Transmon-based Quantum Processing Units: Design, Control and Implementations

This thesis investigates the engineering challenges in designing superconducting quantum processing units (QPUs) and Josephson parametric amplifiers (JPAs). It also addresses the application of quantum optimal control (QOC) techniques to improve qubit manipulation and performance. The author’s academic journey began in electrical engineering, but has evolved into quantum engineering, where the complexity of quantum mechanics meets the practical demands of engineering. This blend of disciplines underscores the purpose of this research: to bridge the gap between the theoretical foundations of quantum physics and the tangible, hands-on needs of engineering, particularly for those specializing in radio frequency (RF) systems. This work aspires to equip engineers with insights and tools that enable meaningful contributions to quantum computing research. Superconducting qubits have emerged as one of the most promising platforms for scalable QPU design due to their stability, coherence properties and relative ease of manufacturing. However, practical application requires significant engineering to address issues like decoherence, which limits qubit performance and longevity. The author’s research in qubit design focuses on tackling these challenges to develop QPUs that are both reliable and scalable, incorporating practical examples and engineering solutions. A key component in operating quantum processing units is the Josephson parametric amplifier (JPA). JPAs are essential for amplifying weak electromagnetic signals with minimal noise addition, which is necessary for accurate qubit readout. Operating at cryogenic temperatures to exploit quantum effects, JPAs play a pivotal role in maintaining signal integrity during the readout process. The author’s focus in JPA design has been on refining these amplifiers to achieve high gain and low noise, with a practical design example included. Quantum optimal control forms another cornerstone of this thesis. Optimal control techniques are critical for maximizing the efficiency and precision of quantum operations, which is essential for developing reliable quantum circuits. The author’s research in this area adapts optimal control algorithms to the quantum realm, aiming to improve gate fidelity and operational speed even under noise conditions. Through this work, they demonstrated that optimized control pulses can enhance the robustness of qubit operations, establishing a foundation for more precise and scalable quantum computation. Structured to guide readers from the fundamentals of quantum theory to the applied challenges of quantum hardware design and operation, this thesis highlights the role of interdisciplinary engineering in quantum computing. The findings here, including published work on superconducting qubit hardware design, aim to inspire further collaboration between physics and engineering, encouraging RF engineers to explore the possibilities of their expertise within this transformative field. Ultimately, this work underscores the vast potential for innovation and progress at the intersection of quantum mechanics and engineering, inviting future research to build upon its findings for practical quantum technologies.