Voltage detected single spin dynamics in diamond at ambient conditions
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-04-14 |
| Journal | Nature Communications |
| Authors | Sergei Trofimov, K. Lips, Boris Naydenov |
| Institutions | Helmholtz-Zentrum Berlin fĂŒr Materialien und Energie, University of Utah |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research introduces a novel, non-optical method for detecting the spin state of single defect centers in diamond, offering significant advantages for quantum technology device design.
- Core Innovation (SVDMR): The technique, termed Surface Voltage Detected Magnetic Resonance (SVDMR), uses Kelvin Probe Force Microscopy (KPFM) to achieve single-spin readout of nitrogen-vacancy (NV) centers.
- Mechanism: SVDMR detects spin-dependent changes in the diamond surface photovoltage (PV) resulting from charge carrier release and trapping governed by the NV centerâs electron spin state.
- Ambient Operation: All measurements, including coherent spin dynamics (Rabi oscillations), were successfully performed under ambient conditions (room temperature).
- Performance Metrics: Achieved SVDMR contrast up to -4.0% and PV-detected Rabi oscillation contrast up to -17.5% on shallow NV centers (7 nm depth).
- Device Simplification: The PV-based readout eliminates the requirement for a current path through the sample, simplifying device architecture by removing the need for low-resistance contacts or high-gain current amplifiers.
- Broader Applicability: The method is potentially applicable to other solid-state systems, such as V2 centers in silicon carbide (SiC), and can be used to image non-fluorescing defects.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV Center Depth | 7 | nm | Shallow implantation below the diamond surface |
| Diamond Thickness | 50 | ”m | Electronic grade CVD plate |
| Nitrogen Implantation Energy | 5 | keV | Used for NV creation |
| Nitrogen Implantation Dose | 5 * 109 | ions/cm2 | Used for NV creation |
| Excitation Wavelength | 520 | nm | Continuous Wave (CW) Green Laser |
| KPFM AC Voltage Amplitude (Vac) | 6 | V | Applied to the cantilever for detection |
| KPFM AC Frequency (fac) | 3 | kHz | Used for lock-in detection |
| SVDMR Contrast (Maximum) | -4.0 | % | Measured on a single NV center |
| PV-Detected Rabi Contrast (Maximum) | -17.5 | % | Measured on a single NV center |
| Signal Response Time (KPFM) | ~10 | ms | Limited by lock-in detection and surface carrier capture rate |
| Annealing Temperature (Maximum) | 1000 | °C | Post-implantation processing step |
| MW Power (Rabi Experiments) | -14 | dBm | Used for coherent spin manipulation |
Key Methodologies
Section titled âKey MethodologiesâThe experiments utilized a combined Confocal-AFM setup and frequency-modulated KPFM to detect spin-dependent photovoltage changes.
- Sample Material: A thin electronic grade diamond plate (3 mm x 3 mm x 50 ”m) grown by Chemical Vapor Deposition (CVD) was used.
- NV Creation: Shallow NV centers were created via 5 keV nitrogen ion implantation (dose 5 * 109 ions/cm2).
- Post-Processing Annealing: The sample underwent multi-step annealing, ramping up to 1000 °C for 2 hours, followed by cooling.
- Surface Cleaning: The diamond surface was cleaned using a tri-acid mixture (nitric, perchloric, and sulfuric acids).
- Electrode Fabrication: Gold micro-strip lines were deposited on the surface to serve as electrical grounding contacts and for applying microwaves (MW).
- KPFM Setup: Measurements were performed using conductive cantilevers in a frequency-modulated sideband KPFM mode (Vac = 6 V, fac = 3 kHz).
- Optical Excitation: A CW green laser (520 nm) was focused to a diffraction-limited spot underneath the sample.
- SVDMR Protocol (CW): The NV center was continuously illuminated while the MW frequency was swept around the electron spin resonance. The resulting change in the Contact Potential Difference (CPD) was measured via KPFM.
- Coherent Dynamics (Pulsed): Rabi oscillations were measured using a pulsed MW output encoded in a low-frequency envelope, allowing the detection of coherent spin dynamics via the PV signal.
- PV Signal Extraction: Photovoltage (PV) images were obtained by subtracting the KPFM signal measured without laser illumination from the signal measured under illumination.
Commercial Applications
Section titled âCommercial ApplicationsâThe development of SVDMR provides a robust, simplified alternative to conventional optical and electrical spin readout methods, primarily benefiting the quantum technology sector.
- Quantum Sensing: Enables the design of compact, ambient-condition quantum sensors (e.g., magnetometers, electrometers) that rely on NV centers, simplifying the integration of readout electronics.
- Solid-State Qubits: Provides a pathway for electrical readout of quantum information encoded in the spin state of solid-state defects (qubits) without requiring complex optical collection systems.
- Simplified Device Fabrication: Eliminates the need for low-resistance ohmic contacts required for current-based electrical readout, lowering fabrication complexity and cost for quantum devices.
- Advanced Material Characterization: The ability to detect non-fluorescing defects via surface voltage contrast opens new avenues for searching and characterizing novel defect centers in diamond and other wide-bandgap materials.
- Alternative Quantum Platforms: The technique is potentially transferable to other critical quantum systems, including V2 centers in silicon carbide (SiC) and silicon-vacancy (SiV) centers in diamond.
View Original Abstract
Abstract Defect centres in crystals like diamond or silicon find a wide application in quantum technology, where the detection and control of their quantum states is crucial for their implementation as quantum sensors and qubits. The quantum information is usually encoded in the spin state of these defect centres, but they also often possess a charge which is typically not utilized. We report here the detection of elementary charges bound to single nitrogen-vacancy (NV) centres several nanometres below the diamond surface using Kelvin Probe Force Microscopy (KPFM) under laser illumination. Moreover, the measured signal depends on the NVâs electron spin state, thus allowing to perform a non-optical single spin readout, a technique we refer to as âSurface Voltage Detected Magnetic Resonanceâ (SVDMR). Our method opens a way of coherent spin dynamics detection for quantum sensing applications and could be potentially applied to other solid state systems. We believe that this voltage-based readout would help to simplify the design of devices for quantum technology.