Claude Cohen-Tannoudji Biography (1933-)


Cohen-Tannoudji was born April 1, 1933, in Constantine, Algeria. He studied at Ecole Normale Superieure from 1953 until 1957, when he received his agrégation. He earned his D.Sc. (Ph.D.) from the University of Paris in physics in 1962. While a graduate student, he studied under 1966 Nobel Prize winner Alfred Kastler. His thesis advisor was Jean Brossel. Following in both of his mentors' theoretical footsteps, Cohen-Tannoudji has arguably becometheir most distinguished student. Also, while still a student as well as shortly after graduation, from 1960-64, Cohen-Tannoudji worked as a researcher at the Centre National La Recherche Scientifique in Paris. He then served as aprofessor at the University of Paris from 1964-73.

In his early research, Cohen-Tannoudji studied the phenomenon that formed thefoundation of his later work. Cohen-Tannoudji worked methodically, predicting theoretically, then demonstrating his theories through experiments. His investigations concerned atoms and their energy levels. He found that energy levels shifted a small amount when, in a field intensely radiated with light, they absorbed and emitted photons of light. (Photons are the smallest pieces ofelectromagnetic energy.) This is Cohen-Tannoudji's so-called light shift discovery.

It was in the 1970s that Cohen-Tannoudji came up with another theory that eventually was applied specifically to lasers. His theory explained the interactions between high-intensity electromagnetic fields and the atoms within them.When an atom is surrounded by photons, it is constantly absorbing and re-emitting them. He described the atom as being "dressed" by the photons. This observation became important when it was applied to lasers in the late 1970s andbeyond.

By the 1980s, Cohen-Tannoudji theorized specifically about the light (of a laser) and its effect on the motion of an atom. His experiments in laser cooling were a response to other scientists' work with laser beams, cooling atoms,and trapping atoms. Cohen-Tannoudji, leading his own team of experts, focusedon the modification of atomic motion when it interacted with photons. He hadhis first breakthrough in 1985, when he saw that an atom in motion slows ina standing light wave. As the laser beam intensifies, the atom slows increasingly. Because a material's temperature measures how fast its atoms are moving, this effect came to be known as "Sisyphus cooling," named for the Greek mythological personage who had to roll a stone up a hill for eternity. However,this method was limited in its cooling effects.

By 1988 Cohen-Tannoudji brought together his "dressed" atom ideas with the problems raised by the cooling and trapping atoms theories in order to try to bring the temperature of atoms closer to absolute zero. A few years later, Cohen-Tannoudji had an unexpected breakthrough when studying an atom trapped ina standing light wave. He found that it was dependent on optical pumping, anadvanced laser technology in which emits light energy in pulses. This approach keeps the atoms from rebounding, in effect "trapping" them. This type of Sisyphus cooling brought the temperature to 0.18 millionths of degree above absolute zero. The phenomenon had been anticipated by Albert Einstein and others.

In the 1990s, Cohen received important recognition for his work: the Julius Edgar Lilienfeld Prize from the American Physics Society (1992), the Charles Hard Townes medal from the Optical Society of America (1993), the Harvey prizein science and technology from Technion, Israel (1996). Also in 1996, Cohen-Tannoudji won the Médaille d'Or of the National Center for ScientificResearch, the highest honor a scientist can receive in France. He won the Médaille specifically for his research in atoms and related cooling methods. In 1997 Cohen-Tannoudji shared the Nobel Prize in physics for his explanation of the phenomenon and his "trapping" discovery.

Cohen-Tannoudji's work has opened up long range research possibilities, but affects basic physics as well. It can be used to study atomic structure, as well as help bridge the frontier between classical and quantum physics. Cohen-Tannoudji's theories also have proven useful for practical technology now andin the future. Ultracold atoms can be used to create more precise atomic clocks. (Atomic clocks are devices which use the constant frequency associated with some atomic and subatomic phenomena to define an accurate and reproducibletime scale.) His theories are also influential in the development of measuring instruments of extreme precision. Indeed, an atomic laser might be possible. (An atomic laser would be like an ordinary one, save atoms would take theplace of photons used in ordinary lasers.)

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