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This Week at Physics

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Events on Thursday, November 7th, 2019

R. G. Herb Condensed Matter Seminar
Atom-based Silicon Devices for Quantum Technologies
Time: 11:00 am
Place: 5310 Chamberlin Hall
Speaker: Dr. Rick Silver, NIST
Abstract: NIST is using atomically precise fabrication to develop electronic devices for use in quantum information processing, quantum materials research and quantum sensing. We are using hydrogen-based scanning probe lithography to enable deterministic placement of individual dopant atoms with atomically aligned contacts and gates to fabricate single electron transistors, single atom transistors, few-donor/quantum dot devices for spin manipulation, and arrayed few-donor devices for quantum materials and analog quantum simulation research. We have developed robust lithography, device relocation, and contact processes that enable routine electrical measurement of atomically precise devices with an emphasis on atom-scale control of the device geometry. In addition to our fabrication technology, I will discuss the characterization of atomic-scale tunnel junctions and single electron transistors that demonstrate stable coulomb blockade oscillations with charge offset drift of 0.007e per day. I will present measurements of tunnel coupling in single electron transistors and donor-dot devices where the tunnel gap is controlled at the atomic scale as well as measurements and modeling of single and few atom transistors that display large electron addition energies, consistent with single or few dopant atom charging energies. We have recently extended our STM-patterning to fabricate coupled arrays of few atom clusters having multiple donors per dot, including a functional 3Ă—3 quantum dot array device. Using the Si(100)2x1 surface reconstruction as an atomic ruler, we design the separation between nearest neighbor dots to be in the regime from weakly coupled to strongly coupled. We are analyzing the tunnel couplings and energy spectra in individual dots versus across an array of coupled dots to explore the rich physics of dot-arrays. Bio: Richard Silver is a physicist leading the atom-based silicon quantum electronics effort at NIST. His research focusses on fabrication, design, and measurement of atom-based Si structures that rely on single or few atoms, precisely placed within an epitaxial silicon environment for solid state quantum computing and analog quantum simulation. He received his bachelors in physics from the University of California at Berkeley and his PhD in physics from University of Texas at Austin. He is an adjunct professor with the physics department at the University of Maryland, College Park.
Host: Eriksson
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Cosmology Journal Club
Time: 12:00 pm
Place: 5242 Chamberlin Hall
Abstract: Please visit the following link for more details:
http://cmb.physics.wisc.edu/journal/index.html
Feel free to bring your lunch!
If you have questions or comments about this journal club, would like to propose a topic or volunteer to introduce a paper, please email Ross Cawthon (cawthon@wisc.edu) and Santanu Das (sdas33@wisc.edu).
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Astronomy Colloquium
"Star Formation and Nuclear Activity: Dwarf Galaxies to Ultraluminous Infrared Galaxies"
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee and cookies 3:30 PM, Talk begins 3:45 PM
Speaker: George Privon, University of Florida
Abstract: The stellar mass of star forming galaxies is thought to increase in a quasi-steady state, where the rate depends on the gas fraction and star formation efficiency, which evolve with redshift. Galaxy mergers can lead to more rapid growth while active galactic nuclei have been argued to play an important role in halting star formation. These processes are tied together through the multi-phase interstellar medium. I will discuss programs exploring so-called "dense gas" tracers and the behavior of starbursts in merging dwarf galaxies. I will also describe a theoretical/modeling program to use galaxy formation simulations as "ground truth" for interpreting observational tracers of the ISM. This use of multiwavelength tracers and hydrodynamic simulations probes galaxy evolution along axes of nuclear activity, redshift, gas fraction, and metallicity. From these studies I will show new results on identification of heavily obscured AGN and intriguing differences in how mergers affect the evolution of high gas fraction galaxies.
Host: Professor Emeritus Jay Gallagher
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