Magnon-mediated qubit coupling determined via dissipation measurements
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-01-02 |
| Journal | Proceedings of the National Academy of Sciences |
| Authors | Masaya Fukami, Jonathan C. Marcks, Denis R. Candido, Leah R. Weiss, Benjamin Soloway |
| Institutions | Argonne National Laboratory, Advanced Institute of Materials Science |
| Citations | 22 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research experimentally quantifies the magnon-mediated coupling in a hybrid quantum system (HQS) consisting of Nitrogen-Vacancy (NV) centers in diamond interfaced with Yttrium Iron Garnet (YIG).
- Core Achievement: First experimental determination of the magnon-mediated NV-NV coupling strength (geff) by measuring the magnon-induced self-energy (Ï).
- Coupling Quantification: The upper bound for the effective NV-NV coupling strength was estimated at geff â 2Ï * 2 Hz at zero distance (r=0).
- Methodology: The approach combines room-temperature longitudinal relaxation (T1) measurements of the NV centers with quantitative analysis using the Fluctuation-Dissipation and Kramers-Kronig relations to extract the real (Ïâ) and imaginary (Ïâ) parts of the self-energy.
- Physical Mechanism: The coupling is primarily driven by magnetic dipole-dipole interactions between the NV centers and thermally populated surface magnon modes (MSSWs) in the YIG film.
- Engineering Significance: This technique provides a versatile, room-temperature tool to characterize weakly coupled HQS platforms, simplifying the feedback mechanism necessary for engineering entangled solid-state systems without requiring complex millikelvin environments.
- Performance Metric: The calculated gate-to-decoherence ratio (GDR) for the system was approximately 3 near 72 G, indicating potential for useful two-qubit gates if decoherence were limited only by magnons.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Operating Temperature (T) | 299.6 ± 0.3 | K | Room temperature, measured at sample base |
| NV Center Zero-Field Splitting (DNV) | 2Ï * 2.87 | GHz | Intrinsic NV property |
| Electron Gyromagnetic Ratio (Îł) | 2Ï * 2.8 | MHz/G | Absolute value |
| YIG Saturation Magnetization (Ms) | 1,716 | G/”0 | Fitted parameter used in theoretical model |
| NV-YIG Interface Distance (hNV) | 400 ± 5 | nm | Calibrated via optical interference fringes |
| NV Implantation Depth | 7.7 ± 3.0 | nm | From the bottom surface of the diamond slab |
| YIG Film Thickness | 3 | ”m | Material geometry |
| Diamond Slab Thickness | 100 | ”m | Material geometry |
| GGG Substrate Thickness | 500 | ”m | Material geometry |
| Magnon-Induced Self-Energy (Re[Ï]) | â 2Ï * 2 | Hz | Upper bound estimate for geff(r=0) |
| Maximum Coupling/Dissipation Ratio ( | Ïâ/Ïâ | ) | â 2.5 |
| Room-Temperature T1 Rate (Resonance) | â 45 | ”s-1 | Observed at 82 G (1/T1 â 250 * 0.18 ”s-1) |
| Projected Low-Temperature T1 Extension | â 75 | Factor | Anticipated extension at T = 4 K |
Key Methodologies
Section titled âKey Methodologiesâ- Sample Fabrication: An ensemble of NV centers was created via nitrogen implantation into a 100-”m-thick diamond slab. This slab was then placed face-down (implanted side toward YIG) onto a 3-”m-thick YIG film grown on a 500-”m-thick Gadolinium Gallium Garnet (GGG) substrate.
- NV-YIG Interface: The NV centers were positioned approximately 400 nm from the YIG surface, with the NV axis (111) parallel to the YIG surface.
- Experimental Setup: Measurements were conducted at room temperature (299.6 K) using a confocal microscope for optical initialization (532-nm laser) and readout (PL detection). A copper wire was used to apply pulsed microwave tones.
- Magnetic Field Control: An external magnetic field H was applied parallel to the diamond/YIG surface. The field was swept through the resonance condition where the NV transition frequency (fNV) overlapped with the surface magnon plateau frequency (fp).
- Longitudinal Relaxometry (T1): The longitudinal relaxation time T1 was measured for the |ms = 0> â |ms = -1> transition by monitoring the decay of the differential PL signal over elapsed time (t).
- Dissipation Measurement (Ïâ): The magnon-induced increase in the relaxation rate, Î(1/T1), was used to calculate the imaginary part of the self-energy (Ïâ), representing dissipation, via the Fluctuation-Dissipation theorem.
- Coupling Determination (Ïâ): The real part of the self-energy (Ïâ), representing the energy shift and providing the upper bound for the NV-NV coupling (geff), was calculated from the measured Ïâ spectrum using the Kramers-Kronig relation.
Commercial Applications
Section titled âCommercial Applicationsâ- Quantum Information Processing (QIP): The ability to characterize and quantify long-range coupling mechanisms is essential for scaling up solid-state quantum computers, particularly for creating robust, magnon-mediated entanglement pathways between distant spin qubits.
- Hybrid Quantum Systems (HQS) Design: Provides a critical feedback mechanism for engineers designing HQSs (NV-magnon, superconducting qubit-magnon) to optimize material interfaces and geometries (e.g., YIG nanobars or waveguides) to maximize the coupling strength (geff) and cooperativity (C).
- Quantum Spintronics: Advances the field of spintronics by enabling the use of delocalized spin waves (magnons) as coherent information carriers to link localized spin defects, potentially leading to novel quantum transducers and memory elements.
- Room-Temperature Quantum Metrology: The methodology allows for the characterization of fundamental quantum interactions at ambient conditions, reducing the reliance on expensive and complex cryogenic infrastructure for initial device testing and optimization.
- Magnetic Sensor Calibration: The precise measurement of NV center interaction with magnetic noise generated by magnons can be used to calibrate and improve the sensitivity of NV-based magnetic field sensors operating near magnetic materials.
View Original Abstract
Controlled interaction between localized and delocalized solid-state spin systems offers a compelling platform for on-chip quantum information processing with quantum spintronics. Hybrid quantum systems (HQSs) of localized nitrogen-vacancy (NV) centers in diamond and delocalized magnon modes in ferrimagnetsâsystems with naturally commensurate energiesâhave recently attracted significant attention, especially for interconnecting isolated spin qubits at length-scales far beyond those set by the dipolar coupling. However, despite extensive theoretical efforts, there is a lack of experimental characterization of the magnon-mediated interaction between NV centers, which is necessary to develop such hybrid quantum architectures. Here, we experimentally determine the magnon-mediated NV-NV coupling from the magnon-induced self-energy of NV centers. Our results are quantitatively consistent with a model in which the NV center is coupled to magnons by dipolar interactions. This work provides a versatile tool to characterize HQSs in the absence of strong coupling, informing future efforts to engineer entangled solid-state systems.