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This Week at Physics

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Events During the Week of November 13th through November 19th, 2011

Monday, November 14th, 2011

Condensed Matter Theory Group Seminar
Interaction effects on localization
Time: 4:30 pm
Place: 5310 Chamberlin
Speaker: Peter Wölfle, Karlsruhe Institute of Technology, Germany
Abstract: Anderson localization is influenced by interaction effects in various ways. First, interaction processes destroy the phase coherence and limit localization at finite temperature in all dimensions. Secondly, interaction gives rise to a new type of quantum correction to the conductivity. Thirdly, the metal-insulator transition is modified by interaction effects in ways not completely understood yet. I review the renormalization group theory of disordered interacting electron systems. Finally, a comparison with experimental data on selected systems is presented.
Host: Perkins
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Tuesday, November 15th, 2011

Chaos & Complex Systems Seminar
Teaching computers to extract complex information from news articles
Time: 12:05 pm
Place: 4274 Chamberlin
Speaker: Jude Shavlik, Jude Shavlik, UW Department of Computer Science
Host: Sprott
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Wednesday, November 16th, 2011

Department Meeting
Canceled
Time: 12:15 pm
Place: 5280 Chamberlin Hall
MEETING CANCELED
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Thursday, November 17th, 2011

R. G. Herb Condensed Matter Seminar
Resonant Passage of Spin States in a Triple Quantum Dot
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Xuedong Hu, University of Buffalo
Abstract: Experimental and theoretical research on spin qubits in quantum dots are progressing toward systems with multiple spins in multiple dots. Among the many quantum information processing tasks that can be accomplished by such a multi-qubit system is the coherent transfer of quantum states on chip, which is an essential capability of a practical quantum computer. In this talk I will discuss our recent work on the physics of adiabatic quantum teleportation in a triple dot system. In particular, we show that a teleportation process over a three-spin chain can be mapped exactly onto two parallel and coherent adiabatic passages, one for each spin orientation. When the time evolution is not adiabatic, we find that the fidelity of information transfer displays a strong oscillatory behavior, and it is possible to have high fidelity when the switching frequency of the qubit interactions is a subharmonic of the characteristic energy splitting of the three-spin system. This resonant operation of an adiabatic passage protocol of spin states is both fast and robust, and points to a new way to perform other quantum gates.
Host: Coppersmith
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Magic, precise, and electroweak
Time: 2:30 pm
Place: 4274 Chamberlin Hall
Speaker: Andrei Derevianko, University of Nevada-Reno
Abstract: Precision timepieces are marvels of human ingenuity. Over the past half-a-century, precision time-keeping has been carried out with atomic clocks. I will review a novel and rapidly developing class of atomic clocks, optical lattice clocks. At their projected accuracy level, these would neither lose nor gain a fraction of a second over estimated age of the Universe. In other words, if someone were to build such a clock at the Big Bang and if such a timepiece were to survive the 14 billion years, the clock would be off by no more than a mere second. I will also talk about the next frontier: nuclear clock.

In the second part I will overview atomic searches for new physics beyond the Standard Model of elementary particles. I will report on a refined analysis of table-top experiments on violation of mirror symmetry in atoms that sets powerful constraints on a hypothesized particle, the extra Z-boson. Our raised bound on the Z' masses improves upon the Tevatron results and carves out a lower-energy part of the discovery reach of the Large Hadron Collider.
Host: Mark Saffman
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Graduate Introductory Seminar
Condensed Matter Experimental Seminar
Time: 5:30 pm
Place: 2223 Chamberlin Hall
Speaker: Eriksson, Himpsel, Lagally, McDermott, Onellion, Rzchowski, Winokur
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Friday, November 18th, 2011

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
Condensation of excitons and polaritons
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Peter Littlewood, Argonne National Laboratory
Abstract: Macroscopic phase coherence is one of the most remarkable manifestations of quantum mechanics, yet it seems to be the inevitable ground state of interacting many-body systems. In the last two decades, the familiar examples of superfluid He and conventional superconductors have been joined by exotic and high temperature superconductors, ultra-cold atomic gases, both bosonic and fermionic, and recently systems of excitons, magnons, and exciton-photon superpositions called polaritons, the subject of this talk.

An exciton is the solid-state analogue of positronium, made up of an electron and a hole in a semiconductor, bound together by the Coulomb interaction. The idea that a dense system of electrons and holes would be unstable toward an excitonic (electrical) insulator is one of the key ideas underlying metal-insulator transition physics. The further possibility that an exciton fluid would be a Bose-Einstein condensate was raised over 40 years ago, and has been the subject of an extensive experimental search in a variety of condensed matter systems. Such a condensate would naturally exhibit phase coherence. Lately, some novel experiments with planar optical microcavities make use of the mixing of excitons with photons to create a composite boson called a polariton that has a very light mass, and is thus a good candidate for a high-temperature Bose condensate. Good evidence for spontaneous coherence has now been obtained, though there are special issues to resolve considering the effects of low dimensionality, disorder, strong interactions, and especially strong decoherence associated with decay of the condensate into environmental photons---since the condensate is a special kind of laser.
Host: Perkins
Poster: http://www.physics.wisc.edu/twap/posters/2011/2291.pdf
Video: https://vod.physics.wisc.edu/media/2011_11_18.m4v
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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2011/2011-11-14.pdf

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