An equivalent circuit for a two-state quantum system coupled to a single-mode electromagnetic cavity

The development of nanostructures as components of macroscopic electrical circuits puts into evidence the necessity of providing integrated models of the entire system. The most natural approach is to represent such nanostructures by equivalent circuits to be imbedded in the model of the macroscopic structure. In the paper we discuss to which extent such a task can be accomplished and in particular how it fits the available circuit software for numerical simulations. We present as a meaningful example the circuit model for an atom, described as a two-state quantum system, coupled with a single mode cavity in a n-photon state; such a simple system describes a quantum oscillator realized by the interaction of the electromagnetic field with matter.