Quantum Engineering of Superconducting Qubits
William Oliver, Massachusetts Institute of Technology
Superconducting qubits are coherent artificial atoms assembled from electrical circuit elements and microwave optical components. Their lithographic scalability, compatibility with microwave control, and operability at nanosecond time scales all converge to make the superconducting qubit a highly attractive candidate for the constituent logical elements of a quantum information processor.
In this talk, we revisit the design, fabrication, and control of the superconducting flux qubit. By adding a high-Q capacitor, we dramatically improve its reproducibility, coherence, and anharmonicity. We discuss in a detail the noise spectroscopy and coherence characterization of a device with T1 = 55 ms and T2 = 90 ms. We identify quasiparticles as causing temporal variability in the T1. We introduce and demonstrate a stochastic control technique that effectively pumps these quasiparticles away and thereby stabilizes and improves T1.