1. A photonic quantum logic gate with modifiable logic operation characteristics, comprising: a first quantum differentiator that separates first and second orthogonal states of a first photon and inputs each for individual processing by first and second quantum modifiers, respectively; said modifiers' processing involving a self-interference section operating in either a first or a second mode which output, respectively, either the same or the alternative of the input state; at least a first path of at least one state of at least a second photon arranged to alter the mode of self-interference undergone by at least one of the first photon's states in at least one of the modifiers; and a quantum integrator that assembles the first and second modifiers' outputs and channels them into a single unified output.