Colloquium Fall 1997
We describe the on-going controversy on the effect that electrostatic screening may have on the nuclear reactions in the Sun. We show why and where many good people were wrong, how NOT to calculate the effect and how the effect should be calculated.
An applied chemical potential difference between two weakly coupled macroscopic quantum systems should generate mass current oscillations between them. In superconductors, where the weak coupling is usually achieved by using a Josephson tunnel junction, this oscillating current is sometimes called the AC Josepson Effect.
I will describe recent experiments, with an array of 100 nm diameter apertures, which have confirmed the existence of these quantum oscillations in superfluid 3He-B. I will also report on the first direct measurement of the current phase-difference relation, I(phi), for a superfluid 3He weak link, along with a number of other phenomena associated with the Josephson effect which have now been observed in 3He. In addition, a newly discovered metastable macroscopic quantum state will be discussed.
This experiment reveals several remarkable phenomena heretofore inaccessible to superconducting Josephson junctions, such as direct observation of quantum oscillations and continuous knowledge of the dynamics of the quantum phase difference. I will also describe how the observation of a sine-like I(phi) relation lays the foundation for the future creation of a superfluid analog of a dc-SQUID.
November 10 Special Location: THH 101
December 2 Note Special Day & Location: SLH 102
The low energy excitations of fractional quantum Hall (FQH) liquids carry fractional quantum numbers such as charge and statistics. This directly affects the noise spectrum of the FQH current, and, conversely, the noise data provides direct evidence for fractional quantum numbers. In this talk, I will show in detail how the mesurement of shot noise can generally be used as a powerful tool to study the nature of the fractionally charged FQH quasiparticles. Recently, this tool has been succesfully used in the first transport observations of fractional charge by two experimental groups, one in Saclay and the other at the Weizmann Institute. I will also discuss a device which could allow for the direct observation of fractional statistics.