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I What is detailed balance?

  1. Dec 10, 2017 #1
    In quantum mechanics, I've learned that when there are incident photons with energy spectral density ##ρ(ω)## , two states system with ##E_i## and ##E_n## (##E_n > E_i##) goes through transition (absorption and emission) with transition rate [tex]Γ_{i→n}=Γ_{n→i}=\frac {2π}{ħ}|V_{ni}|^2ρ(E_n-E_i).[/tex]Is this detailed balance,? Wikipedia says that detailed balance definition is that "At equilibrium, each elementary process should be equilibrated by its reverse process."
    Actually when I calculate transition rates with two states system, it seems that both emission and absorption process always have the same transition rate. Can I refer this as detailed balance? Thanks
     
  2. jcsd
  3. Dec 11, 2017 #2
    The probability in a Markov process for a particular transition from eg. i to n is given by (transition rate i->n)*(probability of i), or ##\Gamma_{i \rightarrow n} P_i##. The detailed balance condition says that there is an equilibrium probability distribution ##\Pi_i## for the process (for instance a Boltzmann distribution) such that ##\Gamma_{i \rightarrow n} \Pi_i = \Gamma_{n \rightarrow i} \Pi_n##, ie. the transition probabilities and their reverse cancel each other for each pair of states i and n. Taking the Boltzmann distribution in particular, this means that ##\Gamma_{i \rightarrow n} e^{- \beta E_i} = \Gamma_{n \rightarrow i} e^{- \beta E_n}##.
     
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