Microwave probing of topological insulator-based Josephson quantum circuits
File(s)
Author(s)
Liu, Chenlu
Type
Thesis or dissertation
Abstract
Majorana zero modes (MZMs) are exotic quasiparticles predicted to emerge in specific condensed matter systems, such as superconductor-topological insulator hybrids. Their anticipated non-Abelian exchange statistics could lead to robust quantum computing, mitigating issues of environmental noise that challenge existing quantum platforms like superconducting qubits. However, definitive evidence of MZMs remains elusive. This thesis explores the integration of three-dimensional topological insulators (3DTIs) with superconducting qubits within circuit quantum electrodynamics (cQED) to leverage 3DTI properties for MZM detection. Through the fabrication, characterization, and analysis of fixed-frequency and flux-tunable TImon devices, this work establishes a foundation for future experimental advancements in MZM detection using transmon qubits.
Chapter 4 confirms the compatibility of topological insulator Josephson junctions (TI JJs) with cQED systems, demonstrating effective control and coherence in a fixed-frequency TI-based transmon (TImon) device. The primarily diffusive nature of TI JJs was inferred from qubit anharmonicity and flux-tuning patterns observed in a separate flux-tunable TImon, indicating minimal ballistic contributions.
Chapter 5 tests the feasibility of using the TImon platform for MZM detection by subjecting the fixed-frequency TImon in Chapter 4 to an in-plane magnetic field of 900 mT. Although the device demonstrated field compatibility, definitive MZM signatures were not observed. Neither were exotic magnetic effects of 3DTI likely due to interference effects in the diffusive TI JJs.
Chapter 6 addresses the challenges posed by the diffusive nature of TI JJs through microwave spectroscopy and DC transport measurements. These experiments further confirmed the diffusive behavior and identified design limitations, providing guidance for future device modifications. The next steps include redesigning the qubit frequency to 15-20 GHz range for compatibility with higher temperatures around 1.6 K.
Chapter 4 confirms the compatibility of topological insulator Josephson junctions (TI JJs) with cQED systems, demonstrating effective control and coherence in a fixed-frequency TI-based transmon (TImon) device. The primarily diffusive nature of TI JJs was inferred from qubit anharmonicity and flux-tuning patterns observed in a separate flux-tunable TImon, indicating minimal ballistic contributions.
Chapter 5 tests the feasibility of using the TImon platform for MZM detection by subjecting the fixed-frequency TImon in Chapter 4 to an in-plane magnetic field of 900 mT. Although the device demonstrated field compatibility, definitive MZM signatures were not observed. Neither were exotic magnetic effects of 3DTI likely due to interference effects in the diffusive TI JJs.
Chapter 6 addresses the challenges posed by the diffusive nature of TI JJs through microwave spectroscopy and DC transport measurements. These experiments further confirmed the diffusive behavior and identified design limitations, providing guidance for future device modifications. The next steps include redesigning the qubit frequency to 15-20 GHz range for compatibility with higher temperatures around 1.6 K.
Version
Open Access
Date Issued
2024-06
Date Awarded
2024-09
Copyright Statement
Creative Commons Attribution NonCommercial Licence
Advisor
Connolly, Malcolm
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)