Serge Haroche, Collège de France & École Normale Supérieure
Quantum Non-Demolition Measurement of Light: The Birth, Life and Death of Trapped Photons
Physics Division Colloquium - 5 October 2007

Microwave photons, trapped in a cavity over time intervals reaching half a second, are non-destructively detected by a beam of Rydberg atoms. This quantum non-demolition procedure allows us to witness directly the birth, life and death of individual photons and reveals for the first time the quantum jumps of light. Coherent states of radiation containing several photons progressively collapse into Fock states, as successive atoms extract information from the field. The subsequent history of these states is observed while the field cascades down step by step towards vacuum due to cavity damping. A statistical analysis of a large number of field trajectories confirms all the dynamical properties of light predicted by the quantum theory of radiation. Applications of these ideal measurements to studies of fundamental light properties will be discussed.

ANL Physics Division Colloquium Schedule