Sensing chiral magnetic noise via quantum impurity relaxometry
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-12-04 |
| Journal | Physical review. B./Physical review. B |
| Authors | Avinash Rustagi, Iacopo Bertelli, Toeno van der Sar, Pramey Upadhyaya |
| Institutions | Huygens Institute for History and Culture of the Netherlands, Leiden University |
| Citations | 29 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research presents a validated theoretical framework for Quantum Impurity (QI) relaxometry, specifically focusing on sensing magnon dynamics in ferromagnetic thin films.
- Quantitative Accuracy: The developed âchiral theoryâ achieves excellent quantitative agreement with experimental relaxation rates (Î) measured in NV-Permalloy (Py) and NV-Yttrium Iron Garnet (YIG) hybrids, eliminating the need for arbitrary scaling factors required by previous models.
- Chirality as Key Mechanism: The theory establishes that chiral coupling between prototypical spin >1/2 QIs (like NV centers) and thin-film magnons is central to determining the impurity relaxation rate.
- Experimental Validation: New experiments on NV-Nickel (Ni) hybrids confirm the theoryâs prediction of a crossover between the two relaxation rates (Î- and Î+) as a function of external magnetic field (Hext). This crossover is a unique signature of chiral coupling.
- Enhanced Sensing Capability: QI-relaxometry is confirmed as a sensitive, local, and non-invasive technique, offering nm-spatial and GHz frequency resolution for probing magnetic dynamics.
- Advanced Magnonics: The results are critical for understanding and modeling decoherence in hybrid quantum platforms that integrate magnetic materials, advancing the field of magnonics.
Technical Specifications
Section titled âTechnical SpecificationsâThe following specifications are derived from the experimental benchmarks and theoretical parameters used in the study, primarily focusing on NV-center hybrid systems.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV-Py Film Thickness (L) | 30 | nm | Fig. 2a benchmark |
| NV-YIG Film Thickness (L) | 20 | nm | Fig. 2b benchmark |
| NV-Ni Film Thickness (L) | 40 | nm | New experimental data (Fig. 4) |
| NV Center Depth (dQI) | 40 ± 5 | nm | NV-Nickel experiment |
| NV-Py Saturation Magnetization (Ms) | 800 | emu/cc | Permalloy (Py) |
| NV-YIG Saturation Magnetization (Ms) | 124 | emu/cc | Yttrium Iron Garnet (YIG) |
| YIG Gilbert Damping (α) | 0.0001 | - | Extremely low damping material |
| Py Gilbert Damping (α) | 0.015 | - | Typical metallic ferromagnet |
| External Field Range (Hext) | 0 to 50 | mT | Range for relaxation rate measurements |
| Relaxation Rate (Î) Range | 0.01 to 1.0 | ”s-1 | Measured rates (Fig. 2a, 4) |
| Spatial Resolution | nm | - | QI-relaxometry capability |
| Frequency Resolution | GHz | - | QI-relaxometry capability |
Key Methodologies
Section titled âKey MethodologiesâThe study combines theoretical modeling with experimental validation using solid-state quantum sensors.
- Theoretical Framework Integration: The general framework of quantum relaxometry was combined with the Landau-Lifshitz-Gilbert (LLG) phenomenology to model magnon dynamics and their resulting magnetic noise in thin films.
- Chiral Theory Formulation: The model explicitly included both out-of-plane and in-plane magnetization deviations, accounting for the finite ellipticity of magnons. This captures the chiral nature of the magnetic noise resulting from the combination of bulk (Pm â m x âm) and surface (Ïm â m · n) magnetic charges.
- Hybrid Sample Fabrication (NV-Nickel): NV centers were implanted 10 nm below the diamond surface. A 30 nm SiO2 spacer layer was deposited, followed by the evaporation of a 40 nm Nickel (Ni) thin film.
- Relaxation Rate Measurement (Relaxometry): The two spin relaxation rates (Î+ and Î-) corresponding to the ms = 0 â +1 and ms = 0 â -1 transitions were measured. This involved initializing the NV spin, waiting for a variable time (Ï), and characterizing the spin state via photoluminescence readout.
- Crossover Signature Confirmation: Measurements were performed by sweeping the external magnetic field (Hext). The experimental observation of the crossover point (where Î+ = Î-) at approximately 15 mT in the NV-Nickel hybrid confirmed the predictive power of the chiral theory.
Commercial Applications
Section titled âCommercial ApplicationsâThis technology provides critical tools and understanding necessary for advancing several high-tech fields, particularly those involving hybrid quantum systems and novel magnetic materials.
- Quantum Sensing and Metrology:
- Product: Highly localized magnetic field sensors (nm scale) capable of operating from cryogenic to room temperatures.
- Application: Non-invasive mapping of dynamic magnetic fields and noise sources in integrated circuits and novel materials.
- Magnonics and Spintronics:
- Application: Designing and optimizing magnon-based information carriers and logic devices by accurately modeling and minimizing decoherence caused by magnetic noise.
- Product: Predictive simulation tools for hybrid quantum-magnetic systems, validated by the chiral theory.
- Topological Materials Research:
- Application: Probing exotic chiral phenomena in condensed matter, such as one-way propagating magnetic modes (topological magnon insulators) and chiral electronic modes, which generate unique chiral magnetic noise signatures.
- Quantum Computing and Qubit Development:
- Application: Characterizing and controlling decoherence in solid-state qubits (like NV or SiV centers) when integrated with magnetic materials, which is crucial for scalable quantum hardware.
- Materials Characterization:
- Application: High-frequency (GHz) characterization of magnetic thin films, providing accurate measurements of fundamental parameters like Gilbert damping (α) and exchange constants (Aex).
View Original Abstract
We present a theory for quantum impurity relaxometry of magnons in thin films, exhibiting quantitative agreement with recent experiments without needing arbitrary scale factors used in theoretical models thus far. Our theory reveals that chiral coupling between prototypical spin >1/2 quantum impurities and magnons plays a central role in determining impurity relaxation, which is further corroborated by our experiments on nickel films interfaced with nitrogen-vacancy centers. Along with advancing magnonics and understanding decoherence in hybrid quantum platforms with magnets, the ability of a quantum impurity spin to sense chiral magnetic noise presents an opportunity to probe chiral phenomena in condensed matter.