  We report the quantum calibration of a magnetic force microscope (MFM) by
measuring the two-dimensional magnetic stray field distribution of the MFM tip
using a single nitrogen vacancy (NV) center in diamond. From the measured stray
field distribution and the mechanical properties of the cantilever a
calibration function is derived allowing to convert MFM images to quantum
calibrated stray field maps. This novel approach overcomes limitations of prior
MFM calibration schemes and allows quantum calibrated nanoscale stray field
measurements in a field range inaccessible to scanning NV magnetometry. Quantum
calibrated measurements of a stray field reference sample allow its use as a
transfer standard, opening the road towards fast and easily accessible quantum
traceable calibrations of virtually any MFM.
