Branching processes in quantum electronics

Noise and random fluctuations play an important role in quantum electronic devices and systems. Such fluctuations reside, for example, in the random c reation of photons in optical amplifying media and in the generation of ele ctron-hole pairs in ionizing regions of semiconductor devices. We provide a n overview of the fundamental random branching processes that underlie opti cal and electronic gain. We describe branching processes as concatenations of basic elements that comprise filtered Poisson processes (shot noise) dri ving secondary Poisson processes. In the presence of feedback, these elemen tary processes become self-exciting in nature; they are then suitable for c haracterizing squeezed light and sub-Poisson photon emissions.