  We revisit the quantum oscillator model of the electromagnetic field and
conclude that, while the nonlocal positive and negative frequency ladder
operators generate a photon Fock basis, the Hermitian field operators obtained
by second quantization of real Maxwell fields describe photon-antiphoton pairs
that couple locally to Fermionic matter and can be modeled classically. Their
commutation relations define a scalar product that can be the basis of a first
quantized theory of single photons. Since a one-photon state collapses to a
zero-photon state when the photon is counted, the field describing it must be
interpreted as a probability amplitude.
