  Despite its versatility and high chemical specificity, conventional NMR
spectroscopy is limited in measurement throughput due to the need for
high-homogeneity magnetic fields, necessitating sequential sample analysis, and
bulky devices. Here, we propose a multichannel NMR device that overcomes these
limitations that leverages the zero-to-ultralow field (ZULF) regime, where
simultaneous detection of multiple samples is carried out via an array of
compact optically pumped magnetometers (OPMs). A magnetic field is used only
for pre-polarization, permitting the use of large-bore, high-field,
inhomogeneous magnets that can accommodate many samples concurrently. Through
systematic advances, we demonstrate high-sensitivity, high resolution ZULF NMR
spectroscopy with sensitivity comparable to benchtop NMR systems. The
spectroscopy remains robust without the need for field shimming for periods on
the order of weeks. We show the detection of ZULF NMR signals from organic
molecules without isotopic enrichment, and demonstrate the parallelized
detection of three distinct samples simultaneously as a proof-of-concept, with
the potential to scale further to over 100 channels at a cost comparable to
high-resolution liquid state NMR systems. This work sets the stage for using
multichannel "NMR camera" devices for inline reaction monitoring, robotic
chemistry, quality control, and high-throughput assays.
