Optical activation and detection of charge transport between individual colour centres in diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-10-22 |
| Journal | Nature Electronics |
| Authors | Artur Lozovoi, Harishankar Jayakumar, Damon Daw, György Vizkelethy, Edward S. Bielejec |
| Institutions | City College of New York, The Graduate Center, CUNY |
| Citations | 54 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Core Achievement: Demonstrated controlled, photo-induced charge transport (hole injection and trapping) between discrete, individually addressed Nitrogen-Vacancy (NV) centers separated by several micrometers (2.5 to 9.5 ”m) in bulk diamond at room temperature.
- Giant Cross-Section: Measured an exceptionally large hole capture cross-section (Ïh â 3 x 10-3 ”m2), which is orders of magnitude greater than typical ensemble measurements, attributed to unscreened Coulomb potentials in the high-purity crystal.
- Carrier Filtering: Utilized a spin-to-charge conversion (SCC) protocol combined with optically detected magnetic resonance (ODMR) to confirm that >75% of the trapped carriers originated specifically from the optically excited âsourceâ NV, filtering out background defects.
- Transport Mechanism: The results are consistent with the Langevin regime of cascade trapping, where the carrier mean-free path (~15 nm) is comparable to the Onsager trapping radius (~10 nm).
- Quantum Bus Potential: The ability to encode the spin state of a source qubit into the charge state of a distant target defect establishes the feasibility of using free carriers as a quantum bus to mediate effective interactions between paramagnetic defects in solid-state chips.
- Control Demonstrated: External electric fields (E â 120 mV ”m-1) were shown to progressively block inter-NV carrier transport, offering a pathway for active control.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Host Material | Type 2a Diamond | N/A | Electronic-grade crystal, [100] orientation. |
| Intrinsic Nitrogen Concentration | †5 | ppb | High purity, corresponding to inter-N separation ℠200 nm. |
| Ion Implantation Energy | 20 | MeV | N+ ions used for deep NV creation. |
| NV Implantation Depth | ~9 to ~10 | ”m | Deep implantation to minimize surface effects. |
| NV Separation Distance (d) | 2.5 to 9.5 | ”m | Range tested for inter-defect carrier transport. |
| Operating Temperature | Room | Temperature | All experiments conducted under ambient conditions. |
| Green Excitation (Source) | 520 | nm | Used for NV ionization (carrier generation). |
| Red Excitation (SCC) | 632 | nm | Used simultaneously with green for optimal SCC contrast. |
| Readout Wavelength | 594 | nm | Used for charge-state preserving NV fluorescence readout. |
| Experimental Hole Capture Cross Section (Ïh) | 3 x 10-3 | ”m2 | Measured value, derived from charge conversion time. |
| Onsager Trapping Radius (rt) | ~10 | nm | Calculated for room temperature diamond (Δ = 5.7Δ0). |
| Carrier Mean-Free Path (l) | ~15 | nm | Inferred value, supporting the Langevin (diffusive) transport regime. |
| Electric Field for Transport Blocking (E) | ~120 | mV ”m-1 | Field strength required to block carrier transport (60 V across 500 ”m gap). |
| Source NV Ionization Rate (kion) | ~106 | s-1 | Estimated at 2 mW, 520 nm laser power. |
Key Methodologies
Section titled âKey Methodologiesâ- NV Array Engineering: Nitrogen ions (N+) were accelerated using a tandem ion accelerator to 20 MeV and focused into ~1 ”m diameter spots on the diamond surface, creating spatially patterned NV centers approximately 10 ”m deep.
- Defect Conversion and Purification: A six-step high-vacuum annealing protocol (up to 1200 °C for 2 h) was implemented to convert implanted nitrogen into NV centers. This was followed by a tri-acid mixture treatment (nitric, sulfuric, perchloric) to remove surface impurities and graphite.
- Confocal Microscopy and Readout: A home-built confocal microscope with an oil-immersion objective (NA=1.3) and three pulsed/CW diode lasers (520 nm, 632 nm, 594 nm) was used for diffraction-limited illumination (~0.5 ”m spot) and single-photon counting detection.
- Charge Transport Protocol: The âsourceâ NV was subjected to prolonged 520 nm laser parking to induce cycles of ionization (NV- â NV0 + e-) and recombination (NV0 + h+ â NV-), generating a stream of free holes (h+).
- Target Charge State Monitoring: The distant âtargetâ NV was monitored via low-power 594 nm fluorescence readout. Hole capture by the target (NV- + h+ â NV0) resulted in a measurable decrease in fluorescence (bleaching).
- Carrier Source Filtering (SCC): A Spin-to-Charge Conversion (SCC) protocol was applied to the source NV, using simultaneous green/red excitation and resonant MW driving (~2.87 GHz). This spin-dependent ionization filtered the carrier stream, confirming the dominance of source NV-generated carriers over background defects.
- Cross-Section Measurement: The NV hole capture rate (Ï-1) was measured as a function of the inter-defect distance (d). The observed inverse square dependence (Ï-1 â d-2) was used, along with known ionization rates, to directly calculate the NV carrier trapping cross-section (Ïh).
Commercial Applications
Section titled âCommercial Applicationsâ- Quantum Computing and Communication: Utilizing free carriers as a robust, room-temperature quantum bus to mediate interactions between distant solid-state spin qubits (e.g., NV centers), enabling scalable quantum architectures.
- Enhanced Quantum Sensing: Implementing spin-encoded photo-generated carriers to enhance the detection sensitivity of point defects, particularly those with low quantum yield (e.g., rare earth ions) or those emitting at impractical wavelengths (e.g., SiV0).
- Solid-State Electrometry: Leveraging the charge state control and transport mechanisms for advanced electric field sensing, potentially monitoring metastable space-charge potentials in wide-bandgap semiconductors.
- Defect Engineering and Materials Science: Providing a direct method to measure fundamental parameters like carrier trapping cross-sections in high-purity semiconductors, critical for optimizing defect creation and stability in quantum materials.
- Optoelectronic Devices: Developing all-diamond diode structures and exploring electroluminescence produced by controlled electron-hole recombination at individual color centers for integrated quantum devices.