h2. Dynamics

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$s(t)=e^{-t/T_{2}}\int P(r)e^{-i\int^{t}_{0}\omega(r,t')dt'}dr$
{latex}
* Coherent - when $\omega$ is not a function of $r$ (There are no interesting dynamics)
* Stationary - when $\omega$ is not a function of time (the system can be refucus by a $\pi$ pulse for any time)
* Incoherent - stationary and not coherent, explicitly $\omega$ is a function of $r$ (interesting question is the distribution of $\omega(r)$
* Decoherent - when $\omega$ is a function of time and $r$, and the t dependence is stochastic/Marchovian (interesting dynamics: distribution of $\omega(r)$, spectral density of $\omega(r)$)
* Periodic - $\omega$ is a simple function of time (interesting dynamics: distribution of $\omega(r)$ at the characteristic frequency)