Optical-power-dependent Splitting of Magnetic Resonance in Nitrogen-vacancy Centers in Diamond

At a Glance

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	The University of Tokyo, National Institute for Materials Science
Citations	6
Analysis	Full AI Review Included

Technical Documentation & Analysis: Optical Power Dependence in NV Diamond

Source Paper: Ito et al., Optical-power-dependent splitting of magnetic resonance in nitrogen-vacancy centers in diamond (arXiv:2307.04414v1, 10 Jul 2023).

Executive Summary

This research confirms that the accuracy of NV-based quantum sensing is fundamentally limited by the optical power dependence of the Optically Detected Magnetic Resonance (ODMR) splitting ($\Delta$). The findings strongly validate the necessity of using high-quality MPCVD Single Crystal Diamond (SCD) for precision magnetometry.

Core Phenomenon: The ODMR splitting width ($\Delta$) exhibits an exponential decay and saturation behavior as the green excitation power ($P_{opt}$) increases.
Accuracy Degradation: This power dependence introduces an error equivalent to tens of $\mu$T in magnetic field measurements, particularly problematic for $\mu$T-order sensing applications.
Material Quality is Key: The decay amplitude (A), which quantifies the severity of the power dependence, was found to be highly sample-dependent. High-quality MPCVD bulk diamond (#3) exhibited a decay amplitude 20 times smaller than commercial nanodiamonds (NDs).
Mechanism Inference: The phenomenon is correlated with crystal deformation and impurity density, suggesting that photoionization of charge traps (impurities) is the underlying cause.
6CCVD Validation: The study explicitly recommends using diamonds with fewer impurities and less deformation—a direct endorsement of 6CCVD’s low-strain, high-purity MPCVD SCD material for achieving stable, accurate quantum sensing platforms.
Material Recipe: The high-performance bulk sample was a custom MPCVD film featuring a 5 µm ¹⁵N-doped layer on a 70 µm undoped SCD substrate.

Technical Specifications

Parameter	Value	Unit	Context
Diamond Synthesis Method	MPCVD	N/A	Bulk Diamond Film (#3)
Bulk Film Thickness (Total)	~75	µm	70 µm undoped + 5 µm ¹⁵N doped
Nitrogen Concentration [N] (Bulk #3)	~10	ppm	Estimated, consistent with T₂
NV Center Concentration [NV] (Bulk #3)	~4	ppb	Spontaneously formed
Coherence Time (T₂) (Bulk #3)	29	µs	Measured by Hahn echo [30]
ODMR Splitting Decay Amplitude (A)	~0.1	MHz	Bulk Diamond (#3)
ODMR Splitting Decay Amplitude (A)	~2	MHz	Nanodiamonds (NDs)
A Ratio (NDs:Bulk)	~20:1	N/A	Demonstrates superior stability of bulk SCD
Saturation Power ($P_{o}$) (Bulk #3)	~7.4	kW/cm²	Exponential decay fitting
Laser Excitation Wavelength	520	nm	Green laser
Laser Spot Diameter (FWHM)	386 ± 2	nm	Used for $P_{opt}$ calibration
Maximum Magnetic Field Applied	196.7	µT	Biased field (Condition C)

Key Methodologies

The experimental success hinges on precise MPCVD material control and highly calibrated optical and microwave systems.

MPCVD Growth Recipe: The high-quality bulk diamond (#3) was synthesized using a custom MPCVD system. A 5 µm ¹⁵N-doped layer was overgrown on a 70 µm undoped Type Ib (100) SCD substrate. The doping gas ratio was ¹⁵N/C = 4000 ppm.
Sample Preparation: Nanodiamonds (50 nm and 100 nm) were spin-coated onto a cover glass. The bulk SCD film was fixed directly to the coplanar waveguide antenna using carbon tape.
ODMR Setup: Measurements were performed in a confocal system at room temperature. A 520 nm green laser was used for NV initialization and readout. Red photoluminescence (PL) was filtered (514 nm notch, 650 nm long-pass) and detected by an Avalanche Photodiode (APD).
Microwave (MW) Delivery: Spin manipulation was achieved using a coplanar waveguide antenna (18 µm thick copper foil, 2 mm centerline) on a 1.6 mm thick PCB substrate, impedance matched to 50 Ω. MW power was fixed across all measurements.
Magnetic Field Application: External magnetic fields were applied using two coils (perpendicular and parallel to the optical axis) to achieve three conditions: Zero field (6.3 µT), Environmental field (88.7 µT), and Biased field (196.7 µT).
Data Analysis: ODMR spectra were fitted using a double Lorentzian function to extract the splitting width ($\Delta$). The optical power dependence of $\Delta$ was analyzed using the exponential decay function: $\Delta(P_{opt}) = A \exp(-P_{opt}/P_{o}) + \Delta_{o}$.

6CCVD Solutions & Capabilities

The research clearly demonstrates that minimizing impurities and crystal strain—hallmarks of high-quality MPCVD SCD—is essential for stable, accurate NV magnetometry. 6CCVD is uniquely positioned to supply the materials required to replicate and advance this critical quantum sensing research.

Applicable Materials

To replicate the high-performance bulk diamond (#3) and minimize optical power dependence, the following 6CCVD materials are required:

Optical Grade Single Crystal Diamond (SCD): Our MPCVD SCD is grown with ultra-low impurity levels (Type IIa/IIb characteristics) and minimal strain, directly addressing the paper’s conclusion that low-deformation material is necessary for accurate $\mu$T-order sensing.
Custom ¹⁵N Doped SCD: We specialize in precise gas-phase doping. We can replicate the ¹⁵N doping used in the study (or ¹⁴N) at controlled concentrations (ppm to ppb) to optimize NV density while maintaining high T₂ coherence times (T₂ = 29 µs achieved in the paper).

Customization Potential

6CCVD’s in-house capabilities allow for the exact engineering of the diamond structure used in this study, or optimization for next-generation devices:

Research Requirement	6CCVD Capability	Specification Match
Layered Structure & Thickness	Custom SCD Film Growth	We can grow films with precise thickness control (0.1 µm to 500 µm), allowing replication of the 5 µm ¹⁵N layer on a custom-thickness undoped substrate (e.g., 70 µm).
Substrate Size & Geometry	Custom Dimensions & Laser Cutting	We provide SCD plates and large-area PCD wafers up to 125 mm. Custom laser cutting ensures precise geometry for integration with MW antennas and optical setups.
MW Antenna Integration	In-House Metalization	We offer deposition of standard metal stacks (Ti/Pt/Au, W/Cu, etc.) directly onto the diamond surface, facilitating the integration of coplanar waveguides used for MW spin manipulation.
Surface Finish	Ultra-Precision Polishing	SCD material is polished to an atomic-scale roughness (Ra < 1 nm), crucial for minimizing optical scattering and maximizing PL collection efficiency in confocal systems.

Engineering Support

6CCVD’s in-house PhD team provides expert consultation on material selection and optimization for quantum sensing applications. We can assist researchers in tailoring doping profiles, film thickness, and surface preparation to minimize the optical power dependence observed in this NV Magnetometry project, ensuring maximum accuracy and stability for next-generation quantum devices.

Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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

Tech Support

Original Source

DOI: https://doi.org/10.7566/jpsj.92.084701