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CESG Seminar: Microwave superconducting circuits: understanding the parametrically flux-pumped SQUID by its electrical impedance

April 24, 2015 @ 3:55 pm - 5:00 pm

Room 1037 ETB

Kyle Sundqvist/Visiting Assistant Professor ECEN/TAMU

Abstract: Superconducting circuits exhibit quantum mechanical properties on the macroscopic level, allowing their use in quantum optics experiments and quantum information applications. Furthermore, parametric amplifiers based on superconducting devices have experienced recent popularity in this field. It is possible to produce superconducting circuits which may sustain and amplify coherent states of microwaves close to the quantum limit. To this end, we describe a circuit understanding of the flux-pumped Superconducting QUantum Interference Device (SQUID). An unpumped SQUID acts as an inductance (the Josephson inductance), whereas a flux-pumped SQUID develops an additional, parallel element which we have coined the “pumpistor.” Parametric gain can be understood as the result of a negative resistance present in this equivalent circuit. We will present how this understanding explains observed phenomena such as quantum squeezing, and immediately provides readily testable predictions for many other circuits containing flux-pumped SQUIDs. Such insights are not always apparent from the Hamiltonian equations of motion.

Bio: Kyle Sundqvist is a Visiting Assistant Professor in the department of Electrical and Computer Engineering at Texas A&M University. He received B.S. degrees in Physics and Astronomy from the University of Washington, Seattle. He received his M.A. and Ph.D. in Physics at the University of California, Berkeley, studying electron and hole transport in ultrapure, sub-Kelvin germanium for improved detectors in the search for particle dark matter. In 2011, he became a postdoctoral researcher at the Chalmers University of Technology in Gothenberg, Sweden. At Chalmers, he researched superconducting devices with application to quantum information. His research focuses on RF-photonic devices using superconducting circuits, including the development of quantum-limited parametric amplifiers for the readout of qubits and the exploration of other condensed matter systems.


April 24, 2015
3:55 pm - 5:00 pm