  Scanning probe microscopy with multi-qubit sensors offers the potential to
improve imaging speed and measure previously inaccessible quantities, such as
two-point correlations. We develop a multiplexed quantum sensing approach with
scanning probes containing two nitrogen-vacancy (NV) centers at the tip apex. A
shared optical channel is used for simultaneous qubit initialization and
readout, while phase- and frequency-dependent microwave spin manipulations are
leveraged for de-multiplexing the optical readout signal. Scanning dual-NV
magnetometry is first demonstrated by simultaneously imaging multiple field
projections of a ferrimagnetic racetrack device. Then, we record the two-point
covariance of spatially correlated field fluctuations across a current-carrying
wire. Our multiplex framework establishes a method to investigate a variety of
spatio-temporal correlations, including phase transitions and electronic noise,
with nanoscale resolution.
