Chu was educated at the University of California, Berkeley, where he obtained his PhD in 1976. He joined Bell Labs in 1978 and, in 1987, took up an appointment as professor of applied physics at Stanford University, California.

In their normal state atoms are subject to a constant random thermal motion which limits the precision of measurements of atomic states. Physicists have therefore sought to slow atoms down as much as possible.

One proposed way to cool atoms was demonstrated in the early 1970s by William Phillips. Phillips had used a single laser and worked with beams of sodium atoms. Chu used six laser beams and worked with a hot gas of sodium atoms. He managed to cool and trap atoms in what he called ‘optical molasses’. By 1985 he had cooled sodium atoms to a temperature of about 240 microkelvins – i.e. a 240 millionth of a degree above absolute zero. The atoms could be trapped in the laser beams for a period of about half a second.

For his work in this field Chu shared the 1997 Nobel Prize for physics with Phillips and Claude Cohen-Tannoudji.