Public Lectures
Claude COHEN-TANNOUDJI
Nobel Laureate in PhysicsCollège de France and
Laboratoire Kastler Brossel, FRANCE
Einstein was the first physicist to introduce the idea that the radiation field is quantized and consists of quanta, called now photons, having an energy hn and a linear momentum hn / c. He extended also the new statistics introduced by Bose for a gas of photons to a perfect gas of atoms, predicting in this way a new spectacular phenomenon, Bose-Einstein condensation.
We will review in this paper a few modern extensions of these ideas. First, multiphoton ionization, where an atom is ionized, not by the absorption of a single photon, as in the first description of the photoelectric effect given by Einstein in 1905, but by the absorption of several photons. We will then show how resonant exchanges of linear momentum between atoms and photons can give rise to huge radiative forces exerted by laser beams on atoms, allowing one to cool these atoms to extremely low temperatures. One of the most spectacular applications of the ultracold atoms obtained by these methods is the observation of Bose-Einstein condensation in ultracold atomic gases. New fascinating perspectives opened by these gaseous condensates will be briefly discussed.
