Optimizing nitrogen-vacancy diamond magnetic sensors and imagers for broadband sensitivity

Abstract

Solid-state spin systems form an increasingly impactful quantum sensing platform. Atomic-scale defects in diamond called nitrogen-vacancy (NV) centers offer high-resolution magnetic sensing and imaging under ambient conditions. NV-based magnetometers have found broad utility thanks to long spin lifetimes at room temperature, coherent microwave spin manipulation, and optical spin-state initialization and readout. Their applications span pure and applied sciences, including condensed matter physics, neuroscience and living systems biology, nuclear magnetic resonance, Earth and planetary science, and industrial vector magnetometry. In this work, we employ ensembles of NV centers for high-sensitivity, broadband magnetic sensing and imaging. We present three experiments, which share a common principal application of time-resolved magnetic field detection from firing neurons.

For each experiment, we implement novel techniques to improve magnetometer performance, optimizing a different variant of the DC magnetic field sensitivity. Among solid-state spin-based sensors, these devices demonstrate record sensitivities to broadband magnetic signals. Nonetheless, the achieved sensitivities remain orders of magnitude away from theoretical limits. Primary obstacles include optical readout fidelities far from unity and typical NV-ensemble dephasing times T*2 thousands of times shorter than spin lifetimes T1. We therefore investigate techniques for improving these key parameters to enable considerable sensitivity enhancements. We develop a strategy for extending T*2 in NV-rich diamonds, which could in turn make exotic techniques to increase readout fidelity more practical. Moreover, we identify methods to optimize diamond fabrication and treatment, and we highlight where further materials science research is warranted.

In short, this work demonstrates advances in NV-ensemble magnetic sensing and establishes a basis for further sensitivity improvements, perhaps even inspiring new innovations to approach fundamental limits.