  One of the challenges faced by optical platforms for quantum technologies is
the implementation of (ultimately) a transistor. The functionality that is hard
to achieve is rectification: having the beam propagating in one direction
transmitted, the other reflected. Here we take up a simple model of such a
rectifying device, a.k.a.~optical diode, consisting of two atoms with different
detuning interacting with light in a one-dimensional waveguide. In previous
studies, it was found that high rectifying efficiencies can be achieved with
coherent states, while it was claimed that the device cannot rectify
single-photon Fock states. In this paper, we clarify the functioning of this
diode. Notably, we show that coherences across the Fock bases in the input
state do not play any role, and thence the rectifying properties of the device
depend only on its behavior on the Fock states. In the process, we show that
some single-photon rectification is predicted when the limit of infinitely-long
pulses is not taken.
