[Colloquium] Reza Jokar Candidacy Exam/Sep 20, 2021

[meganwoodward at uchicago.edu]

This is an announcement of Reza Jokar's Candidacy Exam.
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Candidate: Reza Jokar

Date: Monday, September 20, 2021

Time: 11 am CST

Remote Location: https://uchicago.zoom.us/j/93339877469?pwd=T3h2NnhxdXY4T3NaMStFTE5qWmpBdz09   Meeting ID: 933 3987 7469   Passcode: 463213

Title: In-fridge classical controllers in quantum computing

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 sever 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.

In this thesis, we propose cryogenic controllers 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 “Simple Quantum 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 used 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 implementations of two-qubit gates using SFQ pulses inside the dilution refrigerator 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.

Advisors: Fred Chong

Committee Members: Fred Chong, Hank Hoffmann, and Massoud Pedram