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# Physics Colloquia Archives

## Spring 2007

Thursday, February 8, 2007

**PETER ZOLLER**

Universität Innsbruck

"Condensed matter physics and quantum information processing with cold polar molecules"

We discuss prospects offered by cold polar molecules in the context of implementing strongly interacting condensed matter systems and quantum information processing. In the talk we will first give a general introduction and survey of basic ideas, and then focus on particular examples including realization of general 2D spin models with molecules in optical lattices, the formation of 2D self- assembled lattices of polar molecules, and molecular ensembles as quantum memory.

Thursday, February 15, 2007

**GERALD GABRIELSE**

Harvard Unversity

"New Measurement of the Electron Magnetic Moment and the Fine Structure Constant"

Remarkably, the famous UW measurement of the electron magnetic moment has stood since 1987. With QED theory, this measurement has determined the accepted value of the fine structure constant. This colloquium is about a new Harvard measurement of these fundamental constants. The new measurement has an uncertainty that is about six times smaller, and it shifts the values by 1.7 standard deviations. One electron suspended in a Penning trap is used for the new measurement, like in the old measurement. What is different is that the lowest quantum levels of the spin and cyclotron motion are resolved, and the cyclotron as well as spin frequencies are determined using quantum jump spectroscopy. In addition, a 0.1 K Penning trap that is also a cylindrical microwave cavity is used to control the radiation field, to suppress spontaneous emission by more than a factor of 100, to control cavity shifts, and to eliminate the blackbody photons that otherwise stimulate excitations from the cyclotron ground state. Finally, great signal-to-noise for one-quantum transitions is obtained using electronic feedback to realize the first one-particle self-excited oscillator. The new methods may also allow a million times improved measurement of the 500 times smaller antiproton magnetic moment.

Thursday, February 22, 2007

**BEN OPPENHEIMER**

American Museum of Natural History

"The Lyot Project: Direct Imaging and Spectroscopy of Exoplanets"

Numerous projects are on going to image exoplanets directly, permitting spectroscopic and astrometric study of them at a level of detail never before possible. I will describe my instrumentation and observational work in this area concentrating on the Lyot Project, the world's first optimized coronagraph, and the Gemini Planet Imager, due for first light in December 2010. Results include new portraits of circumstellar disks and a few intriguing companions of nearby stars.

Thursday, March 1, 2007

**MICHAEL SIPSER**

MIT

"Beyond Computation: The P versus NP question"

In a remarkable 1956 letter, the great logician Kurt Godel asked the famous mathematician and computer pioneer John von Neumann whether certain computational problems could be solved without resorting to brute force search. In so doing, he foreshadowed the P versus NP problem, one of the great unanswered questions of contemporary mathematics and theoretical computer science. A solution to this problem would reveal the theoretical limitations of computer power for solving puzzles, cracking codes, proving theorems, and optimizing many practical tasks.

We'll discuss all this and more...

Thursday, March 8, 2007

**TOM LEVENSON**

MIT

"The Suddenly Famous Dr. Einstein"

In collaboration with an Astronomical Event

In April, 1914, Albert Einstein arrived at the top of the European academic scene: Berlin, at once an ambitious imperial capital, and a city determined to be seen as the center civilized life. Berlin. Eighteen years later he left a destitute city on the verge of utter disaster, less than one month before Adolf Hitler became chancellor of Germany. On his arrival, he was little known outside the very small community of professional physicists, with almost no discernable interest in the world beyond that of his family, friends, and colleagues. He left as the Albert Einstein we remember: the architect of much of modern physics, the first modern celebrity – really icon – of reason, and an internationally recognized moral witness to the unfolding catastrophe centered on his adopted home. This colloquium will examine Einstein’s path through his Berlin years as a classic story of education – not in the books-and-blackboards sense, but in the Henry Adams mode, as a considered accumulation of experience. In doing so, I will argue that Einstein’s progress through Berlin offers a unique window not just on the evolution of physics, but on what went so badly wrong in Europe in the first half of the 20th century.

Thursday, March 15, 2007

**JOAN CENTRELLA **

NASA

"Binary Black Holes, Gravitational Waves, and Numerical Relativity"

The final merger of two black holes releases a tremendous amount of energy and is one of the brightest sources in the gravitational wave sky. Observing these sources with gravitational wave detectors requires that we know the radiation waveforms they emit. Since these mergers take place in regions of very strong gravitational fields, we need to solve Einstein's equations of general relativity on a computer in order to calculate these waveforms.

For more than 30 years, scientists have tried to compute these waveforms using the methods of numerical relativity.

The resulting computer codes have been plagued by instabilities, causing them to crash well before the black holes in the binary could complete even a single orbit.

Recently this situation has changed dramatically, with a series of amazing breakthroughs. This talk will take you on this quest for the holy grail of numerical relativity, showing how a spacetime is constructed on a computer to build a simulation laboratory for binary black hole mergers.

We will focus on the recent advances that are revealing these waveforms, and the dramatic new potential for discoveries that arises when these sources will be observed by LIGO and LISA.

Thursday, March 22, 2007

**WILLIAM BIALEK**

Princeton University

"Some physics problems in biological networks"

Most of the interesting things that happen in living organisms require interactions among many components, and it is convenient to think of these as a ``network'' of interactions. We use this language at the level of single molecules (the network of interactions among amino acids that determine protein structure), single cells (the network of protein-DNA interactions responsible for the regulation of gene expression) and complex multicellular organisms (the networks of neurons in our brain). In this talk I'll try to look at two very different kinds of theoretical physics problems that arise in thinking about such networks. The first problems are phenomenological: Given what our experimentalist friends can measure, can we generate a global view of network function and dynamics? I'll argue that maximum entropy methods can be surprisingly useful here, and show how such methods have been used in very recent work on networks of neurons, enzymes, genes and (in disguise) amino acids. In this line of reasoning there are of course interesting connections to statistical mechanics, and we'll see that natural statistical mechanics questions about the underlying models actually teach us something about how the real biological system works, in ways that will be tested through new experiments. In the second half of the talk I'll ask if there are principles from which we might actually be able to predict the structure and dynamics of biological networks. I'll focus on optimization principles, in particular the optimization of information flow. We'll see how essentially the same principle can be used to make successful predictions in two very different contexts, transcriptional regulation and neural coding. Even setting up these arguments forces us to think critically about our understanding of the signals, specificity and noise in these systems, all current topics of research. Although we don't know if we have the right principles, trying to work out the consequences of such optimization again suggests new experiments.

Thursday, April 5, 2007

**JIM KAKALIOS **

University of Minnesota

"The Uncanny Physics of Superhero Comic Books"

While it is not quite true that one can learn physics from superhero comic books, it is the motivation for a Freshman Seminar class I teach at the University of Minnesota entitled: "Everything I Know About Science I Learned from Reading Comic Books". This class covers physics topics ranging from Isaac Newton to the transistor, but there's not an inclined plane or pulley in sight. Rather, *all* of the examples come from superhero comic books, and as much as possible, those times that the superheroes get their physics right! This class inspired me to write a general audience popular science book: THE PHYSICS OF SUPERHEROES.

In this talk I will describe some of the examples from the four-color pages of comic books, along with recent Hollywood movies, used in this class and my book to illustrate basic physical principles such as forces and motion, conservation of energy, electricity and magnetism and elementary quantum mechanics. For example, have you ever wondered how strong you would have to be to "leap a tall building in a single bound?" If you could run as fast as the Flash, could you run up the side of a building or across the ocean, and more importantly, how frequently would you need to eat? If Spider-Man's webbing is as strong as real spider's silk, could it support his weight as he swings between buildings? And who is faster: Superman or the Flash? These and other pressing, real-life questions will be answered in this talk.

More information about the book can be found at: http://www.physicsofsuperheroes.com.

Thursday, April 12, 2007

**HONG LIU**

MIT

"Understanding the Quark-gluon Plasma via String Theory"

Collisions of high-energy gold nuclei at the Relativistic Heavy Ion Collider (RHIC) in Brookhaven National Laboratory create exploding droplets of quark-gluon plasma, the stuff which filled the universe microseconds after the Big Bang. The quark-gluon plasma at RHIC exhibits many surprising properties: it is close to an ideal liquid and it strongly attenuates the high energy quarks trying to plow through it. So far no calculations in QCD have been able to explain these properties satisfactorily, but significant insight has been gained by using techniques from string theory. In the last ten years string theory has revealed a surprising and deep connection between quantum gravity and non-Abelian gauge theories similar to QCD. Such a connection enables one to answer difficult questions in some strongly coupled gauge theories by simple calculations of classical gravity. I will discuss two examples where these string theory techniques have been used to shed light on existing data from RHIC and to make one prediction that can be tested by experiments in the near future.

Thursday, April 19, 2007

**ALESSANDRA LANZARA **

University of California at Berkeley

"Dirac particles in a pencil trace"

The recent discovery of graphene, a two dimensional carbon crystal, has generated a lot of excitement in condensed matter community because of its unusual electronic properties as well as its potential applications. The secret lies in the relativistic character of its charge carriers, which make graphene the ideal system where relativistic quantum physics and condensed matter physics meets.

The novel physical properties resulting from the Dirac nature of quasiparticles in graphene has been investigated by using high resolution angle resolved photoemission spectroscopy. The great potential of graphene for next generation electronic devices is discussed and possible way of inducing a gap in the electronic spectra is discussed.

Thursday, April 26, 2007

**Distinguished Harris Lecture
JAMES E. GUNN **

Princeton University

"Surveys: The Flip Side of Observational Astronomy"

Astronomy in general and cosmology in particular emerged in the last years of the last century as a very strongly statistical subject, requiring very large, well-controlled and well-understood data sets from the real universe. These are sometimes to be analyzed by themselves or, increasingly commonly, to be compared to "observations" of even larger numerical simulations which may encompass several observational surveys. In this lecture I will discuss the desiderata for and the impact of such surveys, concentrating on the design of and results from the Sloan Digital Sky Survey, but discussing as well some older work and some prospects for the future.

Thursday, May 3, 2007

**JOHN BEACOM **

Ohio State

"Neutrinos from Supernova 1987A: What we learned, what we didn't, and the strategies for detecting supernova neutrinos again (soon!)"

Twenty years ago, about twenty electron antineutrinos were detected from the Supernova 1987A explosion, finally confirming that massive stars eventually undergo a violent core-collapse process, thereby forming a neutron star (or black hole). While this opened the field of neutrino astronomy, to date no other neutrinos have been detected from sources beyond the Sun. I will review what we learned from Supernova 1987A, why we need to know more, and how to enable the desired collection of new supernova neutrinos in a timely fashion.

Thursday, May 10, 2007

**MILDRED DRESSELHAUS**

MIT

“Laszlo Tisza and MIT”

**BENOIT MANDELBROT**

Yale University

“Laszlo Tisza and Generalized Thermodynamic”

**SEBASTIEN BALIBAR**

Laboratoire de Physique Statistique de l'ENS

"Laszlo Tisza and Superfluidity"

Superfluidity is a remarkable manifestation of quantum mechanics at the macroscopic level. The 100th anniversary of Laszlo Tisza is an opportunity to recall the history of its discovery, which took place in a period where the world was torn apart by conflicts and wars, the late 1930's and early1940's.

In order to understand how the experimental discovery occurred and how its theoretical understanding was initiated, I analyzed the contributions of J.F.Allen, D. Misener, P. Kapitza, F. London, L. Tisza, L.D. Landau and several other great scientists. I also collected several testimonies which illustrate the intensity of the scientific competition between Cambridge (UK), Moscow, Paris, Leiden, Toronto, Kharkov and Oxford at that time. Of particular interest is the controversy between Landau on one side, London and Tisza on the other, concerning the relevance of Bose-Einstein condensation to the whole issue.

As I will show, Tisza was squeezed between London and Landau, and it was not easy for him to introduce his famous « two-fluid model ».

Nevertheless, Tisza’s work was a major step forward in the understanding of superfluidity. Today, we sit on his shoulders.

Thursday, May 17, 2007

**Distinguished Harris Lecture
BERT HALPERIN**

Harvard University

"One-Dimensional Metals in Theory and Experiment"

Theoretical analysis, dating back to Bethe's pioneering work of 1931, has shown that interacting one-dimensional electron systems differ in important ways from their three-dimensional counterparts. The low-temperature low-energy behavior of a conventional three-dimensional metal is described by Landau's Fermi-Liquid theory, which can be understood by treating the interaction as a weak perturbation to the non-interacting behavior. Predictions for one-dimensional metals, often described as "Luttinger Liquids", differ more radically from a non-interacting system. In recent years, experimental realizations of one-dimensional metals, including single-walled carbon nanotubes, the edges of quantized Hall systems, and "quantum wires" in GaAs heterostructures, have led to direct experimental tests of some of the predictions of Luttinger liquid theory. We shall discuss some of these results, with emphasis on electron-tunneling experiments, including recent work on tunneling between two parallel quantum wires, and evidence for the occurrence of "spin-charge" separation.