  Twisted atomic bilayers are emerging platforms for manipulating chiral
light-matter interaction at the extreme nanoscale, due to their inherent
magnetoelectric responses induced by the finite twist angle and quantum
interlayer coupling between the atomic layers. Recent studies have reported the
direct correspondence between twisted atomic bilayers and chiral metasurfaces,
which features a chiral surface conductivity, in addition to the electric and
magnetic surface conductivities. However, far-field chiral optics in light of
these consitututive conductivities remains unexplored. Within the framework of
the full Maxwell equations, we find that the chiral surface conductivity can be
exploited to realize perfect polarization transformation between linearly
polarized light. Remarkably, such an exotic chiral phenomenon can occur either
for the reflected or transmitted light.
