2010 - 2011 Physics Colloquia

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 Larry Hunter with any questions about colloquia.


 Click here for the spring semester schedule

Fall 2010

Sept. 8 (Wednesday)

Professor William Phillips, NIST

"Spinning atoms with light: a new twist on coherent deBroglie-wave optics"

Physicists have used light and its polarization to manipulate the internal state of atoms since the 19th century.  Early in the 20th century, the momentum of light was used to manipulate the center-of-mass motion of atoms.  Optical pumping, coherent laser excitation, and laser cooling provided additional tools to affect both the internal and external states of atoms.  Bose-Einstein condensation created atomic samples having laser-like deBroglie wave coherence, and coherent atom optics provided mirrors and beamsplitters.  Now, light beams with orbital angular momentum (angular momentum associated not with the optical polarization, but with the shape of the spatial mode), provide a new tool for coherent manipulation of atomic motion, creating coherent rotation of atom clouds, and persistent flow of atoms in toroidal traps.

  

Sept. 9

 5 College - What is New in Physics, 7:30 PM

Professor William Phillips, NIST
"Time, Einstein and the coolest stuff in the universe "
At the beginning of the 20th century Einstein changed the way we think about Nature.  At the beginning of the 21st century Einstein's thinking is shaping one of the key scientific and technological wonders of contemporary life:  atomic clocks, the best timekeepers ever made.  Such super-accurate clocks are essential to industry, commerce, and science; they are the heart of the Global Positioning System (GPS), which guides cars, airplanes, and hikers to their destinations.  Today, atomic clocks are still being improved, using atoms cooled to incredibly low temperatures.  Atomic gases reach temperatures less than a billionth of a degree above Absolute Zero, without freezing.  Such atoms are at the heart of Primary Clocks accurate to better than a second in 80 million years as well as both using and testing some of Einstein's strangest predictions. 
 

This will be a lively, multimedia presentation, including experimental demonstrations and down-to-earth explanations about some of today's most exciting science.

 

Sept. 16

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

Sept. 23

William Tucker ('64) author of "Terrestrial Energy"

"E = mc2: The Key to Our Energy Future"

Why is nuclear energy so far superior to other forms of energy generation?  How does it compare with fossil fuels, wind, solar and other forms of generation?  It's a question that can be answered by the laws of physics known to any freshman.

Why do Americans have so much trouble accepting all this?  That's a question probably only Herodotus, in his wisdom, could answer.

Come find out why.

This talk is cosponsored by the environmental studies program.

 

Sept. 30

Professor Frank Wise, Dept. of Applied Physics, Cornell University

"Quantum Confinement of Electrons in Semiconductor Nanocrystals"

Nanometer-scale crystals of semiconductor materials can be synthesized routinely now.  Dramatic effects on the electronic and optical properties can be observed as consequences of quantum confinement of electrons.  The basic properties of semiconductor nanocrystals will be described, along with applications to bioimaging and future solar cells.

 

Oct. 7

Malcolm Boshier, LANL

"BECs in Painted Potentials"

By providing a way to put almost all of the particles in a system into a

single quantum state, Bose Einstein condensation opens up new possibilities
for controlling the configuration and evolution of quantum systems.  This is
one reason for the continuing excitement surrounding dilute gas
Bose-Einstein condensates (BECs).  To fully exploit this opportunity we
would like to have robust and straightforward methods to create potentials
for trapping BECs which are simultaneously dynamic, fully arbitrary, and
sufficiently stable to not heat the ultracold condensate.  I will discuss
how we have accomplished these goals using a rapidly-moving laser beam that
"paints" a time-averaged optical dipole potential in which we create BECs in
a variety of geometries, including toroids, ring lattices, and square
lattices.  Matter wave interference patterns confirm that the trapped gas is
a condensate.  We have now used the painted potential technique to study the
rotation of toroidal BECs.  In a toroidal trap, Bose-condensed atoms should
flow with a well defined winding number, making it an ideal system to
demonstrate the quantized nature of circulation.  I will explain how we
created BECs in traps rotating at different frequencies and then studied the
resulting superfluid flow in time of flight images.   Our results show that
the rotation of a toroidal BEC is indeed quantized, and that our painted
torus will support superfluid flows with winding number up to five.

Oct. 14

Professor Karen Sauer, George Mason University

"Exploiting Alternative Sources of Magnetization"

The most common way of creating magnetization involves placing particles with a
magnetic moment in a strong magnetic field. Alternative means of creating
magnetization opens up the possibility of working at lower magnetic fields, which are easier and less expensive to generate. In particular, I will focus on two alternative sources of magnetization – electrons polarized by light, and electric quadrupole moments oriented in an electric field gradient. Exploiting these sources permits many interesting applications, including the detection of explosives with an atomic magnetometer, lung imaging, and the creation of high nuclear polarization even in solids.

 Oct. 21

Miguel Novak, The Physics Institute of the Federal University of Rio de Janeiro and UMass
" Nanomagnetism: from magnetic nanoparticles to molecular nanomagnets "

A full description of the magnetic properties of nanoparticles is a
big challenge in science and technology, one of the main reasons is
due to the inherent existence of a distribution of sizes and shapes in
real materials. In this talk the main properties of real magnetic
nanoparticles will be reviewed  and how molecular magnetism has been
helping to understand its properties by providing beautiful
realizations of model systems. Some applications of magnetic
nanoparticles will also be presented.

 Oct. 28 

Nov. 4

Barry Honig, Columbia University Medical Center, Department of Biochemistry and Biophysics and the Center of Computational Bioinformatics

 

Nov. 11

Robert Hargraves, Dartmouth ILEAD

"Aim High"

Aim High proposes using thorium energy to address environmental problems. Mankind's fossil fuel burning releases CO2 into the atmosphere, contributing to global warming and deadly air pollution. Natural resources are rapidly being depleted by world population growth. Safe, inexpensive energy from the liquid fluoride thorium reactor can stop much global warming and raise prosperity of humanity to adopt US and OECD lifestyles, which include lower, sustainable birth rates.

Oak Ridge first developed molten salt reactor technology in 1958-1976. Thorium fuel is transformed to uranium-233 which fissions, producing heat and electric power at a cost less than that from coal power plants -- the only way to dissuade developing nations from burning coal. Thorium produces less than 1% of the long-lived radioactive waste of today's nuclear power plants. Existing nuclear power plant waste can be consumed. One ton of plentiful thorium costing $300,000 provides 1 GW-year of electric energy, enough for a city. A 5-year NASA-style shoot-the-moon project can complete technology development of this inexpensive, safe, clean power.

Robert Hargraves co-authored Liquid Fluoride Thorium Reactors in the July/August 2010 issue of American Scientist. He is currently teaching Energy Policy and Environmental Choices: Rethinking Nuclear Power at Dartmouth ILEAD in Hanover NH. He was Chief Information Officer at Boston Scientific 1994-2000, senior consultant at Arthur D. Little 1982-1994, Vice President Metropolitan Life Insurance Company 1980-1982, President of DTSS Incorporated 1972-1980, and Assistant Professor of Mathematics and Associate Director of Kiewit Computation Center at Dartmouth College 1967-78. He earned a PhD in high energy physics from Brown University 1967, and an AB majoring in both mathematics and physics at Dartmouth College 1961.
This talk is co-sponsored by the Environmental Studies Program.

Nov. 15 (Monday, 4:30 PM, Fayerweather 117, cosponsored with the department of Philosophy)

Prof. Allen Stairs, University of Maryland

"How Spooky is Einstein's Spooky Action at a Distance?"
In 1935, Einstein, Podolsky and Rosen (EPR) published a paper on quantum mechanics that continues to beguile physicists, philosophers and lay people alike. Out of it grew the notion that quantum mechanics involves a "spooky action at a distance" that has given rise to some remarkable claims - physical, philosophical, metaphysical and even "spiritual." While there is no doubt that EPR raised deep and important questions, I will argue that the situation may be a little less spooky than is often assumed.

 

Nov. 18

Brian Wecht, University of Michigan 

"Supersymmetry as a Theoretical Toolbox"

One usually first hears about supersymmetry as the leading candidate for physics beyond the Standard Model. However, many physicists see supersymmetry as useful for an entirely different purpose, namely, as a method of understanding hard problems in quantum field theory. In this talk, I will describe what quantum field theory is, why it's difficult, and how supersymmetry can help us make progress in understanding it.

Nov. 25

Thanksgiving Break


Dec. 2 

            Student Thesis Talks


Dec. 7 (Tuesday)

Student Thesis Talks

 

Dec. 9

Student Thesis Talks


Dec. 16

Reading Period

Dec. 23

Winter Recess


Spring 2011

Jan. 25

David Weld, Massachusetts Institute of Technology

"Thermometry and Cooling with Ultracold Spin Mixtures in Optical Lattices"

Ultracold atoms in optical lattices are expected to exhibit correlated magnetic quantum phases, but only below a Curie or Néel temperature which is typically less than 1 nanoKelvin. Realization and measurement of this low temperature is the most challenging obstacle on the path towards observation of quantum magnetism in lattice-trapped gases.  We use a two-component mixture of rubidium atoms in a 3D lattice to demonstrate a new type of thermometry called spin gradient thermometry, which allows direct measurement of a broad range of temperatures in the Mott insulator. Furthermore, we show that this system enables a powerful new cooling technique analogous to adiabatic demagnetization refrigeration. We present initial results of adiabatic demagnetization cooling experiments, which have achieved temperatures of 350 picoKelvin, lower than any ever measured in any system.  We discuss prospects for the use of these techniques to enable "quantum simulation" experiments.

Jan. 27

Dan McKinsey, Yale

"Direct Dark Matter Detection Using Liquefied Noble Gases"
Astrophysical evidence on a variety of distance scales clearly shows that we cannot account for a large fraction of the mass of the universe. This matter is “dark”, not emitting or absorbing any electromagnetic radiation. A compelling explanation for this missing mass is the existence of Weakly Interacting Massive Particles (WIMPs).
These particles are well motivated by particle physics theories beyond the Standard Model, and the discovery of WIMPs would have enormous impact on both astrophysics and particle physics. WIMPs, if they exist, would occasionally interact with normal matter. With a mass in the range of 1 to 1000 times the mass of the proton, and moving at speeds relative to the Earth of about 220 km/s (the velocity of the Sun around the MilkyWay), WIMPs would only deposit a small amount of energy when scattering with nuclei.
Detectors that are low in radioactivity and sensitive to small energy depositions can search for the rare nuclear recoil events predicted by WIMP models.  In recent years, several new efforts on direct dark matter detection have begun in which the detection material is a noble liquid. Advantages include: large nuclear recoil signals in both scintillation and ionization channels, good scalability to large target masses, effective discrimination against gamma ray backgrounds, easy purification, and reasonable cost.

Feb. 1

Angela Reisetter, St. Olaf College

Dark Matter:  How will we know it when we see it?"

Astronomical observations indicate that the vast majority of the matter in the universe is composed of an unknown substance:  dark matter.  Dark matter has never been detected in our laboratories here on earth, but there is a possibility we may discover it in the next few years.  In this talk, I will review searches for dark matter of the form of Weakly Interacting Massive Particles (WIMPs), including WIMP theory and promising detector concepts.  I will focus in particular on the detectors and data of the Cryongeic Dark Matter Search (SuperCDMS), an international leader in WIMP sensitivity and pioneer in solid state detector technology, which may be one of the first to see a signal.  I will also summarize the current state of the field, including some puzzling results that have been published recently, and what the future might hold as we try to figure out the composition of the universe.

Feb. 3

David Hanneke, University of Colorado

Measuring the Electron Magnetic Moment

Measurements of the electron magnetic moment (the "g-value") probe the electron's interaction with the fluctuating quantum vacuum. With a quantum electrodynamics calculation, they provide the most accurate determination of the fine structure constant. Comparisons with independent determinations of the fine structure constant are among the most precise tests of any physical theory. This talk will present an experiment that measures the g-value with an accuracy of 0.3 parts-per-trillion. The experiment involves trapping a single electron, resolving quantum jumps between harmonic oscillator eigenstates, and evaluating systematic effects related to the coupling of the electron's motion to a microwave cavity. I will conclude with future precision measurement goals including promising new techniques.

Feb. 10

Alexander Sushkov, Yale University

"Why does the universe have more matter than anti-matter? A laboratory search for violation of parity and time-reversal symmetries in a solid ferroelectric"

The study of Nature's discrete symmetries (charge conjugation C, parity P, and time reversal T) is five decades old, but what we know about the breaking of these symmetries is not enough (by ten orders of magnitude) to explain the apparent matter-antimatter asymmetry of the universe. One of the ways to study the breaking of parity and time-reversal symmetries is to search for the permanent electric dipole moment (EDM) of the electron. I will describe an experimental search for this EDM, based on a solid paramagnetic ferroelectric Eu_{0.5} Ba_{0.5} Ti O_3. We search for an electric field-induced magnetization of this material. Using a solid ferroelectric leads to experimental sensitivity enhancement, originating from large densities n = 10^{22} cm^{-3}, and from large effective electric fields E = 10 MV/cm, due to the ferroelectric off-centering of the Eu^{2+} ions in the crystal lattice.

Feb. 17

James Battat, Massachusetts Institute of Technology

"Solar System Tests of Gravity and the Hunt for Dark Matter: Uncovering the Nature of the Dark Universe"

Astrophysical observations interpreted through the lens of General Relativity reveal that 85% of the matter in the Universe is “dark” -- not only invisible to telescopes, but also fundamentally different than any particle known to date.  This discovery cries out for elaboration:  How well do we understand gravity?  What is dark matter?  In the first part of this talk, I will discuss a high-precision test of gravity in the Solar System.  Using pulsed laser light, the Apache Point Observatory Lunar Laser-ranging Operation (APOLLO) measures the Earth-Moon distance with a precision of one millimeter.  This provides the leading sensitivity to many aspects of gravitational physics including the strong equivalence principle, the temporal evolution of Newton's constant, and deviations from the Newtonian 1/r potential.  The second part of the talk focuses on the search for dark matter particles in the laboratory.  I will describe the Dark Matter Time Projection Chamber (DMTPC), which is sensitive to the unambiguous, but as-yet unexploited, signature of dark matter:  the head-wind of particles produced by the Earth’s motion through the Galaxy.  Together, APOLLO and DMTPC will improve our understanding of the dark universe.

Feb. 22

Courtney Lannert, Wellesley College

"Studying Quantum Dynamics in Ultracold Atomic Systems"

Quantum effects underlie many of the fascinating properties of many-particle systems: the superconductor that can conduct electricity with zero resistance, the Bose-Einstein Condensate in which millions of atoms behave as one, magnetic phases that spontaneously develop ordered patterns. These behaviors have their roots in quantum correlations between the particles in the system, which may one day be harnessed to make quantum computers. In order to control and manipulate these correlations, we must understand how quantum systems respond to changes in their environments. In this talk, I will present some recent theoretical and numerical investigations of ``quantum quenches" in which sudden changes in system parameters lead to, for instance, relaxation without dissipation and emergent long-range correlations. The most promising systems in which to test these predictions are in the field of ultracold atoms, in which experimenters can manipulate quantum systems with unprecedented control.

Feb. 24

Ashley Carter, Amherst College

"Using Lasers to Observe the Mechanics of Cellular Life"

Many cellular processes are mechanical. Molecules inside the cell constantly move, bump, interact, and bind. Cellular structures respond to shear forces as well as tension and compression. Finally, the cell itself moves, protrudes, and adheres to external surfaces. How does life solve these mechanical problems? In my talk I will explore this question using a laser technique – optical tweezers. I will first review some key experiments and then focus on an amazing molecule, RecBCD, that can unwind DNA at the blinding speed of 1000 DNA base-pairs per second. While this motor has been elusive to study in the past, I will show that with an improved laser setup we have some new evidence for how RecBCD turns chemical energy into mechanical work. At the end, I will turn my attention to some exciting future studies using lasers to observe the mechanics of cellular life.
 

Mar. 3

Professor Philip B. Allen, Department of Physics & Astronomy, Stony Brook University
"Normal Modes of Vibration: Einstein, Eucken, Debye, and the Birth of Solid-State Physics" 
An amazing scientific revolution happened during the gloriously confusing years 1895-­‐1914. The atom was  finally “seen” and accepted as “real” rather than an unmeasurable idealization. The three  dominant  physicists of the  20th century  (Rutherford, Einstein, and Bohr) were in their youthful prime.  “Chemical Physics”  became a science, which continues to thrive today, as the basis for the material science, electronics and biomedical advances, that still have not reached a horizon. During the years 1906-­‐1913, several key discoveries mark the birth of solid-­‐state physics. Einstein brilliantly applied the early quantum theory of Planck to the problem of mechanical oscillations of molecules, helping to understand the mysterious low temperature suppression of specific heat of solids. Eucken made the first systematic study of heat conductivity, finding that the conductance of solids diminishes as the reciprocal absolute temperature. Einstein was unable to reconcile this with existing theories, but Debye  succeeded. His formulation, "a perfect harmonic crystal is a perfect heat conductor,” is the first example of our modern understanding of solid-­‐state physics. This lecture will be illustrated with some demonstrations of heat conduction, and of the normal modes of vibration, which are the basis of our modern picture.

 

Mar. 10

Professor Maria Kilfoil, University of Massachusetts (co-sponsored by the biochemistry-biophysics program) 
"Cell Mechanics In Vitro and in Living Cells"

Mar. 17

Spring Recess

Mar. 24

Professor Irwin Shapiro, Harvard-Smithsonian Center for Astrophysics

"A Half-Century Quest to Measure Einstein's Prediction of Frame Dragging"

1918 marked the first realization that the then new Einstein Theory of General
Relativity predicts that a rotating mass "drags" inertial frames. A serious
experimental effort to test this prediction has been in progress for the last
half century, culminating in the 2004 launch of the NASA/Stanford Gravity-Probe
B spacecraft, probably the most sophisticated experiment ever launched in terms
of its many novel, innovative features. I will discuss this experiment and the
present status of the analysis, along with the outcome of complementary tests of
frame dragging made in the last decade with the LAGEOS satellites.

Mar. 31

Dr. Taviare Hawkins, UMass

"Measuring the Persistence Length of Stable Microtubules"

The most rigid cytoskeletal filaments are microtubules. They are composed of alpha and beta tubulin dimers that join together to form protofilaments that bind side-to-side into a hollow tube. Microtubules are cylindrical polymer filaments with an outer diameter of 25 nm and an inner diameter of about 17 nm. They range in lengths from microns to millimeters, and serve as the scaffolds for extended cellular shapes. They are essential for cellular division and provide the intracellular highways for protein transport. The microtubule must be rigid to provide cellular support yet flexible to aid during mitosis. We are interested in how the mechanical properties of stable microtubules change over time. We measured the persistence length of freely fluctuating taxol-stabilized microtubules and analyzed them via Fourier decomposition. We found that, the persistence length measurement revealed two populations: one that had a length independent persistence length and one that was length dependent. The length dependent population died out after 24 hours. We also discovered that fluorescent labeling of the filaments affected the persistence length and observed that a higher labeling ratio corresponded to greater flexibility.

Apr. 7

Dr. Matthew Lang, Vanderbilt 

“Single-molecule Studies of ClpXP Fully Loaded”

ClpX is a ring-shaped molecular motor involved in cellular protein degradation. Fueled by ATP, ClpX works in tandem with protease ClpP to recognize, unfold, translocate and finally cleave protein substrates. ClpX is part of the versatile AAA+ family, which carry common structural features while supporting diverse cellular processes. ClpXP activity is probed at the single molecule level using both a single molecule fluorescence assay and a loaded assay employing an optical double-trap geometry for both low noise and passive-force clamping.  In the single molecule fluorescence assay, ClpXP activity is monitored using a series of fluorescently labeled substrates. In the fully loaded assay, a single-chain ClpXP motor with a poly-linked substrate engaged into its pore is tethered between two trapped polystyrene beads held in a dumbbell configuration. The variation in substrate length is monitored throughout degradation by tracking bead separation allowing for direct measurement of: unfolding times, translocation velocity and translocation stepping.

Apr. 14

Prof. David Kaiser, MIT

"How the  Hippies Saved Physics"

In recent years the field of quantum information science   -- an amalgam of topics ranging from quantum encryption, to quantum computing, quantum teleportation, and more -- has catapulted to the cutting edge of physics, sporting a multi-billion-dollar research program, tens of thousands of published research articles, and a viraiety of device prototypes.  This tremendous excitement marks the tail end of a long-simmering Cinderella story.  Long before the big budgets and dedicated teams, the field moldered on the scientific sidelines.  In fact, the field's recent breakthroughs derive, in part, from the hazy, bong-filled excesses of the 1970s New Age movement.  Many of the ideas that now occupy the core of quantum information science once found their home amid an anything-goes counterculture frenzy, a mismash of spoon-bending psychics, Eastern mysticism, LSD trips, and CIA spooks chasing mind-reading dreams.  For the better part of a decade, the concepts that would, in time, blossom into developments like quantum encryption were bandied about in late-night bull sessions and hawked by proponents of a burgeoning self-help movement -- more snake oil than stock option.  This talk describes the field's bumpy transition from New Age to cutting edge.

David Kaiser is an associate professor at MIT, where he teaches in the Program in Science, Technology, and Society and in the Department of Physics.  He completed Ph.D.s in physics and the history of science at Harvard University.  Kaiser is author of the award-winning book, Drawing Theories Apart: The Dispersion of Feynman Diagrams in Postwar Physics, (2005), which traces how Richard Feynman's idiosyncratic approach to quantum physics entered the mainstream.  His latest book, How the Hippies Saved Physics: Science, Counterculture, and the Quantum Revival, will be published this June by W.W. Norton.  Honors include awards from the American Physical Society, the History of Science Society, the British Society for the History of Science, and MIT.

Apr. 21

student thesis talks 
Emine Altuntas: "Real-Time Dynamics of Co-Rotating Vortex Pairs in Bose-Einstein Condensate"s

Thomas Langin: "Generation of Counter-Circulating Vortex Lines in a Bose-Einstein Condensate"
Apr. 26 (Tuesday)

student thesis talks

Andrew Eddins: "Superradiance in Fe^8 Single-Molecule Magnets"

Andrew Greenspon:

Apr. 28

student thesis talks

Ojeh Bikwa:

Thomas McClintock: "The Contribution from Low-Mass X-Ray Binaries to the Positron Annihilation in the Galactic Disk"

Kathryn McKinnon:

May 5   

              Last week of classes.  No Seminar


 

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