Subatomic waves made in
Boulder
By Ann Schrader
Denver Post
Medical/Science Writer
Sept. 10 - Four years ago, physicists in Boulder claimed the
"Holy Grail'' of physics when they created a new type of matter by
chilling atoms into a lockstep formation.
But the creation of Bose-Einstein condensate, which first was predicted
by Albert Einstein more than 70 years ago, was only half of the quest.
Now another group at the same joint research institute has persuaded a
vapor of anti-social subatomic particles called fermions (pronounced
FARE-mee-ons) into a state of matter in which they start working together
and start behaving like waves.
Called the first Fermi degenerate gas of atoms, the ultra-low
temperature quantum, or most basic, state achieved in June by JILA
researchers may lead to more accurate atomic clocks, new insights into
electronic devices and improved superconductivity-based technologies.
The accomplishment announced today in the journal Science "will
probably be at the top of the list of important physics news for this
year,'' said Carl Wieman, the University of Colorado physics professor who
was part of the team that created the Bose-Einstein condensate in 1995.
The successful experiment was conducted by Deborah Jin, 30, a physicist
in the Commerce Department's National Institute of Standards and
Technology physics lab, and Brian DeMarco, 25, a graduate CU-Boulder
physics student.
Just as the Bose-Einstein creators weren't comfortable with the Holy
Grail label, Jin said she wouldn't describe the work that way.
"This is a very important and very fundamental extension of
Bose-Einstein condensation,'' she said, with "a lot of the same
techniques'' being used.
In the weird world of quantum physics, atomic particles are either
fermions such as neutrons, electrons and protons, or they are bosons
(pronounced BOZE-ons). The difference is the "spin'' of the particles'
axis.
Wieman and NIST's Eric Cornell used bosons, which are more neighborly
and are easier to coax into a super-atom, in their potentially Nobel
Prize-winning achievement.
Building on the earlier work, Jin and DeMarco used a puff of potassium
gas. They cooled the gas with diode lasers similar to ones in CD players.
They dropped the temperature of the gas from room temperature to
100-millionths of a degree Celsius above absolute zero. That is the
theoretical temperature where all molecular motion stops. It's about
-459.67 degrees Fahrenheit or -273.16 degrees Celsius.
At that point, they turned off all of the light. Fermions, named for
Nobel Prizewinning physicist Enrico Fermi, whose work led to development
of the atom bomb, don't like to collide. They obey a physics principle
that prohibits them from occupying the same place at the same time.
But continued cooling couldn't happen without collisions, so Jin and
DeMarco had to figure out a way to get the solitary fermions to run into
each other.
They trapped the potassium gas atoms with magnetic fields generated by
running electric current through coils. The magnetic field split the
atoms' energy levels.
Then Jin and DeMarco bathed the gas atoms with lasers and radio waves
so half the atoms were in one quantum state and the other half were in
another. The difference allowed the atoms to collide.
"It's just a beautiful scheme,'' said Dan Kleppner, the Masssachusetts
Institute of Technology physicist who is considered the godfather of
quantum condensation studies.
Jin said the hotter atoms - those with the highest energy - were
allowed to escape, much like the evaporative process of coffee cooling in
a mug.
As more of the hotter atoms "evaporated'' from the magnetic trap, the
temperature of the remaining atoms dropped to their most basic nature and
started behaving in unison.
When the scientists turned off the magnetic trap, the gas of atoms
expanded because energy causes them to fly apart. Atoms with the most
energy travel farthest.
For evidence of their creation, they took a snapshot of the resulting
cloud of atoms.
"How big the cloud got in a certain amount of time tells us about the
energy and temperature of the cloud,'' Jin said.
The head of another team using a different approach to the same puzzle
said the JILA work "has lovely textbook results'' on how fermions behave.
"It's really a spectacular result. . . . We're very impressed,'' said
John Thomas, a physicist at Duke University.
Jin and her team "found the optimum atom . . . and she was able to
rocket right in there,'' Thomas said. "We all know each other, and it's
tremendous fun to be able to do quality science.''
The new finding builds on work by Weiman and Eric Cornell that already
has been suggested as possible Nobel Prizewinning.
"The creation of a Fermi degenerate gas is a major scientific
achievement, and a lot of scientists have been trying to make it ever
since we created the Bose-Einstein condensate,'' Wieman said.
Cornell, the NIST physicist who collaborated with Weiman, said Jin and
DeMarco's achievement "is a considerably more difficult task'' than what
he and Wieman faced and overcame.
Jin's group, among others around the world, would like to push the
envelope even further by getting the fermions to work in pairs if cooled
more.
"We would like to study the properties,'' Jin said, with the ultimate
goal of making fermion condensate.
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