German-born physicist who, with Eric A. Cornell (Cornell, Eric A.) and Carl E. Wieman (Wieman, Carl E.), won the Nobel Prize for Physics in 2001 for creating a new ultracold state of matter, the so-called Bose-Einstein condensate (BEC).

In 1986 Ketterle received a Ph.D. from the University of Munich and the Max Planck Institute for Quantum Optics in Garching, Germany. After postdoctoral work he joined the faculty at the Massachusetts Institute of Technology (MIT) in 1993. He also served as a principal investigator with the Center for Ultracold Atoms, a joint research institution sponsored by MIT, Harvard University, and the National Science Foundation. Ketterle has permanent residency in the United States.

In the early 1990s Ketterle began work on the Bose-Einstein condensate, which had been predicted some 70 years earlier by Albert Einstein (Einstein, Albert) and Satyendra Nath Bose (Bose, Satyendra Nath). Working with a team, Ketterle was able to develop innovative techniques for trapping and cooling atoms, and in September 1995 he succeeded in creating a BEC from sodium atoms. This BEC comprised a much larger sample of atoms than the condensates produced by Wieman and Cornell, and it was used to carry out additional studies, including an interference experiment that provided the first direct evidence of the coherent nature of a BEC. Ketterle's work offered insight into the laws of physics and pointed to possible practical uses of BECs.