Broadband, large-area microwave antenna for optically detected magnetic resonance of nitrogen-vacancy centers in diamond

At a Glance

Metadata	Details
Publication Date	2016-05-01
Journal	Review of Scientific Instruments
Authors	Kento Sasaki, Yasuaki Monnai, Soya Saijo, Ryushiro Fujita, Hideyuki Watanabe
Institutions	Keio University, National Institute of Advanced Industrial Science and Technology
Citations	143
Analysis	Full AI Review Included

Technical Documentation & Analysis: Broadband Microwave Antenna for NV-Center ODMR

This document analyzes the requirements and achievements detailed in the research paper concerning the development of a planar ring antenna for NV-center ODMR. It highlights how 6CCVD’s advanced MPCVD diamond materials and custom fabrication services are essential for replicating, scaling, and advancing this critical quantum sensing technology.

Executive Summary

The research successfully demonstrates a novel planar ring antenna optimized for optically-detected magnetic resonance (ODMR) of Nitrogen-Vacancy (NV) centers in diamond, achieving performance metrics critical for wide-field quantum sensing applications.

High Bandwidth Performance: The antenna achieves a 400 MHz bandwidth centered at 2.87 GHz, ensuring ODMR can be observed under external magnetic fields up to 100 G without requiring frequency adjustment.
Spatial Uniformity: The design delivers a spatially uniform oscillating magnetic field ($B_{ac}$) over a 1 mm diameter area, enabling high-fidelity magnetic field imaging across wide spatial ranges.
Material Requirement: The experiment relied on high-quality, 0.51 mm thick Single Crystal Diamond (SCD) substrates (Type IIa, (001) orientation) coated with a 100 nm N-doped diamond film.
High-Speed Pulsed ODMR: The system supports high-speed pulsed experiments, demonstrating Rabi frequencies up to 10 MHz and theoretically allowing pulse lengths as short as 2.5 ns, critical for dynamical decoupling sequences.
Design Advantage: Placing the antenna beneath the diamond sample leaves the surface open, facilitating integration with objective lenses and specimens (e.g., biological samples) for non-interfering sensing.
6CCVD Value Proposition: Replication and scaling of this technology require precision-engineered SCD substrates with controlled nitrogen doping and specific crystallographic orientation, core specialties of 6CCVD.

Technical Specifications

The following hard data points were extracted from the characterization of the planar ring antenna and the diamond sample used in the ODMR experiments.

Parameter	Value	Unit	Context
Antenna Resonance Frequency ($f_{mw}$)	2.87	GHz	NV electronic spin manipulation
Antenna Bandwidth	400	MHz	Design target for broad field tolerance
Measured Bandwidth (with diamond)	395	MHz	Corresponds to Quality Factor (Q) of ~7
External Magnetic Field Tolerance ($B_0$)	Up to 100	G	Maximum field observed without frequency adjustment
Diamond Substrate Thickness ($t_a$)	0.51	mm	Type IIa (001) SCD used
N-Doped Film Thickness	100	nm	Active NV layer grown by MPCVD
NV Center Density (Ensemble)	Order of 10¹⁵	cm^-3	Required for ensemble sensing
Spatial Uniformity Area	1	mm²	Area over which $B_{ac}$ is uniform
Maximum Rabi Frequency ($f_R$)	10	MHz	Limited by microwave amplifier saturation power
Minimum Pulse Length (Theoretical)	2.5	ns	Limited by 400 MHz antenna bandwidth
Zero-Field Splitting (D)	2.87	GHz	NV ground state property

Key Methodologies

The experimental success relies on precise material engineering and careful microwave circuit design, summarized below:

Material Preparation: A 100 nm thick N-doped diamond film was grown onto a high-quality Type IIa (001) Single Crystal Diamond (SCD) substrate using Microwave Plasma-Assisted Chemical Vapor Deposition (MPCVD).
Antenna Design (Planar Ring Resonator): The antenna was designed as a single-loop coil surrounding a circular hole (radius $r = 0.5$ mm) to concentrate resonant magnetic fields. Key design parameters were tuned using 3D electromagnetic simulation (CST MICROWAVE STUDIO®) to achieve a low Quality factor (Q < 10) and high bandwidth.
Impedance Matching: The feed line width was consecutively varied from 3.3 mm (SMA connector side) to 0.54 mm (ring edge) to achieve impedance matching with instrumental 50 Ω.
S-Parameter Characterization: A vector network analyzer was used to measure the reflection coefficient ($S_{11}$) with and without the diamond sample, confirming the targeted resonance frequency and bandwidth.
ODMR Measurement: Continuous Wave (CW) and pulsed ODMR were performed using a 515 nm green laser for initialization and excitation, and a Single Photon Counting Module (SPCM) for fluorescence detection (637-800 nm).
Rabi Oscillation Analysis: Pulsed ODMR was used to observe Rabi oscillations. The resulting Rabi frequency ($f_R$) was converted into the oscillating magnetic field strength ($B_1$) to map the spatial distribution and uniformity of the antenna’s output.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced diamond materials required to replicate and scale this research for next-generation quantum sensing and imaging systems.

Applicable Materials

To replicate the high-performance ODMR platform, researchers require high-purity, precisely oriented SCD substrates with controlled nitrogen incorporation.

6CCVD Material Solution	Specification	Application Context
Optical Grade SCD (001)	High-purity, low-strain SCD substrates. Standard (001) orientation, essential for aligning NV centers along specific crystallographic axes.	Used as the base material (Type IIa equivalent) for epitaxial growth of the active NV layer.
Controlled N-Doped SCD	SCD films with nitrogen concentrations precisely tuned to achieve ensemble NV densities (e.g., 10¹⁵ cm^-3).	Replicating the 100 nm active sensing layer used in the paper for high-contrast ODMR.
Ultra-Low N SCD	SCD with nitrogen concentration < 1 ppb, ideal for creating isolated, single NV centers (required for nanoscale resolution magnetometry).	Extending the research to single-NV sensing applications, requiring the highest material purity.
Custom Thickness	SCD plates available from 0.1 µm up to 500 µm (or substrates up to 10 mm).	Supplying the exact 0.51 mm thickness used in the paper, or custom thicknesses for optimized antenna coupling.

Customization Potential

The integration of the diamond sample with the planar antenna requires precise dimensions and, potentially, integrated circuitry. 6CCVD offers comprehensive customization services to meet these engineering demands.

Custom Dimensions and Shaping: 6CCVD provides custom laser cutting and shaping services to match the diamond sample size (e.g., 1 mm to 5 mm sides) required for specific antenna designs or objective lens clearances. We offer plates/wafers up to 125 mm (PCD).
Precision Polishing: We guarantee surface roughness (Ra) < 1 nm for SCD, ensuring minimal scattering losses and optimal optical access for the 515 nm laser and fluorescence collection.
Integrated Metalization: For advanced antenna designs or integrated microwave circuitry directly on the diamond, 6CCVD offers in-house metalization services, including Ti/Pt/Au, W, Cu, and Pd, allowing for direct bonding or contact pads.
Boron Doping (BDD): For applications requiring integrated electrical control or high thermal conductivity electrodes, 6CCVD supplies Boron-Doped Diamond (BDD) films and substrates.

Engineering Support

6CCVD’s in-house team of PhD material scientists and quantum engineers specializes in the material requirements for NV-center quantum sensing. We provide authoritative support for:

Material Selection: Assisting researchers in selecting the optimal SCD purity and nitrogen doping level (ensemble vs. single NV) for specific magnetometry or quantum computing projects.
Epitaxial Layer Optimization: Consulting on MPCVD growth recipes to achieve the desired NV depth and density, crucial for balancing sensitivity and spatial resolution.
Global Logistics: Ensuring reliable, DDU (default) or DDP global shipping of sensitive diamond materials directly to research facilities worldwide.

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

View Original Abstract

We report on a microwave planar ring antenna specifically designed for optically detected magnetic resonance (ODMR) of nitrogen-vacancy (NV) centers in diamond. It has the resonance frequency at around 2.87 GHz with the bandwidth of 400 MHz, ensuring that ODMR can be observed under external magnetic fields up to 100 G without the need of adjustment of the resonance frequency. It is also spatially uniform within the 1-mm-diameter center hole, enabling the magnetic-field imaging in the wide spatial range. These features facilitate the experiments on quantum sensing and imaging using NV centers at room temperature.

Tech Support

Original Source

DOI: https://doi.org/10.1063/1.4952418