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Events During the Week of January 11th through January 18th, 2015

Monday, January 12th, 2015

R. G. Herb Condensed Matter Seminar
Studies of Correlations in Low-Disorder 2D Electron Gases in MBE-Grown GaAs
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: John Watson, Purdue
Abstract: GaAs/AlGaAs heterostructures have served as one of the most ideal material systems for studies of electron interactions in mesoscopic physics for the past three decades. The high quality of the 2D electron gases that can be generated in these structures has enabled a wide range of research in topics such as the search for non-Abelian states of matter in the fractional quantum Hall regime and scaleable spin-based quantum computation. In this talk, I will present my work on advancing the state-of-the-art in GaAs materials and devices. In particular, I will discuss advances our group has made to reach low temperature electron mobilities as high as 32 x 106 cm2/Vs and the impact this has had on work in the quantum Hall regime and with spin qubits. In addition, I will discuss progress with density-tuneable devices intended to search for phase transitions in the fractional quantum Hall state at ν = 5/2. Finally, I will present initial results from our work to improve the charge stability of devices useful for spin-based qubits.
Host: Eriksson
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Astronomy Colloquium
From the Interstellar Medium to Prime Time, Making Astronomy News
Time: 12:00 pm - 1:00 pm
Place: 4421 Sterling Hall, Astronomy Colloquium Room (Sandwiches provided)
Speaker: Terry Devitt & Tom Ziemer, UW-Madison Research Communications & Letters and Science Office of Advancement
Abstract: Discussion by Terry Devitt:
As scholars, you know that an act of science is not complete until the research is communicated. For a scientist, this usually means publication in a peer reviewed journal or a presentation or a poster at a scientific meeting. But why stop there? While it is of obvious importance to share your research with your peers, there are other important constituencies that have a genuine interest and stake in your work. To reach those audiences requires packaging results and observations in ways that make them easily accessible to the uninitiated. It also requires communications channels and sometimes expertise to help present, package and disseminate interesting and important research findings. In this talk, we’ll present a template for transforming research findings into news, say a little bit about packaging, discuss what is news, and provide a menu of resources that you can use when you have findings that you think are worth sharing with the wider world.

Discussion by Tom Ziemer:
How can the College of Letters &amp; Science engage alumni and donors and gain their support? We can lay the groundwork by inspiring them through compelling storytelling that maintains — or reawakens — their connection with campus. We'll discuss the sort of stories that will catch the eye and hold the attention of your alumni, donors and friends.<br>
Host: Elijah Bernstein-Cooper
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Tuesday, January 13th, 2015

No events scheduled

Wednesday, January 14th, 2015

R. G. Herb Condensed Matter Seminar
The pumpistor: understanding the parametrically flux-pumped SQUID by its electrical impedance
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Kyle Sundqvist , Texas A&M
Abstract: Parametric amplifiers based on superconducting circuits have experienced recent popularity. 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 a result of a negative resistance of the pumpistor. In the degenerate case, the gain is sensitive to the relative phase between the pump and signal. In this case, a phase-sensitive impedance provides a classical analogy to quantum squeezing found in our experiments.
Conversely, in the nondegenerate case, gain is independent of phase. Here the pump frequency is not a multiple of the signal frequency, and it becomes necessary to consider idler tones. For the nondegenerate three-wave case, we present an intuitive picture for a parametric amplifier containing a flux-pumped SQUID where current at the signal frequency depends upon the load impedance at an idler frequency. This understanding has recently lead to the experimental realization of a SQUID parametric amplifier with strong environmental coupling, allowing for substantially increased bandwidth and dynamic range.
The use of equivalent impedances offers insights not always apparent from the Hamiltonian equations of motion. In particular, our "pumpistor" impedance models immediately provide readily testable predictions for many other circuits containing flux-pumped SQUIDs.
Host: Sue Coppersmith
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Thursday, January 15th, 2015

No events scheduled

Friday, January 16th, 2015

No events scheduled