A novel approach to nanoscale magnetic-field imaging using a thin layer of nitrogen-vacancy (NV) color centers in diamond and combining this with sub-optical-wavelength probing techniques is proposed. Magnetic-field sensing with single NV centers so far has shown a sensitivity of 5 nT/Hz1/2. Already this is sufficient to detect a single electron spin at 50 nm distances or a single nuclear spin at 5 nm. At the same time, the NV center is estimated at 0.3 nm in size. No other magnetic sensor has this sensitivity on this distance scale. Nanoscale magnetic field images have been made with NV centers using scanning-probe techniques, and microscale full-frame imaging with ensembles has been demonstrated. Sub-wavelength stimulated emission depletion microscopy has also been done using single NV centers and achieved better than 10 nm resolution even with low-intensity donut beams.
The approach is to use ensembles to eliminate the need to control a scanning probe with nanometer precision near the object of interest while using depletion microscopy to maintain the spatial resolution. However, to realize this potential one must first better understand the physics of NV ensembles, especially how their magnetic sensitivity depends on NV concentration and interactions with the lasers used in the stimulated-emission-depletion (STED) and ground-state-depletion microscopy (GSD). The project will build on the combined expertise and infrastructure available to the Berkeley and Texas A&M groups. The apex of the project will be magnetic nanoscopy of a biologically relevant system---100 nm diameter magnetic chains in Tritonia diomedea---a sea slug known for its ability to navigate in the Earth's magnetic field.
Intellectual merit: The proposed studies will lead to optimization of the NV-diamond ensembles for spatially-resolved ensemble magnetometry, elucidation of the fundamental physics of the NV-centers (including determination of temperature dependence of the magnetic-resonance parameters, etc.), understanding of the effect of the STED/GSD pump beam on sensitivity, and development of optimized magnetometry methodology based on this knowledge. The anticipated nanoscale sensor will have enough sensitivity to see nanoscale magnetic domains in materials.
Broad impact will be to provide an alternative to magnetic resonance force microscopy with no moving parts. Due to extreme chemical stability of the host and the remote optical detection protocol, NV centers can also be used in microfluidic ``lab-on-a-chip'' systems, allowing chemical analysis and imaging with minute quantities of analytes. This is an important application in industry, security, and medicine, as it allows rapid and universal identification of dangerous substances. A key area of application is magnetic imaging of biological systems which will be demonstrated by measurements on magnetic chains in Tritonia diomedea. The study of color centers in diamond has broad educational impact, as the simple geometry of the NV center is a convenient teaching tool for understanding the broader concepts of quantum mechanics and solid-state physics. NV ensembles can demonstrate the principles of magnetic sensing to students using only a laser pointer and a magnet. Letting K-12 students perform hands-on magnetic sensing, combined with the social mystic of diamonds can also be used as a novel recruiting tool for underrepresented groups such as women. Involvement of undergraduates, specifically through the Berkeley undergraduate-research-apprenticeship program and TAMU's experimental optics course, is planned.
