| Metadata | Details |
|---|
| Publication Date | 2021-01-22 |
| Journal | Nature Communications |
| Authors | Dominik M. Irber, Francesco Poggiali, Fei Kong, Michael Kieschnick, Tobias LĂŒhmann |
| Institutions | University of Rostock, University of Science and Technology of China |
| Citations | 74 |
| Analysis | Full AI Review Included |
- Core Achievement: Demonstration of a robust, all-optical single-shot readout scheme for Nitrogen-Vacancy (NV) centers in diamond, eliminating the requirement for high-efficiency photon collection optics (e.g., immersion lenses).
- Methodology: The protocol utilizes Spin-to-Charge Conversion (SCC) enabled by spin-dependent resonant excitation at cryogenic temperatures, mapping the fragile electron spin state to the stable charge state (NV- or NV0).
- Performance (Deep NV): Achieved a single-shot Signal-to-Noise Ratio (SNR) of 3.5 ± 1.2 and a corrected Readout Fidelity of 96.4 ± 2.2% using photon collection delivering less than 103 clicks/second.
- Shallow NV Validation: Successfully applied the technique to shallow implanted NV centers (~70 nm depth), achieving a near single-shot SNR of 0.99 ± 0.13 and a corrected fidelity of 78.6 ± 2.5%.
- Speed and Efficiency: The method provides a speedup factor of 103 over standard readout for long (ms) sensing protocols, enabling quantum sensing experiments previously limited by acquisition speed.
- Robustness: The scheme is resilient to poor photon collection and promises robustness against strong, misaligned background magnetic fields and high-strain environments.
| Parameter | Value | Unit | Context |
|---|
| Deep NV Readout Fidelity | 96.4 ± 2.2 | % | Corrected fidelity (Ionization + Charge Detection steps). |
| Deep NV Single-Shot SNR | 3.5 ± 1.2 | N/A | Achieved on natural NV center. |
| Shallow NV Readout Fidelity | 78.6 ± 2.5 | % | Corrected fidelity on implanted center. |
| Shallow NV Single-Shot SNR | 0.99 ± 0.13 | N/A | Achieved on implanted NV center (~70 nm depth). |
| Minimum Photon Flux Required | < 103 | clicks/second | Demonstrated single-shot fidelity despite poor collection. |
| Shallow NV Implantation Depth | ~70 | nm | Resulting from 110 keV CN- implant. |
| Resonant Laser Wavelength | 637 | nm | Tuned to the NV- spin 0 transition. |
| Ionization Laser Wavelength | 642 | nm | High-power red diode laser. |
| Initialization Laser Wavelength | 517 | nm | Green diode laser. |
| Deep NV Off-Axial Strain | 1.73 | GHz | Estimated from photoluminescence excitation (PLE). |
| Shallow NV Off-Axial Strain | 12.6 | GHz | Estimated from PLE (high strain environment). |
| Speedup Factor (Long Sensing) | 103 | N/A | Compared to standard readout for long protocols (ms). |
| Charge Readout Time (Deep NV) | 1 | ms | Used for fidelity measurement. |
| Charge Readout Time (Shallow NV) | 5 | ms | Used for fidelity measurement. |
- Experimental Setup: Measurements performed in a home-built confocal microscope utilizing a Helium flow cryostat, allowing for cryogenic operation and line narrowing of optical transitions.
- Optics and Excitation: An air objective (NA 0.95) was used for illumination and collection. Three independently gated lasers were combined: a narrow-band 637 nm resonant laser, a strong 642 nm ionization laser, and a 517 nm green initialization laser.
- Charge Initialization (âCharge Init.â): Performed using the 517 nm green laser to ensure the NV center is in the negative charge state (NV-).
- Spin Initialization: Achieved by repeated resonant depletion of the spin |0) state (using 637 nm laser) followed by a microwave (MW) Ï-pulse to empty the |-1) state, preparing the spin in the |+1) state.
- Spin-Dependent Ionization (SCC): This two-photon process is the heart of the readout. The 637 nm resonant laser provides the first photon, selectively exciting only the spin |0) state. Simultaneously, the high-power 642 nm laser provides the second photon, ionizing the NV- from the excited state to the NV0 charge state. Spin |±1) is protected from excitation and ionization.
- Charge Readout: Low-power detection using the 637 nm resonant laser, made spin-agnostic by applying continuous wave (cw) MW excitation at both ground-state transitions. This allows high-fidelity detection of the charge state (NV- yields high fluorescence; NV0 yields near-zero fluorescence).
- Sample Preparation (Shallow NV): Electronic grade diamond was implanted with CN- ions at 110 keV, followed by high-temperature annealing (up to 1200 °C) and Oxygen plasma surface treatment.
- Quantum Sensing (Long Protocols): The 103 speedup factor enables practical implementation of long (ms) sensing protocols, critical for high-sensitivity magnetometry, electrometry, and thermometry using NV centers.
- Scalable Quantum Registers: High-fidelity single-shot readout on shallow NV centers (~70 nm) is a prerequisite for coupling NV spins to external solid-state devices (e.g., single-electron transistors or surface gates) necessary for building scalable quantum architectures.
- Cryogenic Biological Sensing: The methodâs robustness against poor photon collection allows for sensing applications in environments where high-NA immersion optics are impossible, such as within the entire thickness of biological cryoslices.
- Solid-State Qubit Readout: The technique is transferable to other challenging spin qubit systems, such as defects in Silicon Carbide (SiC), where low photon count rates currently limit single-shot fidelity.
- Diamond Material Engineering: Provides a reliable metric for evaluating the quality and performance of shallow implanted NV centers, guiding optimization of implantation and annealing recipes.
View Original Abstract
Abstract High-fidelity projective readout of a qubitâs state in a single experimental repetition is a prerequisite for various quantum protocols of sensing and computing. Achieving single-shot readout is challenging for solid-state qubits. For Nitrogen-Vacancy (NV) centers in diamond, it has been realized using nuclear memories or resonant excitation at cryogenic temperature. All of these existing approaches have stringent experimental demands. In particular, they require a high efficiency of photon collection, such as immersion optics or all-diamond micro-optics. For some of the most relevant applications, such as shallow implanted NV centers in a cryogenic environment, these tools are unavailable. Here we demonstrate an all-optical spin readout scheme that achieves single-shot fidelity even if photon collection is poor (delivering less than 10 3 clicks/second). The scheme is based on spin-dependent resonant excitation at cryogenic temperature combined with spin-to-charge conversion, mapping the fragile electron spin states to the stable charge states. We prove this technique to work on shallow implanted NV centers, as they are required for sensing and scalable NV-based quantum registers.