Nobel-Winning French Physicist Claude Cohen-Tannoudji Passes Away at 93

French physicist Claude Cohen-Tannoudji, who won the 1997 Nobel Prize in Physics for developing techniques to cool atoms close to absolute zero using laser light, died on October 22 at the age of 93. Born in French Algeria in 1933, he moved to Paris at age 20 and joined a research group led by Alfred Kastler and Jean Brossel, spending most of his career at the Laboratoire Kastler Brossel.

Laser Cooling and Sisyphus Technique

While lasers normally add energy, scientists harnessed their momentum to slow atoms down. In Doppler cooling, laser beams are pointed at atoms from multiple directions so that a moving atom absorbs more photons from the beam it faces. Because the atom absorbs light in one direction but spits it out randomly, its average energy and temperature drop. To push temperatures even lower, U.S. physicist William Phillips and researchers including Jean Dalibard developed Sisyphus cooling in 1988. Inspired by the Greek myth, this technique forces moving atoms to repeatedly climb energy stairs using lasers, after which an optical pump cools them down. Cohen-Tannoudji's team successfully cooled atoms to a few nanokelvins, enabling advanced atomic clocks and atom interferometers.

Indian Connections and Mentorship

Cohen-Tannoudji maintained strong ties with India, including writing a 1994 essay in the Indian journal Current Science to honour the late physicist S. Pancharatnam. He later visited Bengaluru and Mumbai in 1999, delivering the first Homi J. Bhabha Lecture at the Tata Institute of Fundamental Research. In 2001, he co-authored a paper with C.S. Unnikrishnan on a Bose-Einstein condensate in helium. Beyond his research, he was known for his humility and support of peers, encouraging Alain Aspect's early work and organizing meetings that brought Israeli and Arab scientists together.

Context

Absolute zero is the lowest possible temperature where molecular motion comes to a complete halt, though scientists use lasers to reach temperatures just fractions above it. Cooling atoms to these extreme levels allows physicists to study quantum mechanics and atomic behavior with incredible precision. Claude Cohen-Tannoudji's work laid the groundwork for modern quantum technologies that rely on ultra-cold atoms.