The David and Edith Harris Physics Colloquium Archives

Spring 2014 Schedule

FEBRUARY 6, 2014
Harvard University
Hosted by Wolfgang Ketterle

"iOrder of Magnitude Smaller Limit on the Electric Dipole Moment of the Electron"

The Standard Model (SM) of particle physics is known to be incomplete. Extensions to the SM, such as weak-scale Supersymmetry, posit the existence of new particles and interactions that are asymmetric under time-reversal (T), and nearly always predict a small, yet potentially measurable (10-27-10-30 electron electric dipole moment (EDM, de). The EDM is an asymmetric charge distribution along the spin that is also asymmetric under T.
About five years ago, ACME, a collaboration between groups at Yale and Harvard universities (, embarked upon an improved search for the electron EDM. Using the polar molecule thorium monoxide (ThO), we have now measured de =(-2.1+-3.7stat +-2.5syst) X 10-29 This corresponds to an upper limit of |de| < 8.7 X 10-29 with 90 percent confidence, an order of magnitude improvement in sensitivity compared to the previous best limits. Our result constrains T-violating physics at the TeV energy scale.

FEBRUARY 13, 2014
Lorenz Center
Department of Earth, Atmospheric, and Planetary Sciences
Massachusetts Institute of Technology
Hosted by Mehran Kardar

"Branching of Stream Networks"

The geometric complexity of stream networks has long been a source of fascination.  This talk addresses the mechanisms via which such networks branch.  We initially focus on streams incised by groundwater flow.  By representing streams as paths in a diffusing field, we predict a characteristic branching angle of 2pi/5 = 72 degrees. Our observations of bifurcated streams growing in a goundwater field on the Florida Panhandle confirm this model.  Further investigation of stream bifurcations throughout the continental United States suggests that the 2pi/5-bifurcation characterizes landscapes in wet climates, or, more generally, networks driven externally by harmonic fields.

FEBRUARY 20, 2014
Physics in the Interest of Society Colloqium
Carnegie Endowment for International Peace
Hosted by Aron Bernstein

"The Cold War Hangover: Nuclear Risks and Political Realities in the 21st Century"

In April 2009, President Barack Obama recommitted the United States to the “peace and security of a world without nuclear weapons.” However, after signing a modest arms reduction treaty with then Russian President Dmitri Medvedev a year later, progress on this agenda has stalled. James Acton will discuss both the underlying challenges associated with “getting to zero,” as well as the short-term stumbling blocks to continued progress in U.S.-Russian reductions. He will also explore some of the technical issues raised by the current impasse. In particular, officials in Moscow have repeatedly expressed concerns about the vulnerability of Russia’s nuclear forces to U.S. high-precision conventional weapons and have stated that they are unwilling to agree to further nuclear reductions unless these concerns are addressed. But, from a technical perspective, how reasonable are these concerns? And what can be done politically to ease them?

FEBRUARY 27, 2014
University of California, Berkeley
Hosted by Nuh Gedik

"Topological Phenomena in Quantum Matter"

Following the experimental discovery of topological insulators, intensive work over the last five years has revealed that these are just the tip of the iceberg of a wider set of topological phenomena that occur in solids. I will discuss recent breakthroughs in this rapidly advancing field. First, I will talk about Weyl semimetals, which provide a realization of Weyl’s 85 year old equation and which possess an exotic Fermi surface that spans opposite faces of a sample. Next, I will talk about new theoretical development on topological insulators, which have enabled us to access strongly interacting systems, liberating us from the traditional one-electron description of these phases. This has led to the prediction of new physical properties and new phases in interacting systems. Finally, I will discuss the important role quantum entanglement has played in these developments.

MARCH 6, 2014
Princeton University
Hosted by the Society of Physics Students

"Once Upon a Time in Kamchatka:  The Search for Natural Quasicrystals"

Quasicrystals are exotic forms of matter that have symmetries once thought to be forbidden for solids, such as five-fold symmetry in two dimensions or icosahedral symmetry in three dimensions.  They were first hypothesized and discovered in the laboratory 30 years ago, but could Nature have beaten us to the punch? This talk will describe the dozen-year search that eventually answered this question, one of the strangest scientific stories you are ever likely to hear.

MARCH 13, 2014
Harvard University
Hosted by the Physics Graduate Student Council

"Quantum Matter without Quasiparticles"

The quasiparticle concept is the foundation of our understanding of the dynamics of quantum many-body systems. It originated in the theory of metals, which have electron-like quasiparticles; but it is also useful in more exotic states like those found in fractional quantum Hall systems or in one-dimensional wires.  However, modern materials abound in systems to which the quasiparticle picture does not apply, and developing their theoretical description remains one of the most important challenges in condensed matter physics. I will describe recent progress in understanding the dynamics of two systems without quasiparticles: (i) ultracold atoms in optical lattices, and (ii) the nematic quantum critical point of metals with applications to the `strange metal’ found in the high temperature superconductors.

MARCH 20, 2014
Northwestern University
Hosted by Peter Fisher

"The Measure of All Things: Measurement Standards and the Origins of Scientific Values"

This talk examines the origins and meaning of measurement standards--and of the metric system in particular.  It explains why the meter was originally defined as one ten-millionth of the quarter meridian, and recounts the misadventures of the two astronomers who conducted the relevant geodetic measurements during the upheavals of the French Revolution (1792-99).  But as documents I discovered in the Observatoire de Paris show, some of the data for this determination was "fudged," and worse, this fact was known and covered up at the time.  The episode illustrates a transformation in scientific values: both because it gave rise to modern error theory and because it heralded a new sense of proper scientific practice.  These measurements also contributed--in the long run and in the face of considerable resistance--to a new way of assessing the value of commodities in the global economy.

Hosted by Peter Fisher

"Our Mathematical Universe: From Inflationary B-modes to Precision 3D Mapping of our Cosmos"

I survey how we humans have repeatedly underestimated not only the size of our cosmos, but also the power of our humans minds to understand it using mathematical equations. My examples include the recent discovery of B-modes in the cosmic microwave background, providing smoking-gun evidence for quantum gravity, Hawking radiation, and cosmological inflation. I also highlight mysteries such as the nature of dark matter, dark energy and our early universe, and how creating the largest-ever 3D maps of our universe can shed new light on them.

APRIL 10, 2014
Max Planck Institute for the Structure and Dynamics of Matter, Hamburg; Department of Physics, University of Oxford
Hosted by Nuh Gedik

"Optical Control of Solids by “Nonlinear Phononics”"

In this talk, I will discuss some of our recent work aimed at controlling the properties of condensed matter with light. The goal is to use light to switch the electronic, magnetic and structural phases of matter, understand phase competition, control emergent properties at ultrahigh speed and maybe develop new strategies for high bit rate devices. I will focus on the development of strong field mid infrared excitation of infrared active vibrations, which we drive directly with THz pulses. By driving vibrations that break inversion symmetry to large amplitudes, we explore a regime of coherent control in which the phonon couples quadratically to other degrees of freedom, a situation that rarely occurs near equilibrium, where low thermally populated modes act linearly on anharmonically coupled excitations. I will discuss our results in the control of electronic and magnetic phases and our discovery of light induced superconductivity in the normal state of cuprates. I will also discuss how X-ray Free Electron Lasers can aid this research, allowing for the crystallography of transient states to be determined.

APRIL 17, 2014
University of California, Berkeley
Hosted by Wolfgang Ketterle

"Cavity Optomechanics with a Gas of Cold Atoms"

In cavity optomechanical systems, the motion of a mechanical element is sensed by its influence on the field within an electromagnetic resonator.  While their experimental realizations are diverse, with mechanical elements ranging from picogram-scale nanofabricated filaments to the kilogram-scale mirrors of the LIGO detector and optical systems ranging from stripline resonators to kilometers-long optical cavities, such systems are converging on the common goal of quantum limited operation.   I will discuss the use of ensembles of ultracold trapped atoms as mechanical elements within a high-finesse optical cavity.  With this system, we realize cavity optomechanics in a regime where both the "opto" and the "mechanics" portions of the hybrid system show distinct quantum mechanical features.  I will conclude by describing experiments to sense forces at the standard quantum limit.

APRIL 24, 2014
University of Massachusetts, Amherst
Hosted by Jesse Thaler

"Fundamental Symmetries of the Early Universe and the Origin of Matter"

Explaining why the universe contains more matter than antimatter remains an open problem at the interface of particle and nuclear physics with cosmology. While the Standard Model of particle physics cannot provide an explanation, various candidates for physics beyond the Standard Model may do so by breaking fundamental symmetries. Among the most interesting and testable scenarios are those that would have generated the matter-antimatter asymmetry roughly 10 picoseconds after the Big Bang. I discuss recent theoretical ideas for such scenarios, developments in computing their dynamics, and prospects for testing their viability with experiments at the high energy and high intensity frontiers.

MAY 1, 2014
California Institute of Technology
Hosted by Deepto Chakrabarty

"The Nuclear Spectroscopic Telescope Array (NuSTAR) High-Energy X-ray Mission: Bringing the High Energy Universe into Focus"

The Nuclear Spectroscopic Telescope Array, the first focusing high-energy X-ray  (3 – 79 keV) telescope in orbit, extends sensitive X-ray observations above the band pass where Chandra and XMM-Newton operate.   With an unprecedented combination of sensitivity, spectral and imaging resolution above 10 keV, NuSTAR is advancing our understanding of black holes, neutron stars, and supernova remnants.  I will describe the mission, and present science highlights to-date from the two-year baseline mission.

MAY 8, 2014
Cornell University
Hosted by Jeremy England

"Flight of the Fruit Fly"

There comes a time in each of our lives where we grab a thick section of the morning paper, roll it up and set off to do battle with one of nature’s most accomplished aviators - the fly. If however, instead of swatting we could magnify our view and experience the world in slow motion we would be privy to a world-class ballet full of graceful figure-eight wing strokes, effortless pirouettes, and astonishing acrobatics. After watching such a magnificent display, who among us could destroy this virtuoso? How do flies produce acrobatic maneuvers with such precision? What control mechanisms do they need to maneuver? More abstractly, what problem are they solving as they fly? Despite pioneering studies of flight control in tethered insects, robotic wing experiments, and fluid dynamics simulations that have revealed basic mechanisms for unsteady force generation during steady flight, the answers to these questions remain elusive. In this talk I will discuss our strategy for investigating these unanswered questions. I will begin by describing our automated apparatus for recording the free flight of fruit flies and our technique called Hull Reconstruction Motion Tracking (HRMT) for backing out the wing and body kinematics. I will then show that these techniques can be used to reveal the underlying mechanisms for flight maneuvers, wing actuation, and flight stability. Finally, I will comment on the implications of these discoveries for investigations aimed at elucidating the evolution of flight.

MAY 15, 2014
JILA, NIST and, University of Colorado, Boulder
Hosted by the Undergraduate Women in Physics

"Building with Crystals of Light: From Clocks to Computers"

Understanding the behavior of interacting electrons in solids or liquids is at the heart of modern quantum science and necessary for technological advances. However, the complexity of their interactions  generally prevents us from coming up with an exact mathematical description of their behavior. Precisely engineered ultracold gases are emerging as a powerful tool for unraveling these challenging physical problems. Atoms or molecules cooled down to ultra-low temperatures and  trapped in artificial crystals of light  behave like electrons in a solid crystal. In  contrast to electrons in solids, however,  atomic systems  have the advantage that  they are free of defects or disorder and fully tunable.

In this talk, I will present our recent developments at JILA on using atoms and molecules in crystals of light for the investigation of complex many-body phenomena and magnetism.  I will also explain how atoms inside crystals of light can be used to create the best atomic clock in the world. Finally, I will discuss a new research direction of using clocks not only as precise time keepers but also as unique quantum laboratories for the investigation of new forms of matter with no known counterpart in Nature.