CAMBRIDGE, Mass., Sept. 12 -- Using lasers, lenses and magnetic fields, MIT scientists have cooled a sodium gas to the lowest temperature ever recorded -- only half-a-billionth of a degree above absolute zero. The work, to be reported in today's issue of Science, beats the previous record by a factor of six, and is the first time a gas was cooled below 1 nanokelvin (one-billionth of a degree).
"To go below one nanokelvin is a little like running a mile under four minutes for the first time," said Nobel laureate Wolfgang Ketterle, co-leader of the team.
Ultralow-temperature gases could lead to vast improvements in precision measurements by allowing better atomic clocks and sensors for gravity and rotation, said David E. Pritchard, a pioneer in atom optics and atom interferometry and co-leader of the MIT group.
The researchers also expect new phenomena to occur at such low temperatures involving, for example, how cold atoms interact with surfaces and how atoms move when they are confined to a narrow channel or layer. These gases form a remarkable state of matter called a quantum fluid, so studying their properties also provides new insights into the basic physics of matter, they said.
For reaching the record-low temperatures, sodium, solid at room temperature, is heated to 300 degrees Celsius to make it a gas. Next, techniques called laser cooling and evaporative cooling get the gas to the starting point for the latest experiment. The researchers force the gas through a meter-long tube, where it slams into light particles from a laser being fired in the opposite direction. In a fraction of a second, the collisions slow the atoms from 1,000 meters per second to 30 meters per second. They are cooled further in a spherical container where lasers pummel them from all sides. They are then placed in a magnetic bowl where the hottest atoms float away like steam evaporating.
The MIT researchers invented a novel way of confining atoms, which they call a "gravito-magnetic trap," in which the magnetic fields act together with gravitational forces to keep the atoms trapped.
In 1995, a group at the University of Colorado at Boulder and an MIT group led by Ketterle cooled atomic gases to below one microkelvin (one-millionth of a degree above absolute zero). In doing so they discovered a new form of matter, the Bose-Einstein condensate, where the particles march in lockstep instead of flitting around independently. The discovery of Bose-Einstein condensates was recognized with the 2001 Nobel Prize in physics, which Ketterle shared with his Boulder colleagues Eric Cornell and Carl Wieman.
Since this breakthrough, many groups worldwide now routinely reach nanokelvin temperatures; the lowest temperature reported before now was 3 nanokelvin. The new record set by the MIT group is 500 picokelvin, or six times lower.
For more information, visit: www.mit.edu