Catching the elementary step of excitation of a coherent light state by a single photon

A new class of non-classical light states has been experimentally generated and their complete phase-space characterization has been achieved by quantum homodyne tomography. Such states are produced by the action of the photon creation operator on a coherent light eld and are thus the result of the elementary excitation process of a classical eld by a single quantum. Being intermediate between a single-photon Fock state and a coherent one, they o er the unique opportunity to closely follow the smooth evolution between the particle-like and the wave-like behavior of the light eld.