In a lab in Colorado, inside a jar cooled to the lowest temperature ever reached on Earth or anywhere else, scientists have created a form of matter that has never existed before anywhere in the universe -- something they have dubbed a "superatom."
In their creation, Carl Weiman and Eric Cornell of the University of Colorado at Boulder cooled a few thousand atoms of rubidium gas to a temperature so low that they lost their individual identities and acted as if they were a single atom.
"It's a spectacular discovery," said Daniel Kleppner, a physicist at the Massachusetts Institute of Technology who had been trying for years to create this new form of matter, technically called a Bose-Einstein condensate. Dr. Weiman, one of the two who beat him to the punch, had been his student.
In classical physics, there are only three possible states of matter: solid, liquid and gas. The differences between them lie in how the individual atoms in the substance interact. In recent decades, the picture has become somewhat muddier, with other states such as plasma -- electrically charged gas -- added to the list. The form created in Colorado is considered yet another state of matter.
Dr. Weiman and Dr. Cornell created the superatom on June 5, and their report is being published today in the journal Science.
The existence of this exotic form of matter was predicted in 1924 by Indian physicist Satyendra Nath Bose and Albert Einstein.
While nobody can yet predict exactly what the work might lead to, Dr. Cornell pointed out that other forms of supercold matter have important, unique properties: When some solids are cooled, they lose all resistance to the flow of electricity and become "superconductors." When some liquids are cooled to extremely low temperatures, they become "superfluids," capable of flowing without resistance, even flowing uphill.
When a gas is cooled to even lower temperatures, Dr. Cornell wondered, "is there a 'super-something' associated with this gas?"
The difficulty was to produce the low temperature -- a billion times colder than the coldest depths of outer space -- that would cause atoms to come to a standstill.
The temperature achieved by the Colorado team was estimated at 2 nanokelvins, or two-billionths of a degree above absolute zero, the theoretical, unachievable temperature at which all atoms would be perfectly still.
They did it with a combination of techniques. First, they cooled atoms of the metallic element rubidium by placing them in a vacuum chamber and shining laser beams at them from all sides. "What the atom feels is like water squirting in from all sides," Dr. Cornell said. "If they try to move in any direction, they feel more pressure."
That effectively eliminates most of the atoms' motion, which is the scientific definition of heat. This technique can cool the rubidium to a millionth of a degree above absolute zero. "For a number of years, that was as cold as anything had got," Dr. Cornell said. "We needed a new trick."
The new trick was a magnetic field, manipulated in a way that kept the atoms confined in a virtual "bowl" of magnetic force, a bowl that Dr. Weiman likened to "a super-Thermos bottle."
Then, they cooled the gas still further by allowing part of it to "evaporate" away. "If you've ever ordered a cup of coffee to go," Dr. Weiman said, "you know it's very important to keep the lid on . . . to keep it from getting cold." To cool the rubidium atoms, in effect, "We take off the lid."
With the magnetic field, he said, the atoms were "cooled to many hundreds of times colder than anything has gotten before."