Practical Applications of Quantum Sensing - A Simple Method to Enhance the Sensitivity of Nitrogen-Vacancy-Based Temperature Sensors

At a Glance

Metadata	Details
Publication Date	2020-05-22
Journal	Physical Review Applied
Authors	Ekaterina Moreva, E. Bernardi, P. Traina, Sosso A, S. Ditalia Tchernij
Institutions	Istituto Nazionale di Fisica Nucleare, Sezione di Torino, Australian Nuclear Science and Technology Organisation
Citations	35
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Sensitivity NV Thermometry

This document analyzes the research paper “Practical applications of quantum sensing: a simple method to enhance sensitivity of Nitrogen-Vacancy-based temperature sensors” and outlines how 6CCVD’s advanced MPCVD diamond materials and processing capabilities can support, replicate, and extend this critical quantum sensing research.

Executive Summary

Core Achievement: Demonstration of a novel continuous-wave (CW) optically detected magnetic resonance (ODMR) technique utilizing Nitrogen-Vacancy (NV) centers in diamond for high-sensitivity thermometry.
Sensitivity Record: Achieved an unprecedented temperature sensitivity of 4.8 mK/Hz^1/2 in micro/nanoscale volumes (~1 µm³), comparable to the theoretical CW shot-noise limit.
Methodology: The technique employs a Transverse Magnetic Field (TF) regime, which suppresses the ¹⁴N hyperfine splitting, resulting in enhanced ODMR contrast and reduced linewidth.
Noise Resilience: Crucially, the TF method protects the measurement from environmental magnetic noise fluctuations, a major limitation in standard NV sensing protocols (e.g., Simultaneous Hyperfine Driving, SHfD).
Material Basis: The sensor utilized a low-nitrogen, low-boron CVD Single Crystal Diamond (SCD) substrate (3x3x0.3 mm³) with a shallow, implanted NV layer (~10 nm thick).
Application Potential: This simple, robust, and highly sensitive technique is ideal for advancing quantum-assisted temperature sensing, particularly in nanoscale thermometry and biocompatible biosensing applications.

Technical Specifications

The following hard data points were extracted from the experimental results and material parameters:

Parameter	Value	Unit	Context
Temperature Sensitivity (TF Regime)	4.8 ± 0.4	mK/Hz^1/2	Achieved noise floor in ~1 µm³ sensing volume
Sensitivity Enhancement (vs. SHfD)	~3	Factor	Improvement achieved by TF method
CW Shot-Noise Limit (Calculated)	4.7	mK/Hz^1/2	Theoretical physical limit for the setup
Zero-Field Splitting (D_gs)	~2.87	GHz	At room temperature
Temperature Dependence (c_T)	-74.2	kHz/K	Calibrated value for ZFS shift
Diamond Substrate Dimensions	3 x 3 x 0.3	mm³	Element Six CVD sample used
Substitutional Nitrogen Concentration	< 1	ppm	Required purity for SCD material
Boron Concentration	< 0.05	ppm	Required purity for SCD material
¹⁴N⁺ Implantation Energy	10	keV	Used to create shallow NV layer
Implantation Fluence	10¹⁴	ions/cm²	Density of implanted ions
Annealing Temperature	950	°C	Post-implantation thermal treatment
Bulk Thermal Conductivity (Diamond)	2500	W·m^-1·K^-1	Used for temperature reference comparison

Key Methodologies

The experiment successfully demonstrated enhanced NV thermometry sensitivity using a simplified CW ODMR setup in a transverse magnetic field regime.

Material Selection and Preparation:
- Used a high-purity CVD Single Crystal Diamond (SCD) substrate (3x3x0.3 mm³) with extremely low concentrations of substitutional nitrogen (N < 1 ppm) and boron (B < 0.05 ppm).
NV Center Fabrication:
- A shallow NV layer (~10 nm thick) was created via 10 keV ¹⁴N⁺ ion implantation at a fluence of 10¹⁴ ions/cm².
- The sample was subsequently annealed at 950 °C for 2 hours to activate the NV centers.
Optical and Microwave Setup:
- Confocal inverted microscope setup adapted for single-photon sensitivity.
- Excitation provided by a 532 nm Nd:YAG laser (80 mW power) focused via an air objective (NA=0.67).
- Microwave (MW) control signal delivered via a custom planar ring antenna designed for the 2.87 GHz spin resonance frequency.
Transverse Field (TF) Sensing Regime:
- A permanent magnet provided a static magnetic field (B_⊥, approximately 6 mT) oriented orthogonally (transverse) to the NV axis.
- This orientation degenerates the hyperfine structure, resulting in higher ODMR contrast and narrower spectral width (Fig. 1).
Lock-In Detection Protocol:
- CW ODMR was performed using a Lock-In Amplifier (LIA) with frequency modulation (f_mod = 1009 Hz, depth 0.6 MHz).
- The MW frequency was fixed at the center of the resonance (where the LIA signal crosses zero) to provide the maximum temperature response slope.
Noise Characterization:
- The TF regime demonstrated superior resilience to environmental magnetic noise, showing the peak corresponding to an injected 25 Hz oscillating magnetic field to be one order of magnitude less prominent than in the standard SHfD method (Fig. 4).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-quality MPCVD diamond materials and custom processing required to replicate, optimize, and scale this high-sensitivity quantum thermometry research.

Research Requirement	6CCVD Solution & Value Proposition
High-Purity SCD Substrates	Optical Grade Single Crystal Diamond (SCD): We supply low-strain SCD wafers with guaranteed purity (N < 1 ppm, B < 0.05 ppm) essential for long NV coherence times and high-contrast ODMR. Available in thicknesses from 0.1 µm to 500 µm.
Custom Dimensions & Thickness	Precision Sizing: The paper used a 3x3 mm² plate. 6CCVD offers custom plates and wafers up to 125 mm in diameter (PCD) and precision laser cutting for SCD plates to match any experimental footprint. Substrates up to 10 mm thick are available.
Shallow NV Layer Integration	Substrate Preparation for Implantation: We provide ultra-smooth, polished SCD substrates (Ra < 1 nm) optimized for subsequent shallow ion implantation (like the 10 keV ¹⁴N⁺ process used here). Our in-house PhD team can consult on material specifications (e.g., orientation, surface termination) to maximize NV yield and minimize strain.
Microwave Antenna Integration	Custom Metalization Services: The experiment requires a microwave planar ring antenna. 6CCVD offers internal metalization capabilities (Au, Pt, Pd, Ti, W, Cu) for depositing high-quality conductive layers directly onto the diamond surface, facilitating integrated device fabrication.
Surface Quality for Confocal Setup	Superior Polishing: High optical throughput is critical. Our SCD polishing capability guarantees roughness Ra < 1 nm, minimizing scattering losses and ensuring optimal focusing for high-NA objectives.
Extension to Nanoscale/Intracellular Sensing	Polycrystalline Diamond (PCD) Films: For extending this technique to nanodiamonds or large-area sensing, 6CCVD provides high-quality PCD films up to 125 mm, offering a cost-effective platform for scaling up quantum sensor arrays.

Engineering Support

6CCVD’s in-house team of expert material scientists and PhD engineers specializes in optimizing diamond properties for quantum applications. We offer comprehensive support for material selection, surface preparation, and integration challenges related to high-sensitivity NV thermometry and similar quantum sensing projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. Global shipping (DDU default, DDP available) ensures rapid delivery of critical materials worldwide.

View Original Abstract

Nitrogen-vacancy centers in diamond allow measurement of environment\nproperties such as temperature, magnetic and electric fields at nanoscale\nlevel, of utmost relevance for several research fields, ranging from\nnanotechnologies to bio-sensing. The working principle is based on the\nmeasurement of the resonance frequency shift of a single nitrogen-vacancy\ncenter (or an ensemble of them), usually detected by by monitoring the center\nphotoluminescence emission intensity. Albeit several schemes have already been\nproposed, the search for the simplest and most effective one is of key\nrelevance for real applications. Here we present a new continuous-wave lock-in\nbased technique able to reach unprecedented sensitivity in temperature\nmeasurement at micro/nanoscale volumes (4.8 mK/Hz$^{1/2}$ in $\mu$m$^3$).\nFurthermore, the present method has the advantage of being insensitive to the\nenviromental magnetic noise, that in general introduces a bias in the\ntemperature measurement.\n

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevapplied.13.054057