| Metadata | Details |
|---|
| Publication Date | 2020-04-09 |
| Journal | Physical Review Applied |
| Authors | Huijie Zheng, Zhiyin Sun, Georgios Chatzidrosos, Chen Zhang, Kazuo Nakamura |
| Institutions | National Institutes for Quantum and Radiological Science and Technology, Helmholtz Institute Mainz |
| Citations | 62 |
| Analysis | Full AI Review Included |
- Core Innovation: Demonstration of a microwave-free vector magnetometer utilizing nitrogen-vacancy (NV) center ensembles in diamond.
- Vector Sensing Mechanism: Leverages the Ground-State Level Anticrossing (GSLAC) at 102.4 mT, eliminating the need for complex microwave control typically required for NV magnetometry.
- Simultaneous Readout: Achieves simultaneous measurement of all three Cartesian magnetic field components (Bx, By, Bz) using orthogonal alternating field modulation and Lock-in Amplifier (LIA) demodulation of the photoluminescence (PL) signal.
- Performance Metric: Exhibits a root mean square (RMS) noise floor of approximately 300 pT /âHz in both longitudinal and transverse directions.
- Operational Range: Provides a wide measurement bandwidth ranging from zero to megahertz.
- Key Advantage: The microwave-free operation is critical for extending NV vector sensing capability to cryogenic temperatures (less than 4K) where thermal management is challenging.
- Scalability: The protocol is broadly applicable to both ensemble sensors and potentially single-NV probes, enabling nanoscale vector imaging.
| Parameter | Value | Unit | Context |
|---|
| RMS Noise Floor | 300 | pT /âHz | Measured sensitivity in all directions |
| Photon Shot Noise Limit (Longitudinal) | 65 | pT /âHz | Calculated limit for z-axis measurement |
| Photon Shot Noise Limit (Transverse) | 60 | pT /âHz | Calculated limit for x-axis measurement |
| GSLAC Axial Field (Bz) | 102.4 | mT | Magnetic field operating point for level anticrossing |
| GSLAC Feature FWHM (Transverse) | 38 | ”T | Full Width at Half Maximum of the transverse magnetic resonance feature |
| Measurement Bandwidth | Zero to Megahertz | Range | Wide bandwidth capability |
| Diamond Isotope Purity | 99.97% | 12C | Single crystal material, essential for narrow GSLAC features |
| Initial Nitrogen Concentration | 3 | ppm | Measured via Electron Paramagnetic Resonance (EPR) |
| NV- Concentration (Post-Conversion) | 0.9 | ppm | Measured via EPR |
| Excitation Wavelength | 532 | nm | Solid-state laser source (Laser Quantum Gem 532) |
| Electron Irradiation Fluence | 1.8 x 1018 | cm-2 | Applied at 2 MeV for NV creation |
- Base Material: Used a 99.97% 12C, (111)-cut single crystal diamond (dimensions: 0.71 mm x 0.69 mm x 0.43 mm).
- Growth Method: Grown via the temperature gradient method at high pressure (6.1 GPa) and high temperature (1430 °C).
- Source Materials: Used a metal solvent containing a nitrogen-getter and carbon powder prepared by pyrolysis of 99.97% 12C-enriched methane.
- NV Creation: Irradiated with 2 MeV electrons (Cockcroft-Walton accelerator) to a total fluence of 1.8 x 1018 cm-2 at room temperature.
- Annealing: Annealed at 800 °C for 5 hours to convert substitutional nitrogen into negatively charged NV centers (NV-).
- Static Field Alignment: A custom electromagnet applies a static bias field (Bs) along the preferential NV axis (z-axis) to position the NV centers precisely at the GSLAC (102.4 mT).
- Transverse Field Modulation (Bmt): Two pairs of Helmholtz coils apply sinusoidal modulating fields (Bmx and Bmy) in the transverse (x-y) plane. These signals share the same frequency but are 90° phase-shifted, creating a rotating transverse field.
- Longitudinal Field Modulation (Bmz): A third modulating field is applied along the z-axis at a different frequency than the transverse modulation.
- Optical Readout: A 532 nm laser excites the NV centers, and the resulting photoluminescence (PL) signal is collected via a parabolic lens and detected by a photodetector.
- Vector Demodulation:
- The PL signal is fed into two Lock-in Amplifiers (LIAs).
- One LIA demodulates the transverse signal, providing the magnitude and angle (phase) of the transverse field (Bx and By components).
- A second LIA demodulates the longitudinal signal, providing the Bz component.
- Calibration: Helmholtz coils are used to calibrate the LIA output response against known AC and DC magnetic fields, ensuring accurate conversion to magnetic field units.
| Industry / Application | Value Proposition | Technical Relevance |
|---|
| Cryogenic Quantum Sensing | Enables vector magnetometry below 4K, overcoming thermal limitations of traditional microwave-based NV sensors. | Microwave-free operation at GSLAC; high 12C purity diamond required for narrow features. |
| Condensed Matter Physics | Mapping magnetization of individual atomic layers in 2D van der Waals materials and elucidating spin order in magnetic systems. | Nanoscale spatial resolution potential (via single-NV extension) combined with full vector capability. |
| Bioimaging and Nanomedicine | Noninvasive tracking of particle motion in intracellular media and discerning the directionality of action-potential firing. | Potential extension to single-NV probes for nanoscale vector sensing under ambient temperatures. |
| Geophysical Surveying | Creation of compact, high-sensitivity vector magnetometers suitable for magnetic navigation and anomaly detection. | High sensitivity (300 pT /âHz) and compact solid-state design. |
| Novel Spin Texture Characterization | Microscopic characterization of complex spin textures (e.g., skyrmions) where vector information is essential to restrict the manifold of possible solutions. | Simultaneous measurement of Bx, By, and Bz components. |
View Original Abstract
Sensing vector magnetic fields is critical to many applications in fundamental physics, bioimaging, and material science. Magnetic-field sensors exploiting nitrogen-vacancy (NV) centers are particularly compelling as they offer high sensitivity and spatial resolution even at nanoscale. Achieving vector magnetometry has, however, often required applying microwaves sequentially or simultaneously, limiting the sensorsâ applications under cryogenic temperature. Here we propose and demonstrate a microwave-free vector magnetometer that simultaneously measures all Cartesian components of a magnetic field using NV ensembles in diamond. In particular, the present magnetometer leverages the level anticrossing in the triplet ground state at 102.4 mT, allowing the measurement of both longitudinal and transverse fields with a wide bandwidth from zero to megahertz range. Full vector sensing capability is proffered by modulating fields along the preferential NV axis and in the transverse plane and subsequent demodulation of the signal. This sensor exhibits a root mean square noise floor of about 300 pT/Hz^(1/2) in all directions. The present technique is broadly applicable to both ensemble sensors and potentially also single-NV sensors, extending the vector capability to nanoscale measurement under ambient temperatures.