The photonic content of a transmission line pulse

Abstract:

It is now common to say that photons can be transmitted along optical fibers or transmission lines. But in many cases, the transmission pulse is defined by a time profile of the field strength, i.e., the electric field or voltage V(t), at the transmission point.
How does this turn into a precise description of the arrival profile of the photons in the pulse? We show that there is a highly nontrivial mathematical relation between the function V(t) and the arrival function of the photons. Paradoxically, when V(t) is strictly limited in time, the photon arrival profile cannot be. This, and the counterintuitive relation between V(t) and the expected number of arriving photons, has consequences for the security of quantum cryptography.