| Metadata | Details |
|---|
| Publication Date | 2022-02-15 |
| Journal | Physical Review Applied |
| Authors | Mason C. Marshall, Reza Ebadi, Connor Hart, Matthew Turner, Mark Ku |
| Institutions | Center for Astrophysics Harvard & Smithsonian, University of Maryland, College Park |
| Citations | 26 |
| Analysis | Full AI Review Included |
- Record Sensitivity Achieved: The research reports a record volume-normalized strain sensitivity of 5(2) x 10-8 / âHz · ”m-3, representing a two order-of-magnitude improvement over previous CW-ODMR techniques.
- Magnetic Field Insensitivity: High precision is achieved using strain-Carr-Purcell-Meiboom-Gill (strain-CPMG) quantum interferometry on Nitrogen Vacancy (NV) ensembles, which is inherently insensitive to static and low-frequency magnetic field inhomogeneity.
- Enhanced Coherence: The strain-CPMG protocol enables long ensemble NV electronic spin dephasing times (TD â 20 ”s), significantly longer than the canonical inhomogeneous dephasing time (T2* = 7.5 ”s).
- 3D Mapping Capability: A confocal scanning laser microscope configuration demonstrated quantitative 3D strain mapping with micron-scale spatial resolution, utilizing a small interrogation volume of 0.54(2) ”m3.
- Wide-Field Imaging: A Quantum Diamond Microscope (QDM) configuration demonstrated fast, sensitive, wide-field strain imaging across millimeter-scale sections, suitable for broad material surveys.
- Material Basis: Measurements were performed on high-purity, isotopically enriched (99.995% 12C) single-crystal CVD bulk diamond with low strain gradients.
- Robust Readout: The use of âXY-normalizedâ visibility (vXY) compensates for fluctuations in laser power and microwave amplitude, preventing systematic errors in wide-field imaging.
| Parameter | Value | Unit | Context |
|---|
| Volume-Normalized Strain Sensitivity | 5(2) x 10-8 | / âHz · ”m-3 | Record sensitivity achieved via confocal strain-CPMG. |
| Strain-CPMG Dephasing Time (TD) | ~20 | ”s | Measured on NV ensemble in low-strain diamond. |
| Inhomogeneous Dephasing Time (T2*) | 7.5 | ”s | Measured via standard Ramsey sequence. |
| Diamond Isotopic Purity | 99.995% | 12C | Single-crystal CVD bulk diamond (Element Six Ltd.). |
| NV Density (Confocal Section A) | ~0.3 | ppm | Estimated concentration. |
| NV Density (QDM Section B) | ~0.5 | ppm | Estimated concentration. |
| Confocal Interrogation Volume | 0.54(2) | ”m3 | Determined by fitting 3D Gaussian function to fluorescence distribution. |
| Green Excitation Wavelength | 532 | nm | Used for NV initialization and readout. |
| Confocal Objective | 100X, 0.9 | NA | Air objective used for high spatial resolution. |
| QDM External Frame Rate | ~270 | Hz | Achieved using Heliotis HeliCam C3 lock-in camera. |
| Axial Spin-Strain Coupling (A1) | -8.0(5.7) | GHz/strain | Coefficient for axial stress-induced energy shift. |
| Transverse Spin-Strain Coupling (A2) | -12.4(4.7) | GHz/strain | Coefficient for transverse stress-induced energy shift. |
| Calculated Shot Noise Limit (Volume-Normalized) | 3.8 | x 10-8 / âHz · ”m-3 | Theoretical limit for the confocal setup. |
- Strain-CPMG Sequence: The core technique is a variation of the CPMG sequence optimized for strain sensing. It uses two microwave (MW) tones near the two ground-state spin transitions (|0> â |±1>) and employs triplets of Ï-pulses to swap population between the |+1> and |-1> states.
- Magnetic Noise Cancellation: The sequence structure ensures that the accumulated phase due to the linear magnetic field term (ÎłBzSz) cancels out over the full sequence, isolating the measurement to the strain-dependent term (D + Mz)Sz2.
- Confocal Gradiometry: For long-duration confocal scans, a âgradiometryâ configuration was used, alternating measurements between the scan position and a fixed reference position. This compensates for slow temperature drifts (e.g., 0.1 K/hour) that affect the zero-field splitting (D).
- XY-Normalized Visibility (vXY) Readout: To extract the strain shift (Mz) robustly, especially in wide-field imaging where laser and MW power are inhomogeneous, the visibility is calculated using both X and Y quadratures (Equation 5). This normalizes the measurement against fluctuations in the interference fringe amplitude (Ae-Ï/TD).
- QDM Wide-Field Imaging: The Quantum Diamond Microscope (QDM) utilizes a Heliotis HeliCam C3 lock-in camera, which performs hardware subtraction of alternating fluorescence exposures to maximize the 10-bit dynamic range for contrast measurement.
- Strain Gradient Mapping: The denominator of the vXY measurement is used as a signal to identify high-gradient pixels where intra-pixel strain variations cause rapid dephasing and reduce the effective TD.
- Quantum Diamond Engineering: Essential for characterizing and optimizing the growth of high-quality CVD diamond materials by mapping strain features (e.g., crystallographic defects) that limit NV coherence.
- Nanophotonic Device Fabrication: Sensitive measurement of strain induced by nanofabrication processes (etching, deposition) near integrated NV qubits, crucial for maintaining spectral stability and coherence.
- In Situ Stress Sensors: Utilizing micron-scale diamond sections as embedded stress sensors in high-pressure environments (e.g., diamond anvil cells) or soft materials, leveraging the NV centerâs direct integration into the crystal lattice.
- Quantum Metrology and Communication: Enabling strain-mediated control of NV qubit couplings for applications in quantum networking and advanced quantum sensing protocols.
- Dark Matter Detection: Provides the necessary sensitivity (exceeding the 10-7 / âHz · ”m-3 benchmark) and speed required for proposed diamond-based particle detectors designed for directional detection of WIMPs via damage-induced strain.
- Industrial Diamond Characterization: Applicable to characterizing strain in diamonds with higher impurity (nitrogen or 13C) content, expanding utility beyond specially engineered quantum diamonds to industrial devices like diamond knives.
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