Physics Colloquium

Fall 2009

Thursdays 4:00 p.m., Room 104 Physics
Refreshments served at 3:40 p.m.
  Colloquium organizer: Alexey Yamilov
(Link to main colloquium page)

Green - open date
Yellow - tentative (reserved)
Red - firm commitment
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Spring 2010 colloquia
Date Host Speaker Title of the talk Abstract
Sept. 3
Sept. 10
Sept. 17 Jentschura Maarten DeKieviet
Heidelberg University
From Newton to Casimir and back:
fundamental physics using Atomic Beam Spin Echo
   The quantum mechanical nature of (empty) space has far-reaching consequences in many branches of physics, ranging from elementary particles to cosmology. The existence of electromagnetic vacuum fluctuations, for example, manifests itself most impressively in the Casimir force. With the current revolution in nano-technology there is a rising need for a quantitative understanding of this feeble, stochastic force. I will present an experiment, in which the Casimir-Polder force between a single atom and the surface of a solid is determined quantitatively at the %-level. In our Atomic Beam Spin Echo Interferometer, we scatter cold 3He atoms from the attractive part of the atom-surface potential. Since the quantum reflectivity depends very sensitively on the long-range details of the interaction, we have been able to clearly identify the Casimir and the van der Waals branches for a variety of systems. The potential of this experiment is addressed in particular with respect to testing fundamental questions concerning the Casimir force and beyond, like for example possible deviations from Newton’s law of gravity at the nanometer scale.
Sept. 24 Yamilov Klaus Woelk
S&T Chemistry
Novel Toroid Cavity Techniques for in situ NMR Spectroscopy and Imaging Studies
   Nuclear Magnetic Resonance (NMR) has long been used to analyze chemical structures and obtain three-dimensional images for medical diagnosis or materials science analysis. More recently, toroidal cavity detectors and toroidal autoclaves have become prominent resonators for in situ high temperature and pressure NMR spectroscopy, and for spatially resolved NMR investigations such as rotating frame imaging (RFI) or magnetization grating rotating frame diffusiometry (MAGROFI). In the MAGROFI technique, a material is tagged with a magnetization pattern and its decay followed mathematically, for example, by finite-difference analysis that accounts accurately for molecular motion and spin relaxation.
   When the toroid cavity NMR platform is combined with magnetic spin hyperpolarization techniques such as parahydrogen induced polarization (PHIP), the small polarization of nuclear spins at thermal equilibrium can be enhanced up to a factor of 105. Parahydrogen represents the nuclear singlet state of molecular hydrogen with an antisymmetric nuclear spin wavefunction and can physically be separated from, or enriched with respect to, its symmetric-wavefunction counterpart orthohydrogen. The hyperpolarization can be used to substantially enhance the sensitivity and contrast in NMR spectroscopy and imaging, respectively. New applications are proposed with respect to the investigation of chemical reaction mechanisms and medical magnetic resonance imaging.
Oct. 1 Yamilov Jeffrey Catalano
Interfacial Water Ordering, Complex Ion Adsorption, and Redox-Driven Nanoscale Transformations at Mineral-Water Interfaces    Many of the geochemical processes occurring at the Earth’s surface that are important to or influenced by humans occur at the interface between minerals and natural waters.  Such processes affect contaminant fate and transport, biogeochemical element cycling, ore deposit formation, biomineralization, and nuclear waste disposal.  The ability to predict and quantify these and other important processes in nature requires a fundamental understanding of the structure of mineral-water interfaces and the reactions that occur there.  I will present recent synchrotron-based resonant and non-resonant surface X-ray scattering studies that reveal the structure of the nanoscale transition zone between a mineral and an aqueous solution, that identify unexpected complexity in molecular-scale arsenic adsorption mechanisms, and that demonstrate the nanoscale surface transformations of an iron oxide mineral surface that may occur during biogeochemical iron cycling
Oct. 8 Parris Stephan DeBievre
Universite des Science et Technologie de Lille
The Unruh effect revisited    According to the Unruh effect (Unruh 1974) a particle detector uniformly accelerating through Minkowski space-time and coupled to a relativistic quantum field in the vacuum, will detect a black body radiation of particles at a temperature proportional to its acceleration. Stated this way, the effect sounds quite paradoxical. We will present a short history of the subject, and propose a description of the phenomenon in terms of statistical mechanics which we feel helps to clarify it.
Oct. 15 Yamilov Sergey Skipetrov
Anderson localization of classical waves
   Anderson localization is an interference phenomenon leading to inhibition of transport in strongly disordered media. First predicted and studied for electrons in disordered (semi-) conductors at low temperatures, it is now widely recognized to be common for any wave, including light, sound, and elastic waves. These latter “classical” waves appear particularly suitable to study Anderson localization in detail, thanks to the variety and accuracy of possible measurements. Indeed, time-, frequency-, angular- and position-resolved measurements are standard with classical waves, whereas only the measurements of conductance (or resistance) are routine in the realm of electronic transport.
   After a brief introduction to the field of Anderson localization, we will review recent theoretical developments and experiments that significantly advanced our understanding of Anderson localization phenomenon during the past few years. A particular attention will be paid to Anderson localization in three-dimensional (3D) media, where a phase transition is expected between extended and localized regimes (a metal-insulator transition) upon increasing the strength of disorder or varying the frequency of the wave. We will discuss the recently developed self-consistent theory of localization with a position-dependent diffusion coefficient and ultrasonic experiments that provided the first unambiguous demonstration of Anderson localization in 3D. And finally, if time allows, we will say some words about Anderson localization of Bose-Einstein condensates – a fashionable topic that might indeed be relevant for measuring the critical exponents of the Anderson localization transition.
Oct. 23 Bieniek Homecoming:
John Johnson
California Institute of Technology
(BS '99)
The Golden Age of Exoplanet Spin-Orbit Measurements    The angular momentum of the Solar System planets is remarkably well aligned with the spin axis of the Sun. This arrangement supports the hypothesis that the planets and the Sun formed from the same spinning disk of gas and dust. Until very recently, measurement of the spin-orbit alignment of exoplanets had revealed that planets around other stars, most in very close-in orbits (periods less than 10 days), also have well-aligned spin and orbit axes. However, our recent measurements from this past year have revealed that there may be a second class of exoplanets that inhabit very tilted orbits, and that some may even have retrograde configurations. I'll show how spin-orbit measurements are made, and discuss how the distribution of observed spin-orbit angles informs, and challenges, theories of planet migration.
Oct. 29 Vojta Gregory Stewart
U. of Florida
The New Iron Age - Superconductivity in an Odd Place    Bernd Matthias, the Dean of Superconductivity until his death in 1980, used to say about the elements in the periodic table:  "If you make them cold enough, and clean enough, all the metallic elements will be either magnetic or superconducting."  Since February, 2008, there is a new class of superconductor, the so-called iron pnictides, that have relatively high transition temperatures, Tc, (up to 56 K) based on . . . . iron.  This mixture of normally magnetic iron with the supposedly contradictory effect of superconductivity has taken the scientific community by storm. Theorists are busy, experimentalists are in their labs, and it's hard to have a condensed matter seminar on another subject.  After an introduction to superconductivity, including its technological usefulness, we will discuss what's understood (and not) in this new field, particularly the central role of doping.  To conclude, we will focus on just one of the puzzles in this new field:  what is the superconductivity doing in *undoped* (i. e. pure) BaFe2As2?
Nov. 5 Yamilov Gavin King
A Precision Force Microscope for Biophysics Historically, the atomic force microscope (AFM) community has focused on developing sharper tips and higher sensitivity force detection schemes as a means for improved instrument performance. Yet, unwanted mechanical drift between an AFM tip and sample remains a critical, largely unaddressed issue that limits tip-sample stability, registration, and the signal-to-noise ratio during imaging. We have developed novel optical stabilization techniques to locally monitor and actively compensate for drift in AFM measurements. In this talk I will present an overview of our results in the context of biological applications. Further, I will present our preliminary data applying this instrument towards precision force spectroscopy of membrane proteins. Looking towards the future, an optically stabilized AFM should enable a variety of precision measurements of biological phenomena, such as direct real-time observation of protein conformational fluctuations in physiologically relevant conditions.
Nov. 12 Jentschura Gerald Gabrielse
Harvard University
Tests of Fundamental Symmetries at Low Energies One electron, suspended by itself and cooled to the ground state of its cyclotron motion in a magnetic field, is used to measure the electron magnetic moment about 15 times more accurately than any previous measurement -- to 3 parts in 10^{13}.  The fine structure constant is determined more than an order of magnitude more accurately by this measurement, along with QED theory, than by any other method.  One positron should soon be available so that the electron and positron moments can be compared at the new level of precision  to make the most stringent test of CPT invariance with a lepton system.  Hundreds of millions of positron, along with millions of antiprotons, are now being used to make antihydrogen atoms which eventually will be used for precise spectroscopic comparisons of antihydrogen and hydrogen atoms.  A new measurement with ThO molecules seeks to determine the electric dipole moment of the electron to test and constrain proposed extensions to the standard model of particle physics. 
Nov. 19 Yamilov/Vojta Yamilov/Vojta 2009 Novel prize
in Physics
This year's Nobel prize was awarded to Charles K. Kao "for groundbreaking achievements concerning the transmission of light in fibers for optical communication" and to Willard S. Boyle  and George E. Smith "for the invention of an imaging semiconductor circuit – the CCD sensor". We will discuss the history of the subjects as well as physical and societal significance of the discoveries which lead to the award.
Dec. 3 Yamilov Sixteen Annual Laird D. Schearer Prize Competition
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