Optical-power-dependent Splitting of Magnetic Resonance in Nitrogen-vacancy Centers in Diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-07-05 |
| Journal | Journal of the Physical Society of Japan |
| Authors | Shunji Ito, Moeta Tsukamoto, K. Ogawa, Tokuyuki Teraji, Kento Sasaki |
| Institutions | National Institute for Materials Science, The University of Tokyo |
| Citations | 6 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study investigates the critical dependence of Optically Detected Magnetic Resonance (ODMR) splitting (Î) on optical excitation power (Popt) in nitrogen-vacancy (NV) centers, a key factor for accurate quantum sensing.
- Unexpected Phenomenon: The ODMR splitting (Î), which is used to calculate magnetic field strength, decreases exponentially and saturates as the optical power (Popt) increases (tested up to 38.4 kW/cm2).
- Impact on Accuracy: This Popt dependence can introduce errors equivalent to tens of ”T in magnetic field measurements if not properly accounted for.
- Universality and Mechanism: The phenomenon is observed in both high-impurity nanodiamonds (NDs) and low-impurity single-crystal bulk diamond, suggesting it is an intrinsic property of the NV center.
- Sample Dependence: The decay amplitude (A) is highly dependent on sample quality, being approximately 20 times smaller in the low-impurity bulk diamond than in NDs.
- Saturation Power (Po): The optical power required for saturation (Po) is relatively sample-independent (~3.8 kW/cm2 for NDs, ~7.4 kW/cm2 for bulk), indicating a common underlying relaxation process.
- Proposed Solution: The effect is likely caused by photoionization of impurities (charge traps) time-averaging out local non-axisymmetry deformation (strain/electric fields). Engineers should use diamonds with fewer impurities or operate sensors above the Po saturation level for maximum accuracy.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Excitation Wavelength | 520 | nm | Green laser source |
| Optical Power Range (Popt) | 0.55 to 38.4 | kW/cm2 | Range tested for ODMR dependence |
| Laser Spot Diameter (FWHM) | 386 ± 2 | nm | Used for Popt calibration |
| ND Grain Size (Sample #1) | 50 | nm | Commercial nanodiamonds |
| Bulk Film Thickness (15N doped layer) | ~5 | ”m | CVD grown layer on substrate |
| Bulk Film Total Thickness | ~70 | ”m | Undoped CVD layer thickness |
| Nitrogen Concentration ([N]) (NDs) | ~100 | ppm | Typical Type 1b raw material |
| Nitrogen Concentration ([N]) (Bulk #3) | ~10 | ppm | Low impurity CVD film |
| NV Concentration ([NV]) (Bulk #3) | ~4 | ppb | Very low concentration in bulk sample |
| Coherence Time (T2) (Bulk #3) | 29 | ”s | Measured by Hahn echo |
| ODMR Splitting (Î) (NDs, Low Popt) | 11.5 ± 0.2 | MHz | Condition 2A, Popt = 0.55 kW/cm2 |
| ODMR Splitting (Î) (Bulk, Low Popt) | 3.55 ± 0.02 | MHz | Condition 3A, Popt = 0.55 kW/cm2 |
| Saturation Power (Po) (NDs) | ~3.8 | kW/cm2 | Exponential decay fitting parameter |
| Saturation Power (Po) (Bulk #3) | ~7.4 | kW/cm2 | Exponential decay fitting parameter |
| Max Temperature Change (Estimated) | ~12 | K | Based on ZFS shift (850 kHz) |
| Magnetic Field (Biased, C) | 196.7 | ”T | Applied field for 2C condition |
Key Methodologies
Section titled âKey MethodologiesâThe study utilized a confocal microscopy system at room temperature, focusing on precise control and calibration of the optical power and magnetic environment.
- Sample Preparation (NDs): Nanodiamonds (50 nm and 100 nm) were spin-coated onto a cover glass at 600 rpm, creating a film typically 200-1000 nm thick.
- Sample Preparation (Bulk Diamond): A single-crystal (100) diamond substrate was used for Microwave Plasma Chemical Vapor Deposition (MPCVD). An undoped film (~70 ”m) was grown, followed by a 15N doped layer (~5 ”m) using 12C concentrated methane gas (4000 ppm 15N/C ratio).
- Optical Power Calibration: Green laser intensity was measured using an optical power meter. The irradiation area was determined by fitting the photoluminescence (PL) map of a single NV center with a 2D Gaussian function, yielding a spot diameter (FWHM) of 386 ± 2 nm.
- ODMR Measurement: NV centers were continuously irradiated with the 520 nm green laser and microwaves (MW) delivered via a coplanar waveguide antenna. The PL contrast was measured as a function of MW frequency.
- Magnetic Field Control: Two coils (perpendicular and parallel to the optical axis) were used to generate three conditions: zero field (A, 6.3 ”T), environmental field (B, 88.7 ”T), and biased field (C, 196.7 ”T).
- Data Fitting and Analysis: ODMR spectra were fitted using a double Lorentzian function to extract the splitting width (Î). The dependence of Î on Popt was quantitatively analyzed using an exponential decay model: Î(Popt) = A exp(-Popt/Po) + Îo.
Commercial Applications
Section titled âCommercial ApplicationsâThe findings are crucial for optimizing NV-based quantum sensors, particularly those requiring high accuracy or wide-field operation.
- High-Accuracy Magnetometry: Essential for achieving ”T-order or better accuracy in magnetic field measurements by compensating for the optical power dependence of the ODMR splitting.
- Wide-Field Imaging: Critical for systems using CMOS cameras and NV ensembles, where inhomogeneous optical power across the field of view could otherwise lead to spatially varying measurement errors in magnetic field or temperature maps.
- Quantum Sensing Platforms: Applicable to various NV sensing applications, including measuring electron flow in graphene, stray fields from antiferromagnets, and local temperature sensing.
- Diamond Material Specification: Provides engineering criteria for selecting or fabricating optimal diamond materials (low impurity density, low strain/deformation) to minimize the optical power dependence (i.e., minimizing the amplitude A).
- Sensor Operating Protocol: Establishes the need for operating NV sensors at high optical power (above the saturation power Po) to ensure stable, power-independent splitting values.
View Original Abstract
Nitrogen-vacancy (NV) centers in diamonds are a powerful tool for accurate\nmagnetic field measurements. The key is precisely estimating the\nfield-dependent splitting width of the optically detected magnetic resonance\n(ODMR) spectra of the NV centers. In this study, we investigate the optical\npower dependence of the ODMR spectra using NV ensemble in nanodiamonds (NDs)\nand a single-crystal bulk diamond. We find that the splitting width\nexponentially decays and is saturated as the optical power increases.\nComparison between NDs and a bulk sample shows that while the decay amplitude\nis sample-dependent, the optical power at which the decay saturates is almost\nsample-independent. We propose that this unexpected phenomenon is an intrinsic\nproperty of the NV center due to non-axisymmetry deformation or impurities. Our\nfinding indicates that diamonds with less deformation are advantageous for\naccurate magnetic field measurements.\n