0 Slow light

Consider a classical model of matter in which spectral lines are associated with oscillators. In particular, consider a gas with two closely spaced spectral lines, ω1,2 = ω0 ±∆/2, where ∆ ≪ ω0. Each line has the same damping constant (and spectral width) γ, where γ ≪ ∆. Classically, one might expect these oscillators to correspond to the “V” configuration of atomic levels sketched in Fig. 1a), in which both higher levels can decay to the ground state by emission of photons of frequencies ω1 and ω2. However, quantum mechanics also permits the “Λ” configuration sketched in Fig. 1b) in which the highest level can decay to the ground state via emission of a photon of frequency ω1 as well as to the intermediate level via emission at frequency ω2.