ScienceNow

 

22 Feb 2002

 

 

 New State of Matter Not So New?

 

  BOSTON--The 2001 Nobel Prize in Physics honored three researchers for coaxing hordes of atoms into a single quantum state. But the bizarre phenomenon known as Bose-Einstein condensation was actually spotted many years before the prize-winning work, one of the new laureates said 16 February at the annual meeting of the American Association for the Advancement of Science, publisher of ScienceNOW.

Bose-Einstein condensation occurs when certain types of particles are cooled to near absolute zero and suddenly collapse en masse into the single quantum state with the least energy and no momentum. Predicted in 1924, such condensation was achieved in 1995 by Eric Cornell and Carl Wieman of JILA in Boulder, Colorado, and independently by Wolfgang Ketterle of the Massachusetts Institute of Technology in Cambridge. The researchers used lasers and magnetic fields to cool gases of atoms such as rubidium and sodium, and in December, the three received the Nobel prize for their efforts (Science, 19 October 2001, p. 503).

But Bose-Einstein condensation was seen decades ago in liquid helium, Ketterle mentioned during a presentation at the meeting, acknowledging a controversial claim by John Reppy of Cornell University in Ithaca, New York. Physicists generally agree that the atoms in superfluid helium-4 is not a Bose-Einstein condensate (BEC) in the original sense of the term because its atoms interact too strongly. Reppy studied an exception: tiny amounts of helium trapped in nanometer-sized pores of a spongelike glass called Vycor. Even though the pores keep its atoms too far apart to jostle one another much, the helium still behaves like a three-dimensional fluid. In 1983 Reppy and colleagues reported results that suggested the helium was sloshing through the glass as a true BEC.

Ketterle says that Reppy brought this finding to his attention a couple of years ago and that the priority claim is fair. "I think the results appeared conclusive," Ketterle says. But co-laureate Wieman says that Reppy's claim is "really a stretch" and that Ketterle may have acknowledged the helium experiments to appease Reppy. "Ketterle is being gracious," Wieman says, "and Reppy makes a lot of noise."

--ADRIAN CHO

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 © 2001 by the American Association for the Advancement of Science.