Coupling nitrogen-vacancy center spins in diamond to a grape dimer
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-12-19 |
| Journal | Physical Review Applied |
| Authors | Ali Fawaz, Sarath Raman Nair, Thomas Volz |
| Institutions | Macquarie University, ARC Centre of Excellence for Engineered Quantum Systems |
| Citations | 2 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research validates the use of high-permittivity dielectric resonators, specifically grape dimers, as highly efficient concentrators for microwave (MW) magnetic fields, enabling enhanced coupling to solid-state quantum systems.
- Core Achievement: Demonstrated efficient coupling between an ensemble of Nitrogen-Vacancy (N-V) spins in nanodiamonds (NDs) and the magnetic field component of the MW hotspot formed between two grapes.
- Performance Metric: Optically Detected Magnetic Resonance (ODMR) contrast was enhanced by more than a factor of 2 when the N-V spins were placed in the grape dimer gap compared to the bare antenna setup.
- Field Amplification: The experimental magnetic field amplification factor (Bgrapes/Bno grapes) was estimated at 2.1 ± 0.4. Finite-Element Method (FEM) simulations confirmed amplification factors ranging from 1.9 to 6.2, depending on material absorption.
- Mechanism: The field enhancement is caused by Morphological-Dependent Resonances (MDRs) within the high-dielectric aqueous medium (Re(Δr) â 80 at 2.5 GHz), which concentrates the MW energy into a strong evanescent magnetic field hotspot in the gap.
- Resonator Characteristics: The simulated resonance occurred at 2.855 GHz with a Q factor of approximately 114, demonstrating a compact, water-based cavity design.
- Engineering Implication: This study provides a foundation for designing compact, high-permittivity dielectric MW resonators for room-temperature quantum technologies, particularly solid-state maser platforms.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| N-V Ground State Splitting (D) | 2.87 | GHz | MW transition frequency (ms=0 to ms=±1) |
| Simulated Resonance Frequency | 2.855 | GHz | Peak magnetic field response |
| Simulated Q Factor | ~114 | Dimensionless | Calculated from 25 MHz linewidth |
| Experimental Field Amplification | 2.1 ± 0.4 | Ratio | Bgrapes / Bno grapes (2-mm antenna offset) |
| Simulated Field Amplification (Max) | 6.2 | Ratio | Calculated for zero absorption (Im(Δr) = 0i) |
| Water Relative Permittivity (Real) | ~80 | Dimensionless | Re(Δr) at 2.5 GHz |
| Optimal Grape Gap Size (Experimental) | 0.5 | mm | Gap size yielding maximum ODMR contrast |
| Grape Major Axis Length (Model) | 27 | mm | Dimensions used in FEM simulation |
| MW Antenna Diameter | 1 | mm | Vertical straight copper wire |
| Simulated Hotspot FWHM | 6.2 | mm | Full Width at Half Maximum of the magnetic hotspot |
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized a hybrid quantum-classical setup combining solid-state spin sensing with a macroscopic dielectric resonator, verified by electromagnetic simulation.
- Spin Sensor Preparation: Nanodiamonds (NDs) containing N-V centers were affixed to the tip of a multimode optical fiber, serving as the localized magnetic field probe.
- MW Excitation: A 1-mm diameter vertical copper wire, acting as an off-resonant stubbed antenna, was driven by a MW generator (Agilent E8257D) and a 16W amplifier. The antenna was positioned 5 mm orthogonal to the dimer axis.
- Resonator Assembly: Two white seedless grapes (modeled as 27 mm x 17 mm ellipsoids) were placed on a platform, forming a dimer gap (varied from 0.5 mm to 2.0 mm) around the N-V fiber tip.
- ODMR Measurement: N-V spins were optically polarized and excited using a nonresonant green laser. The resulting red fluorescence (600-800 nm) was monitored while sweeping the MW frequency near 2.87 GHz.
- Data Extraction: ODMR profiles were analyzed using a double-inverted Lorentzian fit to determine the contrast, which is directly proportional to the magnetic field coupling strength.
- Numerical Verification (FEM): Finite-Element Method (FEM) simulations (COMSOL 6.0) were performed, modeling the ellipsoidal grape dimers and the dipole antenna source, to map the magnetic field contour and confirm the formation of the MDR-induced hotspot at 2.87 GHz.
- Amplification Calculation: The experimental field amplification factor was calculated by taking the ratio of the extracted ODMR contrast with grapes present versus the contrast measured with the bare antenna setup.
Commercial Applications
Section titled âCommercial ApplicationsâThis research contributes directly to the development of compact, high-efficiency microwave components, particularly in the field of quantum engineering.
- Room-Temperature Masers: Provides a novel design concept for solid-state maser platforms by utilizing high-permittivity dielectric geometries (like water-based or composite materials) to achieve strong spin-field coupling in a compact volume.
- Compact Quantum Sensors: Enables the design of highly sensitive magnetic field sensors based on N-V centers by maximizing the MW driving field strength in a localized area, improving signal-to-noise ratio and efficiency.
- Dielectric Resonator Design: Offers an alternative approach to traditional metal or sapphire MW cavities, focusing on high-refractive-index materials (Δr greater than 80) to create smaller, more integrated resonator structures for microwave photonics.
- Integrated Quantum Circuits: The compactness of the water-based cavity design suggests potential for developing highly integrated, on-chip maser or quantum control platforms.
- Microwave Component Miniaturization: The principles of MDR-based field concentration can be applied to miniaturize various MW components used in satellite technology and communication systems.
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=âhttp://www.w3.org/1998/Math/MathMLâ display=âinlineâ overflow=âscrollâ><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=âhttp://www.w3.org/1998/Math/MathMLâ display=âinlineâ overflow=âscrollâ><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=âhttp://www.w3.org/1998/Math/MathMLâ display=âinlineâ overflow=âscrollâ><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