Experiments on Flux Qubits with Pi-shifters


Book Description

The results of the research re-ported in this work show that tunable gap flux qubits have a potential for building quantum registers. Cavities coupled to flux qubits can be used for in-formation storage and transfer between qubits. SFS π-shifters provide a simple approach to bias multi-qubit circuits. A possibility to change the qubit resonance frequency while preserving qubit coherence enables implementation of switchable coupling between qubits and cavities.







Fundamentals and Frontiers of the Josephson Effect


Book Description

This book provides a comprehensive and up-to-date description of the Josephson effect, a topic of never-ending interest in both fundamental and applied physics. In this volume, world-renowned experts present the unique aspects of the physics of the Josephson effect, resulting from the use of new materials, of hybrid architectures and from the possibility of realizing nanoscale junctions. These new experimental capabilities lead to systems where novel coherent phenomena and transport processes emerge. All this is of great relevance and impact, especially when combined with the didactic approach of the book. The reader will benefit from a general and modern view of coherent phenomena in weakly-coupled superconductors on a macroscopic scale. Topics that have been only recently discussed in specialized papers and in short reviews are described here for the first time and organized in a general framework. An important section of the book is also devoted to applications, with focus on long-term, future applications. In addition to a significant number of illustrations, the book includes numerous tables for comparative studies on technical aspects.




Quantum Sensing Experiments with Superconducting Qubits


Book Description

Quantum sensing is a vast and emerging field enabling in-situ studies of quantum systems and hence the development of quantum hybrid systems. This work creates the fundament of direct superconducting-magnetic hybrid systems by developing a local microwave sensing scheme and studying the influence of a static magnetic field on a superconducting qubit. Finally, a proof-of-principle hybrid system is demonstrated, which opens the path towards superconducting-magnetic quantum circuits.




High Quality Nb/Al-AlOx/Nb Josephson Junctions


Book Description

Diese Arbeit beschreibt die Entwicklung einer Technologie für die Herstellung hochqualitativer sub-μm Nb/Al-AlOx/Nb-Josephson-Kontakte. Mit den dadurch entstandenen Bauteilen wurden verschiedene experimentell zuvor noch nicht beobachtete makroskopische Quanteneffekte nachgewiesen. Weiterhin wurden Nb-basierte Phasen-Qubits entworfen, hergestellt und gemessen, die längere Kohärenzzeiten als vergleichbare Bauelemente aus der Literatur aufweisen.




Quantum Computing


Book Description

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.




Investigation of coherent microscopic defects inside the tunneling barrier of a Josephson junction


Book Description

In disordered solids, two-level atomic-tunneling systems are present in large quantity. Only recently, superconducting qubits opened a door for a detection and individual coherent manipulation of such microscopic quantum systems. We succeeded to tune the resonance frequencies of these systems by applying external strain on the qubit chip. Moreover, we observed and analyzed the interaction between two coupled tunneling systems.




Experimental Quantum Computation and Information


Book Description

This Fermi Summer School of Physics on "Experimental Quantum Information and Computing" represents a primer on one of the most intriguing and rapidly expanding new areas of physics. In this part, the interest in quantum information (QI) science is due to the discovery that a computer operating on quantum mechanical principles can solve certain important computational problems exponentially faster than any conceivable classical computer. But this interest is also due to the interdisciplinary nature of the field: the rapid growth is attributable, in part, to the stimulating confluence of researchers and ideas from physics, chemistry, mathematics, information theory, and computer science. Physics plays a paramount role in QI science, as we realize that computing is itself a physical process subject to physical laws. The incredible growth of classical computers and information processors in the 20th century stems from Turing's notion that a computer is independent of the physical device actually being used; be they relays, vacuum tubes, or semiconductor transistors. As we strive to build useful quantum information processors into the 21st century, we thus look for any physical system that obeys the laws of quantum mechanics, from single photons and atoms to quantum superconducting devices. These Fermi lectures take us on a journey through these and other promising current experimental candidates for QI processing, spanning quantum optics and laser physics, atomic and molecular physics, physical chemistry, and condensed-matter physics. While this broad coverage of experimental physics represents a challenge to the student, such an appreciation of these fields will be critical in the future success of quantum technology. Indeed, the most exciting feature of QI science is that the technology ultimately leading to a quantum processor is likely presently unknown.




Physics and Applications of the Josephson Effect


Book Description

Cover -- Contents -- CHAPTER 1 Weak Superconductivity8212; Phenomenological Aspects -- 146;1 Macroscopic Quantum System -- 146;2 Coupled Superconductors -- 146;3 Single Electron Tunneling -- 146;4 Josephson Equations -- 146;5 Magnetic Field Effects -- 146;6 Barrier Free Energy -- 146;7 Electrodynamics of the Josephson Junction -- 146;8 Other Josephson Structures -- CHAPTER 2 Microscopic Theory -- 1 Tunneling Hamiltonian Formalism -- 2 General Expression for the Total Current -- 3 Tunneling Current for Constant Voltage -- 4 Expressions of Iqpi44; Iqp44; IJ144; IJ2 -- 5 Tunneling Current in the B46;C46;S46; Approximation -- 6 The 34;cos w34; Problem -- CHAPTER 3 Magnitude and Temperature Dependence of the Critical Current -- 346;1 Josephson Current for V61;0 -- 346;2 B46;C46;S46; Approximation -- 346;3 Strong Coupling Effects -- 346;4 Effects of Paramagnetic Impurities -- 346;5 Measurement Techniques -- CHAPTER 4 34;Small34; Junctions in a Magnetic Field -- 446;1 Josephson Penetration Depth -- 446;2 Small Junctions -- 446;3 Uniform Tunneling Current Distribution -- 446;4 Nonuniform Tunneling Current Density -- CHAPTER 5 Large Junctions8212;Static Self45;Field Effects -- 546;1 Approximate Analysis -- 546;2 Analysis of Owen and Scalapino -- 546;3 Effects of the Junction Geometrical Configuration -- CHAPTER 6 Voltage Current Characteristics -- 646;1 V45;I Curves of Various Weak Links -- 646;2 Resistively Shunted Junction Model58; Autonomous Case -- 646;3 Current Biased Tunneling Junction -- 646;4 Effects of Thermal Fluctuations -- CHAPTER 7 Other Superconducting Weak Link Structures -- 746;1 Metal Barrier Junctions -- 746;2 Semiconducting Barrier Junctions -- 746;3 Bridge45;Type Junctions -- 746;4 Point Contact Weak Links -- CHAPTER 8 Device Fabrication Technology -- 846;1 Josephson Tunneling Junctions -- 846;2 Junction Electrodes -- 846;3 Oxide Barriers -- 846;4 Junction Patterning -- 846;5 Simple Procedures for Preparing Oxide Barrier Junctions -- 846;6 Semiconductor Barriers -- 846;7 Bridge45;Type Weak Links -- 846;8 Point Contact Structures -- CHAPTER 9 Resonant Modes In Tunneling Structures -- 946;1 Josephson Junction as a Transmission Line -- 946;2 Resonant Modes for Low Q Junctions -- 946;3 Junction of Infinite Length -- 946;4 Nonuniform Current Density Distribution -- CHAPTER 10 Fluxon Dynamics -- 1046;1 The Sine Gordon Equation -- 1046;2 Nonlinear Standing Waves on a Rectangular Junction -- 1046;3 Effects of Losses and Bias -- 1046;4 Zero Field Steps -- 1046;5 Perturbative Analysis of Fluxon Dynamics -- 1046;6 Effects of Flux Flow on D46;C46; Voltage45;Current Characteristics -- 1046;7 Two Dimensional Junctions -- CHAPTER 11 High Frequency Properties and Applications of the Josephson Effect -- 1146;1 Simple Voltage Source Model -- 1146;2 Tunneling Junctions in External Microwave Radiation -- 1146;3 Current Source Model -- 1146;4 Emission of Radiation -- 1146;5 Detection of Radiation -- 1146;6 Parametric Amplification -- 1146;7 The Determina.




Dynamics of Josephson Junctions and Circuits


Book Description

"This monograph is intended to give a relatively complete review of Josephson junction dynamics as it stands in the mid-1980's. The main idea of the author is to present the reader with as many useful results as possible by the simplest means, rather than to demonstrate theoretical muscle. This is why almost all the topics requiring elaborate techniques for their analysis are shifted to the ends of the chapters and the most complex chapters, to the end of the book. Topics which are of relatively minor importance for further discussion are mainly presented in the form of 'problems' at the end of the sections." -- from Preface.