A diamond spin qubit scanning probe microscope

The properties of a physical system only exist in relation to its environment. This thesis presents the development of a novel spin qubit scanning probe microscope operating over a wide range of environmental conditions. The qubit, which sits at the heart of the microscope, is realized by a nitrogen vacancy (NV) defect in diamond, which in its negatively charged configuration is extremely sensitive to local magnetic fields. We further leverage this local sensitivity by integrating the NV center into a scanning probe microscope (SPM) tip, allowing us to record spatially resolved images of near-surface magnetic structures.

Before we can run, we must first walk. To test the capabilities of the NV, we demonstrate electron paramagnetic resonance on an encapsulated nitrogen spin (N@C60) using a single near-surface NV center in diamond at 4.7 K. Exploiting the strong magnetic dipolar interaction between the NV and endofullerene electronic spins, we demonstrate RF pulse controlled Rabi oscillations and measure spin-echos on an encapsulated spin. This measurement, while novel, also exposed us to the limitations of using a "fixed" NV center.

These limitations motivated us to design and construct an entirely new NV scanning probe microscope (NV-SPM). This NV-SPM is capable of operating from ambient pressure to ultra-high vacuum (1e-9 mbar), from room to cryogenic temperatures (4.7 K), and from zero-field to high vector magnetic fields (1 T). In addition, the system is capable of generating nanosecond pulsed RF excitation up to 20 GHz, can perform confocal imaging and second-order photon correlation, can record real-time optical spectra, and features both active and passive damping to minimize vibrations. The system functionality is tied together with a custom-built software package, which allows for advanced levels of measurement sequencing, control and analysis.

To test the nanoscale imaging capabilities of the NV-SPM, we probed domain wall structures in synthetic antiferromagnetic (SAF) thin films. Unlike ferromagnetic materials, SAF films only exhibit a weak net magnetic moment, which generally demands techniques such as X-ray photoemission electron microscopy or spin-polarized scanning tunneling microscopy. These techniques either require complex synchrotron facilities, or are limited to electronically conducting samples. An NV-SPM, on the other hand, places no such restrictions. We perform nanoscale, all-optical relaxometry measurements on SAF films at ambient conditions, and observe clear domain wall structures in good agreement with our magnetic force microscopy measurements on the same sample.

As this thesis demonstrates, near-surface NV centers are incredible quantum sensors. Despite this, they are also subject to a number of other effects, such as charge state transitions, which often lead to a loss of coherence. We perform the first measurements examining the charge state behavior of the NV center in diamond tips as a function of vacuum. Us