Diverse Charge Tunneling in Hybrid Quantum Confined Systems
L. Han (TU Delft - QRD/Kouwenhoven Lab)
Leo Kouwenhoven – Promotor (TU Delft - QRD/Kouwenhoven Lab, TU Delft - QN/Kouwenhoven Lab)
S. Goswami – Copromotor (TU Delft - QRD/Goswami Lab)
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Abstract
This thesis focuses on the progress made toward constructing Majorana-based topological qubits using nanowire-based hybrid superconducting-semiconductor quantum dot systems. It specifically investigates the application of dispersive gate sensing in these systems, emphasizing the characterization of diverse charge tunneling events and the understanding of forthcoming parity readout signals for potential topological qubits in their simplified forms. Through a combination of chip design, fabrication, cryogenic measurements at base temperatures, data analysis, and theoretical simulations, our findings have emerged.
The main idea of this thesis is to separate the two interfering paths required for qubit readout and to understand each path individually. One path connects two quantum dots through a semiconductor reference arm, while the other connects them via a superconducting island. Key achievements include the implementation of dispersive gate sensing on normal dots within dot-island systems, revealing charge tunneling processes and demonstrating the efficacy of this technique for investigating subgap excitations. Our work extends to characterizing spin-orbit field orientations in InSb nanowire-based double quantum dots, emphasizing that dispersive gate sensing is an effective tool for situations where transport measurements are not feasible. Additionally, novel methods for measuring capacitance in micro- and nanoscale devices using RF resonators have been validated, showcasing sensitivity suitable for both room temperature and cryogenic applications. The latest developments return to the exploration of one of the core segments of topological qubits, focusing on charge tunneling processes in a hybrid dot-island-dot system, and highlighting the tunability between elastic cotunneling and cross-Andreev reflection.
The findings presented in this thesis not only contribute to the understanding of hybrid quantum systems but also pave the way for future research in topological quantum computing, emphasizing the potential of dispersive gate sensing in advancing the field.