Mondays, 4:00 P.M. Ronald Geballe Auditorium, Rm. A102
Coffee and cookies at 3:45 P.M. in the lobby

Spring Quarter Colloquium Chair: Professor Eric Adelberger

March 27: no colloquium scheduled

April 3:
Richard Packard, University of California, Berkeley
Title: "Superfluid weak links: physics and applications"
Abstract: During the past few years arrays of nanometer sized apertures connecting reservoirs of superfluid helium have been found to exhibit properties described by the two Josephson equations. This talk will describe some of the experiments, in 3He below 1mK, and in 4He near 2K, which reveal the quantum nature of these weak links. Both of these superfluids exhibit Josephson oscillations, the so called “quantum whistle”. As temperature rises, 4He weak link arrays morph continuously from a phase slip regime into a Josephson sine-like current-phase relation. It is still a mystery why these arrays exhibit quantum coherence over thousands of apertures. Sensitive matter wave interferometers/rotation sensors, analogous to the superconducting dc-squid, have been demonstrated in both 3He and 4He. These condensed-matter quantum interferometers may be used to examine some fundamental interactions in nature.
http://www.physics.berkeley.edu/research/packard/

April 10:
Andreas Karch, University of Washington
Title: "Phoenix from ashes -- a string theory of the strong interactions?"
Abstract: As a theory of quantum gravity string theory has had some early successes but has been hitting roadblocks which I will review together with some recent ideas of how to get around them. As a theory of the strong interactions string theory had fallen out of favor long ago, but has experienced a recent revival. String theory has been employed to solve theories that are similar to QCD and some of the qualitative lessons that have been learned about those cousins of QCD might help us understand phenomena RHIC is uncovering in heavy ion collisions. String theory is also guiding some recently developed models of hadrons based on the idea of holography. I'll present some new results employing both these approaches to the QCD/string connection.

April 17:
Dam Son, University of Washington
Title: "Viscosity, black holes, and the Relativistic Heavy Ion Collider"
Abstract: Viscosity is a very old physical concept, introduced to physics in the 19th century.  However, it is extremely difficult to compute theoretically the viscosity in strongly interacting systems.  In this talk I will describe some recent developments in string theory that allow one to compute, in a very easy way, the viscosity in a class of strongly-interacting quantum field theories.  I will also talk about the efforts to measure the viscosity of the quark-gluon plasma created at the Relativistic Heavy Ion Collider.

April 24:
Julianne Dalcanton, Department of Astronomy, University of Washington
Title: "Galaxy Formation as a Probe of Dark Matter"
Abstract: Galaxies are one of the most effective tracers of the structure of dark matter on megaparsec to kiloparsec scales. Within the context of cold dark matter theories, the basic paradigm of galaxy formation is largely worked out and is remarkably successful at predicting the spatial distribution of galaxies and their internal properties. I will give an overview of the successes of current models, but point to the many areas where substantial discrepancies remain. These discrepancies between theory and observation are most severe on small scales (<1kpc) and high densities.

May 1:
David Cobden, University of Washington
Title: "Carbon nanotubes for studying the physics of correlated electrons in one dimension"
Abstract:The behavior of interacting identical particles confined to a line (ie, moving in only 1D) has long been a theoretical testbed of ideas, but until recently it was viewed as having limited verifiability in the laboratory. Recently this view changed, largely as a result of the discovery a decade ago of single-walled carbon nanotubes. Nanotubes act as beautiful molecular 'quantum wires' with 1D electronic dispersion, and they also have many feasible applications which motivate better understanding their fundamental properties. The single-electron properties of nanotubes, such as the excitation spectra of nanotube quantum dots (essentially, particles in a 1D box), have by now been well established. On the other hand the consequences of electron-electron interactions in this low dimensional system are varied and still only partially understood. This talk will survey some of the interaction and correlation phenomena that can be investigated in nanotubes using electrical transport measurements. They include the Kondo effect, the Luttinger liquid, and localization in either a random or a periodic potential.

May 8:
Ramesh Narayan, Department of Astronomy, Harvard University
Title: "Astrophysical Black Holes"
Abstract: An astrophysical black hole is completely described with only two parameters, its mass and its dimensionless spin. A few dozen black holes have been discovered so far, and their masses have been measured. Just recently, spin estimates have been obtained for a few holes, thus completing the characterization of these objects. In several candidate black hole systems, there is strong circumstantial evidence for the presence of event horizons. The talk will review these topics.

May 15:
Jan Hall, Joint Institute for Laboratory Astrophysics
Title: "Defining and Measuring Optical Frequencies"
Abstract: Time has been of serious interest since man turned agrarian, but became of critical interest with the expansion of lucrative international trade: “inevitable” shipwrecks could be avoided by better knowledge of position (mainly longitude) at sea. Parliament’s Longitude Prize of 1714 (about $10 M in current terms) attracted John Harrison's attention and some40 years of his inventive work. In 1761 his H-4 clock demonstrated 1/5 s/d , δν /ν ~2.5 x10 -6 even while at sea. This was several-fold better that the requirement, but only half the Prize was initially paid: in part the controversy was about IP!

Modern scientists are attracted to Frequency Definition and Measurement because of its scaling with the number of measurements: N − 3/2 for the precision. Frequency reference based on a Cs hyperfine transition was introduced in the 1950's, officially adopted in 1967, and was realized ever more perfectly over the years using atomic beam resonance methods. The ultimate of this long evolution was NIST-7 which had an evaluated inaccuracy ~ 5 x10 -15. Also in 2001, the laser-based method of Cs Atomic Fountains reached a level 5-fold improved, and in only two years after its introduction. New technology like lasers can speed things up!

The long coherent interaction time of atoms in a fountain strongly attracts us to suitably-weak optical (rather than rf) transitions, since then the line Q can be ~10 14. (Other effective schemes are ions in an ion trap or atoms in a suitable optical lattice trap.) In early 2000 there were many such lines known, with many groups independently working on their own favorites, but with no real way to compare the clock performances. Then the Miraculous Millennium-Year Confluence of Progress occurred: UltraFast Lasers generated 10 fs pulses with a stable repetition rate; MicroStructure fiber designs had evolved to exhibit near zero dispersion at the fs laser’s central wavelength, setting the stage for Ultra-NonLinear Response and drastic pulse bandwidth expansion, even beyond an optical octave (these gave the “Optical Frequency Comb” currently being celebrated); UltraStable laser design could offer control concepts and tools to make the Comb carry the stability of the reference source; Progress in UltraSensitive Spectroscopy sets the stage for major additional gains in the stabilities of optical reference sources. Additionally, industrial progress in power stability of the fs laser’s pump laser allows the comb-lines to have sub-Hz linewidths, thanks to the extremely small amplitude noise which minimizes amplitude-phase noise conversion. Measurements by the Garching team, expanded by NIST-Boulder work shows that the comb approach allows relative frequency measurements to be made in the 10 -17 domain, even though the unit of Hz is realizable only with 100-fold inferior accuracy. Work in Boulder shows that both timing and frequency information can be disseminated via optical fiber with minimal precision loss, after active correction of both fiber-added phase noise and time-delay jitter.

The next big race is now on: who can discover an optical transition frequency or fundamental constant that is changing a little bit in time? There might also be a Prize for connecting e-uv comb-lines with a Mö ssbauer γ -Ray line.

May 22: (this speaker was selected by the graduate students)
Joseph Kapusta, University of Minnesota
Title: "Physics at RHIC"
Abstract:The Relativistic Heavy Ion Collider (RHIC) has provided a wealth of data, some of it quite amazing, with more to come.  Among the most significant findings are exhibitions of collective flow, jet quenching, and thermal equilibrium of observed hadrons at a temperature of about 170 million electron-volts.  I will outline a theoretical program of the Duke and Minnesota groups that describes nuclear collisions from first impact until final hadronic free-streaming.  Various pieces are already in place, including coarse graining of the initial gluon fields (Color Glass Condensate), parton production and minijets, relativistic fluid flow, and late stage hadron scattering.  Our calculations give initial energy densities of order 500 GeV per cubic fermi.  By varying the temperature or energy density dependence of transport coefficients it ought to be possible to infer the critical behavior of the equation of state of QCD.

May 29: Holiday - no colloquium