  By utilizing strong optical resonant interactions in arrays of atoms with
electric dipole transitions, we show how to synthesize collective optical
responses that correspond to those formed by arrays of magnetic dipoles and
other multipoles. Optically active magnetism with the strength comparable with
that of electric dipole transitions is achieved in collective excitation
eigenmodes of the array. By controlling the atomic level shifts, an array of
spectrally overlapping, crossed electric and magnetic dipoles can be excited,
providing a physical realization of a nearly-reflectionless quantum Huygens'
surface with the full $2\pi$ phase control of the transmitted light that allows
for extreme wavefront engineering even at a single photon level. We illustrate
this by transforming a plane wave into a vortex beam.
