NV-plasmonics - modifying optical emission of an NV− center via plasmonic metal nanoparticles

At a Glance

Metadata	Details
Publication Date	2022-10-19
Journal	Nanophotonics
Authors	Harini Hapuarachchi, Francesco Campaioli, Jared H. Cole
Institutions	RMIT University, Quantum (Australia)
Citations	13
Analysis	Full AI Review Included

Technical Documentation & Analysis: NV-Plasmonics for Enhanced Quantum Emitters

Reference Paper: Hapuarachchi et al., “NV-plasmonics: modifying optical emission of an NV- center via plasmonic metal nanoparticles,” Nanophotonics 2 022; 11(21): 4919-4927.

Executive Summary

This research validates a critical pathway for enhancing the performance of Nitrogen-Vacancy (NV^-) centers in diamond, a key limitation for scaling quantum technologies. The core findings and value proposition are summarized below:

Performance Breakthrough: Demonstrated that coupling NV centers with plasmonic metal nanoparticles (MNPs) significantly enhances optical emission, overcoming the inherent limitation of low brightness in NV sensing applications.
Quantified Enhancement: Achieved up to 6 times enhancement in total NV emission intensity and a 7.5 times increase in the excited state decay rate at room temperature using a 30 nm radius Gold Nanoparticle (AuNP).
Tunability and Control: The theoretical model confirms the ability to precisely control NV fluorescence (both enhancement and suppression) by tuning parameters including MNP type (Au, Ag), size, NV orientation, and the permittivity of the submerging medium (Air, Water, PMMA).
Modeling Validation: Developed a rigorous theoretical model incorporating ³E vibronic levels and Generalized Nonlocal Optical Response (GNOR) theory, successfully explaining existing experimental measurements in both the presence and absence of MNPs.
Application Potential: This technology enables the development of higher precision quantum sensors (magnetometry, thermometry) and scalable nanophotonic devices operating in the near-infrared therapeutic window (650-900 nm).
6CCVD Material Requirement: Replication and scaling of this research require ultra-high purity, low-strain Single Crystal Diamond (SCD) substrates, which 6CCVD provides with custom dimensions and integrated metalization capabilities.

Technical Specifications

The following hard data points were extracted from the analysis of the NV-MNP hybrid system:

Parameter	Value	Unit	Context
NV Emission Enhancement	~6	Times	Optimal NV^--AuNP configuration (R = 38 nm)
Excited State Decay Rate Enhancement	~7.5	Times	Optimal NV^--AuNP configuration
Zero Phonon Line (ZPL) Enhancement	~6	Times	Compared to isolated NV center
Optimal NV-MNP Separation (R)	38	nm	Center-to-center separation
Gold Nanoparticle Radius (r_m)	30	nm	Used for optimal enhancement
Silver Nanoparticle Radius (r_m)	7	nm	Used for plasmon resonance study
Input Laser Wavelength	532	nm	Green excitation source
NV Emission Wavelength Range	650-900	nm	Near-infrared therapeutic window
Operating Environment	Room	Temperature	Ambient conditions
Submerging Medium Refractive Index (n)	1.0, 1.33, 1.495	N/A	Air, Water, and PMMA, respectively
NV Center Optical States Modeled	³A₂ (Ground), ³E (Excited)	N/A	Multi-level atom model including vibronic levels

Key Methodologies

The theoretical and experimental approach focused on modeling and validating the complex exciton-plasmon interaction at the nanoscale:

NV Center Abstraction: The NV center was modeled as a multi-level open quantum system, incorporating $n + 1$ vibronic levels in the ³A₂ ground state and two excited states (including the upper ³E vibronic state) to account for radiative and nonradiative losses via Lindblad operators.
Hybrid Hamiltonian Development: A laboratory reference frame NV Hamiltonian was derived, assuming dipole-dipole interaction between the NV center and the MNP, which accounts for the total effective electric field ($E_{tot}$) experienced by the NV center.
Plasmonic Response Modeling: The polarizability $\alpha(\omega_d)$ of the MNPs was calculated using the Generalized Nonlocal Optical Response (GNOR) theory to accurately capture finite size and nonlocal effects, particularly for small nanoparticles.
Nonlinear System Solution: The nonlinear evolution of the NV density matrix was solved using a computationally efficient piecewise superoperator procedure in a rotating reference frame, incorporating decoherence mechanisms and MNP-induced modifications to both the local electric field and decay rates.
Experimental Replication: The model was validated against existing experimental data involving a nanodiamond hosting a single NV center coupled to a 30 nm radius AuNP on an inverted confocal microscope platform, illuminated by a 532 nm laser.
Parameter Sweeps: Systematic investigation was performed by sweeping MNP radius ($r_m$), NV-MNP separation ($R$), external field polarization angle ($\theta$), and submerging medium permittivity ($\epsilon_b$) to optimize emission control.

6CCVD Solutions & Capabilities

This research confirms the critical role of high-quality diamond substrates and precise material engineering in advancing NV-based quantum technologies. 6CCVD is uniquely positioned to supply the foundational materials and custom fabrication services required to replicate, scale, and extend this work into integrated devices.

Applicable Materials

To achieve the high coherence and low strain necessary for optimal NV center performance and plasmonic coupling, researchers require the highest quality diamond:

Electronic Grade Single Crystal Diamond (SCD): Essential for controlled NV creation (via implantation/annealing) and ensuring long spin coherence times. 6CCVD provides SCD with ultra-low nitrogen content and minimal strain, crucial for maximizing the quantum efficiency (QE) of the NV center.
Custom Nanodiamond Precursors: For applications requiring NV centers embedded in nanodiamonds (as used in the paper), 6CCVD can supply high-purity SCD material suitable for subsequent milling or etching processes to create optimized nanodiamond particles.

Customization Potential for Integrated Devices

The paper highlights the need for precise nanoscale control over the NV-MNP geometry. 6CCVD offers comprehensive customization capabilities to transition this research from proof-of-concept to integrated quantum devices:

Research Requirement	6CCVD Solution & Capability	Technical Advantage
Integrated Plasmonic Structures	Custom Metalization Services	Internal capability to deposit Au, Ag, Ti, Pt, Pd, W, or Cu layers directly onto the diamond surface, enabling the fabrication of patterned MNPs or plasmonic waveguides in situ.
Optimized Optical Interface	Ultra-Smooth Polishing	SCD polishing to Ra < 1 nm minimizes surface scattering losses, critical for efficient coupling of the 532 nm excitation and the 650-900 nm NV emission.
Scalable Sensor Arrays	Large Area PCD/SCD Wafers	Supply of plates/wafers up to 125 mm (PCD) and custom SCD substrates (up to 500 µm thick) for developing high-density arrays of enhanced NV sensors.
Thin Membrane Fabrication	Custom Thickness Control	SCD and PCD thicknesses ranging from 0.1 µm to 500 µm, allowing for the creation of thin diamond membranes necessary for specific optical coupling geometries or high-numerical aperture collection.

Engineering Support

The optimization of NV-plasmonic systems depends heavily on material properties (strain, surface termination, nitrogen concentration) and precise metal layer design.

Consultation on Material Selection: 6CCVD’s in-house PhD team specializes in MPCVD growth and defect engineering, offering expert consultation on optimizing diamond material parameters (e.g., nitrogen concentration, surface termination) for similar NV-Plasmonic Quantum Sensing projects.
Global Logistics: We ensure reliable, global delivery of sensitive materials, with DDU default shipping and DDP options available worldwide.

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

View Original Abstract

Abstract The nitrogen-vacancy (NV) center in diamond is very sensitive to magnetic and electric fields, strain, and temperature. In addition, it is possible to optically interrogate individual defects, making it an ideal quantum-limited sensor with nanoscale resolution. A key limitation for the application of NV sensing is the optical brightness and collection efficiency of these defects. Plasmonic resonances of metal nanoparticles have been used in a variety of applications to increase the brightness and efficiency of quantum emitters, and therefore are a promising tool to improve NV sensing. However, the interaction between NV centers and plasmonic structures is largely unexplored. In particular, the back-action between NV and plasmonic nanoparticles is nonlinear and depends on optical wavelength, nanoparticle position, and metal type. Here we present the general theory of NV-plasmonic nanoparticle interactions. We detail how the interplay between NV response, including optical and vibrational signatures, and the plasmonic response of the metal nanoparticle results in modifications to the emission spectra. Our model is able to explain quantitatively the existing experimental measurements of NV centers near metal nanoparticles. In addition, it provides a pathway to developing new plasmonic structures to improve readout efficiencies in a range of applications for the NV center. This will enable higher precision sensors, with greater bandwidth as well as new readout modalities for quantum computing and communication.

Tech Support

Original Source

DOI: https://doi.org/10.1515/nanoph-2022-0429