Claude Cohen-Tannoudji
active c. 1933, Constantine, French Algeria
French physicist who shared the 1997 Nobel Prize in Physics for elucidating laser cooling below the Doppler limit (Sisyphus cooling).
Born in Constantine, French Algeria, Cohen-Tannoudji completed his doctorate at the École Normale Supérieure in 1962 under Alfred Kastler, who passed on the methods of optical pumping. A theorist of quantum optics, he developed with Jean Dalibard the dressed-atom formalism and, in 1988–1989, explained how polarization gradients in counter-propagating lasers cool atoms below the Doppler limit — 'Sisyphus cooling', reaching microkelvin temperatures. He became professor at the Collège de France in 1973 and authored the classic textbook series on quantum mechanics with Diu and Laloë.
Nobel-winning work
Cohen-Tannoudji explained why laser-cooled atoms in Paris and at NIST reached temperatures far below the supposed Doppler limit. With Dalibard he showed that polarization gradients create a spatially modulated optical potential: atoms repeatedly climb a hill, losing kinetic energy, then are optically pumped into the next valley — the 'Sisyphus' cycle (1989).
He also conceived velocity-selective coherent population trapping (1988), where atoms fall into a dark state immune to photon scattering, achieving sub-recoil (nanokelvin) temperatures — the deepest laser cooling known.
Workplaces: Collège de France, École Normale Supérieure
France