Fabrication of oriented NV center arrays in diamond via femtosecond laser writing and reorientation

At a Glance

Metadata	Details
Publication Date	2025-09-23
Journal	Frontiers in Quantum Science and Technology
Authors	Kai Klink, Andrew Kirkpatrick, Yukihiro Tadokoro, Jonas N. Becker, Shannon Singer Nicley
Analysis	Full AI Review Included

Technical Documentation & Analysis: Deterministic NV Center Alignment via Femtosecond Laser Reorientation

This document analyzes the research paper “Fabrication of oriented NV center arrays in diamond via femtosecond laser writing and reorientation” (Klink et al., 2025) and outlines how 6CCVD’s advanced MPCVD diamond materials and processing capabilities directly support and enable the scalability of this critical quantum technology.

Executive Summary

The research successfully demonstrates an all-optical method for achieving deterministic orientation control of single Nitrogen-Vacancy (NV) centers in diamond, a breakthrough essential for high-performance quantum sensing and computing.

Deterministic Orientation Control: Achieved post-fabrication alignment of laser-written NV centers along specific crystallographic axes (e.g., [111] parallel to the optical axis) using femtosecond laser annealing and in situ polarization analysis.
Enhanced Sensitivity: Alignment along the optical axis maximizes light collection efficiency (37% to 44% relative improvement demonstrated), potentially leading to a factor of four increase in magnetic sensitivity compared to randomly oriented arrays.
Scalable Fabrication: The method preserves the high spatial precision of ultrafast laser writing, enabling the scalable fabrication of uniformly oriented NV- arrays (10 µm pitch demonstrated).
Material Requirements: Success relies on high-quality Single Crystal Diamond (SCD) substrates with precise control over crystallographic orientation ((100) and (111)) and substitutional nitrogen content (10 ppb to 80 ppb).
Single Emitter Confirmation: Fabricated centers were confirmed as single emitters with high purity (background-corrected g²(0) as low as 0.1).
6CCVD Value Proposition: 6CCVD provides the necessary Optical Grade SCD substrates, custom nitrogen doping, and ultra-low surface roughness polishing (Ra < 1 nm) required to replicate and scale this advanced defect engineering technique.

Technical Specifications

The following hard data points were extracted from the methodology and results sections, highlighting the precision required for successful NV center reorientation.

Parameter	Value	Unit	Context
Substrate Orientation Tested	(111) and (100)	N/A	Required for orientation-dependent polarization analysis
(111) Substrate Nitrogen Content	10	ppb	HPHT grown, used for NV source
(100) Substrate Nitrogen Content	80	ppb	CVD grown, used for NV source
(100) Substrate Surface Roughness (Ra)	1	nm	Critical for high-NA oil immersion objective
Objective Numerical Aperture (NA)	1.45	N/A	Oil immersion objective used for writing and detection
Fabrication Laser Wavelength	515	nm	Yb:KYW laser source
Seed Pulse Duration	270	fs	Used for initial vacancy generation
Diffusion Pulse Energy	1.19	nJ	Used for reorientation/annealing
NV Center Fabrication Depth	20	µm	Depth chosen to minimize surface effects
Array Pitch	10	µm	Spacing of the fabricated NV array
Single Photon Purity (g²(0))	0.1 to 0.25	N/A	Confirmed single NV- center emission
Collection Efficiency Improvement	37.2 to 44.3	%	Relative difference between aligned (NV1) and misaligned (NV2) centers

Key Methodologies

The experiment utilized a highly controlled, multi-step process combining ultrafast laser writing, in situ confocal microscopy, and polarization analysis.

Substrate Preparation: High-quality SCD diamond substrates (both (111) and (100) orientations) were selected, featuring controlled substitutional nitrogen content (10 ppb to 80 ppb) and precision polishing (Ra < 5 nm).
Aberration-Corrected Laser Writing: A home-built system using 515 nm, 270 fs pulses and a Spatial Light Modulator (SLM) compensated for spherical aberration caused by the diamond’s high refractive index.
NV Center Formation: Vacancies were generated by a high-energy seed pulse (1.47 nJ) via multiphoton ionization, followed by a 200 kHz train of lower-energy diffusion pulses (1.19 nJ) to mobilize vacancies until they combined with substitutional nitrogen to form an NV- center.
In Situ Orientation Detection: A confocal microscope (532 nm CW excitation) monitored fluorescence. Polarization analysis, achieved by rotating a 1/2 waveplate in front of a polarizing beam splitter, determined the NV center’s initial crystallographic orientation based on the emission pattern.
All-Optical Reorientation: If the initial orientation was undesirable, an additional diffusion pulse train (femtosecond laser annealing) was applied. This process stochastically dissociates and reforms the NV center, causing reorientation.
Iterative Alignment: Polarization measurements were repeated until the desired orientation (e.g., [111] parallel to the optical axis) was achieved, confirming deterministic alignment.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-specification diamond materials required to scale this femtosecond laser defect engineering technique for commercial and research applications.

Applicable Materials

To replicate and extend this research, 6CCVD recommends Optical Grade Single Crystal Diamond (SCD) with customized specifications:

Material: Optical Grade SCD (High Purity, Low Birefringence).
Orientation: Standard (100) and (111) wafers, or custom miscut angles (e.g., 3° or 4° miscut) to match specific experimental geometries.
Nitrogen Doping: Custom Doping Specifications are essential. We provide precise control over substitutional nitrogen concentration (N_s) during MPCVD growth, enabling researchers to optimize NV yield in the 10 ppb to 80 ppb range demonstrated in the paper.

Material and Processing Capabilities for Quantum Defect Engineering

Research Requirement	6CCVD Solution & Capability	Technical Advantage
Ultra-Low Surface Roughness (Ra < 1 nm to 5 nm)	Precision Polishing Service	We guarantee Ra < 1 nm for SCD wafers, minimizing optical scatter and ensuring optimal coupling efficiency for high-NA oil immersion objectives (1.45 NA).
Custom Substrate Thickness (20 µm NV depth)	Custom Thickness Control	SCD plates available from 0.1 µm to 500 µm, and substrates up to 10 mm thick, allowing precise control over the working distance and minimizing lensing effects.
Scalable Array Fabrication (10 µm pitch)	Large Format Diamond Supply	We offer SCD wafers and Polycrystalline Diamond (PCD) plates up to 125 mm in diameter, enabling the fabrication of large, high-density, uniformly oriented NV arrays.
Integrated Quantum Circuits (Future Need)	Custom Metalization Services	Internal capability for depositing Au, Pt, Pd, Ti, W, and Cu films. This is crucial for integrating NV arrays with microwave antennas or photonic structures.
Global Supply Chain	Global Shipping (DDU/DDP)	Reliable, insured global delivery ensures researchers receive high-value materials quickly and efficiently.

Engineering Support

6CCVD’s in-house PhD team specializes in diamond defect engineering and material optimization for quantum applications. We offer consultation services to assist researchers in:

Material Selection: Choosing the optimal SCD grade and nitrogen concentration (N_s) to maximize NV- yield and coherence time for specific femtosecond laser writing recipes.
Surface Preparation: Defining polishing specifications and miscut angles necessary for advanced optical coupling and minimizing strain.
Customization: Designing unique diamond geometries or metalization patterns required for integrating oriented NV arrays into photonic quantum technologies or vector magnetometry devices.

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

View Original Abstract

Introduction Nitrogen-vacancy (NV) centers in diamond are widely recognized as highly promising solid-state quantum sensors due to their long room temperature coherence times and atomic-scale size, which enable exceptional sensitivity and nanoscale spatial resolution under ambient conditions. Ultrafast laser writing has demonstrated the deterministic spatial control of individual NV − centers, however, the resulting random orientation of the defect axis limits the magnetic field sensitivity and signal contrast. Methods We developed an all-optical approach for reorienting laser-written NV − centers to lie along a specific crystallographic axis using femtosecond laser annealing. The orientation is determined by polarization analysis, and the annealing and subsequent polarization analysis are repeated until the desired orientation is observed. Results Our method achieves deterministic alignment of NV − centers along the optical axis in (111)-oriented diamond substrates and allows selection between two observable orientation classes in (100)-oriented substrates. The reorientation preserves spatial ordering while producing uniform orientation across arrays of NV − centers. Discussion This approach enables scalable fabrication of orientation-controlled NV − arrays, and paves the way for scalable, high performance quantum devices based on orientation-controlled NV − centers.

Tech Support

Original Source

DOI: https://doi.org/10.3389/frqst.2025.1667545

References

2008 - Nanoscale imaging magnetometry with diamond spins under ambient conditions [Crossref]
2023 - All-optical nuclear quantum sensing using nitrogen-vacancy centers in diamond [Crossref]
2019 - A ten-qubit solid-state spin register with quantum memory up to one minute [Crossref]
2018 - Probing condensed matter physics with magnetometry based on nitrogen-vacancy centres in diamond [Crossref]
2017 - Laser writing of coherent colour centres in diamond [Crossref]
2019 - Laser writing of individual nitrogen-vacancy defects in diamond with near-unity yield [Crossref]
2024 - Laser activation of single group-iv colour centres in diamond [Crossref]
2014 - Complete determination of the orientation of NV centers with radially polarized beams [Crossref]
2011 - Electric-field sensing using single diamond spins [Crossref]
2012 - Production of oriented nitrogen-vacancy color centers in synthetic diamond [Crossref]