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This Week at Physics

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Events During the Week of December 16th through December 23rd, 2012

Monday, December 17th, 2012

Condensed Matter Theory Group Seminar
Dissipative generation of entanglement
Time: 4:30 pm
Place: 5310 Chamberlin
Speaker: Mark Saffman
Abstract: Advances in measurement and control of quantum systems that have been achieved over the last several decades were recognized with the Nobel prize this year. For the non-specialist I'll give a brief overview of what has been done, how they did it, and why many people consider this important. I will then present some of our current research, which combines coherent and dissipative dynamics to forge a powerful mechanism for generating entanglement. Detailed calculations with Rydberg atoms predict strong entanglement at distance scales that greatly exceed what can be achieved with coherent dynamics alone. Applications to finding ground states of many-body spin Hamiltonians will also be mentioned.
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Tuesday, December 18th, 2012

No events scheduled

Wednesday, December 19th, 2012

No events scheduled

Thursday, December 20th, 2012

R. G. Herb Condensed Matter Seminar
Electronic Transport in Bi2Se3 Thin Films in the Topological Insulator Regime
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Dohun Kim, University of Maryland
Abstract: The 3D topological insulators (TIs) have an insulating bulk but metallic surface states stemming from band inversion due to strong spin-orbit interaction, whose existence is guaranteed by the topology of the band structure of the insulator. Like graphene, the STI surface state generically has a Dirac electronic spectrum with massless electrons and a vanishing bandgap at a Dirac point. In this talk, I will discuss experiments on the TI material Bi2Se3, which has a single topological Dirac surface state. Field effect transistors consisting of thin (5-17 nm) Bi2Se3 are fabricated by mechanical exfoliation of single crystals, and electrochemical and/or chemical gating methods are used to move the Fermi energy into the bulk bandgap, revealing the ambipolar gapless nature of transport in the Bi2Se3 surface states [1]. The minimum conductivity of the topological surface state is understood within the self-consistent theory of Dirac electrons in the presence of charged impurities. The intrinsic finite-temperature resistivity of the topological surface state due to electron-acoustic phonon scattering is measured to be 60 times larger than that of graphene largely due to the smaller Fermi and sound velocities in Bi2Se3 [2], which will have implications for topological electronic devices operating at room temperature. I will also discuss about our recent observation of 2D weak anti-localization (WAL) behavior in the low field magneto transport, which stems from topological surface states. By investigating gate-tuned WAL behaviors, I will show that WAL in TI regime is extraordinarily sensitive to sub-meV coupling between top and bottom topological surfaces, and interplay of phase coherence time and inter surface tunneling time results interesting crossovers from coupled single channel to decoupled multichannel coherent transports.

[1] D. Kim et al., Nature Phys. 8, 460 (2012).
[2] D. Kim et al., Phys. Rev. Lett. 109, 166801 (2012).
Host: Eriksson
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Friday, December 21st, 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:
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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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2012/2012-12-17.pdf

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