Development of an ultrahigh-vacuum-compatible cryogen-free scanning nitrogen-vacancy magnetometer

Scanning nitrogen-vacancy (NV) magnetometry has emerged as a powerful technique for nanoscale magnetic imaging owing to its high spatial resolution, high magnetic sensitivity, and noninvasive optical readout. For low-temperature operation, existing scanning NV microscopes have been implemented in different cryogenic systems, including liquid-helium cryostats and closed-cycle refrigerators. However, ultrahigh-vacuum compatibility and in situ sample/probe exchange remain largely unavailable in these systems, hindering measurements on pristine and surface-sensitive quantum materials. Here, we report a cryogen-free ultrahigh-vacuum scanning nitrogen-vacancy microscope equipped with an in-vacuum three-axis vector superconducting magnet, reaching a base pressure of 2 × 10-10 Torr and sample temperatures down to 2 K. The system enables in situ exchange and separate temperature control of both the sample and the probe. A pillar-array diamond probe architecture is implemented to provide flexible selection of NV centers with different crystallographic orientations, allowing access to complementary magnetic-field projections of a single spin texture. System performance is verified through thermal characterization, single-NV characterization, NV-sample distance calibration, and magnetic imaging demonstrations, which include imaging the same skyrmion bubble with two nitrogen-vacancy centers of different orientations in CoFeB and resolving individual superconducting vortices in bulk NbSe2.