Steven Chu, 1948–, U.S. physicist and government official, b. St. Louis, Mo., grad. Univ. of Rochester (B.S., A.B. 1970), Univ. of California, Berkeley (Ph.D. 1976). He worked from 1978 at Bell Labs (from 1983 as head of its quantum electronics research department), where he began developing laser techniques for manipulating individual atoms and molecules and determining their properties. For developing a laser array that could be used to slow and capture atoms for study, he was awarded the 1997 Nobel Prize in Physics with Claude Cohen-Tannoudji and William D. Phillips. From 1987 to 2004, Chu was professor of physics and applied physics at Stanford, where he developed "optical tweezers," a laboratory technique in which lasers are used to trap one end of a molecule and hold it suspended so that an individual molecule's properties can be studied. In 2004 he became director of the Lawrence Berkeley National Laboratory, where he focused especially on developing research into alternative and renewable energy. Chu then served as secretary of energy (2009–13) under President Barack Obama; in that post he also sought to promote the development of cleaner energy technologies.