Events at Physics |
Events During the Week of March 29th through April 5th, 2009
Monday, March 30th, 2009
- Quantum Computing Seminar
- Single Charge Detection in Silicon Using Vertically Coupled Al and Si Single-Electron Transistors
- Time: 1:00 pm
- Place: 5280 Chamberlin
- Speaker: Luyan Sun, Laboratory for Physical Sciences, University of Maryland
- Abstract: The background charges in Si/SiO2 systems may be sources of decoherence for Si qubits. Understanding the charge environment is thus important for potential quantum information processing in Si. In this talk I will show that at low temperature an Al-AlOx-Al single electron transistor (SET) acting as the gate of a narrow (~ 100 nm) metal-oxide-semiconductor field-effect transistor can induce a self-aligned and vertically-coupled Si SET at the Si/SiO2 interface. Then I will demonstrate the detection of a single charge defect, either a single charge trap at the Si/SiO2 interface or a single donor in the Si substrate, using such an SET sandwich architecture. In conclusion, I will briefly discuss the high mobility two-dimensional electron systems fabricated in our group on hydrogen-terminated silicon (111) surfaces and our new approach to detecting donor electrons in silicon using a scanned probe based on a quartz tuning fork.
- Host: Mark Friesen
Tuesday, March 31st, 2009
- R. G. Herb Condensed Matter Seminar
- Room Temperature demonstration of Quantum Cellular Automata formed by Single Si Atom Quantum Dots
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Baseer Haider, University of Alberta
- Abstract: A device architecture for computing with quantum dots, Quantum Cellular Automata, points to a new paradigm for computation that goes beyond the conventional semiconductor technology roadmap to achieve ultra low power consumption. The Quantum Cellular Automata scheme is based upon "cells" of tunnel coupled quantum dots and electrostatic interaction between adjacent cells to transmit binary information and perform computations. Efforts to fabricate Quantum Cellular Automata devices have so far been limited by the need for extreme cryogenic conditions and by the debilitating effects of stray charges. It is conceivable that fabrication on a smaller scale can circumvent these limitations. Here we demonstrate that single atoms in a solid state environment can serve as quantum dots and that such quantum dots can be controllably tunnel coupled to embody the building block of a Quantum Cellular Automata Cells. Such cells exhibit "selfbiasing" effect, that is, the electron occupation is set by cell geometry. The binary state of the cell may be controlled electrostatically. This cell operates at room temperature and is largely immune to stray charges that are more than 30 Angstroms away from the cell.
- Host: Mark Friesen
- Chaos & Complex Systems Seminar
- The origins of emergent behavior in bacterial communities
- Time: 12:05 pm
- Place: 4274 Chamberlin
- Speaker: Douglas B. Weibel, UW Department of Biochemistry
- Abstract: Bacteria sense surfaces and undergo physiological changes, which programs their growth and motility and coordinates their behavior. The resulting bacterial communities display 'emergent' properties in which the coordination of the behavior of cells is not predictable from the sum of the individual components (e.g. cells). The resulting structures behave as multicellular organisms and collectively colonize niches in search of nutrients and other growth factors. The transition of a group of 'individual' bacterial cells to collective, multicellular behavior is accompanied by the upregulation of pathogenic factors, suggesting that in this state the organisms are preparing to invade a host. An understanding of the mechanisms that control and regulate the switch from individual behavior to multicellular behavior will identify mechanisms and targets that may play a role in preventing and treating microbial pathogenesis. We are particularly fascinated by the mechanisms that cells use to coordinate their movement on surfaces. In contrast to our understanding of the biophysics involved in the motility of bacterial cells (e.g. Escherichia coli) in bulk fluids, almost nothing is known about the mechanisms that play a role in cell motility on surfaces. We are exploring two physical mechanisms that may play a role in the coordination of cellular movement on surfaces based on: i) physical interactions between cells mediated by bundling between flagella on adjacent cells; and ii) physical interactions between cells in close proximity to each other that are produced by the disturbance in the local fluid field by the rotation of the cells during motility. In this talk I present recent work from our group on both mechanisms and demonstrate that bacterial 'swarming' may be one of the most tractable experimental systems for identifying the mechanisms that drive systems toward emergent behavior. These experiments may shed light on systems that extend far beyond microbial systems, and include financial markets, weather, and population dynamics.
- High Energy Seminar
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- DUSEL - Progress on the Deep Underground Science and Engineering Laboratory
- Time: 4:00 pm - 5:00 pm
- Place: 4274 Chamberlin(Coffee and Cookies at 3:45 pm)
- Speaker: Kevin Lesko, Lawrence Berkeley National Laboratory
- Host: Karsten Heeger
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- DUSEL - Progress on the Deep Underground Science and Engineering Laboratory
- Time: 4:00 pm
- Place: 4274 Chamberlin
- Speaker: Kevin Lesko, Lawrence Berkeley National Laboratory
- Abstract: Joint HEP Seminar/NPAC Forum
- Host: Karsten Heeger
Wednesday, April 1st, 2009
- No events scheduled
Thursday, April 2nd, 2009
- R. G. Herb Condensed Matter Seminar
- Nonequilibrium effects in single-channel and two-channel Kondo systems
- Time: 10:00 am
- Place: Chamberlin 5310
- Speaker: Aditi Mitra, New York University
- Abstract: It is now experimentally possible to realize both a single channel as well as a two channel Kondo system in nanoscale structures, opening up the possibility of studying the nonequilibrium properties of these systems. After a brief review of the experiments, I will present theoretical results for the effect of current flow on a single channel Kondo system, and the effect of a sudden quench on a two channel Kondo system. For voltages smaller than the Kondo temperature, the single channel Kondo system shows behavior consistent with a weakly perturbed Fermi liquid. On the other hand what makes a two channel Kondo system interesting is that it is one of the simplest examples of a non-Fermi liquid. It will be shown how this non-Fermi liquid behavior affects the time evolution of the system after a quench.
- Host: Maxim Vavilov
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Echoes of Supersymmetry: Baryon Asymmetry, Relic Q-balls, and Gravity Waves
- Time: 4:00 pm
- Place: 4274 Chamberlin
- Speaker: Alex Kusenko, UCLA
- Abstract: If supersymmetry is realized in nature, even at some very high energy scales, it has important cosmological consequences. A generic prediction of supersymmetry is the flat directions in the potential, along which a scalar condensate can form at the end of inflation. This condensate is generically unstable; its evolution and its fragmentation into Q-balls can generate the baryon asymmetry, dark matter, and the gravity waves that can be observed by upcoming detectors.
- Host: M J Ramsey-Musolf
Friday, April 3rd, 2009
- Physics Department Colloquium
- Neutrinos, and the Dark Side of the Light Fermions
- Time: 4:00 pm
- Place: 2241 Chamberlin Hall (coffee at 3:30 pm)
- Speaker: Alex Kusenko, UCLA
- Abstract: The past decade has been marked by some remarkable discoveries in the neutrino physics: the particles once believed to be massless have turned out to be massive and have shown evidence of lepton family number violation, as well as other interesting phenomena. While this is exciting, the future may hold even more dramatic discoveries, the hints for which begin to appear in astrophysics and cosmology. The observed neutrino masses imply the existence of some yet undiscovered "right-handed" states, which can be very massive and unreachable, but which can also be light enough to constitute the cosmological dark matter and to account for a number of astrophysical phenomena, from supernova asymmetries and the pulsar kicks to the peculiarities in the reionization and formation of the first stars. I will review the recent progress in neutrino physics, as well as the clues that may lead to future discoveries.
- Host: Ramsey-Musolf