Highly sensitive magnetometer boosts biomagnetic sensing by closing sensor-to-sample distance

Detecting biomagnetic fields, such as in magnetoencephalography — a technique for understanding pathologies such as seizures — has remained a challenge for researchers due to steep signal decays with distance. Diamond quantum sensors are uniquely suited to minimize this sensor-to-sample distance.

Araki et al. developed a highly sensitive Ramsey-based ensemble magnetometer for biomagnetic field sensing. Utilizing a printed-circuit-board microwave antenna, the group’s device shortens the sensor-to-sample distance to 2 millimeters, achieving an effective detection capability directly from the source previously unattainable by conventional high-power approaches.

The device marks a departure from conventional sensors, where high-power laser-based approaches create thermal issues in samples.

“The true innovation of our work lies in a conceptual shift: moving away from simply chasing absolute sensitivity, which typically requires high thermal loads, to optimizing the effective signal-to-noise ratio in a practical, close-proximity geometry,” said author Takayuki Iwasaki. “By demonstrating how to overcome the thermal barriers of pulsed protocols, we hope this paper paves the way for a broader transition in the field from conventional continuous-wave optically detected magnetic resonance methods to more advanced, Ramsey-based biomagnetic sensors.”

Comparable Ramsey applications have achieved a 6.5-millimeter sensor-to-sample distance.

The device employed a waveguide technique that trapped light in high-pressure, high-temperature diamond samples treated with electron beam radiation, housing nitrogen-vacancy centers, which boosted the device’s photon conversion efficiency to 9.5%

The new magnetometer detects magnetic fields as weak as 77.7 picoteslas, maintaining a minimal temperature increase of 13 K and an average sensor-to-sample distance of 2.5 millimeters, boosting the signal-to-noise ratio.

To maintain a high sensitivity during extended biomagnetic field measurements, the group next plans to implement active microwave feedback that dynamically tracks and cancels ambient temperature drift.

Source: “A highly sensitive diamond NV magnetometer using Ramsey interferometry with a short sensor-to-sample distance,” by Yuta Araki, Takeharu Sekiguchi, Yuji Hatano, Naota Sekiguchi, Chikara Shinei, Masashi Miyakawa, Takashi Taniguchi, Tokuyuki Teraji, Hiroshi Abe, Shinobu Onoda, Takeshi Ohshima, Takayuki Shibata, Mutsuko Hatano, and Takayuki Iwasaki, Applied Physics Letters (2026). The article can be accessed at https://doi.org/10.1063/5.0334709 .