Date

Name & Address

Spintronics is an emerging field aimed at using the electron's spin instead of its charge for information processing and computation. This talk will describe how basic research in this field employs beams of light that behave analogously to conventional electrodes. We will provide an overview of recent fast optical experiments that reveal how the electron's spin memory in semiconductors is influenced by electrical doping, spatial motion, interfaces, and hyperfine interactions. In the latter case, electron spins not only serve as a magnetometer of local nuclear fields, but can also be used to induce NMR with near-visible light rather than conventional radio-frequency fields

If you heat nuclei up (as in the big bang or in heavy ion collision experiments) or squeeze them (as within neutron stars) new phases of matter result. After a brief look at hot quark matter, usually called a quark-gluon plasma, I focus on the rather different physics of cold, dense, quark matter. Most physical properties of this stuff are governed by the nature of the BCS pairing therein. At high enough density, the result is a color superconductor that nevertheless turns out to behave like a transparent insulator if probed electromagnetically. At lower densities, quark matter may in a certain sense be crystalline. I end with speculations on consequences for the physics of compact stars.

Last year at the LEP accelerator in Geveva, Switzerland, three experiments reported a possible sighting of a long sought particle: the Higgs boson, which is so important to particle physics that one Nobel laureate has dubbed it the "God particle." I will discuss the significance of the Higgs boson to physics, describe the experimental techniques used in Geneva and to be used by future experiments, discuss the evidence for its existence ... and make a few remarks about the sociology of large physics groups and important discoveries.

We thank the following speakers for their contribution to making the Physics Colloquium a continued success...

More than a mile beneath the Canadian Shield is a detector filled with 1000 tons of pure heavy water and 8000 tons of ordinary light water. The Sudbury Neutrino Observatory, built by a Canada-US-UK collaboration, has been taking data for two years. SNO uses heavy water in order to make an unambiguous determination of whether neutrinos emitted by the sun, created as electron neutrinos, arrive at earth in a state with a different flavor (mu, tau, or possibly sterile). The shortfall of the number of solar neutrinos observed experimentally over the last 30 years compared to the predictions of solar models could be explained if that happened. Such a transformation can occur if physical neutrinos have rest mass and not a unique flavor. Neutrino mass is a major issue in physics because the completely successful Standard Model does not include it, and because massive neutrinos may play a role in shaping the evolution of the universe.

Quantum phenomena are usually only observable on microscopic scales. A typical macroscopic object is so strongly coupled to its environment that it rapidly decoheres into a classically well-defined state. In the early 1980s, Leggett and collaborators proposed that under suitable conditions, some macroscopic systems, most notably superconductors, could be sufficiently well isolated from their environment to be put into a superposition of macroscopically distinct states, a la Schroedinger's cat. I will present recent experimental evidence* that a SQUID (Superconducting QUantum Interference Device) can be put into a superposition of magnetic-flux states that differ by ~1 microampere in current and ~10^{10} Bohr agnetons in magnetic moment. Using pulsed microwaves, we psuedo-spectroscopically measure the energy levels of the SQUID and find a level anticrossing at the point where the two flux states would classically become degenerate. At the anticrossing the eigenstates of the SQUID have become the symmetric and antisymmetric superpositions of the macroscopically distinct flux states. I will discuss current efforts to observe the quantum coherent oscillations of the SQUID's flux between these two states. * J. R. Friedman et al., Nature 406, 43 (2000).

Most galactic nuclei contain point-like objects of mass between one million and one billion solar masses. The most conservative hypothesis is that these objects are black holes. A few percent of galactic nuclei are very bright, outshining their parent galaxy by as much as two orders of magnitude. These "active" nuclei are believed to derive their power from either the gravitational potential energy of interstellar plasma falling into the black hole, the rotational energy of the black hole, or both. I will describe a program of numerical modelling of these systems designed to probe the implications of strong field gravity in astrophysical settings, and use it to illustrate some interesting strong field effects.

Biological motor proteins are micro engines that take the chemical energy of a fuel molecule, ATP, and turn it into mechanical work. Much of the motility of eukaryotic cells is produced by two types of motor proteins, the myosins and the kinesins, which interact with protein polymers. The molecular mechanism of energy transduction by these proteins has been the focus of extensive investigation. Results from spectroscopic methods have been combined with mechanical measurements to provide insight into the conformational changes that occur in these proteins, which lead to force production. These results suggest that both proteins can produce force and mechanical work by acting as "thermal ratchets" , e.g. by trapping high energy conformations of the proteins that are populated by thermal fluctuations.

With recent developments in computer technology where the density of microcircuits and nanodevices is increasing very rapidly, heat management has become a major problem. An effective and elegant solution is the application of thermoacoustic engines for cooling and heat pumping. Such engines have a long history; they work on the principle that heat, above a critical threshold level, can be converted to coherent sound or, conversely, when run backwards, that sound can pump heat up a temperature gradient. The fundamental mechanism leading to directed motion by taming thermal noise will be presented. This type of engine is interesting and it is important for applications especially since it uses environmentally-safe gases and it has essentially no moving parts. Microminiaturization of thermoacoustic engines is in progress and their direct interfacing with microcircuits for heat management will be discussed.

Proteins form a unique state of matter, with some properties characteristic of solids, some of liquids, some of polymers, and some of glasses. 4 Gy of evolution have perfected their structure and function. The study of proteins and other biomolecules yields new concepts and new insights into old problems. Possibly the most important concept is that of the energy landscape: Proteins can assume a very large number of somewhat different structures, characterized by a rough energy landscape. Each valley in the landscape corresponds to a particular protein conformation, called a conformational substate. The existence of an energy landscape has been confirmed by many experiments, in particular by a characteristic Debye-Waller factor, nonexponential time dependence of relaxation phenomena, and spectral and kinetic hole burning. A main goal of the protein physics is the exploration of the energy landscape, of the laws governing motions in the landscape, and of their connection to structure and function. The dynamics of the motions within the landscape involve molecular tunneling, the effect of friction (Kramers theory), the effect of collective motions, and non-Arrhenius behavior.

I show that the postulate of finite-size scaling, or self similarity, which is widely studied in the context of critical phenomena in statistical physics, naturally leads to power law relationships in ecology between a) species richness and area, b) endemism and area, c) box-counting range and abundance, d) box-counting range and box area, e) intraspecific aggregation and abundance, and the spatial distribution of species abundances. Theory also predicts testable relationships among these patterns, including numerical values for exponents, which I show are in excellent agreement with observation. I also discuss possible mechanisms for the origin of self similarity in ecology.

As the size of electronic devices shrinks towards nanometer dimensions, the wave properties of electrons will play an increasingly important role in determining device behavior. One can already imagine future device engineers beginning their task with the question "What are the optics?" This regime is already being explored in laboratories around the world and is the subject of this presentation. The surface states of noble metals form a nearly ideal two-dimensional electron gas. The scanning tunneling microscope (STM) may be used as a tool to directly image the density distribution of the surface state electrons at a particular energy, or to measure their spectrum at a particular point in space. In addition, we use the atom-manipulation capabilities of the STM to position atoms to form a variety of electron optical structures such as wave guides, reflectors and resonators known as "quantum corrals." We have learned to perturb the states of a quantum corral by introducing an atom to the corral's interior. By judicious choice of the size and shape of the corral we can arrange it so that this perturbation is made to have a large effect at a position remote from the perturbing atom. We call this a "quantum mirage." I will discuss the physics of the mirage and some of its more intriguing features. We will find that the mirage effect is in fact classical and is a common property of any wave-resonant system. Finally, I will touch on some of the information transport and processing properties of the mirage and show how electron devices which exploit wave optics can do things that conventional electronics devices cannot.

Nanobiotechnology is the marriage of biology with the nanotechnological advances in materials, instrumentation and processing in order to realize a fundamentally new understanding of biological function as well as to visualize and manipulate hierarchical supramolecular assemblies. An important goal is the development and execution of methodologies for the determination of biological structures in the 5 nm - 500 nm 'mesoscale' size range, thus providing the important architectural and functional information of specific aggregates of nucleic acids, lipids and proteins which constitute important cellular machinery. We have utilized natural and genetically engineered lipid-protein complexes based on the human, together with scanned probe methodologies, to understand the reactivity of lipoproteins on surfaces and to stabilize and incorporate single membrane proteins in nanostructured phospholipid bilayers. These resultant supramolecular architectures allow the direct visualization of single membrane protein structures and measurement of physical properties on single molecules. The ability to directly probe the function of single proteins incorporated into defined membrane assemblies is haaaving enormous impact on the understanding and control of biological signaling and receptor mediated growth control processes. For instance, we have incorporated the hepatic cytochrome P450 systems from the endoplasmic reticulum as well as single G-protein coupled receptors into nanobilayers to provide a soluble, monodisperse and high-throughput assays for structure - function correlation.