  A pair of resonant laser fields can drive a three-level system into a dark
state where it seizes to absorb and emit radiation due to destructive
interference. We propose a scheme to search for this resonance by randomly
changing the frequency of one of the fields each time a fluorescence photon is
detected. The longer the system is probed, the more likely the frequency is
close to resonance and the system populates the dark state. Due to the
correspondingly long waiting times between detection events, the evolution is
non-ergodic and the precision of the frequency estimate does not follow from
the conventional Cram\'er-Rao bound of parameter estimation. Instead, a
L\'{e}vy statistical analysis yields the scaling of the estimation error with
time for precision probing of this kind.
