  The direct-current (dc) $\sigma_{xx}^{dc}$ and alternating-current (ac)
$\sigma_{xx}^{ac}=\sigma_1-i\sigma_2$ conductivities of a wide (46 nm) GaAs
quantum well with the bilayer electron density distribution are measured. It is
found that the magnetic field dependence of $\sigma_{xx}$ exhibits three sets
of oscillations related to the transitions between Landau levels in symmetric
and antisymmetric subbands and with the transitions occurring owing to the
Zeeman splitting of these subbands. The analysis of the frequency dependence of
the ac conductivity and the $\sigma_1 / \sigma_2$ ratio demonstrates that the
conductivity at the minima of oscillations is determined by the hopping
mechanism.
