ABSTRACT
Dirac introduced his enormously practical quantum bra–ket notation in 1939 as a “new notation for quantum mechanics” (Dirac 1939). Also, he discussed in his classic book Principles of Quantum Mechanics, first published in 1930 (Dirac 1978), the essence of interference as a one-photon phenomenon. He did so within a macroscopic framework using concepts such as “a beam of light consisting of a large number of photons,” beam splitters,” and “translational states of a photon” (Dirac 1978). That primordial and illuminating discussion surely qualifies Dirac as the father of quantum optics.
