# Quantum optical master equation

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In Quantum Noise by Gardiner and Zoller (p. 86f) they derive and write a version of the quantum optical master equation.

$\dot{\rho}_S (t) = -\frac{i}{\hbar} [H_\mathrm{sys} ,\rho_S] - \sum_m \frac{\pi \omega_m}{2\hbar } \bigg( \bar{N}(\omega_m) +1 \bigg) \kappa (\omega_m)^2 [\rho_S X_m^+ -X^{-}_{m} \rho_S , X] + \mathrm{ ... more\, terms ... }$

Eq. 3.6.64 (and eq. 3.6.67) do not make dimensional sense to me. The units of the derivative of the density operator should be frequency.

The units of terms in the sums are those of $\omega_m \kappa^2 X^2/\hbar$ where $\kappa^2$ was defined (on p. 45) to be the spring constant of a harmonic oscillator.

On that page they also write energy terms as $\kappa^2 X^2$. This means that the terms have dimension of frequency-squared.

Is there a mistake in the book or am I misunderstanding the meaning of some part of the equation? (the derivation of the equation is not given in the book; they write instead "one finds, after some labour".

## More definitions from the book

X is a system operator and $X = \sum_m (X_m^+ + X_m^- )$ where

$[H_\mathrm{sys}, X_m^\pm ] = \pm \hbar \omega_m X_m^\pm$

and the total system Hamiltonian is written (eq. 3.1.5) as

$H = H_\mathrm{sys} + \frac{1}{2} \sum_n \big[ (p_n-\kappa_n X)^2 + \omega_n^2 q_n^2 \big]$

This post imported from StackExchange Physics at 2015-11-02 22:13 (UTC), posted by SE-user HansHarhoff
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