Atom  Cavity  (a)  (b)  (c)  (d)  Figure 1: (Color online). (a) System under study: a two-level atom undergoing pure dephasing coupled to a cavity. (b) Equivalent classical system: two connected boxes exchanging a quantum of energy. (c) Equivalent system in the spontaneous emission regime, and (d) in the continuous pumping regime, respectively. 23