What light is and how to describe it has always been a central subject in physics.As our understanding has increased, so have our theories changed: geometrical optics, wave optics and quantum optics are increasingly sophisticated descriptions, each referring to a larger class of phenomena than its predecessor.But how exactly are these theories related? How and when tonic shower cap wave optics reduces to geometric optics is a rather simple problem.Similarly, how quantum optics reduces to wave optics has also been considered to be a very simple business.It is not so.
As we show here the classical limit of quantum optics is a far more complicated issue; it is in fact dramatically more involved and it requires a complete revision of all our intuitions.The read more revised intuitions can then serve as a guide to finding novel quantum effects.