High-fidelity single-shot readout of single electron spin in diamond with spin-to-charge conversion

At a Glance

Metadata	Details
Publication Date	2021-03-09
Journal	Nature Communications
Authors	Qi Zhang, Yuhang Guo, Wentao Ji, Mengqi Wang, Jun Yin
Institutions	Hefei National Center for Physical Sciences at Nanoscale, CAS Key Laboratory of Urban Pollutant Conversion
Citations	60
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Fidelity Single-Shot Readout in Diamond

This document analyzes the research paper “High-fidelity single-shot readout of single electron spin in diamond with spin-to-charge conversion” and outlines how 6CCVD’s advanced MPCVD diamond materials and customization capabilities can support and extend this critical quantum technology research.

Executive Summary

The research successfully demonstrates a robust method for achieving high-fidelity single-shot readout of Nitrogen-Vacancy (NV) electron spins in diamond, a crucial step toward fault-tolerant quantum computing.

Core Achievement: Achieved an overall single-shot readout fidelity of 95.4% ± 0.2% using a novel Near-Infrared (NIR)-assisted Spin-to-Charge Conversion (SCC) technique.
Performance Improvement: This fidelity significantly exceeds the previous limit of the standard resonance fluorescence method (79.6%) under similar high-strain conditions.
Mechanism: The SCC method leverages NIR light (1064 nm) to rapidly ionize the excited state (converting NV^- to NV⁰) before the detrimental spin-flip relaxation occurs.
Robustness: High fidelity was maintained despite high non-axial strain ($\delta$ = 5.9 GHz) and a fast spin-flip rate ($\Gamma_{\text{flip}}$ = 0.75 MHz), conditions that typically degrade readout performance.
Scalability Potential: Theoretical projections indicate that by increasing the ionization rate ($\Gamma_{\text{ion}}$) via higher NIR power, this technique is experimentally feasible to exceed the 99.9% fault-tolerant threshold.
Applications: The technique is highly applicable to scalable quantum networks, integrated optoelectronic devices, and high-efficiency quantum sensing, particularly in bio-samples where NIR light minimizes photo-damage.

Technical Specifications

The following table summarizes the key quantitative parameters and performance metrics extracted from the research.

Parameter	Value	Unit	Context
Single-Shot Readout Fidelity (SCC)	95.4 ± 0.2	%	Achieved average fidelity with Auxiliary Correction.
Projected Fault-Tolerant Fidelity	> 99.9	%	Target fidelity achievable with higher $\Gamma_{\text{ion}}$.
Spin-Flip Rate ($\Gamma_{\text{flip}}$)	0.75 ± 0.02	MHz	Observed rate due to high non-axial strain.
Non-Axial Strain ($\delta$)	5.9	GHz	Strain induced by solid immersion lens (SIL) fabrication.
Charge Readout Fidelity ($F_{\text{charge}}$)	99.96 ± 0.02	%	Non-demolition readout of NV^- state.
Maximum Ionization Rate ($\Gamma_{\text{ion}}$)	2.79 ± 0.08	MHz	Highest rate achieved using 1064 nm NIR laser.
NIR Ionization Rate Coefficient	67.0 ± 6.7	kHz/mW	Dependence of $\Gamma_{\text{ion}}$ on 1064 nm power.
Operating Temperature	8	K	Cryogenic conditions required for resonance excitation.
Magnetic Field	585	G	Applied field to lift spin degeneracy.
SCC Duration (Optimal)	~ 10	µs	Time required to achieve maximum fidelity.

Key Methodologies

The high-fidelity readout was achieved by combining cryogenic resonance excitation with a spin-selective photoionization process assisted by NIR light.

Material Environment: Experiments were conducted on a bulk NV center embedded within a solid immersion lens (SIL) structure, operating at a cryogenic temperature of 8 K.
Magnetic Field Application: A 585 G magnetic field was aligned to the NV axis to lift the degeneracy between the $|+1\rangle$ and $|-1\rangle$ spin states.
Spin Initialization: The NV spin was initialized to the desired state (e.g., $|0\rangle$) using a 532 nm laser pulse (3 µs) followed by measurement-based charge state post-selection.
Spin-to-Charge Conversion (SCC): The core process involved simultaneous illumination using the cycling transition ($E_y$) and a Near-Infrared (NIR) laser (1064 nm). This rapidly converts the spin state $|0\rangle$ to the charge state NV⁰.
Auxiliary Correction: To mitigate leakage population trapped in the auxiliary state ($|-1\rangle$), an MWAUX $\pi$ pulse was applied to transfer this population back to $|0\rangle$, allowing for subsequent ionization and higher conversion efficiency.
Charge Readout: The final charge state (fluorescent NV^- or dark NV⁰) was determined by detecting the photon number during a 500 µs integration window, providing near-unity charge readout fidelity.

6CCVD Solutions & Capabilities

This research highlights the critical need for high-quality, low-defect diamond substrates for advancing quantum technologies. 6CCVD is uniquely positioned to supply the materials and customization services required to replicate, optimize, and scale this Spin-to-Charge Conversion (SCC) technique.

Applicable Materials

To replicate or extend this research, particularly in achieving the low-strain environment necessary for fault-tolerant thresholds, researchers require ultra-high purity Single Crystal Diamond (SCD).

6CCVD Material Recommendation	Specification & Relevance to Research
Optical Grade Single Crystal Diamond (SCD)	Required for isolated NV centers and high optical transmission. Our SCD features extremely low nitrogen concentration (PPM level) for precise NV creation and minimal background fluorescence.
Low-Strain SCD Substrates	The paper notes that high strain ($\delta$ = 5.9 GHz) limits performance ($\Gamma_{\text{flip}}$ = 0.75 MHz). 6CCVD provides SCD optimized for low intrinsic strain, crucial for achieving the predicted $\Gamma_{\text{flip}}$ = 0.2 MHz required to exceed 99.9% fidelity.
Custom SCD Thickness	We offer SCD plates from 0.1 µm up to 500 µm thickness, allowing researchers to select the optimal depth for NV implantation and subsequent fabrication of solid immersion lenses (SILs) or integrated waveguides.

Customization Potential

The integration of NV centers into scalable quantum devices, as discussed in the paper, necessitates advanced material processing and integration capabilities.

Custom Dimensions and Polishing: 6CCVD supplies SCD wafers with custom dimensions and offers industry-leading polishing services, achieving surface roughness Ra < 1 nm (SCD). This ultra-smooth surface is essential for minimizing scattering losses when fabricating integrated optical structures like SILs or microcavities.
Metalization Services: The experiment utilizes microwave pulses (MWAUX) for spin manipulation. For integrated quantum circuits, 6CCVD offers in-house, custom metalization capabilities, including Au, Pt, Pd, Ti, W, and Cu. This allows for the direct fabrication of microwave striplines or electrodes onto the diamond surface.
Large-Area Polycrystalline Diamond (PCD): For applications requiring large-scale integrated optoelectronic devices, 6CCVD offers high-quality PCD wafers up to 125 mm in diameter, polished to Ra < 5 nm.

Engineering Support

The success of the SCC method relies heavily on the material quality and the ability to manage strain and defect density.

Strain Management Consultation: 6CCVD’s in-house PhD team specializes in MPCVD growth optimization. We can assist researchers in selecting the ideal SCD material and orientation to minimize intrinsic strain, directly addressing the main limiting factor ($\Gamma_{\text{flip}}$) identified in this research.
NV Creation Optimization: We provide consultation on optimizing diamond substrates for subsequent NV creation (e.g., implantation, annealing) to ensure high yield and optimal spin properties for similar NV Center Quantum Readout projects.
Global Logistics: We ensure reliable, global shipping (DDU default, DDP available) of sensitive diamond materials, supporting international research collaborations.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41467-021-21781-5