What’s the meaning of decay rate in optical Bloch equations?

[wangvivi]

TL;DR

there is a parameter called decay rate（Γ or γ)in the optcial bloch equation or the equation of motion for the atomic probability amplitude.what‘s the meaning of it?

i have some questions about decay rate.
1：why do we need decay rate in these equations?
2：is it a constant for a specific medium?
3：it can be changed with respect to some conditions like temprature or pressure?
4：how can i know the decay rate of some energy levels in 85Rubidium

 

[Hyperfine]

TL;DR Summary: there is a parameter called decay rate（Γ or γ)in the optcial bloch equation or the equation of motion for the atomic probability amplitude.what‘s the meaning of it?

i have some questions about decay rate.
1：why do we need decay rate in these equations?
2：is it a constant for a specific medium?
3：it can be changed with respect to some conditions like temprature or pressure?
4：how can i know the decay rate of some energy levels in 85Rubidium

$\gamma$ describes spontaneous radiative decay between the two energy levels.

For quite detailed quantitative information on atoms, consult NIST Atomic Spectral Database.