William Phillips

William Daniel Phillips was born in Wilkes-Barre, Pennsylvania, on 5 November 1948, to two social workers, and has described a childhood laboratory in the family basement of the standard hazardous kind. He studied at Juniata College and took his doctorate at MIT in 1976 under Daniel Kleppner, measuring the magnetic moment of the proton in water. In 1978 he joined the National Bureau of Standards — now NIST — in Gaithersburg, Maryland, and has stayed there for his whole career, an unusually long tenure at a single government laboratory for a Nobel laureate.

His first major contribution was the Zeeman slower (1982), a device of great practical importance. A laser can slow an atomic beam by radiation pressure, but as the atoms slow they Doppler-shift out of resonance and stop absorbing. Phillips's answer was a tapered magnetic field along the beam path that Zeeman-shifts the atomic levels by exactly the amount needed to keep the atoms in resonance the whole way down. Sodium atoms could now be brought from a thermal beam to a near standstill, and the Zeeman slower is still standard equipment in cold-atom laboratories.

His second was an accident of good metrology. In 1988 Phillips's group measured the temperature of optical molasses carefully, using a time-of-flight method, and found about 40 µK where the Doppler theory predicted a floor of 240 µK. The atoms were six times colder than they were allowed to be. Rather than dismiss the result he pressed it, and it triggered the theoretical work by Cohen-Tannoudji and Dalibard that produced the Sisyphus mechanism — an example, often cited, of an experiment being trusted over a theory and being right.

Phillips shared the 1997 Nobel Prize in Physics with Chu and Cohen-Tannoudji. His group at NIST went on to work on atomic fountain clocks — which underpin the modern definition of the second — Bose–Einstein condensates, optical lattices, and quantum information. He is a noted and enthusiastic public lecturer, and a devout Methodist who has spoken often about seeing no conflict between his science and his faith.