Diamond NV Center Magnetometry Achieves 280 T Dynamic Range and 670 fT/√Hz Sensitivity

Quantum sensors, particularly those leveraging the unique properties of nitrogen-vacancy centres in diamond, represent a significant advance in precision measurement, but existing devices often struggle with both sensitivity and the range of magnetic fields they can accurately detect. Florian Schall, Lukas Lindner, and Yves Rottstaedt, along with colleagues at the Fraunhofer Institute for Applied Solid State Physics IAF and the University of Leipzig, now present a novel approach that overcomes these limitations. Their research introduces a laser-enhanced system where magnetic fields influence the laser’s operating point, generating a strong and easily detectable signal. The resulting magnetometer achieves an unprecedented combination of sensitivity and dynamic range, offering a 780-fold improvement over conventional fluorescence-based techniques and paving the way for more effective applications in areas such as brain imaging, navigation systems, and the detection of subtle magnetic anomalies.

However, standard formulas for calculating this sensitivity assume weak signals, and this research demonstrates that these formulas become inaccurate with high-contrast signals. To address this, scientists developed a corrected formula that accurately predicts sensitivity even with strong signals. This correction is crucial for interpreting experimental results and maximizing LTM performance. Experimental verification using red light measurements confirmed the accuracy of the new formula, demonstrating its ability to predict sensitivity improvements achieved through increased signal strength.

Laser Magnetometry Using Diamond NV Centers

Scientists have engineered a highly sensitive magnetometer by integrating nitrogen-vacancy (NV) centers in diamond into a laser cavity. This innovative approach leverages the unique optical and spin properties of NV centers to modulate laser emission, enabling high-contrast magnetic field measurements. The diamond acts as a magnetic-field-dependent component within the laser cavity, directly linking magnetic field strength to the laser’s output. The system utilizes a laser operating at a specific wavelength matched to the energy levels of the NV centers.

These centers are first excited with a green laser, initiating a cascade of energy transitions that influence how laser light is absorbed within the cavity. A microwave field, tuned to a specific frequency, coherently drives transitions between the spin states of the NV centers, further modulating the laser output and amplifying the signal. Researchers meticulously measured the laser’s power output under varying conditions, revealing a remarkable 100% contrast in signal when the microwave field resonates with the spin transition. This high contrast, achieved by operating the laser close to its threshold, allows for a photon-shot-noise-limited sensitivity of 670 femtotesla per root Hertz, representing a 780-fold improvement over traditional fluorescence-based methods and vapor cell magnetometers.

Laser Cavity Boosts Diamond Magnetic Sensing

This innovative approach overcomes limitations inherent in traditional NV-center magnetometers, which typically suffer from low optical contrast and restricted measurement ranges. The team demonstrated a system exhibiting 100% optical contrast and a strong output signal reaching up to 50 milliwatts. The core of this advancement lies in incorporating the NV centers into a laser cavity, where shifts in the laser threshold directly correlate with changes in the surrounding magnetic field.

This allows for highly sensitive detection, achieving a photon-shot-noise-limited sensitivity of 670 femtotesla per root Hertz. Crucially, the system boasts an exceptionally wide dynamic range of 280 microtesla, enabling the detection of both weak and strong magnetic fields without saturation. Experiments confirm that the laser’s output is entirely controlled by the quantum state of the NV centers, allowing for precise manipulation and measurement of magnetic fields. By operating the laser close to its threshold, scientists amplified the signal and maximized contrast, achieving the unprecedented 100% optical response. This breakthrough opens doors to a new generation of magnetic field sensors with applications spanning diverse fields, including magnetoencephalography, precise magnetic navigation systems, and enhanced magnetic anomaly detection.

Laser Cavity Boosts NV Center Magnetometry Performance

The team achieves 100% optical contrast and strong signal intensities, representing a substantial improvement over traditional fluorescence-based readout methods and vapor cell magnetometers. This new approach yields a dynamic range of 280 microtesla combined with a photon-shot-noise-limited sensitivity of 670 femtotesla per root Hertz, improving sensing parameters by a factor of 780 compared to existing technologies. The enhanced performance opens possibilities for next-generation applications in areas such as magnetoencephalography, magnetic navigation, and magnetic anomaly detection.

While the achieved sensitivity is already within a factor of three of the best currently reported values for NV magnetometry, the authors note that this was achieved using a simple measurement setup. They suggest that incorporating additional techniques could lead to even greater improvements in the future. The authors acknowledge that the current system amplifies environmental magnetic noise and that further sensitivity gains could be realised by combining the technique with magnetic flux concentrators. This research paves the way for even more sensitive and versatile magnetic field sensors based on diamond NV centers.