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<div class="PlainText">This is an announcement of Reza Jokar's Dissertation Defense.<br>
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Candidate: Reza Jokar<br>
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Date: Thursday, February 17, 2022<br>
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Time: 11 am CST<br>
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Remote Location: <a href="https://uchicago.zoom.us/j/98201401525?pwd=Uk81eWJzNXlHdlhEOWZ6KzlZYlVXdz09">
https://uchicago.zoom.us/j/98201401525?pwd=Uk81eWJzNXlHdlhEOWZ6KzlZYlVXdz09</a> Meeting ID: 982 0140 1525 Passcode: 327563<br>
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Title: In-fridge classical controllers in quantum computing<br>
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Abstract: Today's superconducting quantum computer prototypes rely on a classical controller at room temperature that controls the qubits inside the dilution refrigerator. This approach is simple and straightforward, however, it introduces significant scalability
challenges: (1) quantum error mitigation techniques that are based on room temperature error decoding face exponential latency overhead due to the data backlog caused by the slow decoding process; (2) scalability is limited due to massive costs of generating
and routing the microwave control signals.<br>
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In this thesis, novel cryogenic controllers are proposed to address the aforementioned challenges. First, we develop an in-fridge classical accelerator for error decoding using ultra-fast superconducting Single Flux Quantum (SFQ) logic technology to avoid the
exponential latency overhead. By enabling practical implementation of quantum error mitigation, we expand the compute volume of near-term machines by factors between 3,402 and 11,163. Second, we develop an in-fridge classical controller using SFQ logic to
generate and route the control signals inside the dilution refrigerator. We use state-of-the-art SFQ synthesis tools to calculate the power and area of our in-fridge controller, and show that it can operate within the tight power and area budget of dilution
refrigerators at >42,000-qubit scales. Finally, we investigate the practical implications of SFQ-based two-qubit gates and show that they can achieve similar gate fidelity and gate time to that of microwave-based gates. The results of this thesis show that
cryogenic controllers play a key role in increasing the scalability and computing power of near-term quantum machines.<br>
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Advisors: Fred Chong<br>
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Committee Members: Hank Hoffmann, Fred Chong, and Massoud Pedram<br>
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