Scanning nitrogen-vacancy magnetometry down to 350mK

We report on the implementation of a scanning nitrogen-vacancy (NV) magnetometer in a dry dilution refrigerator. Using pulsed optically detected magnetic resonance combined with efficient microwave delivery through a co-planar waveguide, we reach a base temperature of 350 mK, limited by experimental heat load and thermalization of the probe. We demonstrate scanning NV magnetometry by imaging superconducting vortices in a 50-nm-thin aluminum microstructure. The sensitivity of our measurements is approximately 3 {\mu}T per square root Hz. Our work demonstrates the feasibility for performing non-invasive magnetic field imaging with scanning NV centers at sub-Kelvin temperatures.