Dalgarno-Lewis exact summation method, we are able to calculate the Stark susceptibilities and analyze several important physical effects. We show the energy level shifts due to the quadratic Stark effect are equivalent to, and can be mapped onto, those produced by an external stress. Furthermore, we show the energy level shifts, combined with the unique valley-orbit splitting of the Li donor in Si, spin-orbit interaction and specially tuned external stress, leads to a very strong modulation of the donor spin g-factor and electron spin resonance (ESR) lines by the electric field. We propose a complete quantum computing scheme based on Li donors in Si. With the system under external biaxial stress, the qubits are encoded on a ground state Zeeman doublet and arc coupled via the acoustic-phonon-mediated long-range spin-spin interaction. We utilize g-factor control of the qubits to perform a specially-designed sequence of electric field impulses in order to execute both the cz gate and the universal CNOT gate. Using the quadratic Stark effect calculations and electron-phonon decoherence times, we estimate that the typical two-qubit gate time is on the order of ~ 1 [us] with a quality factor of [~ 10 -6]. A possible extension to these results is the piezoelastic control of spin qubits in semiconductors, which may open new avenues in solid state quantum information processing. This work has been supported by the following agencies: the National Security Agency (NSA), the Army Research Office (ARO) and the National Aeronautics and Space Administration (NASA).

Diamond nitrogen vacancy (NV) color centers can transform quantum information science into practical quantum information technology, including fast, safe computing. Quantum Information Processing with Diamond looks at the principles of quantum information science, diamond materials, and their applications. Part one provides an introduction to quantum information processing using diamond, as well as its principles and fabrication techniques. Part two outlines experimental demonstrations of quantum information processing using diamond, and the emerging applications of diamond for quantum information science. It contains chapters on quantum key distribution, quantum microscopy, the hybridization of quantum systems, and building quantum optical devices. Part three outlines promising directions and future trends in diamond technologies for quantum information processing and sensing. Quantum Information Processing with Diamond is a key reference for R&D managers in industrial sectors such as conventional electronics, communication engineering, computer science, biotechnology, quantum optics, quantum mechanics, quantum computing, quantum cryptology, and nanotechnology, as well as academics in physics, chemistry, biology, and engineering. Brings together the topics of diamond and quantum information processing Looks at applications such as quantum computing, neural circuits, and in vivo monitoring of processes at the molecular scale

The thesis gives the first experimental demonstration of a new quantum bit (“qubit”) that fuses two promising physical implementations for the storage and manipulation of quantum information – the electromagnetic modes of superconducting circuits, and the spins of electrons trapped in semiconductor quantum dots – and has the potential to inherit beneficial aspects of both. This new qubit consists of the spin of an individual superconducting quasiparticle trapped in a Josephson junction made from a semiconductor nanowire. Due to spin-orbit coupling in the nanowire, the supercurrent flowing through the nanowire depends on the quasiparticle spin state. This thesis shows how to harness this spin-dependent supercurrent to achieve both spin detection and coherent spin manipulation. This thesis also represents a significant advancement to our understanding and control of Andreev levels and thus of superconductivity. Andreev levels, microscopic fermionic modes that exist in all Josephson junctions, are the microscopic origin of the famous Josephson effect, and are also the parent states of Majorana modes in the nanowire junctions investigated in this thesis. The results in this thesis are therefore crucial for the development of Majorana-based topological information processing.

This book gathers high-quality, peer-reviewed research papers presented at the Second International Conference on Computer Science, Engineering and Education Applications (ICCSEEA2019), held in Kiev, Ukraine on 26–27 January 2019, and jointly organized by the National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute” and the International Research Association of Modern Education and Computer Science. The papers discuss state-of-the-art topics and advances in computer science; neural networks; pattern recognition; engineering techniques; genetic coding systems; deep learning and its medical applications; and knowledge representation and its applications in education. Given its scope, the book offers an excellent resource for researchers, engineers, management practitioners, and graduate and undergraduate students interested in computer science and its applications in engineering and education.