Low-Charge-Noise Nitrogen-Vacancy Centers in Diamond Created Using Laser Writing with a Solid-Immersion Lens

At a Glance

Metadata	Details
Publication Date	2021-06-03
Journal	ACS Photonics
Authors	Viktoria Yurgens, Josh A. Zuber, Sigurd Flågan, Marta De Luca, Brendan Shields
Institutions	University of Warsaw, University of Basel
Citations	42
Analysis	Full AI Review Included

Technical Documentation & Analysis: Low Charge-Noise NV Centers via t-SIL Laser Writing

Executive Summary

This research demonstrates a breakthrough in creating high-quality, low charge-noise Nitrogen-Vacancy (NV) centers in bulk diamond using femtosecond pulsed laser writing facilitated by a truncated solid-immersion lens (t-SIL). This technique is critical for advancing solid-state quantum systems.

Record Low Charge Noise: The resulting NV centers exhibit exceptionally narrow optical linewidths, with means ranging from 62.1 MHz to 74.5 MHz, approaching the lifetime limit (~13 MHz).
High Yield of Coherent Emitters: Up to 92.3% of the created NV centers demonstrated inhomogeneous broadening below the critical 100 MHz threshold required for high-fidelity two-photon quantum interference.
Tunneling Breakdown Regime: The use of the t-SIL enabled vacancy creation at ultra-low pulse energies (down to 5.8 nJ), operating in the tunneling breakdown regime ($\gamma \ll 1$), which minimizes lattice damage and surface graphitization.
Depth Control and Bulk Processing: NV centers were successfully created across the full depth of the 40 µm bulk diamond sample (1 µm to 40 µm from the surface).
6CCVD Material Relevance: The methodology relies on ultra-high purity, electronic-grade Single Crystal Diamond (SCD) substrates, a core offering of 6CCVD, essential for replicating and scaling this low-noise quantum platform.

Technical Specifications

The following hard data points were extracted from the research paper, detailing the performance and processing parameters of the NV center creation.

Parameter	Value	Unit	Context
Mean Optical Linewidth (Samples A/B)	62.1	MHz	Inhomogeneous broadening, low charge noise
Linewidth Probability (< 100 MHz)	Up to 92.3	%	ECDF metric for quantum coherence
Minimum Laser Pulse Energy	5.8	nJ	Threshold for vacancy creation in bulk diamond
Laser Wavelength	800	nm	Femtosecond pulsed laser source
Pulse Duration	~35	fs	Used for laser writing
NV Creation Depth Range	1 to 40	µm	Achieved across the full depth of the substrate
Annealing Temperature	1100	°C	Post-processing step for NV formation
Diamond Substrate Thickness	40	µm	Electronic-grade SCD
Native Nitrogen Concentration ([N])	< 5	ppb	Ultra-low purity requirement
Resultant Numerical Aperture (NA)	~1.8	N/A	Achieved using t-SIL and standard objective

Key Methodologies

The creation of low charge-noise NV centers relies on precise control over the laser-writing environment and subsequent thermal processing.

Material Selection: Use of 40 µm thick, electronic-grade Single Crystal Diamond (SCD) with ultra-low native nitrogen concentration ([N] < 5 ppb).
Optical Setup: Implementation of a truncated hemispherical cubic zirconia Solid-Immersion Lens (t-SIL, n=2.14) combined with a standard air objective (NA=0.85 or 0.9) to maximize the resultant NA (~1.8) and minimize spherical aberration.
Laser Writing Parameters: Irradiation using 800 nm, ~35 fs femtosecond laser pulses, tuned to operate in the tunneling breakdown regime ($\gamma \ll 1$) at energies as low as 5.8 nJ per pulse.
Depth Control: Precise focusing of the laser beam at controlled depths (1 µm to 40 µm) below the diamond surface, enabled by the t-SIL to prevent surface graphitization.
Thermal Annealing: Post-irradiation annealing of the diamond samples in vacuum at 1100 °C for three hours to mobilize vacancies, allowing them to combine with native nitrogen impurities to form NV centers.
Characterization: Linewidth measurement via Photoluminescence Excitation (PLE) scans in a liquid helium bath cryostat, utilizing a 532 nm repump laser for charge-state stabilization.

6CCVD Solutions & Capabilities

The success of this research hinges on the availability of high-quality, ultra-pure diamond material and the ability to customize dimensions for subsequent device integration. 6CCVD is uniquely positioned to supply the necessary materials and engineering services to replicate and extend this work into scalable quantum devices.

Applicable Materials

To replicate the low charge-noise environment demonstrated in this paper, researchers require the highest purity diamond available.

6CCVD Material	Specification	Application Relevance
High-Purity SCD	[N] < 5 ppb, Electronic Grade	Direct match for the substrate used in the study. Essential for minimizing parasitic defects and charge noise.
Optical Grade SCD	Ra < 1 nm polishing	Required for high-fidelity optical coupling and integration into Fabry-Perot microcavities (the stated future goal of the research).
Custom Thickness SCD	0.1 µm to 500 µm	Necessary for thinning bulk diamond into few-micron-thick membranes for photonic integration and cavity QED experiments.

Customization Potential

The research highlights the need for integrating these high-quality NV centers into photonic devices, which requires specialized material preparation. 6CCVD’s advanced fabrication capabilities directly address these requirements:

Custom Dimensions and Thickness: The paper notes that future work requires thinning the diamond down to a few-micron-thick membrane. 6CCVD provides custom SCD plates and wafers with thicknesses ranging from 0.1 µm up to 500 µm, allowing researchers to specify the exact membrane thickness needed for optimal cavity coupling.
Advanced Polishing: Achieving high-quality optical interfaces is paramount. 6CCVD guarantees Ra < 1 nm surface roughness on SCD, ensuring minimal scattering losses when integrating t-SILs or fabricating microcavities.
Metalization Services: While the paper focuses on NV creation, future device integration (e.g., for electrodes or contacts) will require metal layers. 6CCVD offers in-house custom metalization including Au, Pt, Pd, Ti, W, and Cu, tailored to specific device geometries.

Engineering Support

The successful creation of NV centers in the tunneling breakdown regime is highly sensitive to material purity and crystal quality. 6CCVD’s in-house PhD team specializes in MPCVD growth parameters and material selection for quantum applications.

Material Consultation: Our experts can assist researchers in selecting the optimal SCD purity and orientation for similar quantum sensing and spin-photon entanglement projects, ensuring the lowest possible native defect density.
Global Logistics: 6CCVD supports global research efforts with reliable Global Shipping (DDU default, DDP available), ensuring prompt delivery of custom diamond materials worldwide.

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

View Original Abstract

We report on pulsed-laser-induced generation of nitrogen-vacancy (NV) centers in diamond facilitated by a solid-immersion lens (SIL). The SIL enables laser writing at energies as low as 5.8 nJ per pulse and allows vacancies to be formed close to a diamond surface without inducing surface graphitization. We operate in the previously unexplored regime, where lattice vacancies are created following tunneling breakdown rather than multiphoton ionization. We present three samples in which NV center arrays were laser-written at distances between similar to 1 and 40 mu m from a diamond surface, all presenting narrow distributions of optical linewidths with means between 62.1 and 74.5 MHz. The linewidths include the effect of long-term spectral diffusion induced by a 532 nm repump laser for charge-state stabilization, thereby emphasizing the particularly low-charge-noise environment of the created color centers. Such high-quality NV centers are excellent candidates for practical applications employing two-photon quantum interference with separate NV centers. Finally, we propose a model for disentangling power broadening from inhomogeneous broadening in the NV center optical linewidth.

Tech Support

Original Source

DOI: https://doi.org/10.1021/acsphotonics.1c00274