MIT Physicists Create Superfluid from Fermions

Physicists classify all elementary particles as either bosons (which have an integer quantum spin) or fermions (which have a half-integer spin). Ten years ago, researchers at the University of Colorado and MIT cooled bosons to temperatures so low that they formed a superfluid – a completely frictionless or zero-viscosity state sometimes known as a Bose-Einstein condensate, since it was predicted in the 1920s by Satyendra Nath Bose and Albert Einstein. In the June 23 issue of Nature, an MIT team led by Wolfgang Ketterle reports that they’ve done the same for fermions.

The researchers cooled atoms of a lithium-6 isotope to 50 billionths of one degree Kelvin above absolute zero, then trapped the atoms inside the electric and magnetic fields produced by infrared laser beams. When they set the gas spinning using another laser, a latticework of tiny vortices appeared; these vortices are one signature of a superfluid.

The ability to create superfluids from fermions in the lab could be key to understanding a related phenomenon, superconductivity, in which metals are cooled to temperatures so low that flowing electrons encounter zero resistance. It could also shed light on the workings of neutron stars and quark-gluon plasmas, which are thought to have pervaded the universe shortly after the big bang.

The work is described at length in MIT News and a commentary in Nature.