Utilising NV based quantum sensing for velocimetry at the nanoscale

At a Glance

Metadata	Details
Publication Date	2020-03-24
Journal	Scientific Reports
Authors	D. Cohen, Ramil Nigmatullin, Oded Kenneth, Fedor Jelezko, Maxim Khodas
Institutions	Center for Integrated Quantum Science and Technology, Technion – Israel Institute of Technology
Citations	20
Analysis	Full AI Review Included

Technical Documentation: Nanoscale Velocimetry via NV-Based Quantum Sensing

This document analyzes the requirements and achievements of the research paper “Utilising NV based quantum sensing for velocimetry at the nanoscale” and maps them directly to the advanced material solutions offered by 6CCVD.

Executive Summary

The research demonstrates a novel, non-intrusive quantum sensing method for measuring fluid drift velocity (velocimetry) at the nanoscale, specifically targeting microfluidic and nanofluidic applications.

Core Value Proposition: Proposes a setup utilizing shallow Nitrogen-Vacancy (NV) centers in diamond to sense magnetic noise induced by flowing liquid nuclear spins, enabling velocity estimation near channel boundaries.
Performance Superiority: The NV-based scheme significantly outperforms current fluorescence-based velocimetry methods, remaining effective even when diffusion noise dominates the fluid dynamics.
Sensitivity Enhancement: By utilizing non-Lorentzian analysis of the power spectrum, the technique achieves sensitivity improvements of up to three orders of magnitude in fractional uncertainty compared to standard Lorentzian models.
Critical Material Requirement: Success hinges on the use of high-purity diamond substrates capable of hosting ultra-shallow NV ensembles (optimal depths between 5 nm and 25 nm) with long spin coherence times (T₂).
Key Application: Provides a crucial tool for investigating flow profiles near microfluidic channel boundaries, addressing the fundamental “no-slip” boundary condition debate in nanoscale fluid dynamics.
Measurement Protocols: Velocity is deduced from the power spectrum S(ω) or the magnetic correlation function C(t), depending on the fluid viscosity and the NV coherence time (T₂).

Technical Specifications

The following hard data points were extracted from the analysis of the proposed quantum velocimetry scheme:

Parameter	Value	Unit	Context
Optimal NV Depth (Water)	15	nm	Power spectrum estimation regime
Optimal NV Depth (Oil/Viscous Fluids)	25	nm	Correlation function estimation regime
Assumed NV Coherence Time (T₂)	100	µs	Required for high-sensitivity measurements
Water Self-Diffusion Coefficient (D)	2.3 x 10³	nm²/µs	Standard experimental parameter
Water Nuclei Number Density (n)	33	nm^-3	Standard experimental parameter
Dimensionless Velocity (v=1)	150	mm/s	Corresponds to optimal depth (d=15 nm)
Fractional Uncertainty (Ensemble, Water, 15 nm)	0.15 / sqrt(T * A)	(mm/s) / (µm)²	Achieved using power spectrum method
Sensitivity Improvement Factor (Low Freq.)	Factor of (d/v)²	N/A	Over standard Lorentzian model
Surface Polishing Requirement (SCD)	Ra < 1	nm	Essential for minimizing boundary effects

Key Methodologies

The proposed nanoscale velocimetry scheme relies on advanced quantum sensing techniques applied to fluid dynamics:

NV Center Initialization: Nitrogen-Vacancy (NV) centers in diamond are optically initialized and read out at room temperature, acting as nanoscale magnetometers.
Magnetic Noise Induction: The random motion of nuclear spins within the flowing liquid (e.g., water, oil) induces a fluctuating magnetic field on the shallow NV ensemble.
Decoherence Spectroscopy: The relaxation rate (Γ) of the NV quantum state is measured using decoherence spectroscopy (or spin relaxation), where Γ is proportional to the power spectrum S(ω) of the magnetic noise.
Flow Parameter Deduction: The mean drift velocity (v) and self-diffusion coefficient (D) are deduced by analyzing how the flow dynamics change the width and peak of the power spectrum S(ω) or the decay rate of the magnetic correlation function C(t).
Non-Lorentzian Modeling: To achieve high sensitivity, the analysis moves beyond the standard Lorentzian approximation, incorporating the non-analytic behavior of the power spectrum (decaying as t^-3/2 in the time domain or 1/sqrt(ω/ω_D) at low frequencies) resulting from diffusion dynamics.
Optimal Protocol Selection: Researchers must select between measuring the correlation function (optimal for viscous fluids where T₂ < T_D) or the power spectrum (optimal for low viscosity fluids like water where T₂ > T_D).

6CCVD Solutions & Capabilities

This research highlights the critical need for high-quality, precisely engineered diamond substrates to realize high-performance quantum sensors. 6CCVD is uniquely positioned to supply the necessary materials and customization services to replicate and advance this nanoscale velocimetry technology.

Applicable Materials

To achieve the required long coherence times (T₂ ≈ 100 µs) and controlled NV placement (5 nm to 25 nm depth), High Purity Single Crystal Diamond (SCD) is mandatory.

Material Specification	6CCVD Offering	Relevance to Nanoscale Velocimetry
SCD Substrates	High-purity, low-strain SCD wafers	Essential platform for creating shallow NV centers with maximum spin coherence (long T₂), directly impacting measurement sensitivity.
Thickness Control	SCD plates from 0.1 µm to 500 µm	Provides the necessary bulk material for subsequent precise shallow NV implantation or delta-doping techniques.
Surface Quality	SCD Polishing: Ra < 1 nm	Ultra-smooth surfaces are critical for microfluidic applications, minimizing surface scattering and ensuring that the NV centers are placed in the ideal proximity to the fluid boundary layer.

Customization Potential

The integration of NV quantum sensors into microfluidic infrastructure requires highly specific material engineering, which 6CCVD provides as a standard service:

Custom Dimensions: We offer SCD plates and wafers in custom dimensions, including inch-size PCD wafers up to 125mm, suitable for integration into standard microfluidic platforms and Lab-on-a-Chip devices.
Precision Cutting: Custom laser cutting services ensure precise geometries required for flow channel fabrication and alignment with optical readout systems.
Metalization Services: While the NV sensing is non-intrusive, external microwave or RF driving fields are required for the measurement protocols (e.g., dynamical decoupling). 6CCVD provides in-house metalization capabilities (Au, Pt, Pd, Ti, W, Cu) for creating integrated microwave striplines or electrical contacts directly on the diamond surface.

Engineering Support

The optimal performance of this nanoscale velocimetry technique depends heavily on matching the NV depth (d) to the fluid properties (diffusion time T_D) and the NV coherence time (T₂).

Material Selection Consultation: 6CCVD’s in-house PhD team can assist researchers in defining the precise SCD specifications (e.g., nitrogen concentration, surface orientation, and post-processing requirements) needed to achieve the target T₂ and facilitate the creation of ultra-shallow NV ensembles for similar Microfluidic Flow Analysis projects.
Global Logistics: We ensure reliable global shipping (DDU default, DDP available) of sensitive quantum-grade diamond materials, supporting international research efforts.

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

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41598-020-61095-y