Determining the position of a single spin relative to a metallic nanowire
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-04-08 |
| Journal | Journal of Applied Physics |
| Authors | J. F. Da Silva Barbosa, M. Lee, P. Campagne-Ibarcq, P. Jamonneau, Y. Kubo |
| Institutions | Centre National de la Recherche Scientifique, Okinawa Institute of Science and Technology Graduate University |
| Citations | 3 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates a critical step toward hybrid quantum devices by precisely localizing individual Nitrogen-Vacancy (NV) centers relative to a metallic nanowire using vector magnetometry.
- Core Achievement: Determining the relative position of individual NV centers in diamond with respect to an overlying metallic nanowire with an accuracy of approximately 10 nm.
- Methodology: Single-NV vector magnetometry was employed, measuring the vector magnetic field components (Bz and Bâ„) generated by a DC current passing through the nanowire.
- Material System: 15N NV centers implanted into electronic-grade CVD diamond, coupled to a 20 nm thick Aluminum/Titanium nanowire.
- Key Finding: The measured NV positions showed a systematic lateral shift of ~120 nm, attributed to misalignment during the electron-beam lithography steps.
- Quantum Application: The positional data allows for a direct, room-temperature estimation of the spin-microwave coupling constant ($g/2\pi$), yielding values between 0.6 and 1 kHz for a proposed superconducting resonator design.
- Detection Time Estimate: The estimated single-spin detection time for unit signal-to-noise ratio in a resonator setup is predicted to be between 0.6 and 5 seconds.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Positional Accuracy | ~10 | nm | Relative NV position determination. |
| Electron Spin Zero-Field Splitting (D/2Ï) | 2.87 | GHz | NV ground state triplet (S=1). |
| Electron Spin Gyromagnetic Ratio (Îłe/2Ï) | 28 | GHz/T | Standard NV property. |
| 15N Nuclear Gyromagnetic Ratio (ÎłI/2Ï) | -4.3 | MHz/T | Standard 15N property. |
| Implantation Ion | 15N2+ | ions | Used for creating NV centers. |
| Implantation Energy | 7.5 | keV | Determines implantation depth. |
| Implantation Flux | ~2500 | N/”m2 | Nitrogen dose density. |
| SRIM Estimated Depth | 11 ± 5 | nm | Expected depth of NV centers. |
| N to NV Conversion Yield | ~3 | % | Efficiency of defect creation. |
| Nanowire Thickness (Total) | 20 | nm | 5 nm Ti / 15 nm Al layers. |
| Nanowire Width (Typical) | 40 | nm | Fabricated dimension. |
| Nanowire Length | 500 | nm | Fabricated dimension. |
| Nanowire Direction | [110] | Crystalline axis | Direction of current flow. |
| Measured Bz Derivative (az) | 1.4 ± 0.1 | T/A | Field component parallel to NV axis. |
| Measured Bâ„ Derivative (aâ„) | 1.9 ± 0.3 | T/A | Field component perpendicular to NV axis. |
| Nanowire Width Uncertainty (w) | 36 ± 5 | nm | Used in position fitting model. |
| Nanowire Thickness Uncertainty (t) | 20 ± 2 | nm | Used in position fitting model. |
| Estimated Coupling Constant (g/2Ï) | 0.6 to 1 | kHz | Calculated for a superconducting resonator (assuming ÎŽi = 35 nA). |
| Estimated Detection Time (Tdet) | 0.6 to 5 | s | For unit signal-to-noise ratio (assuming Îș=105 s-1, Îł2=105 s-1). |
Key Methodologies
Section titled âKey MethodologiesâThe experiment involved precise diamond preparation, targeted ion implantation, and nanoscale metallization, followed by advanced quantum sensing measurements.
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Diamond Preparation:
- Substrate: Commercial electronic-grade CVD diamond (Element 6).
- Alignment Marks: Patterned via electron-beam lithography (EBL) and etched into the diamond surface.
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Implantation Mask Fabrication:
- Resist: 120 nm thick PMMA layer applied.
- Patterning: EBL used to create an array of holes (~20 nm diameter) aligned precisely to the etched marks.
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Ion Implantation:
- Ions: 15N2+ ions used (resulting in 15N NV centers, which have a nuclear spin I = 1/2).
- Parameters: 7.5 keV energy, flux of ~2500 N/”m2.
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NV Center Creation and Cleaning:
- Annealing: 900 °C for 1 hour in vacuum to mobilize vacancies and form NV centers.
- Acid Cleaning (Multi-step):
- Boiling HNO3:H2SO4:HClO4 (3:4:1) for 6 hours.
- H2SO4:H2O2 (3:1) at 120 °C for 2 hours (Piranha clean).
- Final oxygen plasma clean.
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Nanowire Fabrication (EBL and Evaporation):
- Alignment: EBL used again, aligned to the etched marks, to position nanowires over the implanted NV locations.
- Deposition: Three-angle evaporation through a suspended germanium mask (liftoff technique).
- Layers: 5 nm Titanium adhesion layer, followed by 15 nm Aluminum (total 20 nm thickness).
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Vector Magnetometry Measurement:
- Readout: Optically-Detected Magnetic Resonance (ODMR) using a 532 nm green laser and 637 nm red photoluminescence detection.
- Bz Measurement: Standard ODMR measurement of the Zeeman shift of the electron spin transitions (W±,mI) as a function of DC current (io).
- Bâ„ Measurement: Nuclear spin selective pulse sequence used to measure the nuclear spin oscillation frequency (WNO), which is sensitive to the transverse field Bâ„.
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Position Determination:
- Modeling: The measured magnetic field derivatives (az and aâ„) were fitted to a model of the field generated by an ideal infinite wire.
- Refinement: Finite element method simulations were used to correct for the finite length of the nanowire and account for uncertainties in wire geometry (width 36 ± 5 nm, thickness 20 ± 2 nm).
Commercial Applications
Section titled âCommercial ApplicationsâThe technology developed hereâhigh-precision, nanoscale positioning of quantum defects relative to metallic circuitryâis foundational for several advanced quantum and sensing applications.
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Quantum Computing and Networks:
- Hybrid Qubit Systems: Essential for maximizing the coupling strength ($g$) between solid-state spins (NV centers) and superconducting microwave resonators (Circuit QED architecture).
- Fast Spin Detection: Enables the development of fast, high-fidelity spin detection and entanglement generation necessary for quantum processors and quantum networks.
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Nanoscale Sensing and Metrology:
- Vector Magnetometry: NV centers serve as highly sensitive vector magnetometers, capable of mapping magnetic fields generated by complex nanoscale structures (e.g., magnetic domains, current flow in integrated circuits).
- Probing Magnetic Structures: Used for high-resolution imaging and characterization of magnetic materials and devices at the nanoscale, potentially replacing or complementing techniques like STED/STORM in environments where optical methods fail (e.g., near metallic structures).
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Advanced Materials Engineering (Diamond):
- Controlled Defect Engineering: The precise implantation and localization techniques (using EBL masks and 15N ions) are critical for manufacturing diamond substrates with deterministic placement of quantum defects.
- CVD Diamond Substrates: The use of electronic-grade CVD diamond (like those supplied by Element 6) confirms the material platform necessary for high-coherence quantum devices.
View Original Abstract
The nanoscale localization of individual paramagnetic defects near an electrical circuit is an important step for realizing hybrid quantum devices with strong spin-microwave photon coupling. Here, we fabricate an array of individual nitrogen vacancy (NV) centers in diamond near a metallic nanowire deposited on top of the substrate. We determine the relative position of each NV center with âŒ10 nm accuracy, using it as a vector magnetometer to measure the field generated by passing a DC through the wire.