Steven Chu
active c. 1948, St. Louis, Missouri, USA
American physicist who shared the 1997 Nobel Prize in Physics for laser cooling and trapping of atoms; later the 12th US Secretary of Energy.
Born in St. Louis to Chinese immigrant academics, Chu earned his PhD at Berkeley in 1976, then joined Bell Labs where in 1985 he used six counter-propagating laser beams to create 'optical molasses', cooling sodium atoms to ~240 μK — the Doppler limit then believed fundamental. Moving to Stanford in 1987, he built the first magneto-optical trap and pioneered atom interferometers and optical tweezers for single-molecule biology. From 2009 to 2013 he served as US Secretary of Energy under President Obama, the first scientist laureate to hold a cabinet post.
Nobel-winning work
Chu's 1985 optical molasses exploited Doppler cooling: atoms moving against a red-detuned laser beam absorb photons preferentially from the opposing direction, losing momentum with each absorption–emission cycle. Six beams created a viscous light medium that chilled sodium atoms to ~240 μK and confined them for a fraction of a second.
With the magneto-optical trap (1987) — molasses plus a weak magnetic quadrupole field — atoms could be captured and held for long studies. Though Cohen-Tannoudji and Phillips soon showed sub-Doppler cooling reaches lower temperatures, Chu's methods established laser cooling as a practical tool, enabling Bose–Einstein condensation (2001 Nobel) and atom interferometry.
Workplaces: Stanford University, Bell Laboratories
United States