Liquid helium is the simplest condensed matter system. It exists at temperatures down to absolute zero, is extremely pure, defect free, and devoid of spatial variations in temperature. Because of the simple nature of this system, it can be thought of as “the hydrogen atom” of condensed matter physics. It is an ideal system to test fundamental physical concepts.
The most important aspect of the Helium liquids involves Bose-Einstein Condensation (BEC) into a superfluid state. The superfluid states themselves have been very important model systems to test and demonstrate physical theories. One recent example includes work in which aspects of the Big Bang model are tested by observing quantized vortices. Another recent experiment uses superfluids to test models of intrinsic nucleation of defects.
His Low Temperature group studies both 3He (a Cooper-paired Fermion system) and 4He (a Boson system) to test fundamental physical principles. They have cryostats which cool samples below 160µK. At such low temperatures, they can measure mass currents as low as 5x10-14 gm/s, determine hydrostatic pressures as small as 10-10 atm, and measure displacement as small as 10-15m. They have also developed micro-fabrication techniques to build entire experiments on the micron scale. Their techniques have led to a substantial number of “firsts” including: photographing quantized vortex lines in 4He, demonstrating that fluid circulation is quantized in 3He, proving that Cooper pairing is responsible for superfluidity in 3He, developing a superfluid gyroscope to detect the Earth’s motion, discovering the first superfluid 3He quantum weak links (Josephson junctions), detecting superfluid surface waves in 2-dimensional 3He and making the first superfluid dc-SQUID.
The group’s present research is focused on phenomena which exploit the properties of 3He weak links, 4He phase slippage, superfluid surface waves and He3:He4 mixtures. The specific projects include: 1. The development of a sensitive superfluid dc-SQUID to detect very small absolute rotation. 2. A study of the intrinsic limitations of 4He phase slip rotation sensors. 3. An investigation of the properties of 2-dimensional Fermi superfluid. 4. A demonstration of the Josephson frequency relation in 4He. 5. A search for quantized mass conductance in neutral matter.
A typical graduate student researcher in their group is involved with all aspects of his/her experiment, from the development of the experimental apparatus to the analysis and interpretation of the final data. Such training is intended to develop a well rounded scientist who has many of the skills expected in an experimental physicist.
The group consists of approximately three graduate students, one postdoctoral scientist and a technical assistant. They can accommodate one new graduate student in the group this year.