Physics

2009 - 2010 Physics Colloquia

Submitted by Ellen F. Feld

Unless otherwise noted, all physics seminars and colloquia are held on Thursdays from 4:45 to 6:00, in lecture room 3 of Merrill Science Center. Tea and snacks will be served before seminars at 4:15 in 204 Merrill. If you would like to be mailed seminar announcements, please send an email to Ellen Feld.

Contact colloquium organizer Jonathan Friedman with any questions about colloquia.


 Click here for the spring semester schedule

Fall 2009

Sept. 10

beginning-of-semester pandemonium

Sept. 17

Welcome Back Pizza Party. Student lounge - Merrill 114-116, 4:30PM

Sept. 24

Professor Nathanael Fortune
Department of Physics
Smith College

New Opportunities To Overcome Frustration

The magnetic spins in a frustrated triangular antiferromagnet (TAF) are like three frustrated and lonely curmudgeons on election day : their inclination is to disagree with everyone around them, but they can’t all simultaneously disagree with each other. Asking them to take into account broader public opinion makes finding a solution even harder. In the spin 1/2 antiferromagnet studied here, the curmudgeons play the role of neighboring magnetic “spins” with two possible states and public opinion plays the role of an applied magnetic field.  Not surprisingly, predicting the outcome of the magnetic vote in an arbitrary magnetic field is extremely challenging. One important prediction, however, is that for a particular range of magnetic fields, quantum-fluctuations should induce spins in a TAF to work together to form a surprisingly stable “up-up-down” orientation relative to the field. In this arrangement, two of the "voters" agree to cancel each other out so that the third can ignore the first two. The result should be a plateau in the magnetization versus applied field at 1/3 of the maximum magnetization. This should be a fundamental property of frustrated spin 1/2 Heisenberg TAFs, but evidence for such a quantum-fluctuation induced state has only been found in particular material: the triangular antiferromagnet Cs2CuBr4.  In this talk, I present magnetization, magnetic torque, and magnetothermal measurements in Cs2CuBr4 revealing  new, theoretically unexpected, stable arrangements of spins at still higher fractions of the maximum magnetization. I will discuss how these arrangements might come about thermodynamically and microscopically.  Apparently, when confronted with changes in public opinion, even the most stubborn curmudgeons can repeatedly be induced to work together out of frustration!

Oct. 1

David Schaich '06
Department of Physics
Boston University

Electroweak Symmetry Breaking: An enduring mystery of the standard
model of particle physics, and how we hope to solve it


In the standard model of particle physics, elementary particles acquire mass through the process of "electroweak symmetry breaking".  Although electroweak symmetry breaking is essential to the proven success of the standard model, the precise mechanism responsible for it remains unknown.  The exact nature of electroweak symmetry breaking is one of the greatest (and longest-standing) unsolved mysteries of the standard model.  In this colloquium I will introduce electroweak symmetry breaking, discuss some of the "usual suspects" that may be behind it, and describe how we hope to (finally!) solve this mystery in the near future, at CERN's Large Hadron Collider.

Oct. 8

Professor Mark Silverman
Department of Physics
Trinity College

Is "THE FORCE" with Us?:  Search for Correlated Fluctuations in Nuclear Decay (...and what it may teach us about the stock market)

Claims for a "cosmogenic" force that correlates otherwise independent stochastic events have been made for at least 10 years, based largely on visual inspection of time series of histograms.  To test these claims, a search was made for correlations in the time-series of coincident gamma rays from positron-electron annihilations deriving from beta+ decay of Na-22. Disintegrations were counted within a narrow time window over a period of 167 hours.   The time series and frequencies of events were then examined in a variety of ways for evidence of correlations indicative of quantum-mechanical violating deviations from Poisson statistics.    Correlations in fluctuations signify information and therefore the potential for forecasting future events.   In this seminar I will discuss the statistical tests applied to the time series of nuclear decays-and what they may teach us in regard to forecasting stock-market price changes.

Oct. 15

Professor Eugene Chudnovsky
Department of Physics and Astronomy
CUNY Graduate School and Herbert H. Lehman College

Quantum Magneto-Mechanical Oscillations

In 1915 Einsten and de Haas measured the transfer of angular momentum from “molecular currents” to a macroscopic body by inducing mechanical rotation of the body through magnetization. While the balance of the angular momentum is now well understood, the mechanics of its transfer from atoms to the body as a whole remains obscure. The talk will address the physics of Einstein – de Haas effect, conservation of angular momentum in spin-lattice relaxation, recent experiments and theory on magnetic microcantilevers, and the possibility of quantum magneto-mechanical oscillations. 

Oct. 22

Professor David Bradley
Department of Physics and Astronomy
Vassar College

The Physics of Concert Halls and Fractals: Acoustic Wave Scattering in Critical Listening Environments

The process of scattering is found in many subfields of physics and engineering, including optics, crystallography, telecommunications, and imaging. In acoustics, scattering has applications in several areas including, acoustical oceanography, biomedical ultrasound, and structural vibration. This talk will focus on scattering surfaces in architectural spaces such as classrooms, recording studios, and concert halls. These scattering surfaces can be used to attenuate the effect of strong reflections, which can be detrimental in critical listening environments. An overview of the physics behind acoustic scattering will be given. Solutions will also be presented for the direct scattering problem of characterizing the distribution of scattered acoustic energy from rough surfaces exhibiting fractal geometries. The concept of fractals was developed by Mandelbrot to describe structures exhibiting self-similar characteristics, wherein the geometry is maintained through scale transformation (like mountains and the branching patterns of trees). Fractals are particularly intriguing in acoustic scattering since surface roughness occurs at multiple scales and can cause scattering at a variety of wavelengths, therefore producing scattering across a wider portion of the human audible frequency range: 20 – 20,000 Hz.

Oct. 29

Professor Kofi Odame
Thayer School of Engineering
Dartmouth College

How to be a Good Listener: Solving the Cocktail Party Problem

The human ear is adept at separating a cacophony of competing sounds - the clatter and chatter of a noisy restaurant, for instance - into distinct segments and selectively listening to a particular speaker.  Colin E. Cherry described this as our ability to solve the "cocktail party problem".  If machines could robustly solve the cocktail party problem, there would be tremendous
implications for cochlear implants, automatic speech recognition and computer audition in general.  In this talk, I will describe models and theories of how humans perform sound segregation, and will discuss the challenges that are involved in building a machine that can do the same.

Nov. 5

Professor Fulvio Melia
Department of Physics
University of Arizona

The Cosmic Horizon

Nov. 6  NOTE SPECIAL DAY AND TIME:  Friday Nov. 6, 4:30 pm (Merrill 3)

Professor Fulvio Melia
Department of Physics
University of Arizona

Cracking the Einstein Code

Einstein’s theory of general relativity describes the effect of gravitation on the shape of space and the flow of time. But for more than four decades after its publication, the theory remained largely a curiosity for scientists; however accurate it seemed, Einstein’s mathematical code was one of the most difficult to crack in all of science. That is, until a twenty-nine-year-old  Cambridge graduate solved the great riddle in 1963. Roy Kerr’s  solution emerged coincidentally with the discovery of black holes that  same year and provided fertile testing ground (at long last) for general   relativity. Today, scientists routinely cite the Kerr solution, but   even among specialists, few know the story of how Kerr cracked Einstein’s code.   In this talk, we will see how Kerr came to make his breakthrough. Today more than 300 million supermassive black holes are suspected of anchoring their host galaxies across the cosmos, and the Kerr solution is what astronomers and astrophysicists use to describe much of their behavior.

Nov. 12

Professor Michael Graf
Department of Physics
Boston College

The Lives and Deaths of Muons: Probing Magnetism in Condensed Matter

Muon spin relaxation/rotation (muSR) is an extremely sensitive local probe of the magnetic properties of materials, capable of detecting changes in the local field of less than a gauss. In this talk I will give an overview of the basic principles underlying the technique, and how we can extract physically relevant information about our sample. I'll illustrate these ideas using some examples from my research on magnetic superconductors and the single ion magnet system of Ho substituted for Y in a host crystal of LiYF4.

Nov. 19

Paul Hamilton
Department of Physics
Yale University

Search for the electric dipole moment of the electron

Electric dipole moments (EDMs) of fundamental particles in the Standard Model are so vanishingly small there is little chance they could ever be observed.  However, most theories beyond the Standard Model, e.g. supersymmetry, predict EDMs that could soon be observable.  In addition, the same physics responsible for EDMs could also help to explain the mysterious fact that the universe today consists almost solely of matter and not antimatter.

In this talk, I'll discuss how searches for EDMs with tabletop experiments can be sensitive to effects at energy scales typically reached only in particle colliders such as LHC.  In particular I'll focus on an experiment being carried out at Yale using lead oxide molecules.  I'll discuss several unique features of diatomic molecules that allow us to place extraordinarily precise limits on the electron EDM.  Finally, I'll briefly discuss two new electron EDM experiments that could have sensitivities several orders of magnitude beyond today's experiments.

Nov. 26

Thanksgiving Break

Dec. 3

Dr. Lorenzo Maccone
MIT

A Quantum Solution to the Arrow-of-Time Dilemma


The arrow of time dilemma: the laws of physics are invariant for time inversion, whereas the familiar phenomena we see  everyday are not (i.e. entropy increases).  I show that, within a quantum mechanical framework, all phenomena which leave a trail of information behind (and hence can be studied by physics) are those where entropy necessarily increases or remains constant. All phenomena where the entropy decreases must not leave any information of their having happened.  This situation is completely indistinguishable from their not having happened at all.  In the light of this observation, the second law of thermodynamics is reduced to a mere tautology: physics cannot study those processes where entropy has decreased, even if they were commonplace.

Dec. 8 (Tuesday) at 4:30 -  SPECIAL DAY AND TIME

Student Thesis Talks

Dec. 10 at 4:30 - SPECIAL TIME

Student Thesis Talks

Dec. 17

Reading Period

Dec. 24

Winter Recess

Spring 2010

Jan. 28

 

Feb. 4


Feb. 11

Prof. Panos Kevrekidis
Department of Mathematics and Statistics
University of Massachusetts - Amherst

The Many Faces of “Discreteness”:  From Granular Crystals and Layered Optical Media to Bose-Einstein Condensates and Beyond

In this talk, we'll touch on different aspects of discrete systems, as they arise in a variety of recent experiments pertinent to physical applications. We will start from the ``traditional'' spatial discreteness and how it affects elastic travelling waves in so-called acoustic or granular crystals. We will continue with a form of discreteness (or, more accurately, periodicity) in the evolution variable for pulses passing through a so-called layered optical medium and we will end with an example where the discrete number of components plays a crucial role in the dynamics of two coupled Bose-Einstein condensates in atomic physics. In each example, we will present the relevant dynamical models and we will attempt to mesh the mathematical analysis and numerical computations with experimental results. Finally, we will present some current and near future mathematical, computational and experimental questions of interest along these directions.

Feb. 18

Prof. Marc Achermann
Department of Physics
University of Massachusetts - Amherst

Optical Excitations and Interactions in Metal and Semiconductor Nanostructures

Advances in producing nanoscale materials have resulted in a wealth of novel nanomaterials with unprecedented optical and electronic properties. I will give an overview of our recent work on semiconductor, metal, and hybrid semiconductor-metal nanostructures. Using time-resolved optical spectroscopy we demonstrate that nanoscale engineering allows us to modify and control basic interactions that affect carrier and energy relaxation and transfer processes. Such processes are of fundamental importance in many photonic materials and electro-optical devices including optical sensors and light emitting and photovoltaic devices.

Feb. 25

Prof. Ryan Hayward
Department of Polymer Science and Engineering
University of Massachusetts

Swelling of constrained hydrogels: New approaches to active polymer microstructures

Soft solids placed under compressive stress can undergo a surface buckling instability leading to formation of sharply-folded creases on their free surfaces.  We study a particular example of this instability that occurs upon swelling of crosslinked polymer networks on rigid substrates; when placed in contact with solvent, they are subjected to compressive swelling stresses due to the constraint against lateral expansion imposed by the substrate.  We have studied a series of surface-attached hydrogels and found the conditions for instability to be rather insensitive to material properties or layer thickness, in accord with simple predictions.  Using temperature-responsive gels, we seek to elucidate the mechanism of crease formation and growth, as well as the evolution of crease structures.  Finally, we take advantage of this instability as a way to create dynamic polymer surfaces with reconfigurable chemical patterns.

Mar. 4

Dr. Lindley Winslow
Department of Physics
MIT

The Little Particle That Could: Neutrinos from the Earth, the Sun and Nuclear Reactors

Neutrinos are the lightest of the fundamental particles that make up the Standard Model of Particle Physics. They were often ignored in favor of their heavier relatives, but in the last decade they have provided exciting and surprising results that are changing our  understanding of particle physics. I will review the physics of the neutrino, and how the use of such diverse sources of neutrinos such as the sun and nuclear reactors were combined with immense detectors to make these discoveries.

Mar. 11

Dr. William Oliver
MIT - Lincoln Lab and the Research Laboratory for Electronics

Amplitude spectroscopy with a superconducting artificial atom

Superconducting persistent-current qubits are quantum-coherent artificial atoms with multiple energy levels. In the presence of large-amplitude harmonic excitation, the qubit state can be driven through one or more of the energy-level avoided crossings. The resulting Landau-Zener-Stueckelberg (LZS) transitions mediate a rich array of quantum-coherent phenomena as a function of the driving amplitude and frequency.

In this talk, we present three demonstrations of LZS-mediated quantum coherence in a strongly-driven niobium persistent-current qubit. The first is Stueckelberg interferometry [1], with which we observed quantum interference fringes in n-photon transition rates, with n = 1…50. The second is microwave-induced cooling [2], by which we achieved effective qubit temperatures < 3 mK. The third is amplitude spectroscopy [3], a new spectroscopy approach that allowed us to probe the energy spectra of our artificial atom from 0.01 – 120 GHz, while driving it at a fixed frequency 0.16 GHz.

[1] W.D. Oliver et al., Science 310, 1653 (2005)
[2] S.O. Valenzuela et al., Science (2006)
[3] D.M. Berns et al., Nature 455, 51 (2008)

Mar. 18

Spring Recess

Mar. 25

Prof. Peter Parker '58
Departments of Physics and Astronomy
Yale University

We are Stardust  - Explosive Nucleosynthesis

Laboratory measurements of nuclear reaction rates are essential for interpreting and understanding nova and supernova nucleosynthesis, etc.  Current laboratory innovations are focused on  -  the production and acceleration of beams of radioactive nuclei in order to measure the rates of reactions involved in explosive nucleosynthesis; together with the continuing development of more and more sophisticated detector systems; and the development and use of underground facilities to increase measurement sensitivity by reducing cosmic-ray background rates.

Apr. 1

Prof. David Roberts '69
Department of Physics
Brandeis University

Very Large Array Studies of the Marvelous Black Hole Binary System SS433

The binary X-ray source SS433 consists of an approximately ten solar mass black hole in close orbit with a luminous but otherwise ordinary star. Matter falls from the star down the deep gravitational well of the black hole, liberating massive amounts of potential energy. Since it contains angular momentum, the accreting gas cannot go directly into the black hole, but forms a disk of gas so hot that it radiates mostly in the X-ray band. Eventually angular momentum is transported out through the accretion disk, and material does spiral into the black hole. This system is a "micro-quasar," a miniature version of the massive accreting black hole systems thought to lie at the heart of active galaxies ("AGN") such as quasars, BL Lac objects, and radio galaxies, where the black holes range from a few million to a few billion solar masses.

The feature of SS433 that sets it apart from other micro-quasars is the oppositely-directed pair of plasma jets streaming away from the system at one-quarter of the speed of light. Unlike any other micro-quasar (or AGN for that matter), the jets are known to contain ionized hydrogen because they emit the typical recombination lines of the Lyman and Balmer series. The jets are visible in the radio band because they also contain highly relativistic plasma and magnetic field, and thus emit via the synchrotron process. They are visible over a distance of several thousand astronomical units. The jet system precesses about a cone of half-angle 20 degrees over a period of 162 days, causing alternate periodic red and blue shifts in the spectral lines from the two jets, and forming an enormous corkscrew out of each jet.

This talk will concentrate on what we have learned from multiple Very Large Array images of the jets as they precess and evolve. Because there is a detailed kinematic model of the jet motions, we can remove the effects of (special) relativity and study the intrinsic properties of the jets. This is the only object in the sky for which this can be done, and should shed light on the enigmatic properties of quasars and quasar jets.

This research is being supported by the William R. Kenan, Jr. Charitable Trust and Brandeis University.

 

Apr. 8

Prof. Robert Hallock
Department of Physics
University of Massachusetts - Amherst

Novel Behavior in Solid 4He – New Tricks in an Old Dog

 In the early 1970’s it was predicted that solid helium might display some unusual superfluid-like behavior.  Several years ago interest in the behavior of solid 4He was rekindled, first by John Goodkind’s group and shortly later in a more dramatic fashion by Eunseong Kim and Moses Chan who showed that when solid helium was put into rotation some of it seemed to be left behind.  Indeed, solid helium has over the past few years shown a variety of very unusual, even surprising, phenomena. Some of these will be briefly reviewed and then experiments that demonstrate the transmission of atoms through the solid in response to an applied chemical potential difference, which deepen the mystery, will be described in more detail. 

Apr. 15

reserved

Apr. 22

Dr. Michael Kavic
Department of Physics
The College of New Jersey

Quantum Gravitational AstrophysicsA theory of quantum gravity is required to properly describe the heart of a black hole or the initial state of our Universe. Much progress has been made in recent years in gaining a theoretical understanding of quantum gravity.In spite of the exotic elements contained in current models, such as extra spatial dimensions, no observational or experimental confirmation of a quantum gravitational theory has come to light. Certain astrophysical systems may probe quantum gravitational effects in a way that can not be replicated by ground based experimentation. I will review several examples of such astrophysical phenomena including outspiraling black hole/pulsar binaries, sparking superconducting cosmic strings, and exploding primordial black hole. The models under investigation and current observational efforts will also be discussed.

Apr. 27 (Tuesday)

Dr. Erik M. Kubik
Wesleyan UniverstyThe Search for Hawking Black HolesIt has been 36 years since Stephen Hawking first theorized the existence of quantum sized black holes which, due to their peculiar property of radiating quantum particles, turn out to be not so black. Strangely, despite this very useful signature for detection, no evidence of their existence has been ever found. Despite this disheartening experimental vacuum, the Hawking black hole has received a new lease on meta stable life with upcoming experiments at the Large Hadron Collider. Some theorists believe the very high LHC collision energies could produce the first signatures of Hawking radiation. This talk will discuss the bizarre properties of the Hawking black hole, how they could be produced at the LHC, and why the world is safe if such objects are created. In addition, based on research conducted at the University of Connecticut, a semi-classical model of these objects is constructed and a possible signature based on black hole-quantum field interactions is identified.

Apr. 29

student thesis talks

May 4

Dr. Ashley Carter
Physics Department
Harvard University

A Physicist's Look at DNA UnwindingThe inside of a cell is a dynamic place. Right now, donut-shaped protein motors are zipping along on your DNA, reading the genetic code and making RNA. Other two-legged protein motors are walking along molecular tracks in your body delivering neurotransmitter to the tips of your toes, a 1-meter trek. How does the cell accomplish all of this coordinated movement, and how can we as physicists build better tools to understand the underlying mechanics? In my talk I will try to answer these questions by reviewing what we know about how these protein machines convert chemical energy into mechanical work, and I will go over some of the amazing breakthroughs in technology that have enabled us to take ³molecular movies². My focus will be on the molecular motor, RecBCD, that can unwind DNA at the blinding speed of 1000 DNA base-pairs per second. This motor has been elusive to study in the past because of its small, Angstrom movements, and because it does not follow the rules of a typical protein motor. However, with improved optics instrumentation, we are now able to take a first look at how this incredibly efficient motor unwinds DNA. 

 

Student attendance at talks

Administrative notes

 

Physics and Astronomy Department

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

Particle Paths