ONR-supported researchers Deborah Jin of the National Institute of Standards and Technology and Brian DeMarco of the University of Colorado at Boulder and JILA -- a joint research institute of NIST and CU -- report in the Sept. 9 issue of Science the achievement of the first Fermi degenerate gas of atoms. In such a gas the atoms behave like waves.
"Not only is this work significant for its impact on future atomic clocks, but it can provide the physics for new classes of electronic devices as well," said ONR Program Officer Peter Reynolds, who sponsored the work.
Similar to experiments performed in 1995 that first created another new state of matter -- the Bose-Einstein condensate -- the JILA group cooled a gas of potassium atoms to ultralow temperatures where the quantum nature of the gas is dominant. However, while the Bose-Einstein experiments used one class of quantum particles known as bosons, the JILA group cooled atoms that are fermions, the other class of quantum particles found in nature. Using laser cooling and magnetic confinement, they cooled about a million potassium atoms to temperatures near 300 nanoKelvin, or less than 1/3 of a millionth of a degree above absolute zero, where the gas became "quantum degenerate."
When a cooled gas reaches quantum degeneracy, each atom stops behaving as a point-like particle and instead behaves like a wave, with the wavelength of each atom overlapping those of neighboring atoms. When bosonic atoms reach this regime they all fall in step with each other, resulting in a Bose-Einstein condensate or "super-atom." When the JILA group cooled fermionic atoms to quantum degeneracy, they instead found, as predicted, that the atoms began to avoid each other, resulting in an "excess" energy in the gas.
Study of this new system will lead to a greater understanding of fermions, which are important throughout physics as the basic building blocks of matter -- electrons, protons, and neutrons -- are all fermions. In addition, the special properties of fermionic atoms could lead to improved atomic clock technology, an area of great interest to the Navy which has the Master Clock at the US Naval Observatory in Washington, D.C. Work will also explore the possibility of achieving a fermionic superfluid state in the gas, which could ultimately shed light on the physics of superconductivity.
"The creation of a degenerate Fermi gas is a major scientific achievement and a lot of scientists have been trying to make it ever since we created the Bose-Einstein condensate," said Carl Wieman, CU-Boulder physics professor and co-creator of the first Bose-Einstein condensate in 1995 with NIST's Eric Cornell. "It will probably be at the top of the list of important physics news for this year." Both Wieman and Cornell were funded by ONR for the work leading to the creation of the Bose-Einstein condensate.
Authors of the Science paper are Deborah Jin and Brian DeMarco. Jin, a NIST physicist, is an associate fellow of JILA and an adjoint assistant professor of physics at CU-Boulder. DeMarco is a graduate student in the CU-Boulder department of physics. In addition to ONR and NIST, this work is supported by the National Science Foundation.
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