Events at Physics |
Events During the Week of November 15th through November 21st, 2009
Monday, November 16th, 2009
- Plasma Physics (Physics/ECE/NE 922) Seminar
- New Directions in Stellarator Optimization/Design
- Time: 12:05 pm
- Place: 2301 Sterling
- Speaker: Donald Spong, Oak Ridge National Laboratory
- High Energy Seminar
- An Inclusive Search for H->WW at CDF
- Time: 4:00 pm
- Place: 5310 Chamberlin
- Speaker: Dr. Matthew Herndon, Wisconsin
- Abstract: The Standard Model of particle physics includes one major undiscovered particle known as the Higgs boson. Experimental evidence and the calculations in the framework of the Standard Model show a large difference in the probability of the electromagnetic and weak interactions at low energy. This fundamental difference is explained by the massiveness of the weak W and Z interaction bosons. The source of this electroweak symmetry breaking in the SM is the Higgs mechanism, which gives mass to the weak bosons and other SM particles. This theory is directly testable by observing the Higgs boson making Higgs boson research one of the primary objectives of modern particle physics. I discuss the status of current searches for the Standard Model Higgs boson at high mass.
- Host: Matthew Herndon
Tuesday, November 17th, 2009
- Chaos & Complex Systems Seminar
- Age Related Macular Degeneration Through the Eye of the Fly
- Time: 12:05 pm
- Place: 5310 Chamberlin (Refreshments will be served)
- Speaker: Nansi Colley, Ophthalmology & Visual Sciences
- Abstract: A highly magnified view of a fruit fly's eye shows the light-sensitive cellular structures known as rhabdomeres. These specialized structures in the retina transform light into electrical impulses that the brain recognizes as "sight." Analogous structures serve the same function in humans. The fly's surprising genetic similarity to humans allows Nansi Colley, PhD, a UW Eye Research Institute scientist, to pinpoint mutations leading to macular degeneration, retinitis pigmentosa, and other vision-threatening diseases.
- Theory/Phenomenology Seminar
- Jets and Jet Substructure at the LHC
- Time: 2:30 pm - 3:30 pm
- Place: 2301 Sterling Hall
- Speaker: David Krohn, Princeton University
- Host: Tao Han
- Astronomy Colloquium
- The subtle Physics of Black Hole Accrection"
- Time: 3:30 pm - 5:00 pm
- Place: 3425 Sterling Hall
- Speaker: Chris Reynolds, University of Maryland
- Abstract: For almost the past 20 years, the paradigm for black hole accretion has highlighted the central role of magnetohydrodynamic (MHD) turbulence. However, only in recent years have high-resolution simulations started to explore the subtle nature of MHD turbulent disks. I will discuss results from a series of simulations focusing on geometrically-thin accretion disks. I shall focus on the dynamics of the disk and the transition to the plunging flow close to the black hole, and explain why the low density "corona" of the disk plays a previously unrecognized and important role in shaping the dynamics of the disk. I shall also present a study of the temporal properties of the accretion flow. I shall end by connecting this theoretical work with a new XMM-Newton observation of the Seyfert galaxy 1H0707-495.
- Host: Professor Sebastian Heinz
Wednesday, November 18th, 2009
- R. G. Herb Condensed Matter Seminar
- Small Josephson Arrays as Protected Qubits
- Time: 11:00 am - 12:00 pm
- Place: 5310 Chamberlin
- Speaker: Michael Gershenson, Rutgers University
- Abstract: Within the past twenty years, there has been a growing realization that superconducting Josephson circuits can behave as macroscopic quantum systems. The last decade witnessed an explosive growth of research the superconducting devices for quantum computation (superconducting qubits). However, the decoherence time for these devices remains insufficiently long for large-scale quantum computing. Recently it was predicted [1-4] that the arrays of small Josephson junctions with nontrivial topology may exhibit a novel phase which is characterized by long-range order of pairs of Cooper pairs in the absence of long-range correlations in single-Cooper-pair condensate. Experimental realization of this novel phase can facilitate the fabrication of fault-tolerant superconducting qubits exponentially protected from local noises. Our experiments [5] with small Josephson arrays show that, indeed, the condensate of pairs of Cooper pairs can be observed in the absence of coherence in the single-Cooper-pair condensate. The charge transport in this regime is due to coherent co-tunneling of pairs of Copper pairs, objects with charge 4e. These experiments suggest that even a relatively small prototype device is well protected against magnetic flux variations.
1. L.B. Ioffe and M.V. Feigel'man, Possible realization of an ideal quantum computer in Josephson junction array, Phys. Rev. B 66, 224503 (2002).
2. B. Doucot and J. Vidal, Pairing of Cooper pairs in a fully frustrated Josephson-junction chain, Phys. Rev. Lett. 88, 227005 (2002).
3. B. Doucot et al., Topological order in the insulating Josephson junction arrays, Phys. Rev. Lett. 90, 107003 (2003).
4. B. Doucot et al., Protected qubits and Chern-Simons theories in Josephson junction arrays, Phys. Rev. B 71, 024505 (2005).
5. S. Gladchenko, D. Olaya, E. Dupont-Ferrier, B. Doucot, L.B. Ioffe, and M.E. Gershenson, Superconducting Nanocircuits for Topologically Protected Qubits, Nature Physics 5, 48 (2009). - Host: Robert McDermott
Thursday, November 19th, 2009
- R. G. Herb Condensed Matter Seminar
- Silicon metal insulator semiconductor nanostructures for solid-state quantum computing
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Malcolm Carroll, Sandia National Laboratory
- Abstract: Development of silicon, enhancement mode, metal insulator semiconductor (MIS) nanostructures for solid-state quantum computing will be described. A primary motivation of this research is the recent unprecedented manipulation of single electron spins in GaAs quantum dots, which has been used to demonstrate a quantum bit [1]. Quantum bits (qubits) are a fundamental element for quantum computing that also represent an extraordinary probe of single electron spin physics in semiconductors. A critical challenge for quantum computing is development of qubits that maintain long spin decoherence times, which will allow the necessary number of spin operations to be done before the information is lost due to spin decoherence. Development of silicon nanostructures for qubits are being pursued around the world because electron spins in silicon are predicted to have long decoherence times.
This talk will focus on silicon quantum dot structures that emulate the GaAs lateral quantum dot qubit [1] but use an enhancement mode field effect transistor (FET) structure. One critical concern for silicon quantum dots that use oxides as insulators in the FET structure is that defects in the metal oxide semiconductor (MOS) stack can produce both detrimental electrostatic and paramagnetic effects on the qubit. Understanding the implications of defects in the Si MOS system is also relevant for other qubit architectures that have nearby dielectric passivated surfaces. Stable, lithographically defined, single-period Coulomb-blockade and single-electron charge sensing in a quantum dot nanostructure using a MOS stack will be presented. A combination of characterization of defects, modeling and consideration of modified approaches that incorporate SiGe or donors provides guidance about the enhancement mode MOS approach for future qubits and quantum circuit micro-architecture.
We wish to acknowledge the research funding support provided by the laboratory directed research and development (LDRD) program at Sandia National Laboratories and the Laboratory of Physical Sciences. Sandia National Labs is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
[1] J. Petta et al., Science 309, 2180 (2005) - Host: Mark Eriksson
- Introductory Graduate Seminar
- Medical Physics
- Time: 5:30 pm
- Place: 2223 Chamberlin Hall
- Speaker: Meyerand, Nickles, Christian, University of Wisconsin Department of Medical Physics
Friday, November 20th, 2009
- Theory/Phenomenology Seminar
- Collider and Flavor Phenomenology in the Scalar Sector of Warped Extra Dimensions
- Time: 2:30 pm - 3:30 pm
- Place: 2301 Sterling Hall
- Speaker: Manuel Toharia, University of Maryland
- Host: Tao Han
- Physics Department Colloquium
- Superconductivity at the Dawn of the Iron Age
- Time: 4:00 pm
- Place: 2241 Chamberlin Hall (coffee at 3:30 pm)
- Speaker: Zlatko Tesanovich, John Hopkins University
- Abstract: Recent discovery of iron-based high-temperature superconductors hints at a new pathway to the room temperature superconductivity. The new materials feature FeAs layers instead of the signature CuO2 planes of much studied cuprate superconductors. The antiferromagnetism also appears to be involved,although the d-electrons in FeAs seem considerably more mobile than their cuprate cousins. This high mobility, facilitated by a large overlap amongst atomic orbitals of Fe and As, plays a crucial role in warding off Hund's rule and the large local moment magnetism of Fe ions, the archrival of superconductivity. A pedagogical review of the current status of the high-temperature superconductivity field will be presented, highlighting similarities and differences between Fe-pnictides and cuprates and emphasizing the importance of the multiband nature of magnetism and superconductivity in these new materials.
- Host: Chubukov