| Metadata | Details |
|---|
| Publication Date | 2020-06-08 |
| Journal | Materials for Quantum Technology |
| Authors | Denis R. Candido, Gregory D. Fuchs, Ezekiel Johnston-Halperin, Michael E. Flatté |
| Citations | 47 |
| Analysis | Full AI Review Included |
- Core Value Proposition: The proposal demonstrates a practical pathway for achieving strong, coherent coupling between a single diamond Nitrogen-Vacancy (NV) center spin and a single magnon mode, enabling quantum transduction and entanglement over micron length scales.
- Material System: The hybrid system pairs NV centers in isotopically pure 12C diamond with a micron-scale disk (R=500 nm, d=100 nm) of the low-damping organic ferrimagnet, Vanadium Tetracyanoethylene (V[TCNE]x).
- Performance Metrics: Analytical calculations predict a strong spin-magnon coupling strength of $g \sim 2\pi \times 10$ kHz.
- Achieved Cooperativity: The system is predicted to operate in the strong coupling regime with a high cooperativity of $C_{x} \approx 15$ at ultra-low temperatures (T $\le 100$ mK).
- NV Center Positioning: Optimal performance is achieved for NV centers positioned a minimum of 30 nm below the diamond surface, balancing strong fringe field coupling with long spin coherence time ($T_{2}^{*}$).
- Material Advantage: V[TCNE]x is favored over conventional Yttrium Iron Garnet (YIG) due to its lower magnetic damping ($\alpha = 4 \times 10^{-5}$) and significantly reduced demagnetization field, which facilitates resonant tuning with the NV spin levels.
- Scalability: This scheme allows for the entanglement of NV centers separated by approximately 1 ”m, a distance far exceeding the limits of direct dipole coupling (< 20 nm).
| Parameter | Value | Unit | Context |
|---|
| Predicted Cooperativity ($C_{x}$) | 15 | Dimensionless | For the $\lambda = (6,1,1)$ magnon mode at T $\le 100$ mK. |
| Spin-Magnon Coupling Strength ($g$) | $2\pi \times 10$ | kHz | Predicted for NV spin 30 nm below the surface. |
| V[TCNE]x Disk Radius (R) | 500 | nm | Used in analytical model for strong coupling. |
| V[TCNE]x Disk Thickness (d) | 100 | nm | Used in analytical model. |
| NV Center Depth ($z$) | $\ge 30$ | nm | Minimum depth required to maintain bulk-like $T_{2}^{*}$ coherence. |
| NV Center Coherence Time ($T_{2}^{*}$) | $1.5 \times 10^{-3}$ | s | Assumed value in isotopically pure 12C diamond. |
| V[TCNE]x Gilbert Damping ($\alpha$) | $4 \times 10^{-5}$ | Dimensionless | Low intrinsic damping factor. |
| Magnon Damping Rate ($\eta$) | $2\pi \times 100$ | kHz | Derived from the Gilbert parameter. |
| Saturation Magnetization ($M_{s}$) | 7560 | A/m | V[TCNE]x material factor. |
| Resonance Frequency ($f$) | 1.30 | GHz | Frequency of the NV $ |
| External DC Magnetic Field ($B_{dc}$) | $\approx 56$ | mT | Required for resonant tuning along the [111] axis. |
| Entanglement Separation | $\approx 1$ | ”m | Distance between NV centers coupled via the magnon mode (2R). |
| YIG Thin-Film Damping ($\alpha_{YIG}$) | $1.5 \times 10^{-3}$ to $18 \times 10^{-3}$ | Dimensionless | Observed low-temperature damping, significantly higher than V[TCNE]x. |
- Material Integration and Growth: V[TCNE]x, an organic ferrimagnet, is proposed for direct deposition onto a single-crystal (111) diamond substrate. This avoids the substantial lattice mismatch hurdles associated with integrating conventional magnetic materials like YIG.
- Microstructure Fabrication: The V[TCNE]x film must be patterned into micron-scale disks (R=500 nm, d=100 nm) using lithography while preserving its intrinsic low magnetic damping ($\alpha = 4 \times 10^{-5}$).
- NV Center Implantation: NV centers must be implanted into the diamond substrate with high spatial precision ($\approx 20$ nm) at a depth of $\ge 30$ nm to maximize coupling via the magnetic fringe fields while mitigating surface spin noise that degrades $T_{2}^{*}$.
- Magnon Mode Engineering: High angular index magnon modes (e.g., $m=6$) are selected. These modes localize the in-plane magnetic fringe fields near the disk edge, efficiently coupling to the perpendicular NV spin axis.
- Resonant Tuning: An external DC magnetic field ($B_{dc}$) is applied along the NV axis to tune the NV spin transition frequency ($|0\rangle \leftrightarrow |-1\rangle$) into resonance with the magnon mode frequency ($\omega_{\lambda} \approx 1.30$ GHz).
- Cryogenic Operation: The system must be cooled to milli-Kelvin temperatures (T $\le 100$ mK) to ensure the magnon mode is in its unoccupied state, minimizing the thermal magnon number ($n \approx 1$) and enabling strong coupling to a single magnon.
- Quantum Gating Mechanism: Lithographically defined wires on the diamond surface are used to generate Oersted fields. These fields allow for shifting the bias magnetic field on microsecond timescales, enabling the NV spin(s) to be controllably brought into and out of resonance with the magnon mode for entanglement operations.
- Quantum Information Processing (QIP): The strong coupling mechanism provides a robust quantum bus for transferring quantum information between distant solid-state qubits (NV centers), crucial for building scalable quantum registers and processors.
- Quantum Repeaters and Networking: The ability to entangle NV centers separated by approximately 1 ”m via a coherent magnon link offers a practical solution for quantum network nodes, overcoming the short range of direct dipole coupling.
- Hybrid Quantum Transduction: The system acts as a transducer, converting quantum information stored in the NV spin state into magnon occupancy, which can potentially be coupled to other quantum systems (e.g., superconducting circuits).
- Advanced Spintronics and Magnonics: The use of low-loss organic ferrimagnets (V[TCNE]x) in microstructures demonstrates a viable path for integrating molecular magnets into solid-state quantum devices, potentially leading to ultra-low power magnonic circuits.
- High-Sensitivity Magnetic Sensing: The coherent coupling and control of single spins near a magnetic microstructure can be leveraged to develop novel, highly localized magnetic field sensors operating at cryogenic temperatures.
View Original Abstract
Abstract We propose an approach to realize a hybrid quantum system composed of a diamond nitrogen-vacancy (NV) center spin coupled to a magnon mode of the low-damping, low-moment organic ferrimagnet vanadium tetracyanoethylene. We derive an analytical expression for the spin-magnon cooperativity as a function of NV position under a micron-scale perpendicularly magnetized disk, and show that, surprisingly, the cooperativity will be higher using this magnetic material than in more conventional materials with larger magnetic moments, due to in part to the reduced demagnetization field. For reasonable experimental parameters, we predict that the spin-magnon-mode coupling strength is g ⌠2ÏĂ10 kHz. For isotopically pure 12 C diamond we predict strong coupling of an NV spin to the unoccupied magnon mode, with cooperativity <mml:math xmlns:mml=âhttp://www.w3.org/1998/Math/MathMLâ display=âinlineâ overflow=âscrollâ> <mml:msub> <mml:mrow> <mml:mi mathvariant=âscriptâ>C</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>15</mml:mn> </mml:math> for a wide range of NV spin locations within the diamond, well within the spatial precision of NV center implantation. Thus our proposal describes a practical pathway for single-spin-state-to-single-magnon-occupancy transduction and for entangling NV centers over micron length scales.