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This Week at Physics

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Events During the Week of November 11th through November 17th, 2012

Monday, November 12th, 2012

Plasma Physics (Physics/ECE/NE 922) Seminar
RMP-Flutter-Induced Plasma Transport in DIII-D
Time: 12:00 pm
Place: 1310 Sterling Hall
Speaker: James Callen, University of Wisconsin-Madison
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Condensed Matter Theory Group Seminar
Quantum Optics with Quantum Dots and Microwave Resonators: Photon and Electron Statistics
Time: 4:30 pm
Place: 5310 Chamberlin
Speaker: Maxim Vavilov
Abstract: I will discuss electron transport through a double quantum dot system coupled to a microwave resonator. First, I analyze the photovoltaic current produced at zero bias across the dots in the presence of microwave drive of the resonator. The conversion of photons to electronic excitations produces an electric current. I show that certain features of this current are due to quantum nature of the electromagnetic field in the resonator. In particular, the photovoltaic current exhibits a double peak dependence on the frequency of an external microwave source.

The distance between the peaks is determined by the strength of interaction between a single photon in the resonator and electrons in the double quantum dot. This double peak feature disappears as strengths of energy and phase relaxation processes increases, recovering a simple classical condition for maximal current when the energy splitting between electronic states in the double quantum dot is equal to the photon energy. Then I discuss properties of electric current and photon field at finite bias across the DQD system and at zero microwave drive. I show that the low frequency current noise is affected by the coupling to photons and that the generated microwave field of the resonator may exhibit either photon bunching or antibunching.
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Tuesday, November 13th, 2012

Chaos & Complex Systems Seminar
Role of biofuels in meeting our future energy demands
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Natalie Hunt, UW Department of Forest Ecology and Management
Abstract: The Renewable Fuels Standards (RFS) set out in the 2007 Energy Independence and Security Act call for an increase in the use of renewable transportation fuels to 36 billion gallons per year by the year 2022. In order to meet these standards, there will be increased demand for cellulosic feedstocks such as agricultural residues and dedicated bioenergy crops. This could result in increased production intensity on existing cropland or expansion of production into environmentally sensitive lands, which will impact soil carbon and nutrient content of agricultural soils. Some of the major questions surrounding biofuels feedstock production include what the long-term impacts of these changed production practices on soil fertility will be and whether or not farmers are willing to manage their land for bioenergy feedstocks. There is much uncertainty around the complex interactions among biophysical crop characteristics, agronomic practices, and the socioeconomic factors of the farmers who will manage the bioenergy feedstocks. The research of these system intersections will determine the role of biofuels in meeting our future energy demands.
Host: Sprott
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Theory Seminar (High Energy/Cosmology)
Cosmological Perturbations: Isocurvature, Vorticity and Magnetic Fields
Time: 4:00 pm
Place: 5280 Chamberlin
Speaker: Adam Christopherson, University of Nottingham
Abstract: In this talk I will discuss some recent, complementary work that I have undertaken using cosmological perturbation theory, a powerful technique for modeling inhomogeneities in the universe. After a brief review of the basics, I introduce isocurvature, or non-adiabatic pressure perturbations, and calculate their spectrum in the settings of standard, concordance cosmology, and inflationary models involving two scalar fields. I then extend the discussion beyond linear perturbations, and show that vorticity can be sourced at second order with only scalar perturbations, the source term being quadratic in the gradients of first order energy density and non-adiabatic pressure perturbations. I present a first estimate of this vorticity's power spectrum, and highlight some potential observational consequences. One of these is the possible sourcing of sizeable magnetic fields, and I briefly sketch some current work on including magnetic fields in perturbation theory in a consistent way. I close with some ideas for future work.
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Wednesday, November 14th, 2012

Department Meeting
Time: 12:15 pm
Place: 5310 Chamberlin Hall
TOPICS
* Update and Announcements by Chair
* Matters Arising

CLOSED MEETING
*Closed meeting to discuss personnel matters pursuant to Section 19.85(1)(c). Closed to all but Associate Professors and Full Professors.
* Possible Promotion of Assistant --Second Discussion

ANNOUNCEMENTS
* Congratulations to Duncan L. Carlsmith and Larry Watson for being named 2012 UW Teaching Academy Fellows.
* The dates for the prospective grad visits for 2013 have been set. They will be March 1-3 and March 15-17, 2013. If possible, please reserve these dates now as these are important events in the recruiting process and faculty participation is critical.
* Department Meeting dates are scheduled for November 28th, and December 12th.

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Thursday, November 15th, 2012

R. G. Herb Condensed Matter Seminar
On-chip cavity quantum phonodynamics
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Charles Tahan, Laboratory for Physical Science
Abstract: The progression of technology relies in part on the identification and control of components, such as confined electrons or photons, from which systems of greater complexity are built. Once a curiosity, it now looks like nanomechanical systems can also have good, robust properties for classical and quantum devices. I will discuss our recent work on controlling phonons at the quantum level. We have introduced a way to engineer a sound-based analogue of cavity-QED allowing for composite quantum objects called phonitons to be formed [1]. We show how this system can be used to probe phonon-qubit (sound-matter) interactions and properties, form complex many-body systems, and be practically realized. Recently, we have shown [2] how an on-chip version of this system can be constructed allowing integration with other phononic components such as photon-phonon translators.

[1] Phys. Rev. Lett. 107, 235502 (2011)
[2] http://arxiv.org/abs/1208.1776

Charles Tahan received B.S. degrees in physics and computer science with highest honors from the College of William and Mary in 2000 and a Ph.D. in condensed matter theory from the University of Wisconsin-Madison in 2005, where his work focused on silicon quantum computing. From 2005-2007 he was a National Science Foundation Distinguished International Postdoctoral Research Fellow at the Cavendish Laboratory of the University of Cambridge, UK, with visiting research positions at the University of Melbourne, Australia, and the University of Tokyo, Japan. During this time he co-invented the field of "solid light" with a proposal for strongly-correlated polariton systems. From 2007-2009 he was a technical consultant in the Defense Advanced Research Projects Agency's (DARPA) Microsystems Technology Office (MTO), helping to create the Quantum Entanglement Science and Technology (QuEST) program among others. Presently, he is a program manager in the quantum computing group at the Laboratory for Physical Sciences where he also has a research group in quantum information and device theory. His current research interests focus on solid-state quantum computing, nano/optomechanics, fundamental open problems in quantum information processing, and solid-state devices that exhibit enhanced functionality due to their quantum behavior.
Host: Friesen
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Neutrino Oscillations: Present Status and Future Plans
Time: 2:30 pm
Place: 4274 Chamberlin
Speaker: Jenny Thomas, University College London
Abstract: I will give an overview of the status of the field focussing on the implication of the new results from the summer conferences for the future direction. I will then talk about some of the more exciting and innovative options for the future, specifically with FNAL's NuMI beam.
Host: Albrecht Karle
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Graduate Introductory Seminar
Plasma Physics
Time: 5:45 pm
Place: 2223 Chamberlin Hall
Speaker: Boldyrev, Forest, Sarff, Schnack, Terry, Zweibel, UW Madison
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Friday, November 16th, 2012

Cosmology Journal Club
An Informal discussion about a broad variety of arXiv papers related to Cosmology
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
Please 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 Le Zhang (lzhang263@wisc.edu)
Host: Peter Timbie
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Physics Department Colloquium
Physics at the edge: Plasmas with dynamic sheaths
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Uwe Czarnetzki, Ruhr University Bochum
Abstract: Plasmas generated by applying a radio-frequency potential across a gas at low pressure between two electrodes are called capacitively coupled plasmas (CCP). They find frequent application in semiconductor and solar-cell production and other fields of industry. The physics of CCPs is dominated by the non-linear dynamics of the space-charge sheaths in front of the electrodes. This dynamics determines the ion as well as the electron energy distribution function, provides the main stochastic electron heating mechanism, and is also essential for trapping of energetic electrons. If a certain asymmetry between the sheaths at the two electrodes exists, the non-linearity leads to self-generated high frequency current oscillations which can strongly enhance the electron heating. Usually the asymmetry results from the geometrical size of the electrodes. However, by applying non-sinusoidal waveforms the symmetry can be broken even in the case of geometrical symmetry. This so called aEurooeelectrical asymmetry effectaEuro provides a simple and elegant way of external control where in particular the ion energy can be adjusted. The underlying physics will be explained by experimental results, analytical models, and particle-in-cell/Monte-Carlo simulations.
Host: Lin
Poster: http://www.physics.wisc.edu/twap/posters/2012/2742.pdf
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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2012/2012-11-12.pdf

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