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This Week at Physics

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Events on Thursday, October 11th, 2012

R. G. Herb Condensed Matter Seminar
The Kondo exciton: a quantum quench towards strong spin-reservoir correlations
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Hakan Tureci, Princeton University
Abstract: When a quantum system is subjected to a quantum quench, its subsequent dynamics is governed by energy scales that become ever lower with increasing time: whereas the transient behavior right after the quench depends on high-energy excitations, the asymptotic long-time evolution is determined by low-lying excitations close to the final ground state. Thus, time- or frequency-resolved probes of the dynamics after a quantum quench offers insight into the nature of the system's eigenstates across the entire energy spectrum. We recently proposed [1] that such a quantum quench for the single-impurity Anderson Model can be induced by the sudden creation of an exciton in a quantum dot via optical absorption of an incident photon of definite frequency. The subsequent emergence of correlations between the spin degrees of freedom of the dot and a tunnel-coupled low-temperature Fermionic reservoir, ultimately leading to the Kondo effect, can be accurately mapped out through an optical absorption experiment. This experiment was recently carried out [2] with semiconductor quantum dots coupled to a degenerate electron gas, demonstrating experimentally for the first time the optical signature of Kondo correlations. I will discuss the theory behind the resulting lineshape that is found to unveil three very different dynamical regimes, corresponding to short, intermediate and long times after the initial excitation, which are in turn described by the three renormalization group fixed points of the Anderson Model. At low temperatures and just beyond the absorption threshold, the lineshape is dominated by a power-law singularity, with an exponent that is a universal function of magnetic field and gate voltage.

[1] H. E. Tureci et al., Phys. Rev. Lett. 106, 107402 (2011).
[2] C. Latta et al., Nature 474, 627 (2011).
Host: Vavilov
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Searches for Lorentz Violation in the Top Quark Sector
Time: 2:30 pm
Place: 4274 Chamberlin
Speaker: Denver Whittington, Indiana University
Abstract: Lorentz symmetry posits that the laws of physics are invariant regardless of the orientation and velocity of the reference frame in which they are measured. Violation of this symmetry can be quantified using the Standard-Model Extension (SME) framework, which predicts the effects that Lorentz violation would have on elementary particles and their interactions. This model predicts a dependence of the production cross section for top and antitop quark pairs on sidereal time as the orientation of the experiment changes with the rotation of the Earth. In this talk I will present the results of a search for Lorentz violation in ttI,, events using data collected with the D0 detector at the Fermilab Tevatron Collider, setting upper limits on parameters within the SME describing the possible strength of Lorentz violation in the top sector. I will also investigate the prospects for extending this analysis using the ATLAS detector at the Large Hadron Collider which, because of the higher rate of top-antitop events at that experiment, has the potential to improve the limits determined at D0.
Host: Karle
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Graduate Introductory Seminar
Condensed Matter Theory
Time: 5:45 pm
Place: 2223 Chamberlin Hall
Speaker: Chubukov, Coppersmith, Joynt, Perkins, Vavilov, UW Madison
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