Physics

Physics Colloquia 2006 - 2007

Submitted by William A. Loinaz

  • Scheduled speakers/dates:

    Fall

    confirmed for Sept. 21: Prof. Peter Khalifah (UMass Chemistry)
    confirmed for Sept. 29 (evening): Lynda Williams (Five College event)
    confirmed for Oct. 5: Laura Newburgh (Columbia)
    confirmed for Oct. 12: Prof. Carol Koleci (WPI)
    confirmed for Oct. 19: Prof. Britton Plourde (Syracuse)
    confirmed for Oct. 26: Prof. Steve Hill (UFl)
    confirmed for Nov. 2: Prof. Steve Lamoreaux (Yale)
    confirmed for Nov. 9: Prof. Catherine Crouch (Swarthmore)
    confirmed for Nov. 16: Prof. Barry Holstein (UMass Amherst)
    confirmed for Nov. 30: Dr. David Divincenzo (IBM)

    Spring

    confirmed for Feb. 15: Prof. Ken Segall (Colgate)
    confirmed for Feb. 22: Prof. Bob Romer (Amherst College)
    confirmed for Mar. 1: Prof. Jack Harris (Yale)
    confirmed for Mar. 8: Prof. Lorenzo Sorbo (UMass Amherst)
    confirmed for Mar. 12: Prof. Alan Guth (MIT) (Five Colleges talk)
    confirmed for Mar. 15: Dr. Wei Chen (Stony Brook)
    confirmed for Mar. 29: Prof. Michael Golay (MIT)
    confirmed for Apr. 5: Prof. Kathy Aidala (Mt. Holyoke)
    confirmed for Apr. 12: Prof. Jefferson W. Tester (MIT)
    confirmed for Apr. 19: Prof. Ward Lopes (Mt. Holyoke)
    confirmed for Apr. 26: Prof. Brian Anderson (Arizona)
    confirmed for May 3: honors thesis talks (Amherst College)

    Pending

    invited but not confirmed: Prof. Tatsu Takeuchi (Virginia Tech)

  • Unscheduled dates:

    Fall 2006

    Sept. 28


    Spring 2007

    Feb. 8


     

  • Thursday, Sept. 7, 2006,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    [reserved for start-of-semester pandemonium]

     

  • Thursday, Sept. 14, 2006,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    [reserved for start-of-semester pizza session]

     

  • Thursday, Sept. 21, 2006,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Prof. Peter Khalifah
    Department of Chemistry
    University of Massachusetts at Amherst

    Title: Solids behaving like molecules: the curious properties of some lanthanum ruthenates

Abstract: 
Although solid state compounds are often interpreted in terms of their atomic orbitals (s,p,d,f or t2g,eg), there are a number of materials with particularly intriguing properties whose bonding is better described in terms of molecular orbitals. The “brother” compounds, La4Ru6O19 and La3Ru3O11 share a common structural framework, but differ in the presence or absence of Ru-Ru bonds within dimers of RuO6 octahedra. The nature of this bonding, and its influence on the quantum criticality of this system will be discussed. The compound La4Ru2O10 is the only example of a ruthenate which undergoes a complete orbital ordering transition. The structural and bonding forces which shape this transition will be discussed, and the evidence for high-temperature orbital excitations (“orbitons”) will be presented.
  • Friday, Sept. 29, 2006,
    *Note unusual day/time*
    Location: Grand Room, Campus Center, Mount Holyoke College
    Time: 8:00 pm
    Five College Event

    Lynda Williams
    Physics Chanteuse

     

  • Thursday, Oct. 5, 2006,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Laura Newburgh
    Columbia University

    Title: Everything You Ever Wanted to Know about Graduate School, and the Universe, in Less That One Hour

    Abstract:

    The discovery of perturbations in the Cosmic Microwave Background(CMB) ushered in a new era of experimental cosmology. One of the most exciting new signatures in the CMB is that of polarization, which is already informing the time scales of reionization, and could possibly help probe inflationary time scales in the universe, beginning about 10-43 seconds after the big bang. The Q/U Imaging Experiement (QUIET) will probe this signature with unprecedented accuracy and help inform next-generation experiments. In addition to discussing QUIET, I will talk about the process of applying, choosing, and going to graduate school, with the hope of clarifying the procedure.

     

  • Thursday, Oct. 12, 2006,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Prof. Carol Koleci
    Worcester Polytechnic Institute

    Title: Resources in Understanding Electromagnetism: Building a Conceptual Bridgefor Physics Learners and Teachers

    Abstract:

    Since the early 1980s, research in the field of Physics Education has enhanced the physics educators toolbox. We have a host of innovative tools which can promote interactive engagement in the classroom, however many students still struggle with fundamental concepts in electromagnetism. WPI and MIT are developing a set of educational materials to be used in conjunction with a suite of electromagnetism visualizations created by researchers and computer developers at MIT*. We will provide a set of problems which feature integrated visualizations in the context of electromagnetism, and we will discuss preliminary findings from a recent pilot study.

     

  • Saturday, Oct. 14, 2006,
    Location: Smith College
    Five College Undergraduate Research Symposium

     

  • Thursday, Oct. 19, 2006,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Prof. Britton Plourde
    Syracuse University

    Title: Quantum Coherence in Superconducting Devices

    Abstract:

    Superconducting devices are ideal systems for exploring quantum coherence at the scale of circuits on a chip. Such investigations could advance fundamental understanding of quantum mechanics at large scales and help develop the building blocks, or qubits, for implementing a quantum computer. One such circuit, the flux qubit, is composed of a superconducting loop and Josephson junctions. I will present measurements performed at the University of California, Berkeley of quantum coherence in these devices, as well as experiments on coupled flux qubits. In addition, I will discuss the prospects for using nanofabricated superconducting structures to probe the quantum coherent properties of vortices, which are quantized bundles of magnetic flux threading a superconductor.

     

  • Thursday, Oct. 26, 2006,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Prof. Steve Hill
    University of Florida

    Title: Magnetic Quantum Tunneling: Insights from Molecules and Magnetic Resonance

    Abstract:

    The miniaturization of magnetic devices to molecular dimensions is critical to advances in magnetic information processing. However, quantum mechanics begins to play a significant role at these dimensions, leading to novel phenomena which are incredibly sensitive to the detailed atomic scale structure of the device. Consequently, conventional top-down approaches to producing nanoscale magnetic particles have serious limitations. For this reason, there is a growing interest in chemical syntheses that provide a bottom-up or molecule-based approach, with atomic scale control of magnetic structure. I will begin this talk with an overview of the fascinating quantum effects that have been discovered from studies of so-called single-molecule magnets (SMMs), including: quantum tunneling of the magnetic moment from 'up' to 'down' through a magnetic anisotropy barrier; and quantum interference between different tunneling trajectories of the magnetization vector (spin) as it rotates from 'up' to 'down' over the Bloch sphere. I will then go on to describe the unique insights that can be obtained concerning these quantum phenomena using novel high-frequency and high-magnetic-field electron paramagnetic resonance techniques.

     

  • Thursday, Nov. 2, 2006,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Prof. Steve Lamoreaux
    Yale University

    Title: The Oklo Natural Nuclear Reactor and the Time Stability of the Fundamental Constants of Nature

    Abstract:

    Two billion years ago, a uranium deposit in Oklo, Gabon,Africa achieved criticality and a nuclear chain reaction was sustained in the deposit for about 100,000 years. Such a reactor was possible because the relative isotopic abundance of U-235 was much greater in the past. By analyzing the isotopic abundances of stable fission products in the deposit, it is possible to determine whether low energy neutron absorption resonance energies were different in the past, and thereby determine whether the fundamental constants of physics have changed. A precise recent analysis of isotopic abundances implied that the fine structure constant has fractionally changed by as much as 45 parts per billion,with six sigma confidence. However, additional modeling of the reactor indicates that this should interpreted as an upper limit on a possible change, and at present is the most restrictive limit.

     

  • Thursday, Nov. 9, 2006,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Prof. Catherine Crouch
    Swarthmore College

    Title: Quantum Christmas Lights: Fluorescence Intermittency from Single Quantum Rods

    Abstract:

    How do single quantum objects, such as molecules and semiconductor nanoparticles, emit light? One intriguing feature of the fluorescence observed from a wide variety of single fluorophores is intermittency, colloquially called blinking. Under steady excitation, single fluorophores do not emit light steadily, but turn on and off, remaining on or off for milliseconds to minutes at a time. Intermittency is fairly well understood in many molecular systems, but it is still poorly understood in semiconductor nanocrystals, tiny crystalline particles of a semiconductor such as cadmium selenide that are only a few nanometers across. Such nanocrystals are the subject of extensive study, both for the prospect of optoelectronic applications and for the fundamental physics of light emission from quantum particles. This talk will introduce the general field of single-nanocrystal fluorescence and present our results on fluorescence intermittency in single rod-shaped nanocrystals.

     

  • Thursday, Nov. 16, 2006,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Prof. Barry Holstein
    University of Massachusetts at Amherst

    Title: How Big is the "Natural" g-factor? New Answers to an Old Question

    Abstract:

    The gyromagnetic ratio or "g-factor" measures the size of a particle's magnetic dipole moment scaled by the Bohr magneton and the spin. Every student of quantum mechanics learns that the "natural" value for this quantity in the case of a spin 1/2---Dirac---particle is g=2 and this value is spectacularly confirmed in experiments involving the electron and muon. The question then arises as to what the "natural" value is for a particle having arbitrary spin. This query was answered in 1953 by Belinfante who proposed that for a particle of spin S---gs=1/S. The so-called "Belinfante conjecture" was then "proved" by various authors over the intervening years. However, recently the question has been reexamined and it has been proposed that the "natural" value should be gs=2, independent of spin. The previous arguments for both viewpoints will be reviewed and a new argument will be presented, which strongly favors gs=2.

     

  • Thanksgiving: Nov. 18-26

     

     

  • Thursday, Nov. 30, 2006,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Dr. David Divincenzo
    IBM

    Title: Implementing Quantum Computing

    Abstract:

    A "standard model" for the physical implementation of a quantum computer was laid out some years ago. It indicated a set of capabilities that had to be achieved to make quantum processing possible: 1) systems with well-characterized qubits must be constructed. 2) These qubits should be initializable to the "0" state. 3) It must be possible to control the one- and two-qubit Hamiltonian of the system, so that unitary quantum logic gates are enacted. 4) Decoherence and imprecision of gate operations must be kept very low. 5) Reliable measurements of the quantum state of individual qubits must be possible. In this talk I will indicate progress towards these goals, after first reviewing why we want to do quantum computation.

     

  • Thursday, Dec. 7, 2006,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Honors thesis presentations:

    Alex Bridges

    Adam Kaplan

    Dan Guest
  • Last day of fall term 2006 classes: Dec. 13

     

  • First day of spring term 2007 classes: Jan. 29

     

  • Thursday, Feb. 1, 2007,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)
    [reserved for early-semester pandemonium]

     

  • Thursday, Feb. 8, 2007,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    no talk

     

  • Thursday, Feb. 15, 2007,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Prof. Ken Segall
    Colgate University

    Title: Vortices, Ratchets and Breathers: Nonlinear Dynamics in Josephson Arrays

    Abstract:

In 1911, the phenomenon of superconductivity was discovered by Heike Kamerlingh Onnes at a lab in the Netherlands. Since then, superconductors have made very important contributions to science and technology. In 1962, in work for which he was awarded the Nobel Prize, Brian Josephson made the remarkable prediction that if two pieces of superconductor were separated by an electrically-insulating material, the electrons in the two superconductors would be able to quantum mechanically travel (or "tunnel") back and forth across the insulator. Such a device is now known as a "Josephson junction" and has led to the fascinating field of superconducting electronics. Josephson junctions and superconducting electronics are now the basis of many cutting-edge physics experiments and important new technologies. In this talk we will focus on our recent work to study different circuits that can be fabricated by "coupling" multiple Josephson junctions together in arrays. The first kind of circuit is called a "Ratchet", and it aims to produce a situation where random noise can move an object in a preferred direction. It can be thought of as a kind of "windmill" or rectifier. In the second circuit, called a Josephson "ladder", two different kind of excitations, called "breathers" and "vortices," can be collided and their interaction can be studied. Both of these circuits need to be described by complex nonlinear theory, and may contain new physical effects that have yet to be observed.
  • Thursday, Feb. 22, 2007,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Prof. Bob Romer
    Amherst College

    Title: Adventures of a Scientific Editor - The American Journal of Physics at Amherst College, 1988-2001
     

  • Thursday, Mar. 1, 2007,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Prof. Jack Harris
    Yale University

    Title: Thermal and quantum fluctuations in micromechanical systems

    Abstract:

    Mechanical systems represent a new class of devices in which it may soon be possible to observe macroscopic quantum effects. These same systems also serve as extremely sensitive detectors for a wide range of phenomena of interest in mesoscopic physics. I will discuss research in both areas, focusing on the important technical challenge of controlling the temperature of a high Q mechanical system. I will describe our recent work on the connection between thermal fluctuations of a cantilever's microscopic degrees of freedom and its macroscopic ones (i.e., its center-of-mass motion), which in some experiments can differ by more than three orders of magnitude. I will also describe ongoing efforts to couple cantilevers to high-finesse optical cavities, which is a promising route to observing quantum effects in mechanical systems.

     

  • Thursday, Mar. 8, 2007,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Prof. Lorenzo Sorbo
    University of Massachusetts at Amherst

    Title: Cosmology: the History of the Universe

    Abstract:

    Since the most ancient times, the humankind has been wondering about
    the origin of the Universe, about its size, about its end. During the
    last century, cosmology has risen to the rank of science, and many of
    these questions can be now addressed. In this talk I will review the
    evolution of cosmology until the most recent times. In particular, I
    will focus on the main measurements that have led to our current
    knowledge of the matter content of the Universe, and to the
    understanding that the nature of the 95% of the matter in the
    Universe is unknown.

     

  • Monday, Mar. 12, 2007,
    Smith College
    7:30 pm (Reception afterwards)

    Five Colleges "What's New in Physics" talk

    Prof. Alan Guth
    MIT

    Title:  Cosmic Inflation and the Accelerating Universe

  • Thursday, Mar. 15, 2007,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Dr. Wei Chen
    Stony Brook University

    Title:  Molecular Electronics: Candidate for Down Scaling of Digital Devices After CMOS?

    Abstract:

    Continued down-scaling of CMOS devices has brought about the information technology that we enjoy today. However, it is estimated that the downscaling of CMOS will not be able to continue due to the restraints of power consumption and fabrication costs in about 10 years time. We have to find some alternatives to meet the needs of information processing for the next generation. Molecular electronics pushes the miniaturization to the molecular level and is one of the possible candidates for post-CMOS devices. In this talk, recent progress will be discussed.

  • Spring Break: Mar. 17-25, 2007
  • Thursday, Mar. 29, 2007,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Prof. Michael Golay
    MIT

    Title: Possible Futures for Nuclear Power

    Abstract:

    Due to factors beyond the control of the nuclear power enterprise society in the US and also internationally appears to be appreciating nuclear power more than has been typical over the past 30 years The existing manpower and technology supply infrastructure is weak and many details about how a nuclear power revival might actually work remain unresolved. Because of slow progress in developing a risk-informed safety regulatory system within the NRC a situation of de-factor technology "lock-in" exists, and only LWRs can be expected in the next wave of nuclear power expansion. USDOE programs for nuclear power technology advancement are largely decoupled from, and of little interest to nuclear utilities. The future role for nuclear power in the energy economy may depend more upon developing technologies for providing products beyond electricity than upon developing better reactors and fuel cycles. US nuclear utilities are interested in building new nuclear power plants, but they are also risk-averse; everyone wants to be the second pioneer. International interest in expanding use of nuclear power is much more confident than in the US, and is likely to occur without regard to what may happen here.

     

  • Thursday, Apr 5, 2007,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Prof. Kathy Aidala
    Mt. Holyoke College

    Title:  Imaging electron motion in a two-dimensional electron gas with scanning robe microscopy

    Abstract:

    Electrons confined to fewer than three dimensions show fascinating physics at low temperatures, where quantum effects can be readily observed. A layer of two-dimensional electrons can be confined below the surface of a GaAs/AlGaAs heterostructure. These buried electrons cannot be accessed with traditional imaging techniques. I will discuss results obtained from a home-built liquid helium cooled scanning probe microscope (SPM). A SPM brings a sharp (~20 nm) tip close to the surface of a sample. A charge on the tip capacitively couples to electrons buried beneath the surface. The tip will influence the motion of electrons directly below, in a small region of space. We measure conductance across a quantum point contact (QPC) and record how the conductance changes with the location of the tip. This allows us to map out the electron flow. We have imaged cyclotron orbits in the magnetic focusing geometry, in which two QPCs are placed side-by-side and electrons can follow a semicircular trajectory from one to the other in a perpendicular magnetic field. We understand these images in terms of branched electron flow in a mildly disordered background potential, and interference effects. Theoretical simulations and experimental images agree well.

     

  • Thursday, Apr 12, 2007,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Professor Jefferson W. Tester
    H.P. Meissner Professor of Chemical Engineering
    Massachusetts Institute of Technology

    Title: Transitioning to a Sustainable Energy Future

    Abstract:

    Faced with the issue of providing clean, secure and sustainable energy that is essential to maintaining our social and economic well being, many argue that the U.S. and other developed countries should be pursuing options more aggressively. There are a number of environmental, social, and economic reasons why a transition from our current hydrocarbon-based energy supply system is needed for the long term. While renewable energy from solar, wind, biomass, geothermal, and hydro sources offers the potential for achieving a more sustainable system, the transition to a renewable energy future has been painfully slow. This seminar will examine both the context and options for accelerating such a change. Two specific examples will be explored in detail: 1. geothermal energy for electricity and heat and 2. biomass for transportation fuels.

     

  • Thursday, Apr. 19, 2007,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Prof. Ward Lopes
    Mt. Holyoke College

    Title:  The development of order in ultra-thin PS-PMMA diblock copolymer films.

    Abstract:

    Systems with striped (smectic) symmetry abound in nature. Examples include, for example, the stripes on a zebra fish, the patterns of lines in fingerprints, and the patterns formed in Rayleigh-Bernard convection. Knowledge of how two dimensional systems order is important for techniques like hierarchical self-assembly or diblock copolymer lithography. The applicability of these techniques can be limited by the defects which influence the late stages of ordering. Further, one would like to know whether or not the qualitative features of ordering depend only on the symmetry of the system. We address these concerns by studying the growth of order in weakly-segregated, cylindrical-phase, PS-PMMA diblock copolymer films. Our samples have smectic (striped) symmetry and form a single layer of half-cylinders with more than 100000 repeat spacings. We have found qualitative differences between our results and results reported on strongly segregated cylindrical-phase diblock copolymer films(1) . We find, for example, that the number of dislocations and disclinations are approximately equal and that grain boundaries persist for long times. We will compare our results with numerical simulations of the Swift-Hohenberg Model. We are beginning efforts to use time lapse atomic force microscopy to track disclination dipoles, tripoles, and quadrupoles. (1) Harrison et. al. Science, 290, 1558 (2000); Harrison et. al. Phys. Rev. E, 66, 11706 (2002).

     

  • Thursday, Apr. 26, 2007,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)

    Prof. Brian Anderson
    University of Arizona Optical Sciences Center

    Title:  From quantum indeterminacy to rotating superfluids

    Abstract:

    Atomic-gas Bose-Einstein condensates (BECs) have proven to be exciting systems to use in studying numerous topics in physics. For example, BECs can exhibit phenomena associated with superfluidity. Quantized vortices, the prime signature of a rotating superfluid, may be induced in a trapped BEC by stirring the gas or rotating its confining potential, or even by manipulating the BEC's quantum phase profile. Experiments at the University of Arizona are now showing that the creation of BECs in "bumpy" potentials may also generate vortices - a growing BEC can suddenly start rotating without any deliberate stirring or phase manipulation! These results depend on the merging of smaller isolated condensates with indeterminate relative phases and thus unpredictable interference. In this talk, the concepts of quantum phase and quantized vortices will be reviewed, followed by descriptions and interpretations of new experimental results. These experiments may help us better understand superfluid formation dynamics, and might even aid in the exploration of theories regarding early universe formation.

     

  • Thursday, May 3, 2007,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)
    Senior Honors Thesis presentations:

    Alex Bridges

    Adam Kaplan
  • Thursday, May 10, 2007,
    Amherst College, Merrill 3
    4:45 pm (tea in 204 Merrill @4:15)
    [reserved for end-of-semester pandemonium]
  • Last day of spring term 2007 classes: May 11
 

Physics and Astronomy Department

AC# 2244
Amherst College
Amherst, MA 01002-5000
413-542-2251
Larry Hunter, Chair

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