Almost Absolute Zero: The Story of Laser Cooling and Trapping
by William D. Phillips
Monday, March 26, 2001 | Washington, DC
The technical program on Monday got off to a rousing start with a plenary lecture by Dr. William D. Phillips of the National Institute of Standards and Technology (NIST). Dr. Phillips shared the Nobel Prize in physics for his work on cooling and trapping atoms with laser light. The talk was highly entertaining; perhaps its most noteworthy aspect was the speaker’s ability to distill, with remarkable clarity, complex ideas into understandable terms. Indeed this talk engendered “water-cooler” remarks from the audience such as, “One of the best plenary lectures in recent memory,” and “Now I understand what laser cooling is all about.” Phillips embellished his talk with practical demonstrations and a video clip or two. In true physics style, all the overheads were handwritten and this talk was a testimony (at least to this writer) that content is far more important than style in the scientific world.
Dr. Phillips began his lecture with an admission that he was not an electrochemist, although some of his best friends were. He also pointed out that his story was a partial one, in that many other scientists have contributed to the progress in the field of laser cooling of atoms. He estimated that there were over 100 research groups around the world working in this area.
The first part of the lecture dealt with how lasers cool atoms. This concept is rather counter-intuitive, in that one normally associates lasers with their heating capability, especially in an era of their widespread use in surgical applications. There followed a description of the use of multiple laser beams to create an “optical molasses” in the atom cell; thus slowing down atomic motion. This phenomenon was illustrated with a video clip of Cs atoms and also with a practical demonstration involving balloons being exposed to liquid nitrogen temperature. Dr. Phillips and his co-workers refer to their laser technique as inducing a “Sisyphus” cooling mechanism.
The next aspect of the lecture involved a lucid description of the use of a magnetic “bottle” for confining and trapping cold atoms. Once again, this strategy was explained with a demonstration and a video clip showing a floating magnet.
Temperatures as low as ca. 200 K have been attained and Phillips remarked how the results were actually much better than they had ever anticipated. Temperatures even lower in the pK regime are being achieved by Bose Einstein condensation strategies.
A primary motivation for Dr. Phillips’s low temperature research relates to calibration of the atomic clock. He concluded his lecture with a peek into the future possibilities in this area, particularly in applications related to atomic microscopy, atom interferometers and tweezers, quantum computing, and holography. All in all, this lecture provided a propitious start to an outstanding technical program during the week.