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Events on Tuesday, February 26th, 2013
 R. G. Herb Condensed Matter Seminar
 Gate control of single electron spin in IIIV semiconductor quantum dots: Anisotropy effects
 Time: 10:00 am
 Place: 5280 Chamberlin Hall
 Speaker: Sanjay Prabhakar, Wilfrid Laurier University
 Abstract: Among recent proposals for nextgeneration nonchargebased logic is the notion that a single electron can be trapped and its spin can be manipulated through the application of gate potentials. In the first part of my talk, I present numerical simulations of such spins in singleelectron devices for realistic asymmetric confining potentials in twodimensional electrostatically confined quantum dots. Using both analytical and numerical techniques, I show that breaking the inplane rotational symmetry of the confining potential leads to a significant effect on the tunability of the g factor and on the spinflip rate mediated by phonon with applied gate potentials. In particular, anisotropy either extends the range of the tunability of the gfactor and spinhot spot to larger quantum dots or viceversa. For example, anisotropy reduces the tunability of the gfactor and spin hot spot to smaller quantum dots radius as well as to smaller magnetic fields if we keep the area of the symmetric and asymmetric quantum dots same. It is well known that the cusplike structure due to accidental degeneracy in the phonon mediated spinflip rate can be seen only for the case of pure Rashba spinorbit coupling in symmetric quantum dots. I present new analytical and numerical results which show that the cusplike structure can be seen for pure Dresselhaus spinorbit coupling case in asymmetric quantum dots.
In the second part of my talk, I investigate the geometric phase induced on the spin states during the adiabatic movement of the IIIV semiconductor quantum dots in the plane of twodimensional electron gas under the influence of applied gate potential along the lateral direction. Here, I present the spinflip probabilities during the adiabatic evolution in the presence of the Rashba and the Dresselhaus linear spinorbit interactions. I use the Feynman disentanglement technique to determine the nonAbelian Berry phase and find exact analytical expressions for three special cases: (a) the pure Rashba spinorbit coupling, (b) the pure Dresselhause linear spinorbit coupling, and (c) the mixture of the Rashba and Dresselhaus spinorbit couplings with equal strength. For a mixture of the Rashba and the Dresselhaus spinorbit couplings with unequal strengths, I obtain numerical results by solving the Riccati equation originating from the disentangling procedure. I find that the spinflip probability in the presence of the mixed spinorbit couplings is generally larger than those for the pure Rashba case and for the pure Dresselhaus case, and that the complete spinflip takes place only when the Rashba and the Dresselhaus spinorbit couplings are mixed symmetrically.
References:
Gate control of a quantum dot singleelectron spin in realistic confining potentials: Anisotropy effects; Sanjay Prabhakar and James Raynolds, phys. Rev. B 79, 195307 (2009).
Manipulation of single electron spin in a GaAs quantum dot through the application of geometric phases: The Feynman disentangling technique; Sanjay Prabhakar, James E Raynolds, Akira Inomata and Roderick Melnik, Phys. Rev. B 82, 195306 (2010).
Manipulation of the Lande gfactor in InAs quantum dots through the application of anisotropic gate potentials; Sanjay Prabhakar, James E Raynolds and Roderick Melnik, Phys. Rev. B 84, 155208 (2011).
The influence of anisotropic gate potentials on the phonon induced spinflip rate in GaAs quantum dots; Sanjay Prabhakar, Roderick Melnik and Luis L Bonilla, Applied Physics Letters 100, 023108 (2012).
 Host: Friesen
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 Chaos & Complex Systems Seminar
 The brave cyberworld of science communication
 Time: 12:05 pm
 Place: 4274 Chamberlin (Refreshments will be served)
 Speaker: Dominique Brossard, UW Department of Life Sciences and Communication
 Abstract: As more and more individuals turn to online environments to follow scientific issues and find information about science, recent research is science communication has focused on examining how these online environments may shape public attitudes toward science and public understanding of science. This introduction will discuss patterns of science communication online and present recent research findings in that area. Notably, I will introduce results of an experiment with a national sample of the American population testing the effects of comments on science blogs on readersaEuroTM attitudes toward the scientific issues covered in such blogs. I will also explain the effects of current practices related to online searches on public understanding of science. In light of these results, challenges and opportunities for science as an institution as well as for science and society will be discussed.
 Host: Sprott
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 "Physics Today" Undergrad Colloquium (Physics 301)
 Recent Discoveries in Neutrino Physics
 Time: 1:20 pm
 Place: 2223 Chamberlin
 Speaker: Karsten Heeger, University of Wisconsin Department of Physics
 Abstract: A series of weekly presentations and discussions of current research topics in physics by the scientists involved in those studies designed to expose students to the topics and excitement of the research frontier.
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