Feb. 10, 2005

J.D. Harrington
Headquarters, Washington 
(Phone: 202/358-5678) 

Jane Platt 
Jet Propulsion Laboratory (JPL), Pasadena, Calif. 
(Phone: 818/354-0880 
RELEASE: 05-041

PHYSICISTS HEAR HIGH-TECH WHISTLE WHILE THEY WORK

It was music to the ears of physicists at the University of California 
(UC), Berkeley, when they forced liquid helium-4 through thousands of 
tiny holes and heard a whistling sound. 

Why the big fuss about an odd sound? It seems this breakthrough might 
eventually lead to enhanced earthquake studies and more accurate 
navigation systems, including the Global Positioning System (GPS). 

It all starts with one slippery liquid – helium-4. Ultra-cold helium-4 
becomes a super fluid, meaning it flows without friction. The 
scientists squashed it through an array of apertures 1,000 times 
smaller than the width of a human hair. 

The liquid whooshed faster and faster, until it reached a critical 
velocity. At that point, in a strange phenomenon, a microscopic 
quantum whirlpool dashed across each aperture, carrying away some of 
the helium-4's flow energy. This abruptly slowed the flow. This 
repeated speeding up and slowing down created vibrations, which 
produced a whistling sound going from high to low. A recording of the 
sound, called a quantum whistle, is available online at: 

http://www.nasa.gov/vision/earth/technologies/whistle.html 



"This whistle caught us by surprise," said UC Berkeley physics 
professor, Dr. Richard Packard. "It turns out a single aperture will 
not make the whistle, because of random speed fluctuations. Our 
experiment shows all the flows through the holes are acting together, 
coherently, producing the whistle. We suspect it's like hearing 
thousands of crickets chirping in unison on a summer night," he said. 


Packard said this new phenomenon might lead to improved whistling 
super fluid navigation gyroscopes that detect extremely small 
rotational motion. As their motion changes, the whistle's volume 
would change. This would be especially useful on submarines or 
airplanes in regions where GPS signals are unavailable. 

The GPS navigation system relies on knowing the state of Earth’s 
rotation. Because weather and other factors affect Earth's rotation, 
the GPS system needs constant updating for accuracy. GPS gets its 
Earth rotation data from an array of radio telescopes distributed 
around the world. A very sensitive rotation sensor might complement 
the existing telescope array, providing data quickly and 
inexpensively. 

Super fluid gyroscopes are devices that detect very small rotational 
motion. They use a specially-shaped, super fluid-filled vessel 
containing two aperture arrays; when the vessel rotates, the sound of 
the quantum whistle changes. This provides a telltale clue and allows 
for sensitive measures of the movements. 

"This phenomenon may also permit scientists to develop very sensitive 
rotation sensors to measure small surface twisting signals created 
when an earthquake’s vibrations travel through irregularities in the 
Earth's crust," Packard said. "In fact, we can take this concept even 
further. If seismologists can measure rotation signals from seismic 
activity on Mars, they might learn a lot about martian structure." 

Packard and his colleagues have a history of hearing whistles while 
they work. Their experiments in 1997 and 2001, using liquid helium-3, 
produced a whistle. But the temperatures needed in those experiments 
were extremely low, just a few thousandths of a degree above absolute 
zero, which is almost one million times colder than average room 
temperature. Very few people are trained to work with such ultra-cold 
technology, which limits its potential applications. This latest 
phenomenon occurs at a relatively high temperature of 2 Kelvin, which 
is 2,000 times warmer than the previous helium-3 studies. This might 
make the technology available to more users with off-the-shelf 
cryocoolers. 

This research was conducted under a grant from NASA and the National 
Science Foundation. The findings appeared in the January 27 issue of 
Nature. More information about Packard's research is online at: 

http://www.physics.berkeley.edu/research/packard/ 



JPL, a division of the California Institute of Technology, Pasadena, 
Calif., manages the Quantum Technology in Life Support and Habitation 
Program for NASA's Exploration Systems Mission Directorate. 

	
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