Claude Cohen-Tannoudji


Claude Cohen-Tannoudji shared the 1997 Nobel Prize in physics with Steven Chu and William D. Phillips “for development of methods to cool and trap atoms with laser light.” Cohen-Tannoudji, an atomic physicist, developed a method of describing atoms in a coherent field known dressed states. In this description, the energy levels are described as a mixture of atomic levels “dressed” by a coherent field (for example a laser). Cohen-Tannoudji and members of his group began investigating laser cooling methods using this dressed state approach. This led them to a new idea on laser cooling resulting from spatial modulations and dressed state energy levels. Originally it was called stimulated blue molasses, because the cooling laser fields were off resonance by going above the frequency needed. Chu’s off lasers were either on resonance or below resonant frequency (red shifted) (optical molasses or super molasses). Cohen-Tannoudji’s cooling lasers were very intense and were the first display of what is now called “Sisyphus cooling.” Cohen-Tannoudji’s group was the first to trap neutral atoms in a region of space the size of a wavelength of visible light. Cohen-Tannoudji’s group also helped explain sub-Doppler cooling first seen in Bill Phillips’ experiments.