Fall 2007 Physics Colloquium Schedule
Unless otherwise noted, the physics colloquia are held in Room 307 of the Science and Engineering Research Facility. Refreshments are served at 3:00 p.m. with the talk following at 3:30. The ORNL Physics Division Seminar Schedule might also be of interest. Professor John Quinn is chair of the colloquium program. He may be contacted via e-mail at: jjquinn@utk.edu.
| Date |
Speaker |
Title |
| September 3 | Labor Day Holiday | No Colloquium |
| September 10 | Philip Kim Columbia University |
Relativistic Quantum Physics at Your Pencil Tips: Dirac Fermions in Graphitic Carbon [Abstract] |
| September 17 | Barry Dunning Rice University |
Designer Atoms: Engineering Rydberg Atom Wavepackets
using Pulsed Electric Fields [Abstract] |
| September 24 | Dan Bardayan Oak Ridge National Laboratory |
Radioactive Ion Beams and Gamma-ray Vision of Novae [Abstract] |
| October 1 | John Thomas Duke University |
Is a Strongly Interacting Fermi Gas a Perfect Fluid? [Abstract] |
| October 8 | Sankar Das Sarma University of Maryland |
Basic Interpretation of QM [Abstract] |
| October 15 | Brad Meyer Clemson University |
Old Stars, New Solar Systems, and the r-Process of Nucleosynthesis [Abstract] |
| October 22 | Jian Shen Oak Ridge National Laboratory |
Complexity under Spatial Confinement [Abstract] |
| October 29 | Stefan Spanier UT Physics |
New Physics with the Large Hadron Collider [Abstract] |
| November 5 | Zheng-Tian Lu Argonne National Laboratory |
Atom Trap, Krypton-81, and Saharan Water [Abstract] |
| November 19 [Special Colloquium] |
George Crabtree Argonne National Laboratory |
The Global Energy Challenge [Abstract] |
| November 19 | Lee Roberts Boston University |
Muon (g-2): Renormalization at work all the way down to the weak scale [Abstract] |
| November 26 | No Colloquium | NA |
| December 3 | Curtis Meyer Carnegie Mellon University |
The Hadron Spectrum and QCD [Abstract] |
Abstracts
September 10
Philip Kim, Columbia University
Relativistic Quantum Physics at Your Pencil Tips: Dirac Fermions in Graphitic Carbon
The massless Dirac particle moving at the speed of light has been a fascinating subject in relativistic quantum physics. Graphene, an isolated single atomic layer of graphite, now provides us an opportunity to investigate such exotic effect in low-energy condensed matter systems. The unique electronic band structure of graphene lattice provides a linear dispersion relation where the Fermi velocity replaces the role of the speed of light in usual Dirac Fermion spectrum. In this presentation I will discuss experimental consequence of charged Dirac Fermion spectrum in two representative low dimensional graphitic carbon systems: 1-dimensional carbon nanotubes and 2-dimensional graphene. Combined with semiconductor device fabrication techniques and the development of new methods of nanoscaled material synthesis/manipulation enables us to investigate mesoscopic transport phenomena in these materials. The exotic quantum transport behavior discovered in these materials, such as ballistic charge transport and unusual half-integer quantum Hall effect both of which appear even at room temperature. In addition, the promise of these materials for novel electronic device applications will be discussed.
September 17
Barry Dunning, Rice University
Designer Atoms: Engineering Rydberg Atom Wavepackets using Pulsed Electric
Fields
Advances in experimental technique now allow application of pulsed unidirectional electric fields, termed half-cycle pulses (HCPs), to Rydberg atoms whose characteristic times are much less than the classical electron orbital period. In this limit each HCP simply delivers an impulsive momentum transfer or "kick" to the excited electron. A number of protocols for controlling and manipulating Rydberg atom wavepackets using carefully tailored sequences of HCPs will be described with emphasis on the production of quasi one-dimensional and near circular Rydberg states, on navigating electron wavepackets in phase space, and on studying reversible and irreversible dephasing using electric dipole echoes. Insights provided by this work into classical-quantum correspondence, physics in the ultra-fast ultra-intense regime, and decoherence in mesoscopic quantum systems will be discussed.
September 24
Dan Bardayan, Oak Ridge National Laboratory
Radioactive Ion Beams and Gamma-ray Vision of Novae
The recent launches of gamma-ray telescopes into space have provided an unparalleled opportunity for viewing the Galaxy in this important wavelength range. In particular, the direct observation of gamma rays from novae create a window into the interior of explosions that is not open in the visible range. To interpret these observations, however, we must understand the nuclear reactions and the synthesized unstable nuclei that drive these explosions. At ORNL's Holifield Radioactive Ion Beam Facility, we are making some of the first high-precision measurements with radioactive ion beams that are critical for interpreting these observations. I will focus in my talk on the measurements and techniques we have used to understand the production of 18F in novae, which is a prime target of gamma-ray astronomy. Combining the measurements with nucleosynthesis calculations has dramatically increased the precision of predictions of radioisotope production.
October 1
John E. Thomas, Duke University
Is a Strongly Interacting Fermi Gas a Perfect Fluid?
An optically-trapped mixture of spin ˝-up and spin ˝-down 6Li atoms provides a new paradigm for exploring strongly interacting Fermi systems in nature. This ultracold atomic gas offers unprecedented opportunities to test theoretical techniques that cross interdisciplinary boundaries. A bias magnetic field is used to tune the gas near a Feshbach resonance, where the s-wave scattering length diverges and the interparticle spacing sets the only length scale. Even though it is dilute, an atomic Fermi gas near a Feshbach resonance is the most strongly interacting nonrelativistic system known, enabling tests of recent theories in disciplines from high temperature superconductors to nuclear matter. Strongly interacting Fermi gases also exhibit extremely low viscosity hydrodynamics, of great interest in the quark-gluon plasma and string theory communities, where it has been conjectured that the ratio of the shear viscosity to the entropy density has a universal lower bound, which defines a perfect fluid. I will describe our all-optical cooling methods and our studies of the thermodynamic and hydrodynamic properties of the 6Li cloud. Our measurements of the entropy reveal a high temperature superfluid transition, which occurs at a large fraction of the Fermi temperature. Our most recent estimates of the shear viscosity are obtained from observations of the hydrodynamic expansion of a rotating cloud. Together, these results suggest that a strongly interacting Fermi gas may be the most perfect quantum fluid ever studied.
October 8
Sankar Das Sarma, University of Maryland
Basic Interpretation of QM
Quantum mechanics is the underlying theory of our existence, governing the behavior of the natural world, and as such is astonishingly successful. No experiment in the last 82 years of the existence of quantum mechanics contradicts the predictions of the theory. In the past 50 years, the development of quantum theory in a solid-state setting has led to technology that has revolutionized the modern world through transistors, integrated circuits, computers, lasers, etc. Despite this success we really do not understand the quantum theory in an intuitive manner. This lecture will explore this curious state of affairs, highlighting the quantum based ideas and applications which underpin our modern world, and the sublime strangeness of the theory which eludes an intuitive common sense understanding. Projected future applications of quantum theory such as a quantum computer, which can do things that existing computers can never do, will also be discussed in this context.
October 15
Brad Meyer, Clemson University
Old Stars, New Solar Systems, and the r-Process of Nucleosynthesis
Extinct radioactivities are radioactive species that were once alive in the Solar System but have long since decayed. The presence of these radioactive species in the early Solar System is inferred from excesses in their daughter isotopes that correlate with a stable isotope of the parent element in primitive meteoritical samples. The most famous extinct radioactivity is 26Al, but the presence of nine others has been convincingly demonstrated. This talk focuses on the interesting discrepancy between the inferred initial abundance of the isotopes 129I (half-life = 15.7 million years) and 182Hf (half-life = 9 million years). The inferred early Solar-System abundance of the latter is in line with expectations from continuous Galactic nucleosynthesis but the abundance of the latter is well short of those same expectations. I will discuss the implications of this discrepancy for 1) the circumstances of the Sun's birth, 2) surface abundances in very old stars, and 3) our new proposed site for the r-process of nucleosynthesis.
October 22
Jian Shen, Oak Ridge National Laboratory
Complexity under Spatial Confinement
The two hottest areas of research in condensed matter physics are complexity and nanoscale physics. Interestingly, these two areas have little overlap as most of the nanophysics research work is conducted using “simple” materials of metals or semiconductors instead of complex materials such as transition metal oxides. However, due to the strong electronic correlation, it is exactly the transition metal oxides that will most likely lead to observations of striking new phenomena under spatial confinement. I will use perovskite manganites as model systems to demonstrate how spatial confinement can dramatically affect their transport and magnetic properties. The emerging magnetic and transport behavior is likely associated with the electronic phase separation under confined geometry in the manganites. Some of the new properties such as ultrasharp jumps of magnetoresistance may have significant impact on magnetic recording and sensing technologies.
October 29
Stefan Spanier, University of Tennessee
New Physics with the Large Hadron Collider
CMS is one of two general-purpose proton-proton experiments at CERN’s Large Hadron Collider (LHC) to run at almost ten times higher energy than accelerators operating today. CMS comprises about 2000 scientists from over 170 institutions from about 36 countries. These two experiments are expected to make ground-breaking discoveries. They will be the flagship experiments of particle physics for a decade or more. The physics program comprises the elucidation of the origin of mass with the search for the Higgs particle, the search for new particles and the understanding of forces that act between them and the quest for the unified theory, origin of dark matter, black hole generation etc. The US high-energy physics community, and indeed the world-wide scientific community, has invested a substantial amount of resources to assure the success of the project. First particle collisions are scheduled for May 2008. The high-energy physics group from the University of Tennessee participates in the preparation and commissioning of the pixel sub-detector system of CMS that consists of 66 Million individual detectors itself, and the protection against the irradiation from the accelerator.
November 5
Zheng-Tian Lu, Argonne National Laboratory
Atom Trap, Krypton-81, and Saharan Water
Since radiocarbon dating was first demonstrated in 1949, the field of trace analyses of long-lived cosmogenic isotopes has seen steady growth in both analytical methods and applicable isotopes. The impact of such analyses has reached a wide range of scientific and technological areas. A new method, named Atom Trap Trace Analysis (ATTA), was developed by our group and used to analyze 81Kr (t1/2 = 2.3x105 years, isotopic abundance ~ 1x10-12) in environmental samples. In this method, individual 81Kr atoms are selectively captured and detected with a laser-based atom trap. 81Kr is produced by cosmic rays in the upper atmosphere. It is the ideal tracer for dating ice and groundwater in the age range of 104–106 years. As the first real-world application of ATTA, we have determined the mean residence time of the old groundwater in the Nubian Aquifer located underneath the Sahara Desert. Moreover, this method of capturing and probing atoms of rare isotopes is also applied to experiments that study exotic nuclear structure and test fundamental symmetries..
November 19 [Special Colloquium in the Shiloh Room at the University Center at 1:30 p.m.]
George Crabtree, Argonne National Laboratory
The Global Energy Challenge
The expected doubling of global energy demand by 2050 challenges our traditional patterns of energy production, distribution and use. The continued use of fossil fuels raises concerns about supply, security, environment and climate. New routes are needed for the efficient conversion of energy from chemical fuel, sunlight, and heat to electricity or hydrogen as an energy carrier and finally to end uses like transportation, lighting, and heating. Opportunities for efficient new energy conversion routes based on nanoscale materials will be presented, with emphasis on the sustainable energy technologies they enable.
November 19
Lee Roberts, Boston University
Muon (g-2): Renormalization at Work All the Way Down to the Weak Scale
The anomalous magnetic moment of the muon, a_mu, which is related to the spin g-factor by a_mu = (g_\mu -2)/2, has played a special role in the development of the standard model of particle physics. Because the anomaly of a point lepton results solely from radiative corrections, it has been at the center of the development of quantum electrodynamics, and of the standard model since the first observation of muon spin rotation and parity violation in muon decay. In the standard model, a_\mu has contributions from radiative corrections from quantum electrodynamics; from strongly interacting particles in vacuum polarization loops with quantum numbers that couple to the photon; and from the electroweak gauge bosons. In principle, non-standard model particles could contribute as well, for example the supersymmetric partners of the electroweak bosons, if they exist. The present experimental value differs from theory by 3.4 standard deviations.
December 3
Curtis Meyer, Carnegie Mellon University
The Hadron Spectrum and QCD
Hadrons are particles built from quarks and antiquarks, and make up the majority of visible matter in the universe. We believe that the theory which describes the interactions of the quarks and governs the rules by which the form this matter is Quantum Chromo Dynamics (QCD)---a theory which is extremely difficult to solve. Studying the spectrum of hadrons can yield important insights into nature of this theory. I will discuss ongoing work on three quark particles (baryons) and future work that will be carried out in quark-antiquark systems. In particular, what we hope to learn about QCD from these studies.
Previous Physics Department Colloquia:
- Spring 2007
- Fall 2006
- Spring 2006
- Fall 2005
- Spring 2005
- Fall 2004
- Spring 2004
- Fall 2003
- Spring 2003
- Fall 2002