Photons and Approximate Localisability
A theory of photodetection was produced in the so-called “rotating wave approximation” which is usually an acceptable simplification for optical photons. In considering such delicate issues as the localisability of photons it may be wise to proceed initially without making such an assumption. This chapter calculates the photodetection probability without making this approximation before discussing localisation. It is necessary to have a prescription for calculating the most isotropically localised single photon. A destructive detection of one photon of the pair leaves a single photon in the field to be detected. Such an experiment provides an opportunity to study the properties of a single photon. A priori such a photon is unlikely to be as localised as one constructed mathematically from a generalised imprimitivity. The experimental dimensions are such that the correlated photons are each constructed from a certain momentum range around well-defined wavevectors.