High-Precision Mapping of Diamond Crystal Strain Using Quantum Interferometry

At a Glance

Metadata	Details
Publication Date	2022-02-15
Journal	Physical Review Applied
Authors	Mason C. Marshall, Reza Ebadi, Connor Hart, Matthew Turner, Mark Ku
Institutions	University of Maryland, College Park, University of Delaware
Citations	26
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Precision Diamond Strain Mapping

This document analyzes the research paper “High-precision mapping of diamond crystal strain using quantum interferometry” and outlines how 6CCVD’s advanced MPCVD diamond materials and fabrication services can support, replicate, and extend this cutting-edge quantum sensing research.

Executive Summary

This research establishes a new benchmark for diamond crystal strain measurement, leveraging Nitrogen Vacancy (NV) ensembles and a magnetic-field-insensitive quantum interferometry protocol (strain-CPMG).

Record Sensitivity: Achieved a volume-normalized strain sensitivity of 5(2) x 10^-8/√Hz· µm^-3, representing a two order-of-magnitude improvement over previous work.
Advanced Methodology: Utilized strain-sensitive spin-state interferometry (strain-CPMG) on NV ensembles in high-purity Single Crystal Diamond (SCD).
Dual Imaging Modalities: Demonstrated micron-scale 3D strain mapping using a confocal microscope and high-speed, millimeter-scale wide-field imaging using a Quantum Diamond Microscope (QDM).
Material Requirement: The experiment relied on high-quality, isotopically enriched 99.995% ¹²C CVD SCD with low strain gradients to maximize the strain-CPMG dephasing time (T_D ≈ 20 µs).
Robustness & Extension: The magnetic-field insensitivity of the strain-CPMG technique expands its utility, enabling precise strain measurements in diamonds with higher impurity (e.g., high-N or ¹³C content) where traditional ODMR methods fail.
Key Applications: Provides essential characterization for diamond material engineering, nanofabrication, in situ strain sensing (e.g., diamond anvil cells), and future dark matter detection (WIMPs).

Technical Specifications

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

Parameter	Value	Unit	Context
Volume-Normalized Strain Sensitivity	5(2) x 10^-8	/√Hz· µm^-3	Record sensitivity achieved via strain-CPMG.
Material Purity (Carbon)	99.995%	¹²C	Isotopically purified SCD used for low strain and long T_D.
SCD Dimensions (Chip)	3.4 x 3.4 x 0.1	mm³	Dimensions of the bulk CVD diamond sections A and B.
Ensemble NV Dephasing Time (T₂*)	7.5	µs	Measured using standard Ramsey protocol.
Strain-CPMG Dephasing Time (T_D)	~20	µs	Enhanced coherence time due to magnetic field insensitivity.
Confocal Interrogation Volume	0.54(2)	µm³	Used for quantitative sensitivity characterization.
Axial Spin-Strain Coupling (A₁)	-8.0(5.7)	GHz/strain	Coupling constant for strain component ε_zz.
Planar Spin-Strain Coupling (A₂)	-12.4(4.7)	GHz/strain	Coupling constant for strain components (ε_xx + ε_yy).
QDM Field-of-View (Single Image)	~150 x 150	µm²	Used for high-speed, wide-field strain surveys.
QDM Acquisition Speed	1	second	Time required for high-sensitivity strain imaging per field-of-view.

Key Methodologies

The experiment relied on precise material selection and a specialized quantum control sequence to achieve magnetic-field insensitivity.

Material Selection and Preparation: Used single-crystal CVD bulk diamond (SCD) grown via the {100} orientation, isotopically enriched with ¹²C. NV centers were formed post-growth via electron irradiation and annealing, resulting in densities of 0.3-0.5 ppm.
NV Spin Control: NV ensembles were initialized using a 532 nm green laser and controlled using pulsed microwave (MW) fields broadcast via an omega-loop antenna fabricated on a glass coverslip.
Strain-CPMG Sequence: A modified Carr-Purcell-Meiboom-Gill (CPMG) sequence was employed, optimized for strain sensing. This sequence uses triplets of π-pulses to swap NV populations between the |-1> and |+1> states, ensuring the accumulated phase is independent of the linear magnetic field term (γB_zS_z).
Strain Extraction: The strain-induced energy shift (M_z) was measured by monitoring the interferometric visibility (v) as a function of the common-mode MW detuning (δ_cm).
Confocal Microscopy: A custom-built scanning confocal laser microscope was used to achieve micron-scale spatial resolution and 3D mapping capability, allowing for quantitative characterization of the volume-normalized sensitivity.
Wide-Field Imaging (QDM): A Quantum Diamond Microscope (QDM) with a Heliotis HeliCam C3 lock-in camera was used for fast, wide-field strain surveys (millimeter-scale field-of-view). The XY-normalized visibility (v_XY) protocol was used in the QDM to compensate for laser and MW power inhomogeneity across the large field-of-view.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-specification diamond materials and custom fabrication required to replicate and advance this quantum interferometry research.

Research Requirement/Challenge	6CCVD Solution & Capability	Technical Advantage
High-Purity SCD Material	Optical Grade Single Crystal Diamond (SCD): We supply low-strain, high-coherence SCD wafers and plates, ideal for NV ensemble quantum sensing.	Guarantees the low strain gradients and long T_D necessary to achieve the reported record sensitivity (5 x 10^-8/√Hz· µm^-3).
Custom Dimensions & Thickness	Custom Fabrication Services: Plates/wafers up to 125 mm (PCD) and custom thicknesses: SCD (0.1 µm - 500 µm) and Substrates (up to 10 mm).	Allows researchers to specify exact geometries (e.g., 3.4 x 3.4 x 0.1 mm³ sections) for integration into confocal stages, QDM setups, or high-pressure diamond anvil cells.
Ultra-Smooth Surfaces	Precision Polishing: SCD polishing capability achieving surface roughness Ra < 1 nm.	Essential for minimizing optical scattering and maximizing the signal-to-noise ratio (SNR) required for high-fidelity NV initialization and fluorescence readout.
Integrated MW Structures	Custom Metalization: In-house deposition of standard metals including Au, Pt, Pd, Ti, W, and Cu.	Facilitates the integration of on-chip microwave antennas (like the omega-loop used in the experiment) or electrical contacts for advanced device architectures.
Strain Sensing in Impure Diamonds	Boron-Doped Diamond (BDD) & Polycrystalline Diamond (PCD): The strain-CPMG technique is robust against magnetic inhomogeneity, making it suitable for higher-N or ¹³C content materials.	Enables the use of cost-effective or specialized materials (BDD for electrochemistry, high-N PCD for industrial tools) where strain characterization is critical but high T₂* is not achievable.
Engineering Support	In-House PhD Team Consultation: 6CCVD provides expert engineering support for material selection and specification.	Our team can assist with material selection for similar NV-based strain sensing projects, optimizing NV density and isotopic purity based on the required sensitivity and application environment.

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

View Original Abstract

Crystal strain variation imposes significant limitations on many quantum\nsensing and information applications for solid-state defect qubits in diamond.\nThus, precision measurement and control of diamond crystal strain is a key\nchallenge. Here, we report diamond strain measurements with a unique set of\ncapabilities, including micron-scale spatial resolution, millimeter-scale\nfield-of-view, and a two order-of-magnitude improvement in volume-normalized\nsensitivity over previous work [1], reaching $5(2) \times\n10^{-8}/\sqrt{\rm{Hz}\cdot\rm{\mu m}^3}$ (with spin-strain coupling\ncoefficients representing the dominant systematic uncertainty). We use\nstrain-sensitive spin-state interferometry on ensembles of nitrogen vacancy\n(NV) color centers in single-crystal CVD bulk diamond with low strain\ngradients. This quantum interferometry technique provides insensitivity to\nmagnetic-field inhomogeneity from the electronic and nuclear spin bath, thereby\nenabling long NV ensemble electronic spin dephasing times and enhanced strain\nsensitivity. We demonstrate the strain-sensitive measurement protocol first on\na scanning confocal laser microscope, providing quantitative measurement of\nsensitivity as well as three-dimensional strain mapping; and second on a\nwide-field imaging quantum diamond microscope (QDM). Our strain microscopy\ntechnique enables fast, sensitive characterization for diamond material\nengineering and nanofabrication; as well as diamond-based sensing of strains\napplied externally, as in diamond anvil cells or embedded diamond stress\nsensors, or internally, as by crystal damage due to particle-induced nuclear\nrecoils.\n

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevapplied.17.024041