  We introduce a double quantum (DQ) 4-Ramsey measurement protocol that enables
wide-field magnetic imaging using nitrogen vacancy (NV) centers in diamond,
with enhanced homogeneity of the magnetic sensitivity relative to conventional
single quantum (SQ) techniques. The DQ 4-Ramsey protocol employs
microwave-phase alternation across four consecutive Ramsey (4-Ramsey)
measurements to isolate the desired DQ magnetic signal from any residual SQ
signal induced by microwave pulse errors. In a demonstration experiment
employing a 1-$\mu$m-thick NV layer in a macroscopic diamond chip, the DQ
4-Ramsey protocol provides volume-normalized DC magnetic sensitivity of
$\eta^\text{V}=34\,$nTHz$^{-1/2} \mu$m$^{3/2}$ across a $125\,\mu$m$
\,\times\,125\,\mu $m field of view, with about 5$\times$ less spatial
variation in sensitivity across the field of view compared to a SQ measurement.
The improved robustness and magnetic sensitivity homogeneity of the DQ 4-Ramsey
protocol enable imaging of dynamic, broadband magnetic sources such as
integrated circuits and electrically-active cells.

Quantum Physics;Mesoscale and Nanoscale Physics;Applied Physics;Instrumentation and Detectors