Coupling nitrogen-vacancy center spins in diamond to a grape dimer

At a Glance

Metadata	Details
Publication Date	2024-12-19
Journal	Physical Review Applied
Authors	Ali Fawaz, Sarath Raman Nair, Thomas Volz
Institutions	ARC Centre of Excellence for Engineered Quantum Systems, Macquarie University
Citations	2
Analysis	Full AI Review Included

Technical Documentation & Analysis: N-V Spin Coupling in Dielectric Resonators

Research Paper Analyzed: Fawaz, Nair, and Volz, Coupling nitrogen-vacancy center spins in diamond to a grape dimer, Physical Review Applied 22, 064078 (2024).

Executive Summary

This research validates the use of Nitrogen-Vacancy (N-V) centers in nanodiamonds (NDs) as highly sensitive probes for magnetic field hotspots generated by novel dielectric resonators. The findings are critical for advancing room-temperature quantum technologies and maser platforms.

Core Achievement: Demonstrated efficient coupling of N-V spins to the magnetic field component of a Microwave (MW) hotspot generated by a grape dimer resonator using Optically Detected Magnetic Resonance (ODMR).
Quantum Sensing Validation: Confirms N-V centers in diamond as robust, room-temperature solid-state spin systems suitable for integration into complex MW cavity designs.
Performance Metric: Achieved an ODMR contrast enhancement factor greater than 2, corresponding to an estimated magnetic field amplification factor of 2.1 ± 0.4.
Resonator Design: The study validates the concept of using high-permittivity, water-based dielectric geometries (ε_r ≈ 79.21) to create compact MW resonators operating near the N-V transition frequency (2.87 GHz).
Future Scaling: The work lays the foundation for designing compact, efficient on-chip maser platforms by replacing high-loss water with optimized, low-loss, high-permittivity dielectric materials—a key area where 6CCVD’s custom diamond substrates excel.
6CCVD Value Proposition: We provide the high-purity Single Crystal Diamond (SCD) and large-area Polycrystalline Diamond (PCD) substrates required to transition this proof-of-concept into scalable, integrated quantum devices.

Technical Specifications

The following hard data points were extracted from the experimental and simulation results:

Parameter	Value	Unit	Context
N-V Ground State Splitting (D)	2.87	GHz	Zero-field splitting (ms=0 to ms=±1 transition)
Simulated MW Hotspot Frequency	2.855	GHz	Peak magnetic field resonance
Simulated Resonance Linewidth (FWHM)	25	MHz	For Im(ε_r)=0i (no absorption)
Simulated Q Factor	~114	N/A	Low Q attributed to high dielectric loss of water
Experimental ODMR Contrast Enhancement	>2	Factor	Measured increase with grape dimer present
Experimental Field Amplification Factor	2.1 ± 0.4	Factor	Ratio of magnetic field strength (with/without grapes)
Optimal Grape Gap Size (Experimental)	0.5	mm	Gap size yielding maximum ODMR contrast
Grape Dimensions (Simulated)	27 x 17	mm	Major axis x Minor axis (ellipsoidal model)
MW Antenna Diameter	1	mm	Vertical straight copper wire
MW Antenna Power	16	W	Amplifier output (Minicircuits ZHL-16W-43-S+)
Operating Environment	Room	Temperature	N-V spin preparation and readout

Key Methodologies

The experiment successfully coupled N-V spins to the magnetic field component of the MW resonator using a combination of optical and microwave techniques, verified by Finite-Element Modeling (FEM).

Spin System Preparation: Nanodiamonds (NDs) containing N-V centers were affixed to the tip of a multimode optical fiber, serving as the localized quantum probe.
MW Excitation: A 1-mm copper wire antenna, driven by a 16W amplifier, delivered MW radiation near 2.87 GHz to the system.
Resonator Geometry: Two grapes (modeled as ellipsoidal dielectric dimers, ε_r ≈ 79.21) were positioned around the NDs to create a morphological-dependent resonance (MDR) hotspot.
ODMR Measurement: N-V spins were optically polarized using a green laser (e.g., 520 nm) and read out by detecting the reduction in red fluorescence (600-800 nm) induced by the resonant MW field.
Optimization: ODMR contrast was mapped as a function of antenna distance and grape gap size, identifying an optimal gap of 0.5 mm for maximum field enhancement.
Simulation: Finite-Element Modeling (FEM) using COMSOL 6.0 verified the formation of the magnetic field hotspot and calculated the field amplification factors (ranging from 1.9 to 6.2 depending on simulated absorption).

6CCVD Solutions & Capabilities

This research demonstrates a clear path toward developing compact, high-efficiency MW resonators for quantum sensing and maser applications. To transition from the proof-of-concept (using high-loss grapes) to a stable, scalable, and high-Q integrated platform, researchers require high-quality, custom-engineered diamond materials.

6CCVD is uniquely positioned to supply the necessary MPCVD diamond substrates and fabrication services to replicate and extend this research into commercial quantum devices.

Applicable Materials for Quantum Resonator Development

Application Requirement	Recommended 6CCVD Material	Technical Rationale
High Coherence N-V Qubits	Optical Grade Single Crystal Diamond (SCD)	Provides the lowest strain and highest purity (low residual nitrogen/boron) necessary to achieve millisecond coherence times (T₂) required for high-performance masers and quantum memory.
Large-Area Integrated Resonators	Optical Grade Polycrystalline Diamond (PCD)	Available in plates/wafers up to 125 mm. Offers a stable, low-loss, high-permittivity substrate (replacing water/grapes) for fabricating reproducible, large-scale dielectric resonator arrays.
Integrated Active Components	Boron-Doped Diamond (BDD)	While not used in this specific N-V coupling study, BDD is essential for integrated diamond electronics, offering conductive layers for electrodes or thermal management in complex quantum circuits.

Customization Potential for Scalable Quantum Platforms

The transition from a macroscopic grape dimer to an integrated quantum chip requires precise material engineering and fabrication, all available in-house at 6CCVD:

Custom Dimensions and Thickness: The paper highlights the need for precise resonator dimensions (e.g., 27 mm major axis). 6CCVD provides custom diamond plates and wafers up to 125 mm (PCD) and substrates up to 10 mm thick, allowing researchers to optimize the dielectric geometry for specific resonance frequencies (e.g., 2.87 GHz).
Precision Fabrication: We offer advanced laser cutting and shaping services to create complex dielectric geometries (spherical, ellipsoidal, or toroidal) directly from SCD or PCD, ensuring high dimensional accuracy for predictable MDR performance.
On-Chip MW Circuitry: The experiment used an external copper wire antenna. For integrated quantum systems, 6CCVD offers custom metalization services (Au, Pt, Pd, Ti, W, Cu) to deposit low-loss microwave transmission lines (e.g., CPW or microstrip resonators) directly onto the diamond surface, maximizing coupling efficiency to the N-V spins.
Superior Surface Finish: Achieving high-quality optical readout (ODMR) requires minimal scattering. 6CCVD guarantees ultra-low surface roughness: Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD.

Engineering Support

6CCVD’s in-house team of PhD material scientists and quantum engineers can assist researchers in selecting the optimal diamond grade (SCD vs. PCD), thickness, and surface preparation required for similar MW Resonator and Solid-State Maser projects. We provide global shipping (DDU default, DDP available) for rapid deployment of custom materials worldwide.

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

View Original Abstract

Two grapes irradiated inside a microwave (MW) oven typically produce a series of sparks and can ignite a violent plasma. The underlying cause of the plasma has been attributed to the formation of morphological-dependent resonances (MDRs) in the aqueous dielectric dimers that lead to the generation of a strong evanescent MW hotspot between them. Previous experiments have focused on the electric field component of the field as the driving force behind the plasma ignition. Here we couple an ensemble of nitrogen-vacancy (N-<a:math xmlns:a=“http://www.w3.org/1998/Math/MathML” display=“inline” overflow=“scroll”><a:mi>V</a:mi></a:math>) spins in nanodiamonds (NDs) to the magnetic field component of the dimer MW field. We demonstrate the efficient coupling of the N-<d:math xmlns:d=“http://www.w3.org/1998/Math/MathML” display=“inline” overflow=“scroll”><d:mi>V</d:mi></d:math> spins to the MW magnetic field hotspot formed between the grape dimers using optically detected magnetic resonance (ODMR). The ODMR measurements are performed by coupling N-<g:math xmlns:g=“http://www.w3.org/1998/Math/MathML” display=“inline” overflow=“scroll”><g:mi>V</g:mi></g:math> spins in NDs to the evanescent MW fields of a copper wire. When placing a pair of grapes around the NDs and matching the ND position with the expected magnetic field hotspot, we see an enhancement in the ODMR contrast by more than a factor of 2 compared to the measurements without grapes. Using finite-element modeling, we attribute our experimental observation of the field enhancement to the MW hotspot formation between the grape dimers. The present study not only validates previous work on understanding grape-dimer resonator geometries, but it also opens up another avenue for exploring alternative MW resonator designs for quantum technologies. Published by the American Physical Society 2024

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevapplied.22.064078