Nobel laureate Wieman to discuss 'quantum weirdness' at Hofstadter Lecture

By Esther Landhuis

An unthinkably small and strange world came into focus in 1995 when three physicists created the world's first Bose-Einstein condensate (BEC) ? an ultracold form of matter in which atoms lose their individuality and coalesce into a "superatom."

Carl Wieman, one of the three scientists who shared the 2001 Nobel Prize in physics for this achievement, will deliver a public lecture at 8 p.m. Monday, March 29, in the Teaching Center of the Science and Engineering Quad. His talk, titled "Bose-Einstein Condensation: Quantum Weirdness at the Lowest Temperature in the Universe," is this year's Robert Hofstadter Memorial Lecture. Wieman, who earned his doctorate in physics from Stanford in 1977, will give a more technical colloquium, "Resonant BEC: A New Macroscopic Quantum System," at 4:15 p.m. Tuesday, March 30, at the same location.

To coax a mixture of atoms into behaving identically -- as they would in a Bose-Einstein condensate -- the atoms need to be slowed considerably. This requires cooling them to less than 100 billionths of a degree above absolute zero. At this temperature, the atoms in the condensate move uniformly and provide an excellent study of quantum behavior.

Working out the chilling process was tricky. "One first had to realize how to cool a gas way down without turning it into a little ice cube, which is what it really wants to do," says Wieman, a professor at the University of Colorado at Boulder. "That was half, or more, of the battle."

The battle, in essence, spanned more than 70 years. In 1924, Albert Einstein and Indian physicist Satyendra Nath Bose predicted that a condensate would form at very low temperatures where individual atoms lose their discreteness and start to act as one big wave. But it wasn't until 1995 that Wieman -- along with Eric Cornell of the University of Colorado and the National Institute of Standards and Technology (NIST), and Wolfgang Ketterle of the Massachusetts Institute of Technology -- were able to produce this theorized form of matter in a laboratory. Wieman and Cornell, who are both with JILA, formerly the Joint Institute for Laboratory Astrophysics, achieved Bose-Einstein condensation in rubidium atoms, while Ketterle used sodium.

Key to the Wieman-Cornell approach was the somewhat counterintuitive notion that blasting atoms with laser light could cool them. When you shine light on your hand, for instance, your hand gets hotter as the light gets absorbed and turned into heat. To make atoms colder, light particles -- or photons -- need to bounce off the atoms with more energy than when they first hit the atoms. This happens when a laser is precisely tuned to eject a stream of photons of just the right color, or wavelength. Laser cooling gets the atoms down to about 20 millionths of a degree above absolute zero, Wieman says, but this is still too balmy for Bose-Einstein condensation.

To cool the sample further, his team devised a system in which the highest-energy atoms were allowed to escape a magnetic trap. "Just like steam escaping a coffee cup, the most energetic atoms jump out," taking with them the hottest part of the sample, Wieman says.

In his March 30 technical colloquium, Wieman will discuss more recent efforts to control interactions within condensates. These experiments have revealed what he calls "very interesting and still somewhat unexplained behavior," including supernova-like quantum implosions and explosions that his team has dubbed "Bosenovas." (A supernova is an explosive end to a star's life.)

A deeper understanding of the quantum behaviors of Bose-Einstein condensates may help scientists build devices that measure time and gravitational fields with ever-increasing sensitivity. "If you can control an atom better ? make it move slower, keep it from bumping into things ? you can make a better measurement device with it," Wieman says.

Esther Landhuis is a science-writing intern at Stanford News Service.

Editor Note:

This release was written by science-writing intern Esther Landhuis. Photos of Wieman are available at www.colorado.edu/news/nobel/wiemancornell/photos.html . Credit all photos to: University of Colorado at Boulder, Office of News Services.

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