World's First Atom Laser Carves New Place in Science History
CAMBRIDGE, MASS. — Inside a cramped, cable-draped lab near the Charles River, scientists at the Massachusetts Institute of Technology have built the world's first laser that fires a beam of atoms instead of light.
It is an experimental, rudimentary device. But the ability to manipulate a state of matter, that until recently was only a theory, could foster a technological revolution as dramatic as that sparked by the visible-light laser, some researchers say.
"I'm incredibly excited by this result," says William Phillips, a physicist with the National Institute of Standards and Technology. A year and a half ago, a team from NIST and the University of Colorado became the first group to produce a unique state of matter first hypothesized in the 1920s.
"This is going to carry us into a whole new area of research," Dr. Phillips continues, noting that experiments using atom lasers could help answer nagging, if subtle, questions about quantum mechanics and how it applies to efforts ranging from measuring processes at the subatomic level to attempts to develop ultra-high-speed quantum computing.
Nor will atom lasers be limited to physics labs, he adds. They could lead to applications "we can't even imagine today."
"When the first laser was demonstrated in the early '60s, people said, 'Now that we've got it, what do we do with it?' " says Phillip Schewe, with the American Institute of Physics. Back then, he notes, no one predicted that lasers would be used for everything from etching computer chips and cleaning teeth to putting holes in the nipples of baby bottles.
Wolfgang Ketterle, the MIT physicist leading the research team, notes that because the atom laser requires a very pure vacuum, it's unlikely to find its way to grocery store check-out counters. But he and others envision important uses nonetheless: building more-compact computer chips, developing more accurate clocks to boost the accuracy of navigation satellites, and assembling mini-machines on a scale approaching a billionth of a meter..
"A well-controlled beam of atoms would allow you to deposit atoms with the accuracy of an atom's diameter," says Michael Andrews, a member of the MIT research team and the lead author of one of two papers appearing this week announcing the team's results.
Along with Marc-Oliver Mewes, another member of the research group, Mr. Andrews sits amid the computers and racks of test equipment explaining the team's experiments.
The device, he says, takes advantage of a state of matter known as a Bose-Einstein condensate. According to quantum mechanics, atoms exhibit wavelike properties as well as behave like particles. In the 1920s, physicists Satyendra Nath Bose and Albert Einstein proposed that if a "cloud" of atoms were chilled sufficiently, their wave-like attributes would begin to overlap until they formed a single coherent wave.
In July 1995, the NIST-Colorado research team made the first Bose-Einstein condensate, using lasers and a trap made from magnetic fields to bring the atoms to a temperature within only a tiny fraction of a degree above absolute zero.
The feat was quickly duplicated by researchers at Rice University in Houston and Dr. Ketterle's MIT team. At the time, scientists noted that the condensate's properties were similar to that of light in a laser. They suggested that making an atom laser might be possible, but that it was years away.
"We wanted to push the field rather fast," Andrews explains. So the MIT team set to work trying to figure out how to peel off sections of the condensed-atom cloud and form a beam. They designed a device that uses radio waves to change the way atoms respond to magnetic fields, allowing the atoms to break out of their magnetic trap. By adjusting the strength of the signal, they could control the number of atoms that broke free from the main "cloud." They designed their atom laser so that the smaller clouds of condensate would drop under the influence of gravity - in effect giving the mini-clouds a direction. By pulsing the radio transmitter 200 times a second, they generated a series of tiny clouds that formed a "beam."
But the experimenters still needed proof that the atoms were acting in a coherent manner to establish that the device was a laser.
When light from a laser is split and recombined, it displays a readily visible interference pattern, which testifies to its coherence. Using an argon laser, the team sliced up some of its condensate and using a special camera first developed for astrophysics, the team discovered what Ketterle calls "textbook-like" patterns associated with lasers.
"This work is a big advance," says NIST's Phillips. "It's breathtaking."