Identification and Reversible Optical Switching of NV+ Centers in Diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-03-30 |
| Journal | Advanced Functional Materials |
| Authors | Marcel Dickmann, Lucian Mathes, Ricardo Helm, Vassily Vadimovitch Burwitz, Werner Egger |
| Institutions | Helmholtz-Zentrum Dresden-Rossendorf, Technical University of Munich |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research successfully identifies and characterizes the positively charged nitrogen-vacancy (NV+) center, often referred to as the âdark stateâ, in diamond using advanced positron annihilation spectroscopy (PAS).
- NV+ Detection and Switching: NV+ centers, which are optically inactive and do not trap positrons, were indirectly detected by observing their light-induced charge transition to the positron-trapping neutral state (NV0).
- Quantified Transition Energy: The threshold photon energy required for the NV+ to NV0 charge transition was experimentally determined to be 1.234(8) eV.
- Metastability Confirmed: The light-induced NV0 state was found to be metastable, decaying back to the initial NV+ state when stored in complete darkness.
- Decay Time Constant: The characteristic decay time (t1/e) for the NV0 state to revert to NV+ in darkness was quantified as 1.73(22) h.
- Methodological Advancement: The study validates the use of Positron Annihilation Spectroscopy (PALS) combined with in situ monochromatic light illumination as a unique tool for investigating charge dynamics in deep-level defects like NV centers.
- Engineering Relevance: This precise knowledge of NV+ properties and charge switching dynamics is critical for developing robust quantum circuits and long-lived quantum data storage devices based on diamond NV centers.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Sample Material | Single crystal CVD diamond | N/A | (100) orientation, low impurities (N < 5 ppb, B < 1 ppb). |
| N+ Implantation Energy | 0.5 | MeV | Used to create NV centers. |
| N+ Implantation Fluence | 1.0 ¡ 1014 | cm-2 | Chosen to achieve high NV concentration. |
| Post-Implantation Annealing | 1200 | °C | Performed for 2 h to activate NV centers. |
| NV+ to NV0 Transition Energy | 1.234(8) | eV | Experimentally determined threshold photon energy. |
| NV0 Decay Time (t1/e) | 1.73(22) | h | Characteristic decay time back to NV+ in darkness. |
| Experimental Positron Lifetime (NV0/NV-) | 145(12) | ps | Lifetime component observed after annealing and switching. |
| DFT Calculated Positron Lifetime (NV0) | 141 | ps | Calculated lifetime for a positron trapped in a neutral NV center. |
| DFT Calculated Positron Lifetime (NV-) | 139 | ps | Calculated lifetime for a positron trapped in a negative NV center. |
| PALS Illumination Wavelength | 940 | nm | Corresponds to 1.3 eV photons used for switching. |
| PALS Illumination Intensity | 2.5 ¡ 1015 | photons s-1cm-2 | Nominal intensity used during in situ PALS measurements. |
Key Methodologies
Section titled âKey Methodologiesâ-
Sample Preparation (Implantation and Annealing):
- Single crystal CVD diamond was irradiated with 0.5 MeV N+ ions at a fluence of 1.0 ¡ 1014 cm-2 at room temperature.
- The sample was subsequently annealed at 1200 °C for 2 h to mobilize vacancies and form NV centers (N-V complexes).
-
Positron Annihilation Lifetime Spectroscopy (PALS):
- PALS was performed using the Mono-energetic Positron Spectroscopy (MePS) setup at the ELBE facility (HZDR).
- Measurements were conducted at 4 keV and 12 keV positron implantation energies, corresponding to mean depths of 82 nm and 596 nm, respectively, to probe different defect regions.
- PALS spectra were analyzed using a free-fit model to extract distinct lifetime components (Ďi) and their intensities (Ii), which were correlated with DFT calculations for specific defect types (bulk, NV0, NV-, vacancy clusters).
-
Density Functional Theory (DFT) Calculations:
- Two-Component Density Functional Theory (TC-DFT) using the ABINIT software package was employed.
- Calculations determined the theoretical positron lifetimes for bulk diamond, mono-vacancies (V1), di-vacancies (V2), vacancy clusters (Vn), and NV centers (NV0, NV-) to aid experimental interpretation.
-
In Situ Light Illumination and Spectroscopy:
- Doppler-Broadening Spectroscopy (DBS): Used a 12 keV positron beam to measure the S parameter (lineshape parameter) as a function of illuminating photon energy (1.1 - 1.4 eV).
- Threshold Determination: A sharp step-like increase in the S parameter identified the NV+ to NV0 charge transition threshold at 1.234 eV.
- Decay Measurement: The sample was illuminated (e.g., 1.25 eV photons) and then measured in complete darkness to monitor the time-dependent decrease of the S parameter, yielding the decay time of the metastable NV0 state.
Commercial Applications
Section titled âCommercial ApplicationsâThe precise characterization and control of the NV+ state are crucial for advancing diamond-based quantum technologies:
- Quantum Data Storage and Memory: NV+ centers can be used as spin coherence storage for long-lived nuclear spin states due to the absence of an electronic spin. This enables high-fidelity, long-entanglement times necessary for quantum memory elements.
- Scalable Quantum Computing: The ability to individually switch single NV centers between NV+ and NV-/NV0 states using light or bias voltage provides a novel scheme for building fully scalable quantum computers.
- Quantum Networks: Controlled charge state switching is fundamental for initializing, reading out, and coupling NV centers, which are essential components in quantum network nodes.
- Defect Engineering in Diamond: The methodology provides a powerful non-optical technique for characterizing deep-level defects, allowing material engineers to optimize implantation and annealing recipes to maximize the yield of specific NV charge states (NV+, NV0, or NV-) required for target applications.
- High-Purity Diamond Substrates: The findings inform the required Fermi level control (e.g., through boron doping) necessary to stabilize the NV+ state in high-purity CVD diamond used for advanced quantum devices.
View Original Abstract
Abstract Positive nitrogenâvacancy centers (NV + ) in diamond are predicted to exist in conjunction with neutral (NV 0 ) and negative (NV â ) centers. However, the existence of NV + has only been indirectly inferred through a shift of the Fermi level. Evidence of NV + coexisting with NV 0 and NV - in diamond has not yet been observed. In this paper, positron annihilation spectroscopy in combination with in situ light illumination is applied, in order to investigate the presence of NV + centers in nitrogen implanted and subsequently annealed diamond. Switching of NV + to NV 0 centers is observed with a threshold photon energy of 1.234(8) eV. In complete darkness, a decay of NV 0 centers with a decay time of 1.73(22) h can be detected. In conclusion, previously converted NV 0 centers are metastable and partially decay in darkness, leading to the reformation of NV + centers.