Nobel Lecture: One hundred years of light quanta

Abstract

It can’t have escaped you, after so many recent reminders, that this year marks the one hundredth birthday of the light quantum. I thought I would tell you this morning a few things about its century long biography. Of course we have had light quanta on Earth for eons, in fact ever since the good Lord said “let there be quantum electrodynamics”—which is a modern translation, of course, from the biblical Aramaic. So in this talk I’ll try to tell you what quantum optics is about, but there will hardly be enough time to tell you of the many new directions in which it has led us. Several of those are directions that we would scarcely have anticipated as all of this work started. My own involvement in this subject began somewhere around the middle of the last century, but I would like to describe some of the background of the scene I entered at that point as a student. Let’s begin, for a moment, even before the quantum theory was set in motion by Planck. It is important to recall some of the remarkable things that were found in the 19th century, thanks principally to the work of Thomas Young and Augustin Fresnel. They established within the first 20 years of the 19th century that light is a wave phenomenon, and that these waves, of whatever sort they might be, interpen