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Winter 2011 Colloquium Series

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Colloquia are at 4pm, Thursdays, in 100 Willamette Hall and are preceded by coffee, tea, and cookies at 3:40 in the Willamette Atrium.

The organizer of the Spring Term Colloquia is: Steve Kevan


January 6

Wesley Campbell

University of Maryland / NIST and a Candidate for the Condensed Matter, Biophysics & Optics position

Refreshments begin at 3:40 in the Olum Atrium

Quantum Information Processing with Ultrafast Pulses and Trapped Ions

The field of quantum information science promises computational methods that are more efficient than classical algorithms for certain calculations. In particular, the use of a well-controlled quantum system to simulate a computationally-intense quantum many-body problem is likely to produce nontrivial results in the next couple of years. While still being the leading demonstrated quantum information architecture, the trapped atomic ion processor suffers from impediments to scaling up to more ions from the continuous wave laser mediated quantum gates that are used to perform the computation. I will discuss how the use of mode-locked pulsed lasers enables us to circumvent both the laser-induced decoherence and the motional spectrum crowding issues that currently limit us to around 14 qubits. The use of an optical frequency comb to scale up the number of qubits would open up quantum computations and simulations that will allow us to investigate quantum systems that have been inaccessible to us due to their computational complexity.

Host: Miriam Deutsch


January 13

Michael Raymer

Department of Physics
University of Oregon

One- and Two-Photon Parametric Processes in Quantum Information Technology

The goals of quantum information technology are to transmit, store, and process information in ways not possible using classical-physics-based techniques. One typically uses single atoms (ions, molecules, quantum dots) as quantum memory, and single photons as information carriers. Optical parametric processes allow one to create individual pairs of photons and to interact them via a bosonic exchange interaction. Our group recently pioneered the use of parametric processes in optical fiber as a means to change the color of a single photon, or to interact two photons of different color. These processes have potential for applications in quantum information technology.

Host: Steve Kevan


January 20

Cheng Cen

University of Pittsburgh, Physics/Astronomy

Refreshments begin at 3:40 in the Olum Atrium

Oxide Nanoelectronics on Demand

Control over electronic confinement in the solid state is increasingly challenging as the dimensionality and size scale are reduced. By scanning a biased conducting atomic force microscope (AFM) tip along a programmed trajectory at room temperature, we can reversibly control in nanoscale the metal-insulator transition at the interface of an oxide heterostructure formed from LaAlO3 and SrTiO3. Positive tip voltages produce conducting regions at LaAlO3/SrTiO3 interface directly below the area of contact, through a process analogous to modulation doping. Negative tip voltages restore the area back to insulating state.

Using the technique described above, a variety of rewritable nanosize devices and structures have been studied. These nanoelectronic components are mainly assembled from basic elements including conductive wires and dots whose characteristic dimensions are just a few nanometers. Among the most interesting devices is a sketch-based transistor (SketchFET). Besides the conventional field effect mode, SketchFET can also function in a field-emission mode where it is sensitive to electronic properties changes in surrounding materials. Switching speeds exceeding GHz barrier have been demonstrated. Other examples include in-plane rectifying junctions and field-tunable nanoscale photodetectors. At low temperatures, a variety of electronic, spintronic and superconducting properties are observed, with enormous potential for exploitation in quantum devices.

Host: Miriam Deutsch


January 27

Ludovico Cademartiri

Harvard University, Department of Chemistry and Chemical Biology

Refreshments begin at 3:40 in the Olum Atrium

On the Interaction of Flames with Electric Fields

Flames are one of the first technologies developed by mankind and certainly one of the most pervasive. Combustion processes produce 91% of the world’s energy and are a key to a variety of applications ranging from manufacturing to transportation.
Despite the extensive research conducted on combustion, the sheer complexity of this topic has limited our ability to control flames for purposes such as i) making better use of their energy, and ii) limiting the damage they can make in fires.
In the past few years we have been interested in developing and exploring new and unconventional platforms for the control and understanding of flames. In this talk I will review our recent work on understanding the effect of electric fields on flames. We found that oscillating electric fields can elicit strong macroscopic responses in methane/air non-premixed flames such as deflection, reshaping, and even extinction.

Host: Miriam Deutsch


February 3

Physics Colloquium Canceled

Host:


February 10

Tobias Weidner

University of Washington, Bioengineering

Refreshments begin at 3:40 in the Olum Atrium

Protein Structure Determination at Interfaces: A Challenge for Surface Analysis

Proteins on surfaces play a key role in biomaterials, tissue engineering, drug delivery, diagnostics and biomimetics. True molecular level design in these fields will require high-resolution structure characterization techniques to assess the conformation and orientation of adsorbed proteins along with specific structural motifs used by proteins to interact with surfaces. A current barrier for structure-based design concepts is the general difficulty to characterize surface-bound protein structures. It is the aim of this research program to overcome this barrier and to provide appropriate tools for high-resolution biomolecular structure characterization at material surfaces. Nearly 60.000 protein structures have been solved so far using XRD and NMR techniques. Among those were only around 200 unique membrane proteins and not a single structure of a protein on an inorganic surface has been solved. In this seminar, I will discuss how a suite of complementary surface analytical techniques, such as sum frequency generation (SFG) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy in combination with biochemical labeling, can provide high resolution structural information about surface bound proteins. Site-specific information can be obtained by strategic labeling of individual amino acids with isotope and element markers. The power of these surface analysis strategies will be illustrated through a series of investigations based on model protein – substrate interfaces. This analysis will then be expanded to probe the surface structure of proteins that control and drive biomineralization.

Host: Miriam Deutsch


February 17

Benjamin McMorran

Center for Nanoscale Sci. & Tech. of NIST

Refreshments begin at 3:40 in the Olum Atrium

Electron Vortex Beams, and Other Adventures in Matter Wave Sculpting

Electron vortex beams – composed of free electrons in quantized orbital states – are remarkable for their helically shaped wavefunctions, quantized angular momentum, and magnetic moment. Free electron vortices can be produced and studied in an electron microscope using nanofabricated diffraction holograms. This technique was recently used to generate well-defined free electron vortex beams in various quantized orbital states, with up to 100 h of orbital angular momentum per electron. The wavefront topology and angular momentum of the electrons was measured directly using matter wave interferometry. The unique helical phase, quantized angular momentum, and coherence properties of the electron vortex have several immediate applications in diverse areas of research. For example, using vortex beams with electron energy loss spectra from a magnetic sample reveals the same contrast as magnetic circular dichroism measurements using a synchrotron. This can potentially lead to high resolution, elementally sensitive magnetic imaging capabilities in a transmission electron microscope (TEM). Electron vortices also open a path towards imaging transparent TEM specimens, such as biological materials, using a technique called spiral phase microscopy. The advent of electron vortex beams represents one aspect of a wider effort in de Broglie wavefront engineering using nanofabricated structures.

Host: Miriam Deutsch


February 24

Claudiu A. Stan

Harvard University

Refreshments begin at 3:40 in the Olum Atrium

Studies of ice nucleation in supercooled water using high-throughput microfluidic apparatus

In the absence of preexisting ice, the freezing of water initiates with the nucleation of a small region of ice in supercooled water. The nucleation of ice in supercooled water is relevant to the formation of atmospheric precipitation and to many other branches of science, including the physics and chemistry of water, and the biology of life in cold climates.
Acquiring good quality nucleation data requires large numbers of measurements because nucleation is a stochastic process. We have built an apparatus that supercools and freezes tens of thousands of small drops of water (~100-micron diameter), and measures with high accuracy the temperature of each drop. This instrument can record the largest sets of individual freezing temperatures and has the fastest data acquisition rate among instruments designed to study the nucleation of ice. We used this instrument to measure with high accuracy the rate of homogenous nucleation of ice in pure water, and to investigate the effect of electric fields on the rate of homogenous nucleation.
We also measured the temperature-dependent rates of heterogeneous ice nucleation due to nanoparticles of silica or silver iodide immersed in water. Our heterogeneous nucleation data suggests the existence of multiple mechanisms of heterogeneous nucleation that are dominant in different ranges of temperatures.

Host: Miriam Deutsch


March 10

Greg Stewart

University of Florida

Refreshments begin at 3:40 in the Olum Atrium

Au Contraire – Puzzles and Open Questions in the Iron Pnictide Supercondutors and What the Data Really Imply

Although only three years have passed since the discovery of
‘medium Tc’ superconductivity in the iron pnictides (fluorine doped
LaFeAsO) by Hosono’s group, there are already both a number of settled questions and, perhaps more interestingly, a number of puzzles. Thus, the search for common features amongst the very wide range of materials in this class that have been discovered is still ongoing. After a short introduction into what is known in these materials, a selection of the current directions for further research will be discussed with a focus on specific heat, nodal structure determinations, and materials questions.

Host: Dietrich Belitz