Quantum optics is that branch of optics where the quantum features of light matter[1]. Quantum optics, the union of quantum field theory and physical optics, is undergoing a time of revolutionary change[2].

Quantum optics theory in its modern sense started when Roy Glauber showed, in the early 1960s, how to apply it to classical optics devices such as the Michelson stellar inter-ferometer or the Hanbury Brown and Twiss intensity interferometer. At that time it could have appeared to be an academic exercise without consequence, since the only known phenomenon that demanded quantization of light was spontaneous emission, and it was not clear whether quantum theory was at all useful for describing light freely propagating far from the source. Actually, Glauber developed a clear quantum formalism to describe optics phenomena, and introduced the important notion of quasi-classical states of light, a theoretical tool that allowed physicists to understand why all available sources of light, including lasers, delivered light whose properties could be totally understood in the framework of the semi-classical approach. But in doing so, he paved the way for the discovery of new phenomena which can be understood only if light is considered as a quantum system. It became possible to build sources delivering single photon wave packets, pairs of entangled photons, squeezed beams of light. . .[3].

On the other hand, quantum optics provides a powerful new probe for addressing fundamental issues of quantum mechanics such as complementarity, ad other aspects central to the foundation of quantum physics and philosophy[2].

References:

  1. Quantum Optics in Phase Space, Wolfgang P. Schleich
  2. Quantum Optics, O.Scully and S.Zubairy
  3. Introduction to Quantum Optics, G. Grynberg and A. Aspect and C. Fabre

Picture by: Laboratoire Kastler Brossel