  The quasienergy spectrum of a Bloch electron affected by dc-ac fields is
known to be a fractal function of the so-called electric matching ratio which
is the ratio of the ac field frequency and the Bloch frequency. This paper
studies a manifestation of the fractal spectrum in the system atom in a
standing laser wave, which is a quantum optical realization of a Bloch
electron. It is shown that for an appropriate choice of the system parameters
the atomic survival probability (a quantity measured in laboratory experiments)
develops a fractal structure as a function of the electric matching ratio.
Numerical simulations under classically chaotic scattering conditions show good
agreement with theoretical predictions based on random matrix theory.
