  Applications that envisage utilizing the orbital angular momentum (OAM) at
the single photon level assume that the OAM degrees of freedom that the photons
inherit from the classical wave solutions are orthogonal. To test this critical
assumption, we quantize the beam-like solutions of the vector Helmholtz
equation from first principles to delineate its elementary quantum mechanical
degrees of freedom. We show that although the beam-photon operators do not in
general satisfy the canonical commutation relations, implying that the photon
states they create are not orthogonal, the states are nevertheless bona fide
eigenstates of the number and Hamiltonian operators. The explicit
representation for the photon operators presented in this work forms a natural
basis to study light-matter interactions and quantum information processing at
the single photon level.
