About the Bose-Einstein Condensate
A New Form of Matter
images display the velocity distribution of the cloud of rubidium
atoms at (a) just before the appearance of the Bose-Einstein condensate,
(b) just after the appearance of the condensate and (c) after further
evaporation left a sample of nearly pure condensate. The field of
view of each frame is 200 x 270 micrometers, and corresponds to the
distance the atoms have moved in about 1/20 of a second. The color
corresponds to the number of atoms at each velocity, with red being
the fewest and white being the most. Areas appearing white and light
blue indicate lower velocities. Images courtesy of Mike Matthews,
JILA research team.|
Distinguished Professor Carl E. Wieman of the University of Colorado at
Boulder and Senior Scientist Eric A. Cornell of the National Institute
of Standards and Technology led a team of physicists that created the
world's first Bose-Einstein condensate -- a new form of matter -- on June
The condensate allows scientists to study the strange and extremely small world of quantum physics as if they are looking through a giant magnifying glass. Its creation established a new branch of atomic physics that has provided a treasure-trove of scientific discoveries.
Predicted in 1924 by Albert Einstein, who built on the work of Satyendra Nath Bose, the condensate occurs when the wavelengths of individual atoms begin to overlap and behave in identical fashion, forming a "superatom." The "superatom" occurs when laboratory apparatus is used to chill a group of atoms to just a few hundred billionths of a degree above absolute zero.
Cornell and Wieman likened a Bose-Einstein condensate to an ice crystal forming in cold water and said it has the same relation to ordinary matter as laser light has to light from a light bulb. The atoms within the condensate obey the laws of quantum physics and are as close to absolute zero -- minus 459.67 degrees Fahrenheit or minus 273.15 Celsius -- as the laws of physics allow.
Today, scientists around the world are manipulating condensates made from a variety of gases to probe their scientific properties. The condensate can be used to form an atomic laser and could one day lead to a better atomic clock.
"It really is a new form of matter," Wieman said. "It behaves completely differently from any other material."
A Bose-Einstein condensate was first achieved at 10:54 a.m. June 5, 1995, in a laboratory at JILA, a joint institute of CU-Boulder and NIST. The apparatus that made it is now at the Smithsonian Institution.
As of September 2001 about three dozen other laboratories worldwide had replicated the discovery and were conducting a wide variety of experiments.
Wieman and Cornell are both fellows of JILA, and Cornell is a professor adjoint at CU-Boulder. Both are members of the National Academy of Sciences and both teach undergraduate and graduate students.
The team led by Wieman and Cornell used laser and magnetic traps to create the Bose-Einstein condensate, a tiny ball of rubidium atoms that are as stationary as the laws of quantum mechanics permit. The condensate was formed inside a carrot-sized glass cell. Made visible by a video camera, the condensate looks like the pit in a cherry except that it measures only about 20 microns in diameter or about one-fifth the thickness of a sheet of paper.
In 1997, researchers at the Massachusetts Institute of Technology developed an atom laser based on the Colorado discovery that was able to drip single atoms downward from a micro-spout. In March 1999, scientists at the NIST facility in Gaithersburg, Md., created a device that shoots out streams of atoms in any direction, just as a laser shoots out streams of light.
Made possible by nudging super-cold atoms into a beam, the breakthrough could lead to a new technique for making extremely small computer chips, according to NIST Nobel Laureate William Phillips, who led the team. Eventually, such a device might be able to construct nano-devices one atom at a time.
In February 1999, a team of researchers from Harvard University led by Lene Vestergaard Hau used the Bose-Einstein condensate to slow light - which normally travels at 186,000 miles per second - to just 38 miles per hour by shining a laser light through the condensate. In 2001, Hau's team announced that it had briefly brought a light beam to a complete stop.
On June 18, 1999, JILA researcher Deborah Jin of NIST and CU-Boulder graduate student Brian DeMarco used the technique in achieving the first ever Fermi degenerate gas of atoms, a state of matter in which atoms behave like waves. While the Bose-Einstein experiments used one class of quantum particles known as bosons, Jin and DeMarco cooled atoms that are fermions, the other class of quantum particles found in nature. This was important to physicists because the basic building blocks of matter -- electrons, protons and neutrons -- are all fermions.
Wieman and Cornell are continuing to explore the properties of Bose-Einstein condensates. In 1999 they were the leaders of a group that created the first vortices ever seen in the condensates and also were doing extensive studies of two-component condensates.
In July 2001, Wieman and Cornell were part of a CU-Boulder and JILA team that was able to make a Bose-Einstein condensate shrink -- an event which was followed by a tiny explosion. The team said the phenomenon was similar in some ways to a microscopic supernova explosion and dubbed it a "Bosenova." About half of the original atoms appear to vanish during the process.
"We have gotten down to the nitty-gritty science and have been able to study the behavior of a new material by manipulating it in new and different ways," Wieman said. In doing so, they cooled the matter to 3 billionths of a degree above absolute zero, now the lowest temperature ever achieved.
Wieman started searching for Bose-Einstein condensation in about 1990 with a combination laser and magnetic cooling apparatus that he designed himself. He pioneered the use of $200 diode lasers -- the same type used in compact disc players -- showing they could replace the $150,000 lasers others were using. Cornell joined the effort about a year later.
Wieman's tactics in pursuing the condensation initially were met with skepticism in the scientific community. But as his and Cornell's methods began to show the goal was achievable, several other teams of physicists joined the chase.
Beginning with atoms of rubidium gas at room-temperature, the JILA team first slowed the rubidium and captured it in a trap created by light from the lasers. The infrared beams are aligned so that the atoms are bombarded by a steady stream of photons from all directions -- front, back, left, right, up and down. The wavelength of the photons is chosen so that they will interact only with atoms that are moving toward the photons.
For the atoms, "It's like running in a hail storm so that no matter what direction you run, the hail is always hitting you in the face," Wieman said. "So you stop."
This cools the atoms to about 10 millionths of a degree above absolute zero, still far too hot to produce Bose-Einstein condensation. About 10 million of these cold atoms are captured in the light trap. Once the atoms are trapped, the lasers are turned off and the atoms are kept in place by a magnetic field. Most atoms act like tiny magnets because they contain spinning charged particles like electrons. The atoms can be trapped, or held in place, if a magnetic field is properly arranged around them, the researchers said.
The atoms are further cooled in the magnetic trap by selecting the hottest atoms and kicking them out of the trap. It works in a way similar to the evaporative cooling process that cools a hot cup of coffee -- the hottest atoms leap out of the cup as steam.
The trickiest part was trapping a high enough density of atoms at a cold enough temperature. Cornell came up with an improvement to the standard magnetic trap -- called a time-averaged orbiting potential trap -- that was the final breakthrough allowing them to form the condensate.
Because the coldest atoms had a tendency to fall out of the center of the standard atom trap like marbles dropping through a funnel, Cornell designed a technique to move the funnel around.
"It's like playing keep-away with the atoms because the hole kept circulating faster than the atoms could respond," Cornell said. The result was a Bose-Einstein condensate of about 2,000 rubidium atoms that lasted for 15 seconds to 20 seconds. New machines can now make condensates of much greater numbers of atoms that last for up to 3 minutes.
Working with Cornell and Wieman on the initial Bose-Einstein condensation were postdoctoral researcher Michael Anderson and CU-Boulder graduate students Jason Ensher and Michael Matthews. Over the six years preceding the discovery, the experiment involved eight graduate and three undergraduate students at CU-Boulder.
The research was funded by the National Science Foundation, NIST, the Office of Naval Research and CU-Boulder.
Wieman and Cornell have won several prestigious awards including the Benjamin Franklin Medal in Physics from the Franklin Institute in 2000, the Lorentz Medal from the Royal Netherlands Academy of Arts and Sciences in 1998, the King Faisal International Prize in Science in 1997 and the Fritz London Award for low-temperature physics in 1996.
Cornell has received the National Science Foundation's Alan T. Waterman award in 1997, the Department of Commerce Gold Medal, the Presidential Early Career Award in Science and Engineering and the Stratton award from NIST, the organization's highest scientific award.
Wieman won the 2001 NSF Director's Award for Distinguished Teaching Scholars, the NSF's highest honor for excellence in both teaching and research, and also has won the Richtmyer lecture award from the American Association of Physics Teachers, the Einstein Medal for Laser Science and the Arthur L. Schawlow Prize in Laser Science.
Wieman is a former chair of the JILA research institute, a member of the American Academy of Arts and Sciences and holds an honorary doctorate from the University of Chicago.
JILA, formerly known as the Joint Institute for Laboratory Astrophysics, is an interdisciplinary institute for research and graduate education in the physical sciences located on the campus of the University of Colorado at Boulder.
In March 1999, CU-Boulder's Ph.D. program in atomic and molecular physics was ranked fourth in the nation by U.S. News & World Report. The Massachusetts Institute of Technology was ranked first, followed by Harvard and Stanford.
More information on Bose-Einstein condensation can be found at http://jilawww.colorado.edu/bec/
or visit the Physics 2000 Web site for a description featuring interactive
images at www.Colorado.EDU/physics/2000/bec/index.html.