Diamond quantum sensor for magnetoencephalography

Imaging the currents in the brain is critical to our understanding of brain function and is an important technique to study neurological disorders such as traumatic brain injury, schizophrenia, and epilepsy. The gold standard for high spatial resolution of human visual brain activity is fMRI, but development of lower-cost brain imaging systems is needed to expand access. Electroencephalography (EEG) is a common method of brain functional imaging, involving the placement of arrays of electrodes on or through the scalp. However, electrical signals can be distorted as they propagate through the head, obscuring signal interpretation. Magnetoencephalography (MEG) is a promising method of functional brain imaging that has seen a recent surge of interest. MEG directly images the unattenuated magnetic fields produced by neuronal currents via a helmet sensor-array. However, magnetic fields produced by the brain are extremely faint. For decades, MEG has required ultra-sensitive magnetic field measurements enabled by SQUIDs to noninvasively detect brain activity. However SQUIDs require cryogenic operation, resulting in a cm-scale standoff that limits the achievable spatial resolution and signal strength. More recently, optically-pumped magnetometers (OPMs) have been introduced that have a comparable sensitivity to SQUIDs. However, OPMs must be heated to ~150o C, requiring additional standoff to avoid patient discomfort. They also can only operate in a zero-magnetic field environment, which can typically only be accommodated by costly magnetically-shielded rooms in elite hospitals, and they have a limited dynamic range of ~5 nanotesla. Diamond quantum sensors. We are developing miniature magnetic field diamond quantum sensors that operate at ambient temperatures and in Earth’s magnetic field. They feature a dynamic range of ~1000 nT and a sensor-scalp standoff of ~1 mm, which offers advantages in both signal strength and spatial resolution compared to SQUIDs and OPMs. Their ability to operate in Earth’s magnetic field potentially removes the need of a magnetically shielded environment, expanding MEG access beyond elite hospitals. Our sensor offers these advantages by incorporating three innovations in diamond quantum sensing technology: i) Magnetic flux concentrators. Our team has recently discovered a method of enhancing the magnetic sensitivity of diamond quantum sensors based on ferrite magnetic flux concentrators. ii) Infrared absorption readout. Our team has pioneered an approach to diamond quantum sensing, based on infrared absorption, that offers much higher sensitivity. iii) Mitigating microwave phase noise. We are developing a dual-resonance approach that provides ~300x suppression of microwave phase noise to reach our sensitivity goals. In Phase I, we focus on Aim 1) Build a miniature flux-concentrator diamond sensor with infrared absorption detection. Aim 2) Demonstrate a sensitivity of ~10 femtotesla for 1 second integration.