Spectroscopy of Surface-Induced Noise Using Shallow Spins in Diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2015-01-06 |
| Journal | Physical Review Letters |
| Authors | Yoav Romach, Christoph MĂŒller, Thomas Unden, Lachlan J. Rogers, Taiga Isoda |
| Institutions | Center for Integrated Quantum Science and Technology, UniversitÀt Ulm |
| Citations | 234 |
| Analysis | Full AI Review Included |
Spectroscopy of Surface-Induced Noise Using Shallow Spins in Diamond
Section titled âSpectroscopy of Surface-Induced Noise Using Shallow Spins in DiamondâExecutive Summary
Section titled âExecutive SummaryâThis analysis summarizes the characterization of environmental noise affecting shallow Nitrogen-Vacancy (NV) centers in ultra-high purity (UHP) diamond, a critical field for advancing quantum sensing, nanoscale NMR, and quantum networks.
- Core Research Focus: Detailed noise spectroscopy of NV centers situated 2 to 20 nm from the diamond surface, utilizing UHP substrates where surface noise mechanisms dominate bulk noise.
- Methodology: The use of Carr-Purcell-Meiboom-Gill (CPMG) dynamical decoupling pulse sequences combined with spectral decomposition to map the environmental noise power spectrum, $S(\omega)$.
- Key Discovery (Noise Sources): The measured noise exhibits a complex, unexpected double-Lorentzian structure, proving contributions from two distinct surface-related mechanisms.
- Identified Mechanisms:
- Low Frequency Noise (10-20 ”s correlation time): Consistent with a surface electronic spin bath (scaling inversely with depth squared, 1/$d^{2}$).
- High Frequency Noise (100-250 ns correlation time): Attributed to surface-modified phononic coupling.
- Performance Achievement: Dynamical decoupling was highly effective, achieving record Tâ coherence times of approximately 50 ”s for NV centers located just 2 nm beneath the diamond surface.
- Commercial Relevance: The results guide the design of tailored surface terminations (e.g., specific coatings) necessary to suppress environmental decoherence and enhance sensitivity in diamond-based quantum devices.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Purity (Nitrogen) | < 5 | ppb | Required for ultra-high purity substrates. |
| Diamond Purity (Carbon-13) | < 10-3 | % | Used to minimize bulk spin impurities. |
| Nâș Implantation Energy | 2.5 | keV | Used to create shallow NV centers. |
| NV Depth Range Studied | 2 - 20(5) | nm | Focus on surface-proximal NV centers (e.g., NV2, NV3, NV20). |
| NV Concentration (Targeted) | ~ 107 | cm-2 | Resulting concentration from 108 Nâș ions/cm2 dose. |
| Record Tâ Coherence Time (2 nm NV) | ~ 50 | ”s | Achieved using dynamical decoupling. |
| Tâ Coherence Time (NV20, N=1 pulse) | 64(20) | ”s | Coherence time measured far from the surface (20 nm depth). |
| Tâ Spin Relaxation Time (Shallow NV, RT) | 430 - 960 | ”s | Longitudinal relaxation time measured at room temperature (300 K). |
| Low Frequency Correlation Time (Ïc(1)) | 10 - 20 | ”s | Associated with the surface electronic spin bath. |
| High Frequency Correlation Time (Ïc(2)) | 100 - 250 | ns | Associated with surface-modified phonons. |
| Low Frequency Coupling Strength Scaling (n) | 1.75(21) | dimensionless | Consistent with 1/$d$2 scaling expected for a 2D spin bath. |
| Static Magnetic Field (B) | 454 | G | Standard field used for decoupling measurements. |
| Cryogenic Temperature Study | 10 | K | Used to isolate and characterize phononic effects. |
| Surface Coating Tested | 4 | nm | Molecular Beam Epitaxy (MBE) deposition of Silicon (Si). |
Key Methodologies
Section titled âKey MethodologiesâThe following is a concise summary of the critical steps and material specifications used to execute the surface noise spectroscopy experiment:
- Substrate Selection: Ultra-high purity (UHP) Single Crystal Diamond (SCD) was selected to minimize bulk noise sources (N < 5 ppb, 13C < 10-3%), ensuring the coherence dynamics were dominated by surface effects.
- Shallow NV Creation: Nitrogen-Vacancy centers were introduced via low-energy nitrogen ion (Nâș) implantation (2.5 keV nominal energy, 108 Nâș ions/cm2 dose) to locate the spins within 2-5 nm of the surface.
- NV Depth Calibration: Precise subnanometer depth determination was achieved by using the NV center itself as a sensor, detecting the hydrogen Larmor frequency signal from an immersion oil coating via XY8 pulse sequences.
- Coherence Measurement (Tâ): The NV coherence was measured using periodic dynamical decoupling pulse sequences, specifically Carr-Purcell-Meiboom-Gill (CPMG) sequences, varying the number of pulses ($N$) and the pulse spacing ($\tau$).
- Relaxation Measurement (Tâ): Longitudinal spin relaxation ($T_{1}$) measurements were performed without control pulses to probe high-frequency noise components at the NV Larmor frequency.
- Noise Spectrum Extraction: The coherence decay data $T_{2}(N)$ was deconvolved with the corresponding filter function of the CPMG sequences to spectrally decompose the environmental noise power spectrum $S(\omega)$.
- External Parameter Tuning: The study investigated noise behavior under varying external factors:
- Temperature: Room Temperature (300 K) vs. Cryogenic (10 K).
- Magnetic Field: 454 G (standard) vs. 25 G and 221 G.
- Surface Modification: Uncoated diamond vs. a 4 nm silicon (Si) layer deposited by Molecular Beam Epitaxy (MBE).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is an expert technical supplier providing the high-quality MPCVD diamond substrates, polishing, and customization necessary to replicate and advance this cutting-edge research in quantum materials and spin dynamics.
| Requirement/Challenge (From Paper) | 6CCVD Solution & Capability | Core Value Proposition |
|---|---|---|
| Ultra-High Purity SCD Substrates | Optical Grade Single Crystal Diamond (SCD) engineered with ultra-low impurity levels, crucial for maximizing intrinsic bulk $T_{1}$ and $T_{2}$ times (N and 13C levels customizable to meet strict ppb requirements). | Highest Fidelity Base Material: Ensures the material environment is quiet, allowing researchers to isolate and study surface-related noise without bulk interference. |
| Substrate Surface Quality | Advanced CMP Polishing achieving surface roughness of Ra < 1 nm on SCD wafers. | Optimized for Shallow NV: Minimizes topographic variation, critical for reproducible, high-fidelity shallow NV formation via implantation and controlled surface chemistry studies. |
| Substrate Dimensions for Scaling | SCD and Polycrystalline Diamond (PCD) plates/wafers available in custom dimensions up to 125 mm (PCD) and large-area SCD. | Scalability & Compatibility: Provides the large-format wafers required for transitioning from fundamental single-spin studies to scalable device fabrication and integration with standard semiconductor processes. |
| Custom Surface Modification | In-house Metalization Services: While the paper used Si MBE, 6CCVD offers bespoke metal layer deposition (Ti, W, Au, Pt, Pd, Cu) for tailored surface termination and fabrication of electrodes for electric field studies (suggested future work). | Accelerated R&D: Streamlines the prototyping of hybrid quantum systems by providing pre-metalized substrates ready for immediate testing. |
| Support for Advanced NV Creation | We supply substrates optimized for both low-energy ion implantation (as used here) and for âDelta-Dopingâ (controlled thin-layer MPCVD growth of nitrogen) for alternative shallow NV creation techniques. | Material Versatility: Supports multiple research paths for creating robust, near-surface NV layers for sensing and quantum applications. |
Engineering Support: 6CCVDâs in-house PhD material science team specializes in MPCVD growth recipes and impurity control. We can assist researchers in selecting materials that balance ultra-high purity requirements with specific geometric or doping targets for surface noise mitigation and quantum metrology projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
We report on the noise spectrum experienced by few nanometer deep nitrogen-vacancy centers in diamond as a function of depth, surface coating, magnetic field and temperature. Analysis reveals a double-Lorentzian noise spectrum consistent with a surface electronic spin bath in the low frequency regime, along with a faster noise source attributed to surface-modified phononic coupling. These results shed new light on the mechanisms responsible for surface noise affecting shallow spins at semiconductor interfaces, and suggests possible directions for further studies. We demonstrate dynamical decoupling from the surface noise, paving the way to applications ranging from nanoscale NMR to quantum networks.