  "It is well-known to those who know it" that single-photon interference
experiments can be modeled classically [S. Barnett, arXiv:2207.14632 (2022)].
When a single-photon light pulse was split by a biprism good agreement with a
classical fit was obtained and the photon was counted only once, consistent
with a probabilistic interpr.etation [V. Jacques et al, Eur. Phys. J. D 35, 561
(2002)]. A justification for this "well know result of Quantum Optics" is
implicit in [M. Hawton, Phys. Rev A 104, 052211 (2021)] where a real covariant
field describing a single photon is first quantized. Here the theoretical basis
of this result is reviewed and the theory is extended to multiphoton states and
QED Fock space. The crucial role of the CPT theorem in coupling to charged
matter and resolution of the photon localization problem is discussed.
