Imagine turning on your faucet and watching water flow
out and then flow right back up into the faucet. NASA
scientists have observed a similar phenomenon by using
superfluid helium-4 in laboratory research that could improve
earthquake prediction and spacecraft navigation.
The team of scientists, led by Dr. Dave Pearson of NASA’s
Jet Propulsion Laboratory, Pasadena, Calif., is the first ever
to observe this phenomenon, called the Josephson effect, in
superfluid helium-4, the most common type of helium.
Superfluids allow matter to flow without friction in the same
way that electricity flows without resistance in a
superconductor.
The Josephson effect was first predicted in 1962 by Nobel
Prize Laureate Brian Josephson. For ordinary fluids, a
pressure difference along a pipe causes fluid to flow from the
high pressure to low pressure area; thus, water comes down out
of a faucet and stays there. But with the Josephson effect,
when pressure is applied, fluids begin to oscillate back and
forth, or up and down, at a rate in direct proportion to the
pressure difference. In essence, this effect enables a fluid
to defy gravity.
“My colleagues and I used very high-resolution
thermometers to precisely control the superfluid temperature
to approximately two degrees above absolute zero,” Pearson
said. Absolute zero is the temperature at which scientists
think that no further cooling can occur.
At this extreme cold, helium-4 enters a quantum state, in
which its behavior becomes very odd. By using electrostatic
forces to create a pressure difference across a pipe, Pearson
and his colleagues saw that the fluid began to oscillate from
one end to the other.
This strange effect is created because the fluid begins
obeying laws of quantum mechanics, which govern how atoms
behave at super-low temperatures. “What we see is quantum
mechanics on the macroscopic scale,” Pearson said. “This was
very exciting for us, because we thought various technical
factors would prevent the Josephson effect from occurring.”
The successful observation of the Josephson effect in
superfluid helium-4 allows measurements of very small
rotation, enabling scientists to measure very precisely how
fast Earth rotates. Monitoring Earth’s rotation speed could
yield information on minute movement of tectonic plates, which
may eventually help predict earthquakes.
In addition, this research could lead to extremely
precise, yet simple, gyroscopes to navigate spacecraft. Among
the NASA missions that may benefit is the Terrestrial Planet
Finder, which may use multiple spacecraft flying in very
precise formation to image planets around other stars, looking
for Earthlike planets that may harbor life.
The Josephson effect had been observed in superconductors in
1963, then in isotope helium-3 in 1987, but it has eluded
researchers for 35 years in helium-4. Certain properties of
helium-4 make it easier to work with in laboratories and in
space. The research by Pearson and his team was conducted
under a grant from NASA’s Biological and Physical Research
Program.
Pearson co-authored the quantum experiment paper, which
appears in the May 17 issue of the journal Nature, with Drs.
Talso Chui and Kalyani Sukhatme of JPL and collaborator Dr.
Yury Mukharsky of CEA-DRECAM (Commissariat a l’ Energie
Atomique, Dèpartement de Recherche sur l ‘Etat Condensè, les
Atomes et les Molècules) from Saclay, France. More
information on the BPR Fundamental Physics Program can be
found at the following Web sites:
http://funphysics.jpl.nasa.gov
JPL manages the Fundamental Physics in Microgravity
Research Program for NASA’s Office of Biological and Physical
Research, Washington, D.C. JPL is a division of the California
Institute of Technology in Pasadena.
