Quantum Engineering of Superconducting Qubits
William D. Oliver
MIT Lincoln Laboratory & MIT Department of Physics
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, anharmonicity, and coherence, achieving T1 = 55 ms and T2 = 90 ms. We identify quasiparticles as a leading cause of temporal variability in the T1. We introduce and demonstrate a stochastic control technique that effectively pumps away these quasiparticles and thereby stabilizes and improves T1. We also discuss our demonstrations of 3D integration – bump bonding and through silicon vias – required for larger scale circuit realizations.
For more information:
 J. Bylander, et al., Nature Physics 7, 565 (2011)
 W.D. Oliver & P.B. Welander, MRS Bulletin 38, 816 (2013)
 F. Yan et al., Nature Communications 7, 12964 (2016)
 S. Gustavsson et al., Science 354, 1573 (2016)
 D. Rosenberg et al., in press, npj Quantum Information (2017); arXiv:1706.04116