Masters Defense: Lillian Austin

Characterization and scalable readout and control of superconducting qubits devices

This thesis presents data from the characterization of superconducting qubits, as well as development of a scalable experimental setup to extend measurement and readout capacity. The qubits measured exhibited high readout fidelity, limited by thermal excitations as well as qubit lifetimes of T1  ~ 10-30μs. The performance of single- qubit gates using randomized benchmarking (RB) was also found to approach the limit imposed by T1 (for gate duration 50 ns), with a single physical gate error rate of 0.14%. Single shot readout and qubit state thresholding was implemented in data processing for both Rabi and RB measurements. A currently developing method of data analysis based on Bayesian inference was employed to find the Rabi frequency, and compared to a more conventional analysis method using least squares fitting. Finally, new hardware developed and engineered both in-house at the University of Copenhagen and at partner universities was tested, with the aim of experimental implementation to improve scalability of experimental setups. A setup is presented for single shot readout of 4-qubit devices, with the potential to scale up to 22- qubit devices. Proof-of-concept measurements are presented demonstrating that the setup produces reasonable results for qubit measurements, and areas for further development are discussed.