A Century of Light Quanta

Prof. Roy J. Glauber
Harvard University, Cambridge, USA
Premio Nobel per la Fisica – 2005
http://nobelprize.org/nobel_prizes/physics/laureates/2005/glauber-autobio.html

ABSTRACT: The understandings we associate with quantum theory began a little over a hundred years ago with the discovery that light is divided into quanta that can behave like particles. When massive particles were presently discovered to share the wave- like properties of light, the stage was set for the development of quantum mechanics. It was not until 1927 however, when the mathematics of the new theory was applied to the electro- magnetic field, that we finally had a self-consistent theory of light quanta. The detailed verifications of the theory that followed, were confined to radiation processes involving only one or two light quanta. The theory of multi-quantum phenomena, which began to expand rapidly in the 1950s, has been greatly accelerated by the development of the laser. We shall review the consequent quantum theoretical interpretation of optical coherence and discuss its relation to statistical distributions of light quanta and to recent observations of the behavior of individual quanta.