Prix Nobel physique 2012

Le jury les récompense pour "leurs méthodes expérimentales novatrices qui permettent la mesure et la manipulation des sytèmes quantiques individuels". "Les lauréats ont ouvert la voie d'une nouvelle ère d'expérimentation dans la physique quantique en démontrant l'observation directe de particules quantiques individuelles sans les détruire", précise le communiqué de l'Académie royale des sciences de Suède.

Serge Haroche, 68 ans, avec ses collègues Jean-Michel Raimond (Université Pierre et Marie Curie) et Michel Brune (CNRS), a réussi en 2007 à observer la vie et la mort d'un photon (grain de lumière) et en 2008 à observer le passage du quantique à la physique classique sur un petit paquet de photons. Pour cette expérience, ils ont utilisé un dispositif (une cavité tapissée de miroirs), capable de piéger pendant très longtemps des photons, ainsi qu'une méthode d'observation des photons qui ne les perturbe que très peu. Ils ont ainsi pu observer le passage des photons d'un état atypique du monde quantique à un état correspondant parfaitement à la physique classique, un phénomène appelé "décohérence" qui s'est déroulé sous leurs yeux.

Comme Serge Haroche, David Wineland, né en 1944, a travaillé dans le domaine de l'optique quantique, "étudiant l'interaction fondamentale entre la lumière et la matière", selon le comité Nobel. Les deux lauréats se partageront la récompense de huit millions de couronnes suédoises (929 000 euros). Two physicists who developed techniques to peer in on the most intimate relations between light and matter won the Nobel Prize in Physics on Tuesday. They are Serge Haroche, 68, of the Collège de France and the École Normale Supérieure, in Paris, and David J. Wineland, also 68, of the National Institute of Standards and Technology and the University of Colorado.

Their work, the academy said, enables scientists to directly observe some of the most bizarre effects — like the subatomic analogue of cats that are alive and dead at the same time — predicted by the quantum laws that prevail in the microcosm, and could lead eventually to quantum computers and superaccurate clocks.

Dr. Haroche and Dr. Wineland, who have been good friends for 25 years, have approached the dance between matter and light from opposite sides. Dr. Haroche traps photons in a mirrored cavity whose walls are so finely polished that one photon will bounce back and forth for a tenth of a second — an eternity in atomic physics — before leaking out or being absorbed. Then he sends in a single atom, as a spy, to interact with the light.

Normally, to detect light is to destroy it, since photons are absorbed in our retinas or in the chips in our cameras. But in one case, by observing subtle effects of the light on the atoms, he and his colleagues could count the photons — “as one would do with marbles in a box,” as he put it on his Web site — without destroying them.

In another case, in 1996, Dr. Haroche and his colleagues raised Schrödinger’s cat from the undead by putting their boxed photon into a “cat state” in which it was out of phase with itself, essentially oscillating in opposite directions at the same time. Then by sending in their spy atoms, they measured how long it took for the “cat state” to decay — or decohere in quantumspeak

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