Thesis Defense

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Thesis Defense
Characterization of noise sources in semiconductor qubit devices
Date: Wednesday, June 14th
Time: 9:00 am - 11:00 am
Speaker: Yujun Choi, Department of Physics Graduate Student
Abstract: Quantum computing has garnered substantial attention in recent decades for its potential applications across various domains such as cybersecurity, chemical engineering, logistics optimization, data search, drug synthesis, and machine learning. However, practical utilization of quantum computing faces significant challenges due to considerable overhead. Even with the aid of state-of-the-art quantum error correction codes, millions of physical quantum bits (qubits) are required. This necessity arises from limitations in gate fidelities of qubits resulting from environmental noise. Therefore, it is imperative to investigate noise source characteristics and devise strategies to mitigate their impact on qubits.

Semiconductor qubits offer a promising platform that can be readily expanded by leveraging existing semiconductor industry facilities. In semiconductor devices, an array of detrimental noise sources, such as charge noise, hyperfine noise, evanescent-wave Johnson noise, and phonon-induced noise, can degrade coherence of the qubits. This dissertation specifically focuses on charge noise (1/f noise).

The dissertation commences by introducing a methodology to characterize diverse noise sources through the measurement of coherence times while rotating a vector magnet in a spin qubit device. Subsequently, it presents the application of a technique called noise source driving to enhance coherence of qubits. This approach involves applying an oscillating electric field to the charge noise sources. Following this, the dissertation elucidates a plausible mechanism explaining the pulse-induced resonance frequency shift of a qubit with fluctuations of two-level systems. Lastly, the dissertation discusses future research directions and concludes with closing remarks
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