  We introduce and demonstrate a hybrid optically pumped magnetometer (HOPM)
that simultaneously measures one dc field component and one rf field component
quadrature with a single atomic spin ensemble. The HOPM achieves
sub-pT/$\sqrt{\mathrm{Hz}}$ sensitivity for both dc and rf fields, and is
limited in sensitivity by spin projection noise at low frequencies and by
photon shot noise at high frequencies. We demonstrate with the HOPM a new
application of multiparameter quantum sensing: background-cancelling spread
spectrum magnetic communication. We encode a digital message as rf amplitude,
spread among sixteen channels from \SI{29}{\kilo\hertz} to \SI{33}{\kilo\hertz}
in a noisy magnetic environment, and observe quantum-noise-limited rf magnetic
signal recovery enabled by quantum-noise-limited dc noise cancellation,
reaching noise rejection of \SI{15}{\decibel} at \SI{100}{\hertz} and more than
\SI{20}{\decibel} at \SI{60}{\hertz} and below. We measure signal fidelity
versus signal strength and extrinsic noise in communication of a short text
message. The combination of high sensitivity, quantum-noise-limited
performance, and real-world application potential makes the HOPM ideally suited
for study of high-performance multiparameter quantum sensing.
