Picotesla magnetometry of microwave fields with diamond sensors
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-08-10 |
| Journal | Science Advances |
| Authors | Zhecheng Wang, Fei Kong, Pengju Zhao, Zhehua Huang, Pei Yu |
| Institutions | Suzhou University of Science and Technology, University of Science and Technology of China |
| Citations | 74 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research introduces a novel, simplified approach to high-sensitivity microwave (MW) magnetometry using Nitrogen-Vacancy (NV) centers in diamond, achieving picotesla-level detection without complex spin control pulses.
- Core Innovation: A continuous heterodyne detection scheme is proposed and demonstrated, utilizing a moderate reference MW field to enhance the NV centerâs response to weak signal MWs.
- Record Sensitivity: Achieved a sensitivity of 8.9 pT¡Hz-1/2 for microwave fields operating at 2.9 GHz, significantly improving upon previous NV-based GHz field detection limits (which typically degrade to sub-¾T¡Hz-1/2).
- Simplified Operation: The method removes the requirement for sophisticated control pulses (like pulsed Mollow absorption or dynamical decoupling), greatly benefiting the practical application and scalability of diamond sensors.
- Dynamic Range and Linearity: The sensor maintains a linear response to weak MW fields across five orders of magnitude, demonstrating detectability down to 0.28 pT within a 1000 s measurement time.
- High Resolution: The frequency resolution scales inversely with measurement time (1/t), achieving an ultra-fine resolution of 0.1 mHz over 10000 s.
- Material Basis: The demonstration utilized an ensemble of ~2.8 x 1013 NV centers within a small, high-purity 12C diamond volume (4 x 10-2 mm3).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Microwave Sensitivity (Best) | 8.9 pT¡Hz-1/2 | pT¡Hz-1/2 | Measured at 2.9 GHz, 1000 s total time. |
| Minimum Detectable Field | 0.28 | pT | Achieved within 1000 s measurement time. |
| Operating Frequency | 2.9039 | GHz | Resonant frequency of the NV transition. |
| Frequency Resolution (Best) | 0.1 | mHz | Achieved at 10000 s measurement time (1/t scaling). |
| NV Center Density (Estimated) | 4 | ppm | In the high-doping layer. |
| Total NV Centers (nNV) | ~ 2.8 x 1013 | centers | Within the effective sensor volume. |
| Effective Sensor Volume | 4 x 10-2 | mm3 | Volume of the high-doping layer. |
| Diamond Orientation | 100 | - | Crystal orientation. |
| 12C Isotopic Purity | 99.99 | % | Purity of the ~10 Âľm thick high-doping layer. |
| ODMR Linewidth (FWHM) | 482 | kHz | Measured linewidth (Îν). |
| Optimal Reference MW Field (B1) | 220 | nT | Field strength required for maximal SNR. |
| Laser Power (PL) | 0.8 | W | Moderate power used (below saturation). |
| Sensor Bandwidth (-3 dB) | ~ 100 | Hz | Intrinsic bandwidth limited by relaxation rates. |
| Extended Bandwidth (Max) | 190 | kHz | Achieved using 240 reference MW channels (limited by ODMR linewidth). |
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized a simplified, continuous-wave setup centered around a high-purity diamond sample to perform heterodyne detection.
- Diamond Sample: A 100-oriented diamond with a ~10 Âľm thick, 99.99% 12C isotopic purity layer was used, containing an ensemble of NV centers (~4 ppm density).
- Optical Setup: A 532 nm high-power laser was used for continuous illumination. Fluorescence was collected via an optical compound parabolic concentrator (CPC) and filtered before detection by a photodiode (PDAPC2).
- Magnetic Field Application: An external magnetic field (~12.5 G) was applied perpendicular to the diamond surface to ensure all NV centers had the same Zeeman splittings.
- Microwave Generation: Both the signal MW (b1) and the reference MW (B1) were generated using RF signal generators and radiated via a 5-mm-diameter loop antenna.
- Heterodyne Principle: The signal MW (b1 cos(Ďt)) and the reference MW (B1 cos[(Ď + δ)t + Ď]) were applied simultaneously. The reference field B1 was set to a moderate strength (optimal 220 nT), much weaker than the inhomogeneous transition linewidth (Îν = 482 kHz).
- Signal Extraction: The interference between the two MWs resulted in an oscillation of the NV photoluminescence at the beat frequency (δ). This AC oscillation amplitude, which is linearly proportional to the signal field b1, was extracted using Fourier transform spectroscopy.
- Performance Optimization: Laser power (PL) and reference MW strength (B1) were carefully balanced to maximize the signal-to-noise ratio (SNR), ensuring the noise remained dominated by laser-induced noise rather than photon shot noise.
Commercial Applications
Section titled âCommercial ApplicationsâThe development of a robust, high-sensitivity, and simplified diamond-based MW sensor opens doors for integration across several high-tech sectors.
- Quantum Sensing and Metrology:
- Creating next-generation, solid-state magnetometers capable of operating at ambient conditions without complex cryogenic cooling.
- Facilitating the development of compact, on-chip diamond magnetometers by removing the need for bulky pulsed control hardware.
- RF and Wireless Communication:
- High-sensitivity microwave receivers for advanced radar systems (detecting weak signals).
- Use in sub-THz communication systems and general wireless signal detection due to the diamond sensorâs wide frequency range potential (adjustable up to hundreds of GHz).
- Scientific Instrumentation:
- Enhanced detection sensitivity for Electron Paramagnetic Resonance (EPR) and Nuclear Magnetic Resonance (NMR) spectroscopy, particularly in ultra-high field environments.
- Serving as robust sensors for radio astronomy, capable of detecting weak, high-frequency signals from astronomical sources (e.g., Fast Radio Bursts).
- Extreme Environment Monitoring:
- Magnetometry and sensing applications in harsh conditions, leveraging diamondâs stability at high temperatures (up to 1000 K) and high pressures.
View Original Abstract
Developing robust microwave-field sensors is both fundamentally and practically important with a wide range of applications from astronomy to communication engineering. The nitrogen vacancy (NV) center in diamond is an attractive candidate for such purpose because of its magnetometric sensitivity, stability, and compatibility with ambient conditions. However, the existing NV center-based magnetometers have limited sensitivity in the microwave band. Here, we present a continuous heterodyne detection scheme that can enhance the sensorâs response to weak microwaves, even in the absence of spin controls. Experimentally, we achieve a sensitivity of 8.9 pT Hz â1/2 for microwaves of 2.9 GHz by simultaneously using an ensemble of n NV ~ 2.8 Ă 10 13 NV centers within a sensor volume of 4 Ă 10 â2 mm 3 . Besides, we also achieve 1/ t scaling of frequency resolution up to measurement time t of 10,000 s. Our scheme removes control pulses and thus will greatly benefit practical applications of diamond-based microwave sensors.