Engineering noise resilient superconducting qubits
Fabrication and control of fluxonium and cos (2phi) systems
S. Singh (TU Delft - QRD/Andersen Lab)
L. di Carlo – Promotor (TU Delft - Applied Sciences, TU Delft - QCD/DiCarlo Lab)
C.K. Andersen – Copromotor (TU Delft - Applied Sciences, TU Delft - QRD/Andersen Lab)
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Abstract
Quantum computing has seen remarkable progress over the past decade, with superconducting qubits emerging as one of the leading hardware platforms for its physical realisation. Among the various superconducting qubit architectures, the transmon has been one of the most widely adopted candidates, owing to its relatively simple design and compatibility. However, the transmon suffers from key limitations, most notably its weak anharmonicity and multi-qubit gates using transmon being difficult to execute faster without errors.
In this context, alternative qubit architectures have attracted interest. The fluxonium qubit, with its large anharmonicity and long coherence times, has emerged as a promising candidate for overcoming shortcomings of the transmon. Similarly, the cos(2φ) qubit offers an intriguing design with inherent noise protection, making it a compelling subject of investigation for next-generation superconducting hardware.
Beyond the question of which qubit to build, a central challenge in quantum computing is the realisation of high-fidelity two-qubit gates. Higher gate fidelity directly translates to better quantum operations and is essential for the implementation of error correction protocols. Equally important is the question of how to perform these gates in a fast and practical manner—ideally using simple pulse techniques that minimise the time and effort required for calibration.
This thesis addresses these themes across two broad directions. First, we explore the fabrication of fluxonium and cos(2φ) qubits, developing improved processes and cleanroom techniques to achieve more reliable and reproducible devices. Second, we investigate two-qubit gate operations using analytic pulse techniques, with the goal of realising faster and simpler gates that reduce the overhead associated with pulse calibration. Together, these contributions advance the development of superconducting qubit platforms towards more practical and scalable quantum computing.