  We demonstrate that an aperiodic array of certain quantum networks comprising
magnetic and non-magnetic atoms can act as perfect spin filters for particles
with arbitrary spin state. This can be achieved by introducing minimal
quasi-one dimensionality in the basic structural units building up the array,
along with an appropriate tuning of the potential of the non-magnetic atoms,
the tunnel hopping integral between the non-magnetic atoms and the backbone,
and, in some cases, by tuning an external magnetic field. This latter result
opens up the interesting possibility of designing a flux controlled spin
demultiplexer using quantum networks. The proposed networks have close
resemblance with a family of recently developed photonic lattices, and the
scheme for spin filtering can thus be linked, in principle, to a possibility of
suppressing any one of the two states of polarization of a single photon,
almost at will. We use transfer matrices and a real space renormalization group
scheme to unravel the conditions under which any aperiodic arrangement of such
topologically different structures will filter out any given spin projection.
Our results are analytically exact, and corroborated by extensive numerical
calculations of the spin polarized transmission and the density of states of
such systems.
