Jeudi 18 avril 2013
This year, Bohr’s model of the Hydrogen atom is 100 years old. Height years after
Einstein showed that light is quantized and introduced the concept of photons, the
young Danish physicist announced in 1913 that matter too could be described by
quanta. He postulated that, in the Hydrogen atom, only a set of orbits is allowed,
corresponding to discrete energies and radiuses. He added that emission and
absorption of light by the atom occurs by quantum jumps between these discrete
orbits. These jumps, occurring at random times, are correlated with the appearance
or disappearance of light quanta whose very existence was predicted by Einstein.
Since then, quantum theory has gained considerable precision and complexity, but
remarkably, these century-old concepts remain valid. The experiments of cavity
quantum electrodynamics we perform at Laboratoire Kastler-Brossel on circular Rydberg
atoms, which interact with photons trapped in superconducting cavities, illustrate
straightforwardly the ideas of Bohr and Einstein. The atoms we use are ruled
by Bohr’s model and the photons, which we detect without demolishing them thanks
to these atoms, behave like the photons Einstein thought of trapping and counting
in a box. These studies can hence be considered as the realization of some thought
experiments that these founding fathers of quantum theory had envisioned, yet
believing they would forever stay virtual. I will describe these experiments enabling
the control and manipulation of photons by atoms by showing how they illustrate the
principles of quantum physics and could someday lead to interesting applications
for quantum information processing.
RECRUITMENT DIRECT ACCESS
The Department of Physics
Fête de la Science 2018 