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UBC Theses and Dissertations

Instrumentation and fabrication techniques for semiconductor-based quantum technologies Aghaee Rad, Hanieh


Large-scale quantum computers have the potential to perform calculations that are otherwise impossible, a capability that could power exciting advances in fields such as materials design and optimization. Building large-scale quantum computers with spin qubits is appealing because they have long coherence times and can be fabricated on silicon chips using an industrial process amenable to scaling. State-of-the-art spin qubit systems are still small, having only just reached the 2-qubit and 4-qubit scale, and their performance and scalability are not optimized yet. Connecting large numbers of spin qubits on chips remains a challenge. In this thesis we demonstrate a simplified fabrication process using a single layer of gates to realize hole spin qubits, anticipated to be easier to scale up than conventional approaches, based on quantum dots formed in a germanium quantum wells on silicon substrates. We also devised a novel approach to reduce contact resistance to the quantum well. Using this process we successfully built quantum dots, as evidenced by Coulomb blockade spectroscopy. Future work will demonstrate quantum bits using this process. Optimization of qubits based on quantum devices requires cooling them down below 4 Kelvin and connecting them to microwave control and measurement circuits. Designing a high frequency control and measurement apparatus is challenging since it requires suppression of stray resonances and crosstalk in the setup. Typically each research group designs its own apparatus, or purchases an expensive apparatus that is not possible to customize. In this thesis, we design and test an apparatus for controlling and measuring few-qubit devices using low-frequency and microwave electrical signals, that can be used to optimize qubit devices. Our setup has -40 dB cross-talk with no resonances up to 7 GHz, and has the advantage of being small in size (< 44 mm diameter) so it fits within the bore of a small electromagnet or cryostat. We share our apparatus and design freely with the research community, enabling new groups to more quickly build and customize an apparatus to test their chips. These results will help the quantum computing research community to fabricate and test advanced quantum computing devices faster.

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Attribution-NoDerivatives 4.0 International