Light beats quantum mechanics

The mathematics of quantum theory is based on operators rather than numbers. In optics this simple fact allows statistical quantities, such as the fluctuations in the electric field of a light beam, to be smaller than is allowed by classical physics. Experiments that measure these quantities can generally be divided into two types, depending on whether they measure the wave or the particle properties of light. This is in line with the “complementarity principle” of quantum mechanics, which states that the wave and particle aspects of a system cannot be observed at the same time.