A photon is loosely understood by readers of quantum optics literature as being a 'light particle.' This conceptualization may be roughly traced back to pre-quantum mechanical ideas of light as being composed of indivisible 'corpuscules.' However, in contemporary quantum mechanics, this takes on a different meaning. It not only refers to a particle we refer to as a photon, but also discrete energy quanta that may get emitted or absorbed. Due to the wave-nature of light, many situations involving light propagation may be described in terms of [optical modes](Optical%20mode.md) and the study of these optical modes once they are quantized forms the basis of the _quantum theory of radiation_. Quantum mechanically such modes are modeled by the [quantum harmonic oscillator Hamiltonian](quantum%20harmonic%20oscillator%20Hamiltonian.md), not _photons_. Hence it is argued by Willis Lamb in his paper, Anti-photon (Appl. Phys. B 60, 77-84 (1995)), that the word "photon" should be retired from use in many areas of _quantum optics._ Lamb brings up examples of simple single and multi-mode quantum optical systems. He also points out that the use of the word "photon" becomes more meaningless when referring to quantum mechanical systems of that may be composed infinite [photon number state](photon%20number%20state.md)s. Instead we should refer to _radiation fields_ or simply _radiation_ or _light._ in many situations. --- # Recommended Reading See: [Lamb., W.E. _Anti-photon_ Appl. Phys. B 60, 77-84 (1995)](10.1.1.393.688.pdf) #QuantumMechanics/QuantumOptics