ARLINGTON, VA, March 19, 1999 -- Office of Naval Research-funded physicists at the Commerce Department's National Institute of Standards and Technology have opened a new field of physics. Their experiments demonstrate for the first time that atoms can display some unusual properties previously seen only with high-intensity laser light waves. They reported their findings in the March 18 issue of Nature.
Using sodium atoms cooled to very near absolute zero, the NIST team demonstrated that three atom waves can be mixed together to produce a fourth matter wave. This is an exact analogy to how optical laser beams can be combined to form a new laser light beam. Scientists expect that this new field of non-linear atom optics will parallel the development of non-linear optics, which emerged as scientists discovered many of the strange, unique and unexpected abilities of laser light following the demonstration of the first laser in 1960.
"We are at the threshold of a new area of research: non-linear atom optics," says William D. Phillips, recent Nobel Laureate and leader of the NIST Laser Cooling and Trapping Group. Also working on the atom wave mixing experiments are Steven Rolston, Kristian Helmerson, Paul Julienne, Jesse Simsarian, Edward Hagley and Jesse Wen, all of NIST; Lu Deng of Georgia Southern University; and Marek Trippenbach and Yehuda Band of Ben-Gurion University, Israel. In addition to ONR funding, the work was supported in part by the National Aeronautics and Space Administration.
What is non-linear atom optics? After the invention of the laser, scientists began to note the unusual properties of laser light. The high intensity of the laser beam when passed through a material allows it to create new colors of light from other colors. This and similar phenomena were dubbed non-linear optics. In non-linear atom optics, scientists replace the light waves with atomic matter waves, but no material is needed because unlike light waves the atom waves interact directly with each other.
This first non-linear atom optics experiment demonstrates that atoms coaxed into waves analogous to laser-like light can be combined to create a new wave, just as laser beams can be combined to form a laser beam of another color. To accomplish this, the NIST physicists first created a dense cloud of very cold atoms in which all the atoms had fallen into their lowest possible energy states and become indistinguishable from one another. This exotic state of matter is known as a Bose-Einstein condensate. It was first predicted by Albert Einstein more than 70 years ago, and was first achieved in a gas by another group of ONR-funded physicists at NIST and the University of Colorado in 1995.
Next the scientists pulsed beams of optical laser light with predetermined directions and frequencies onto the Bose-Einstein condensate, thereby splitting the condensate into three distinct, intense matter waves. Each matter wave had a unique velocity and direction. The scientists applied the same rules governing light to determine the necessary velocities and directions to mix the three matter waves so they would form a fourth. As anticipated, the interaction of these matter waves did in fact produce a fourth matter wave with just the properties the scientists had predicted.
"Calculations by ONR funded theorists Paul Julienne, Marek Trippenbach and Yehuda Band showed it should be easy to do," Phillips, whose Nobel prize winning work enabled this new field, explains. "The theory pushed us in a new direction of investigation. We found a nice agreement between their theory and our experiments."
"Up until the early 1960s, people thought all properties of light could be explained by the classical theories covering electromagnetic fields," Phillips explains. "After that time researchers began to understand that light could exhibit strange quantum behavior. Non-linear optics has been key in the development of quantum optics, which explores such behavior. We can now look forward to the analogous development of quantum atom optics," Phillips says. Another possible application is the amplification of matter waves, making a beam of atoms more intense by "creating" additional atoms that are exact quantum copies of those in the original beam.
For more information and to see pictures of matter wave mixing, see http://physics.nist.gov/atomoptics on the World Wide Web.
The Office of Naval Research pursues an integrated science and technology program from basic research through manufacturing technologies. Research areas include oceanography; advanced materials; sensors; electronics; surveillance mine countermeasures; weapons; and surface ship, submarine and aircraft technologies. For more information about ONR programs, refer to the ONR home page at http://www.onr.navy.mil on the World Wide Web.
Journal
Nature