Colloquium Spring 1997
The high temperature superconductors have very interesting electronic properties. For instance, there is strong experimental evidence that the superconducting gap function has the unconventional d-wave symmetry. Experiments also suggest that the antiferromagnetic spin fluctuations and Coulomb correlations play an important role in producing the unusual electronic properties of these materials. Numerical calculations on simple models have been particularly helpful in understanding how d-wave pairing might arise in these materials and how the proximity to the metal-insulator transition modifies the electronic excitations. In this talk we will discuss, in simple terms, the experimental results on the electronic properties of these materials and what we have learned from numerical calculations of simple models. We will also discuss the search for other high temperature superconductors and the newly discovered superconducting cuprate ladder compounds.
The present status of the Homestake, GALLEX, SAGE, and Kamiokande solar neutrino experiments will be reviewed. The discrepancy between all of the experimental results and the theoretical expectations has come to be known as the Solar Neutrino Problem. Possible solutions to this problem will be discussed. The next generation of solar neutrino experiments will be described. Among these is the Sudbury Neutrino Observatory (SNO), which will consist of a 1000 tonne heavy water (D2O) Cerenkov detector that is designed to measure the flux, energy spectrum, and direction of neutrinos from the Sun and supernovae. It is presently under construction in a very low background environment 2000 meters underground near Sudbury, Ontario, Canada. The basic measurements that will be made with the SNO detector are:
- the flux and energy spectrum of electron-type neutrinos reaching the Earth, and
- the total flux of all neutrino types above an energy of 2.2 MeV.
With these two measurements, it will be possible to:
- determine if neutrino oscillations occur, and
- independently test solar models by determining the production rate of high energy electron-type neutrinos in the solar core.
Several years ago a method was proposed (and verified) by which one could optically detect the presence of an object without a photon interacting with it. The method, which relied on the principle of complementarity, worked at best 50% of the time. More recently, we have discovered (and partially demonstrated) a way in which the fraction of interaction-free measurements can be brought arbitrarily close to one, using an application of the quantum Zeno effect. The new method has possible applications in preparing Schroedinger cats, photographing a Bose-Einstein condensate without destroying it, and making Baked Alaska.
The Science-Trained Professional: A New Breed for the New Century
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