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Nobel laureate presents his contribution towards the 'holy grail' of physics

By cooling gasses to near absolute zero and observing them as they behave like lasers and waves, Wolfgang Ketterle has attempted to bring the scientific world closer to what he calls "the "holy grail" of physics: the room-temperature superconductor.

Ketterle, the John D. MacArthur professor of physics at MIT, director of the MIT-Harvard Center for Ultracold Atoms, and 1995 Nobel laureate, tackled the physics of the very very cold in a packed Schwartz Auditorium April 13. The public lecture, titled "When Freezing Cold is Not Cold Enough," was Ketterle's third talk as the Spring 2011 Hans A. Bethe Lecturer.

Since the development of quantum theory in the early 20th century, Ketterle said, physicists have been studying matter at extremely low temperatures, where it often behaves in counterintuitive ways.

Quantum theory helps explain superfluidity, for example: the phenomenon in which some low-temperature liquids cease to be viscous and can flow endlessly with no friction. "When electrons are superfluid we call it superconductivity," Ketterle said. With no resistance to impede their progress, "the electrons go around obstacles like waves go around a stick in the sea."

If electricity for everyday consumption could be conveyed through superconductors, nearly every facet of contemporary technology would be revolutionized, he said. But so far, superconductors only exist at extremely low temperatures.

To better understand the phenomenon, Ketterle studies the simplest materials to exhibit superfluidity: gasses that are up to a billion times more dilute than air. Atoms in such gasses seem to lose their individuality and form one uniform mass that behaves like a superfluid wave -- a state of matter known as a Bose-Einstein condensate (BEC).

While this quantum effect on very cold and dilute gasses was predicted by Satyendra Bose and Albert Einstein in 1925, it took 70 years for super-cooling technology to catch up with their prediction. Ketterle's lab produced a BEC in 1995, four months after two researchers at the University of Colorado-Boulder. All three were awarded the Nobel Prize in Physics in 2001.

But electrons are a fundamentally different particle than those used by Ketterle's team to create the BEC, Ketterle said. Unlike atoms, electrons are "unsocial"; they don't naturally pair up and synchronize into a quantum superfluid state when ultra-cooled.

"This is possible for atoms. We have no idea how to do it for electrons," he said. "But by doing those experiments, we've encouraged theorists to think harder about superconductivity and superfluidity, and they are formulating theories [about them] now."

"I hope it demonstrates to you how scientists think," Ketterle concluded. "They want to show the principle for a system which can probably not solve your problem anyway. But by understanding that system you may learn something and make progress towards your goal."

The Bethe Lectures honor Hans A. Bethe, Cornell professor of physics from 1936 until his death in 2005. Bethe won the Nobel Prize in physics in 1967 for his description of the nuclear processes that power the sun.

Paul Bennetch '12 is a writer intern for the Cornell Chronicle.

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