Quantum Diamond Microscopes for Biological Systems and Integrated Circuits

Abstract

Nitrogen-Vacancy (NV) centers are atom-like point defects in diamond that have been utilized for applications in biological systems, integrated circuits, materials science, geoscience, positioning and navigation, quantum information, and other areas due to their robust performance at room temperature. The optical initialization and readout of the NV electronic spin state has been utilized to parallelize measurements and create simultaneous widefield maps of several parameters, including vector magnetic fields, in a modality known as a Quantum Diamond Microscope (QDM). The robustness and small intrinsic size of the NV centers allow for them to be placed within close proximity of samples of interest, enabling high spatial resolution magnetic field measurements in regimes previously unattainable. We present an introduction to the methods, applications, and performance of QDMs in different scenarios to provide an overview of the technique and motivate what measurements are possible. Next, we give a background to magnetic field analysis and provide intuition for the magnetic inverse problems and challenges associated with it. Neural network techniques are utilized to carry out the magnetic inversion for various current source distributions, and we demonstrate improved robustness to high frequency spatial noise for simulated datasets. In an initial experimental demonstration, we achieve state-of-the-art magnetic sensitivity to measure the bio-magnetic field associated with the propagation of an action potential along axonal structures. This initial result motivated efforts to improve the quality of the diamond sensors through improved characterization of the diamond strain and charge state environments. We demonstrate that our current magnetic imaging sensitivity when combined with machine learning classification methods is sufficient for measuring the unique magnetic fingerprints of the functional state in integrated circuits, enabling further applications in fault detection, quality control, and device security. Finally, we combine our imaging capabilities with lock-in methods to enable fast magnetic imaging applications. Through this effort, we demonstrate a biocompatible, real-time widefield magnetic imager with state-of-the-art magnetic field imaging sensitivity while showing long term viability of cardiomyocyte cell cultures under measurement conditions. Recent Ramsey imaging results have shown that we are on the cusp of the volume normalized sensitivity needed for QDM imaging of bio-magnetic fields.