Colloquium Spring 2003
Martin Luther King Day, University Holiday
Interactions among electrons are responsible for many fascinating effects in condensed matter and atomic physics, from ferromagnetism to superconductivity.
We review our attempts at constructing a laboratory for interacting electron systems using semiconductor quantum dots. In this laboratory we assemble electron and exciton droplets one electron/exciton at a time and probe their electronic properties. The electron droplet assembled from a two-dimensional electron gas using metallic gates will be described. By connecting this droplet to spin polarised leads, the spin state of the droplet can be both manipulated and read. The technique reveals a number of nontrivial effects related to the number of electrons, their spin and their correlations.
Quantum dots enable us to not only look at electrons but also excitons in self-assembled quantum dots. We will show that the electron and hole complexes in these dots form excitonic artificial atoms. The principle underlying their electronic structure, hidden symmetry, bridges between the quantum dot and quantum Hall physics. These atoms are indeed artificial nano-structures without a counterpart in nature and offer interesting possibilities for designing quantum systems.
We conclude by summarising possible impact of quantum dots on nano-spintronics, nano-photonics, and quantum information.
January 28 Note Special Day and Location: SGM 101
Einstein predicted the existence of gravitational waves, ripples of space-time, in 1916; but they are so faint that they have yet to be observed. Gravitational waves are produced by the most energetic events in the universe: collisions between black holes, supernovas, and the Big Bang itself. The observation of gravitational waves would be a spectacular confirmation of Einstein's prediction, and would permit powerful new tests of General Relativity. More importantly, it will open up a new and totally different window on the universe, and inaugurate a radically new field of astrophysics. The LIGO project is part of a worldwide observatory network capable of detecting gravitational waves from astrophysical sources. It began taking scientific data in 2002. We will describe the physics and astrophysics of gravitational waves, discuss the principles of the LIGO detectors, and review at the status of the detectors, the data analysis, and first results.
February 5 Note Special Day and Location: SLH 200
President's Day, University Holiday
February 26 Note Special Day, Location, and Time: SLH 200, 3:15 pm
Over the last eight years, work in superstring and M-theory has led to a number of exciting developments which serve as examples hinting at an exciting view of the nature of spacetime physics at the most fundamental level. The physics involves deep connections between theories of gravity and gauge theories, the latter being well known to form the foundations of the Standard Model of particle physics. The physical and mathematical consequences have yet to be fully explored. We will review some of the key insights obtained about the structure of superstring and M-theory and what it has to teach us, focussing on the important and useful dynamical extended geometrical objects known as "D-Branes". Applications to the quantum mechanics of black holes are discussed, string theory's "enhançon" mechanism for the resolution of certain spacetime singularities, and the role of the mechanism in black hole thermodynamics.
No Colloquium - March APS Meeting
In July, 2002 NASA selected two small explorer missions for flight in 2005 and 2006. The NASA Explorer Program provides frequent, low-cost access to space for physics and astronomy missions with small to mid-sized spacecraft. The Spectroscopy and Photometry of Intergalactic medium's Diffuse Radiations (SPIDR) mission will use imaging ultraviolet spectrographs to look for the Cosmic Web - a filamentary structure of tenuous warm-hot (105 - 106 K) gas predicted by cosmological models. This talk will describe the scientific motivation, measurement approach and the mission design.
Recently, renowned artist David Hockney observed that certain drawings and paintings from as early as the Renaissance seemed almost "photographic" in detail. Following an extensive visual investigation of western art of the past 1000 years, he made the revolutionary claim that artists even of the prominence of van Eyck and Bellini must have used optical aids. However, art historians insisted there was no supporting evidence for such a remarkable assertion. In this talk I show a wealth of optical evidence for his claim that Hockney and I subsequently discovered during an unusual, and remarkably productive, collaboration between an artist and a scientist. I also discuss the unique properties of the "mirror lens" (concave mirror), and some of the implications this work has for the history of science as well as the history of art. These discoveries convincingly demonstrate optical instruments were in use -- by artists, not scientists -- nearly 200 years earlier than previously even thought possible, and account for the remarkable transformation in the reality of portraits that occurred early in the 15th century.
For more information see these Frequently Asked Questions (FAQ).
Acknowledgments: This work was done in collaboration with David Hockney. We gratefully acknowledge David Graves (London), Ultan Guilfoyle (Guggenheim), Martin Kemp (Oxford U.), Masud Mansuripur (U. Arizona), José Sasián (U. Arizona), Richard Schmidt (Los Angeles), and Lawrence Weschler (The New Yorker) for a variety of valuable contributions to our efforts.
In the past five years we have witnessed a remarkable revolution in astro-, particle and nuclear physics. The immensely significant results from the Sudbury Neutrino Observatory and those from Super-K have changed our view of physics and the Standard Model. These neutrino experiments, as well as dark matter searches and double beta decay experiments all require well shielded underground laboratories to succeed. The next generation of experiments in these fields that pursue these new physics horizons require even deeper laboratories. Several characteristic experiments will be explored and site requirements discussed. The current status of the National Underground Scientific Laboratory will be presented.
May 14 Note Special Day, Time and Location: SSC 319 12:30pm