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This Week at Physics

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Events During the Week of February 20th through February 27th, 2011

Sunday, February 20th, 2011

Wonders of Physics
annual show
Time: 1:00 pm
Place: 2103 Chamberlin
Speaker: Clint Sprott
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Wonders of Physics
Annual show
Time: 4:00 pm
Place: 2103 Chamberlin
Speaker: Clint Sprott
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Monday, February 21st, 2011

Plasma Physics (Physics/ECE/NE 922) Seminar
"Current Layer Disruptions and Associated Turbulence in the Magnetic Reconnection Experiment (MRX)"
Time: 12:05 pm
Place: 2241 Chamberlin Hall
Speaker: Seth Dorfman, Princeton Plasma Physics Laboratory
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Condensed Matter Theory Group Seminar
Origin of 1/f magnetic noise in superconducting circuits
Time: 4:30 pm
Place: 5310 Chamberlin
Speaker: Kostyantyn Kechedzhi, Rutgers University
Abstract: We analyze recent experimental data on the complex inductance of dc SQUIDs that show 1/f inductance noise that is highly correlated with conventional 1/f flux noise. We argue that there are two mechanisms likely to give rise to the observed inductance noise: fluctuations in the kinetic inductance of superconducting wires caused by the dynamics of scattering centers; and the dynamics of unpaired spins of electrons localized on or close to the surface of the superconducting wires. We analyze both possibilities in detail and conclude that the latter is likely to be dominating in the experiments. Moreover, we argue that the experimental data imply a formation of long range order in fractal spin structures on the surface of the superconducting wiring. We show that such structures appear naturally in a random system of spins with wide distribution of spin-spin interactions. We perform numerical simulations on the simplest model of this type and show that it exhibits 1 / f1 + ζ magnetization noise with small exponent ζ and reproduces the correlated behavior observed experimentally.
Host: Maxim Vavilov
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Tuesday, February 22nd, 2011

Chaos & Complex Systems Seminar
Chaos in the Three-Body Coulomb Problem
Time: 12:00 pm
Place: 4274 Chamberlin Hall
Speaker: Vladimir Zhdankin, UW-Madison Dept. of Physics
Abstract: The three-body problem is one of the most famous examples of a chaotic system. In the traditional case, the goal is to determine the motion of three massive bodies interacting through Newton's law of universal gravitation. Similarly, the goal in the three-body Coulomb problem is to determine the motion of three electrically charged particles interacting through Coulomb's law. Among other things, this can be used as a classical model of the helium atom (where the effects of quantum mechanics are neglected). This talk will describe and present some numerical solutions to the three-body Coulomb problem. The general solution has a short transient chaotic phase until one particle is ejected from the system, but special initial conditions are found to give chaotic orbits that remain bounded.
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High Energy Seminar
Searching for the Identity of Dark Matter
Time: 3:00 pm
Place: 4274 Chamberlin
Speaker: Lauren Hsu, Fermilab
Abstract: Astrophysical observations have confirmed that ordinary matter<br> makes up only ~15% of the observable matter in the universe. The composition of the remaining non-luminous (dark) matter is<br> unknown. This is a time of great excitement. Efforts on<br> various fronts are racing to elucidate the particle nature of<br> dark matter. With a collection of germanium and silicon<br> crystals cooled to ~50 mK, the Cryogenic Dark Matter Search is<br> looking for the possible rare collision of a prime dark matter<br> candidate, the weakly interacting massive particle (WIMP), with<br> ordinary matter. I will report on recent results from CDMS<br> and discuss the status of the future experimental phases. These include the 10-kg phase of SuperCDMS, which is beginning<br> now, the 100-kg stage at SNOLAB, which has a projected start<br> date of 2013, and looking forward into the future, the 1-ton<br> GEODM.<br>
Host: Karsten Heeger
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Wednesday, February 23rd, 2011

No events scheduled

Thursday, February 24th, 2011

R. G. Herb Condensed Matter Seminar
Hybrid Quantum Information Processing with Circuit QED
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: David Schuster, University of Chicago
Abstract: Quantum computing represents an enormous challenge with the competing requirements of fast manipulation, long storage, and long distance transport of fragile quantum states. Individually these goals have been realized with nanosecond manipulations (quantum circuits), coherence times measured in seconds (atomic ions/nuclear spins), and entanglement transported over kilometers (linear optics). Yet thus far no system has achieved all of the necessary components simultaneously. Just as classical computers have evolved to make use of magnetic, charge, and optical technologies, perhaps the ultimate realization of a quantum computer will also involve hybrid quantum systems. I will describe how superconducting circuits can be used to manipulate single photons, and how they can act as a universal quantum bus to interface with many other physical systems. This hybrid approach can both improve prospects for quantum information science as well as illuminate new physics of the component systems. As a specific example, I will show how superconducting circuits can be coupled to mesoscopic spin ensembles which might serve as a high fidelity quantum memory and also provide a means to access broadband, low temperature (millikelvin), ultra low power (attowatt) electron spin resonance.
Host: Robert McDermott
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Astronomy Colloquium
Young Circumstellar Disks: Exoplanet Diagnostics
Time: 3:45 pm
Place: 4421 Sterling Hall
Speaker: John Wisniewski, University of Washington
Abstract: Circumstellar disks provide a useful astrophysical diagnostic of the formation and early evolution of exoplanets. It is commonly believed that young protoplanetary disks and transitional disks serve as the birthplace of planets, while older debris disks can provide insight into the architecture of exoplanetary systems. Spectacular ground-truth of this disk-exoplanet connection was provided by the recent successful direct imaging of exoplanets in the Fomalhaut, HR 8799, and Beta Pic systems. In this talk, I will discuss how one can use high contrast imaging techniques to spatially resolve circumstellar disk systems. I will focus on the initial results and future prospects from the Subaru Strategic Exploration of Exoplanets and Disks (SEEDS) project, a 5-yr program guaranteed 120 nights on the 8.2m Subaru Telescope to spatially resolve ~200 nearby circumstellar disks and investigate ~300 nearby stars in a direct imaging exoplanet survey. <br>
Host: Barbara Whitney
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Friday, February 25th, 2011

Special High Energy Physics Seminar
"First Results of Higgs Searches and Prospects for 2011/2012 with the ATLAS Detector at the LHC"
Time: 2:30 pm
Place: 5280 Chamberlin Hall
Speaker: Bruce Mellado, UW-Madison Physics Department
Abstract: The Higgs boson is responsible for giving masses to particles. The first results of Higgs searches using data taken in 2010 with the ATLAS detector at the LHC are reported. The sensitivity of Higgs searches with masses in the range 140&amp;amp;lt;M_H&amp;amp;lt;190 GeV is dominated by the decay H-&amp;amp;gt;WW. The details of the search with this channel and the extraction of Standard Model backgrounds are reviewed. Results are compared with those of the Tevatron. The prospects for the Higgs boson discovery in 2011/2012 are also reviewed.
Host: Matthew Herndon
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Physics Department Colloquium
Led by the Nodes: Forging an Understanding of Fe-Based Superconductors
Time: 4:00 pm
Place: 2241 Chamberlin Hall (coffee at 3:30 pm)
Speaker: Peter Hirschfeld, University of Florida
Abstract: The new Fe-based superconductors have occasioned considerable excitement because transition temperatures are high, and it is hoped that comparisons to cuprates will lead to new insights into the essential ingredients for high temperature superconductivity. I will briefly review some similarities and differences to the cuprates, focussing first on normal state magnetic and transport properties. In this respect some of the remarkable properties of these systems can be understood by consideration of the multiorbital character of the multisheeted Fermi surface. Next, I will review what is known about the superconducting state, explaining the basis for the near-consensus that all pnictide materials display spin singlet, orbital s-wave symmetry. Somewhat more controversial are differing reports on gap structure suggested by different experimental probes on different materials, including varying claims of gap nodes or fully gapped behavior. I will argue that such a diversity of gap structures, unexpected based on cuprate intuition, is characteristic of systems with s-symmetry and the unusual band structure of the Fe-based superconductors. They should, and do, display an "intrinsic sensitivity" to small perturbations of electronic structure. I review what is to be expected in this regard from spin fluctuation theories, where multiorbital effects are found again to play a crucial role. Finally, I will discuss how 3-dimensionality influences superconducting order.
Host: Chubokov
Poster: http://www.physics.wisc.edu/twap/posters/2011/2008.pdf
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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2011/2011-02-21.pdf

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