De Kruijf, Antonius Franciscus Mattheus (Mathieu); (2025) Global control and thermal management for silicon spin qubits. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Electron-spin qubits hosted in silicon are a promising platform for quantum computing, since in recent years operation and readout fidelities have exceeded the fault tolerant threshold. Now the manufacturing techniques used to fabricate these devices have to be scaled up. To enable scaling the number of qubits beyond 1000, the quantum processor needs to be integrated with local control electronics. However, the heat dissipated by operation of these electronic control circuits can negatively affect qubit performance. In this work, I develop a primary temperature sensor based on a quantum dot, to monitor the qubit temperature under varying conditions. Real-time monitoring of the local temperature can be used to study the impact of on-chip dissipated heat on the qubit. These sensors are used to define a power budget for integrated electronics. Furthermore, a simple thermal model is developed to predict thermal transport in a quantum chip. This methodology is universal and can be applied to any qubit platform with a local temperature sensor. Finally, I compare the performance of this quantum dot thermometer against other cryogenic thermometers and find this primary thermometer is more sensitive than other common thermometry techniques. To reduce the number of control lines required to control individual qubits, I investigate the use of a 3D microwave resonator to deliver a global oscillating magnetic field to control electron spin qubits. When using the resonator to rotate electron spins, no spin flips are detected. This is attributed to a significant decrease in resonator quality factor which originates from materials with a different thermal contraction. This leads to a misalignment of the two sapphire ring oscillators making up the resonator. Despite this, I’ve used these experiments to characterize various types of charge sensors, and I have identified the RF-SET and RF-SEB as the best sensors for near term applications.

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