  We demonstrate atomic magnetometry using a metasurface polarizing
beamsplitter fabricated on a silicon-on-sapphire (SOS) platform. The
metasurface splits a beam that is near-resonant with the rubidium atoms (795
nm) into orthogonal linear polarizations, enabling measurement of magnetically
sensitive circular birefringence in a rubidium vapor through balanced
polarimetry. We incorporated the metasurface into an atomic magnetometer based
on nonlinear magneto-optical rotation and measured sub-nanotesla sensitivity,
which is limited by low-frequency technical noise and transmission loss through
the metasurface. To our knowledge, this work represents the first demonstration
of SOS nanophotonics for atom-based sensing and paves the way for highly
integrated, miniaturized atomic sensors with enhanced sensitivity and
portability.
