⟨+|ρ(t)|+⟩=12+12cos(ωt).This oscillation is due to the off-diagonal elements of ρ(t), and it is called the coherence of the system (see F...⟨+|ρ(t)|+⟩=12+12cos(ωt).This oscillation is due to the off-diagonal elements of ρ(t), and it is called the coherence of the system (see Fig. This is called decoherence of the system, and the value of γ depends on the physical mechanism that leads to the decoherence. If the state |1⟩ has a larger energy than |0⟩ there may be processes such as spontaneous emission that drive the system to the ground state.
One distinguishes between two extremes: fully coherent and fully incoherent light, while the degree of coherence of practical light is somewhere in between. Generally speaking, the broader the frequen...One distinguishes between two extremes: fully coherent and fully incoherent light, while the degree of coherence of practical light is somewhere in between. Generally speaking, the broader the frequency band of the source, the more incoherent the light is. It is a very important observation that no light is actually completely coherent or completely incoherent. All light is partially coherent, but some light is more coherent than others.
