Gradiometer Using Separated Diamond Quantum Magnetometers

Abstract

The negatively charged nitrogen-vacancy (NV) center in diamonds is known as the spin defect and using its electron spin, magnetometry can be realized even at room temperature with extremely high sensitivity as well as a high dynamic range. However, a magnetically shielded enclosure is usually required to sense weak magnetic fields because environmental magnetic field noises can disturb high sensitivity measurements. Here, we fabricated a gradiometer with variable sensor length that works at room temperature using a pair of diamond samples containing negatively charged NV centers. Each diamond is attached to an optical fiber to enable free sensor placement. Without any magnetically shielding, our gradiometer realizes a magnetic noise spectrum comparable to that of a three-layer magnetically shielded enclosure, reducing the noises at the low-frequency range below 1 Hz as well as at the frequency of 50 Hz (power line frequency) and its harmonics. These results indicate the potential of highly sensitive magnetic sensing by the gradiometer using the NV center for applications in noisy environments such as outdoor and in vehicles.

Fiber-Coupled Diamond Magnetometry with an Unshielded Sensitivity of 30pT/Hz

“…This would be especially effective at reducing the impact of colored mains noise, such as the 50-Hz peak, and potentially also the 1/f noise. Gradiometry has been employed in several other NVC magnetometers [73][74][75][76] and the possibility of implementing gradiometry for our setup is expanded upon in appendix G.…”

Optimizing NV magnetometry for Magnetoneurography and Magnetomyography applications

“…As a reasonable trade-off that avoids a signal suppression by more than 25% and still maintains a good noise suppression, a baselength as long as the application specifically expected sensing distance could be chosen. Ideally, gradiometers are designed with flexible baselengths, which has been realized recently with fiber-coupled NV-magnetometers (Masuyama et al, 2021 ).…”

A wide dynamic range diamond quantum sensor as an electric vehicle battery monitor

“…Two sensors, A and B were placed below and above the busbar for differential measurement [26][27][28][29], as shown in figure 2c. The external noise was eliminated as a common mode extracting the difference between the two sensor outputs.…”