Abstract: Superconducting qubits are one of the leading quantum computing platforms in part due to the nonlinearity of the Josephson junction. High quantum efficiency broadband amplification is a key requirement for high fidelity qubit readout and thus implementing quantum error correction. We illustrate the modeling and design of high quantum efficiency broadband parametric amplifiers using our open source package JosephsonCircuits. These amplifiers are engineered to match the Floquet modes in the amplifier to the eigenmodes of the environment, eliminating a previously ubiquitous noise mechanism in broadband amplifiers. We present the fabrication of such amplifiers using a high-Q qubit fabrication process with state of the art junction critical current uniformity. We detail the characterization of these amplifiers including the highest reported quantum efficiency for a traveling wave parametric amplifier and future directions of on-chip integration and isolation. Finally, we show how qubits with quartic rather than the familiar weakly anharmonic potential enable the first demonstration of near-ultrastrong nonlinear coupling with applications in fast qubit readout and gates.
Bio: Kevin O'Brien is an Associate Professor in the Department of Electrical Engineering and Computer Science at the Massachusetts Institute of Technology where he leads the Quantum Coherent Electronics group (QCE). He obtained his Ph.D. in Physics in 2016 from the University of California at Berkeley on nonlinear light matter interactions in metamaterials. He completed postdoctoral work at UC Berkeley developing high-coherence superconducting quantum processors. He joined MIT EECS and the Research Laboratory of Electronics in 2018. His research focuses on engineering nonlinear and quantum-mechanical light-matter interactions to advance superconducting quantum computing and sensing. Kevin has taught Electromagnetics at the undergraduate and graduate levels at MIT for 6 years and with colleagues developed a set of take-home microwave engineering labs based on NanoVNAs where students build transmission lines, impedance matching circuits, antennas, and other electromagnetic systems.
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