Highly tunable magneto-optical response from magnesium-vacancy color centers in diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-06-18 |
| Journal | npj Quantum Information |
| Authors | Anton Pershin, Gergely Barcza, Ărs Legeza, ĂdĂĄm Gali |
| Institutions | HUN-REN Wigner Research Centre for Physics, Budapest University of Technology and Economics |
| Citations | 22 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThe research identifies the Magnesium-Vacancy (MgV) defect in diamond as a highly promising, tunable solid-state qubit, addressing several limitations of established color centers like the Nitrogen-Vacancy (NV) center.
- Defect Identification and Stability: MgV is confirmed as the most stable simple defect configuration, exhibiting a photostable -1 charge state (MgV-) under green laser photoionization (2.33 eV).
- High Coherence Potential: The MgV- center shows a Zero-Phonon Line (ZPL) at 2.2 eV (557 nm, green emission), matching experimental observations, and possesses a high Debye-Waller factor (0.54), indicating strong coherent emission suitable for quantum communication.
- Tunable Ground States: The defect features two quasi-degenerate spin ground states (doublet 2Eg and quartet 4Eu), separated by a small energy gap of only 22 meV.
- Operational Control: The nature of the ground state can be actively controlled and interconverted by modulating operational conditions, specifically temperature (thermal energy at 300 K is ~27 meV) or applied uniaxial compressive strain.
- Qubit Operation Feasibility: The calculated intrinsic spin-orbit splitting is 220 GHz (dynamically reduced to 30.8 GHz), which is large enough to enable magneto-optical qubit operation and spin-selective population protocols.
- Biological Suitability: The ZPL wavelength (557 nm) is particularly suitable for biological applications, offering an advantage over the longer wavelengths of the NV center (637 nm).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Identified Qubit | Magnesium-Vacancy (MgV-) | N/A | Most stable, photostable charge state. |
| Zero-Phonon Line (ZPL) | 2.2 | eV | Calculated ZPL for the primary 2E(2)g â 2Eg transition. |
| ZPL Wavelength | 557 | nm | Corresponds to green emission, suitable for bioimaging. |
| Debye-Waller Factor (DWF) | 0.54 | N/A | High value, indicating strong coherent emission. |
| Oscillator Strength (fosc) | 0.2 | N/A | High value, confirming bright emission. |
| Transition Dipole Moment (Ό) | 3.4 | D | Calculated for the primary bright transition. |
| Ground State Energy Gap (ÎE) | 22 | meV | Separation between 2Eg (doublet) and 4Eu (quartet) spin states. |
| Thermal Energy (300 K) | ~27 | meV | Sufficient energy to enable thermal spin-conversion. |
| Intrinsic Spin-Orbit Splitting (λ0) | 220 | GHz | Calculated splitting before dynamic Jahn-Teller (JT) effects. |
| Effective Spin Splitting | 30.8 | GHz | Final splitting value after dynamic JT reduction (factor 0.14). |
| Charge Transition Level (0/-1) | 2.1 | eV | Fermi level position required to stabilize the MgV- state. |
| Excitation Energy (Quartet) | ~1.1 | eV | ZPL of the 4Eu state, lying in the near-infrared window. |
Key Methodologies
Section titled âKey MethodologiesâThe electronic and spin properties of the MgV defect were determined using robust theoretical methods, primarily based on Density Functional Theory (DFT) and advanced correlation techniques.
- DFT Calculations (HSE06): Optimized geometries and electronic structures were computed using the HSE06 density functional, employing the projector-augmented wave method with a kinetic energy cutoff of 400 eV (VASP package).
- Supercell Modeling: Mg atoms were incorporated into a 512-carbon atom supercell to simulate bulk diamond properties.
- Charged Defect Correction: The Freysoldt correction scheme (implemented via SXDEFECTALIGN code) was used to accurately compute the formation energies (Eform) of charged defects.
- Optical Property Calculation (ASC): The Zero-Phonon Line (ZPL) and associated phonon sideband were computed using the Adiabatic State Correction (ASC) method.
- Correlation Treatment (CASSCF): The Complete Active Space Self-Consistent Field (CASSCF) method was applied to treat highly correlated states, utilizing an 84 C-atom cluster model and the cc-pVDZ basis set.
- Many-Body Excitation (DMRG): The Density Matrix Renormalization Group (DMRG) approach was used on top of periodic Kohn-Sham orbitals to calculate the many-body electronic excitation spectrum, specifically for a 216-atom diamond model.
Commercial Applications
Section titled âCommercial ApplicationsâThe unique, tunable magneto-optical properties of the MgV- center position it as a strong candidate for several next-generation quantum technologies.
- Quantum Computing and Memory: MgV- serves as a highly controllable solid-state qubit. The ability to tune the ground state via strain or temperature offers a novel mechanism for qubit initialization and manipulation, potentially simplifying complex optical protocols.
- Quantum Sensing (Magnetometry): The large effective spin splitting (30.8 GHz) suggests high sensitivity for detecting magnetic fields, making MgV- suitable for advanced quantum sensors.
- Quantum Communication: The high Debye-Waller factor (0.54) promotes coherent photon emission, which is essential for generating indistinguishable photons required for long-distance quantum networks and repeaters.
- Bioimaging and Quantum Biology: The ZPL at 557 nm (green) is advantageous for biological applications, as this wavelength window typically exhibits less absorption and scattering in biological tissue compared to the 637 nm emission of the NV center.
- Near-Infrared (NIR) Applications: The quartet state (4Eu) exhibits a ZPL at ~1.1 eV, placing it in the NIR window, which is highly desirable for deep-tissue imaging and telecommunication applications.