Born at Constantine (Algeria) on April 1, 1933, he attended school in Algier, the capital, and at the age of 20 he came to Paris, holding an admission to the “École Normale Supérieure”. There, up to 1957, he received an excellent education, in particular in Physics by Alfred Kastler (Nobel Prize in 1966). Finally, in Saclay he gained first experiences in quantum mechanics and nuclear Physics. Then a “summer school” held by the University of Grenoble, with contributions of renowned scientists, gave him a profound insight into the acute problems of theoretical Physics. After his thesis he passed the “Agrégation”, a kind of mastership examination for experimental and theoretical Physics.
In 1960, after his military service, Cohen-Tannoudji came back to Kastler as candidate for a doctor’s degree and worked in a research laboratory of the CNRS on the application of “optical pumping” in order to investigate the behaviour of different isotopes. After his graduation as Ph.D. (in 1967) he developed new efficient methods by which it is possible to energetically “brake” single atoms — floating in a beam — by absorption and emission of (laser) photons, i.e. cool down and finally store them. In this process, light acts on atomic particles like a kind of syrup (“optical molasses”): Additional magnetic fields are able to “detain” the particles in such a way that macroscopically a system of temperatures of few nanokelvin (a billionth degree absolute temperature) — thus producing an “ultra-cold gas”.
The same result, which raises expectations for almost “exciting” applications, was since also achieved by the American scientists Steven Chu and William Phillips. With them, Cohen-Tannoudji shared the Nobel Prize in Physics in 1997.
This text of the Nobel Laureate was taken from the book: "NOBELS. Nobel Laureates photographed by Peter Badge" (WILEY-VCH, 2008):
Claude Cohen-Tannoudji is a French physicist who shared the 1997 physics prize with Steven Chu and William D. Phillips for developing the use of lasers to cool atoms to the extent that they move slowly enough to be examined in detail.
He was born in 1933 in Constantine, Algeria, which was then a French colony. His family, originally from Tangiers (the family name simply means the Cohen family from Tangiers), fled Spanish rule during the Inquisition. He attended school in Algiers and in 1953 entered the École Normale Supérieure (ENS), Paris, to study maths but switched to physics under Alfred Kastler. The research group was small but keen, and he recalls taking experimental data and averaging by hand, due to the lack of computers. After a prolonged spell in the army due to the war in Algeria, Cohen- Tannoudji received his doctorate in 1962. He remained at the ENS as a research scientist, while also teaching at the University of Paris VI from 1964–73 and at the Collège de France from 1973. During this time he developed what is called the dressed atom approach, which describes the interaction of intense light with atoms.
The Collège de France is an egalitarian institution founded by King Francois I in 1530. Lecturers are free to select their own topic and in the early 1980s Cohen-Tannoudji chose to lecture on the new area of radiative forces. In 1984, with Alain Aspect and Jean Dalibard, he formed a new experimental group on laser cooling and trapping, joined later by Christophe Salomon. They invented a new type of cooling mechanism which today has received the name Sisyphus cooling. Co-laureate William Phillips collaborated with the group, and when in 1988 he observed sub-Doppler temperatures, they managed to determine that such low temperatures resulted from a low intensity version of Sisyphus cooling. Steve Chu reached similar conclusions in the US.
With Alain Aspect and Ennio Arimondo, Cohen-Tannoudji expanded on the work of Chu and Phillips, exploring the possibility of applying coherent population trapping to laser cooling. In 1995 they cooled helium atoms to within millionths of a degree above absolute zero slowing the atom to about two centimetres per second. Their work and that of Chu and Phillips, furthered scientists’ understanding of how light and matter interact. Among other practical applications, the techniques they developed can be used to construct atomic clocks and other high-precision instruments. Cohen-Tannoudji and his physics teacher wife Jacqueline married in 1958 and had three children, Alain, Joëlle and Michel. Sadly, Alain died in 1993, of a long illness, at the age of 34.
This text of the Nobel Laureate was taken from the book: "NOBELS. Nobel Laureates photographed by Peter Badge" (WILEY-VCH, 2008).