Direct readout of a nitrogen-vacancy hybrid-spin quantum register in diamond by analysis of photon arrival time

At a Glance

Metadata	Details
Publication Date	2024-05-21
Journal	Physical Review Applied
Authors	Jingyan He, Yu Tian, Zhiyi Hu, Runchuan Ye, Xiangyu Wang
Institutions	Hefei University of Technology, Zhejiang Lab
Citations	3
Analysis	Full AI Review Included

Technical Documentation & Analysis: Direct Readout of NV Hybrid-Spin Quantum Registers

This document analyzes the research paper “Direct Readout of Nitrogen-Vacancy Hybrid-Spin Quantum Register in Diamond by Photon Arrival Time Analysis” to provide technical specifications and align the findings with 6CCVD’s advanced MPCVD diamond capabilities, focusing on solutions for quantum technology researchers.

Executive Summary

Core Achievement: Demonstration of a novel, highly efficient direct readout scheme for Nitrogen-Vacancy (NV) hybrid electron-nuclear spin quantum registers in CVD diamond.
Methodology: Utilizes the Excited State Level Anti-Crossing (ESLAC) phenomenon at approximately 500 Gs, analyzing the photon arrival time traces from a single laser pulse.
Efficiency Gain: Achieved a substantial time-saving factor of up to 32x compared to conventional quantum state diagonal tomography methods for achieving 0.95 fidelity.
Fidelity: Maintained high population readout fidelity (Fp > 0.99 for basis states) at room temperature, validating the direct measurement approach.
Operational Advantage: Eliminates the requirement for complex, lengthy microwave (MW) and radio frequency (RF) spin manipulation sequences prior to readout, significantly reducing decoherence-induced errors.
Material Requirement: The technique is optimized for high-quality, low-strain bulk CVD diamond platforms, essential for stable NV center creation and long spin coherence times.

Technical Specifications

The following hard data points were extracted from the experimental realization and time-cost analysis sections of the research paper:

Parameter	Value	Unit	Context
Operating Temperature	Room Temperature	°C	Confocal microscopy setup
Magnetic Field (ESLAC Point)	~500	Gs	Applied parallel to NV axis (z-direction)
NV Center Depth	10	µm	Embedded in bulk CVD diamond
Excitation Wavelength	532	nm	Green laser source
Time Tagger Resolution	2	ns	Custom-built detection system
Direct Readout Time (Fp=0.95)	6.83 x 10⁸	ns	Time required for direct method
General Readout Time (Fp=0.95)	2.24 x 10¹⁰	ns	Time required for conventional method
Time Acceleration Factor	~32	N/A	Ratio of General to Direct Readout Time
Population Readout Fidelity (Basis States)	> 0.99	N/A	Achieved using Maximum Likelihood Estimation
RF1 Frequency (Calibration)	5.102067	MHz	Used for electron-nuclear double resonance (ENDOR)
RF2 Frequency (Calibration)	2.941124	MHz	Used for electron-nuclear double resonance (ENDOR)

Key Methodologies

The experiment successfully demonstrated direct spin readout by focusing on the NV center’s excited state dynamics under specific magnetic field conditions:

Material Selection: Utilizing an NV center embedded 10 µm deep in a bulk Chemical Vapor Deposition (CVD) diamond sample, indicating the need for high-quality, low-defect Single Crystal Diamond (SCD).
Magnetic Field Alignment: A static magnetic field of approximately 500 Gs was generated using a columnar neodymium magnet and applied parallel to the NV defect axis (z-direction). This field strength is critical for inducing the Excited State Level Anti-Crossing (ESLAC) phenomenon.
Optical Initialization & Readout: A 532 nm green laser, switched via an acoustic-optic modulator (AOM), was used for both optical pumping (initialization) and fluorescence readout.
Time-Resolved Detection: Fluorescence was collected and detected by an Avalanche Photo Diode (APD). The output signal was recorded by a custom-built time tagger with a 2 ns resolution, capturing the photon arrival time traces.
Direct State Determination: The spin state populations were determined by performing optimization (Maximum Likelihood Estimation) on the acquired photon time traces, leveraging the distinct fluorescence decay curves associated with the four hybrid-spin basis states at the ESLAC point.
Fidelity Validation: The method was validated by preparing known test states and superposition states, achieving high fidelity (Fp > 0.99) compared to theoretical predictions.

6CCVD Solutions & Capabilities

6CCVD provides the foundational MPCVD diamond materials and customization services necessary to replicate, scale, and advance this high-efficiency quantum readout research. Our capabilities directly address the stringent material requirements for NV hybrid-spin quantum registers.

Research Requirement	6CCVD Applicable Materials & Services	Technical Value Proposition
High-Purity CVD Diamond Substrate (Essential for long T₂ coherence)	Optical Grade Single Crystal Diamond (SCD) plates.	Provides ultra-low strain and controlled nitrogen content, minimizing decoherence and maximizing the stability of the NV centers required for high-fidelity quantum registers.
Precise Substrate Dimensions (Integration into confocal/ODMR systems)	Custom Dimensions and Thickness: SCD wafers from 0.1 µm to 500 µm; Substrates up to 10 mm thick. PCD wafers up to 125 mm diameter.	Enables precise control over NV implantation depth (e.g., 10 µm used in the paper) and facilitates integration into specialized magnetic field and optical setups.
High-Quality Optical Interface (Maximizing photon collection efficiency)	Precision Polishing Services: Achieves surface roughness Ra < 1 nm on SCD.	Critical for minimizing optical scattering and maximizing the signal-to-noise ratio of the photon arrival time traces, which is the core measurement of this technique.
Future Full-State Tomography (Requires MW/RF control integration)	Custom Metalization: In-house deposition of standard quantum metals (Au, Pt, Pd, Ti, W, Cu).	Allows researchers to integrate on-chip microwave and radio frequency antennas directly onto the diamond surface for complex quantum control, state preparation, and full-state tomography extensions.
Extension to Sensing Applications (Requires specific doping)	Boron-Doped Diamond (BDD) films and substrates.	While the paper focuses on NV centers, 6CCVD offers BDD for electrochemical and high-power electronic applications, providing a versatile platform for related diamond research.

Engineering Support

6CCVD’s in-house PhD team specializes in the growth and characterization of MPCVD diamond for quantum applications. We can assist researchers in optimizing material specifications—such as isotopic purification (e.g., ¹²C enrichment) or controlled nitrogen doping—to maximize the coherence time and ESLAC efficiency for similar NV hybrid-spin quantum register projects.

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

View Original Abstract

Quantum state readout plays a pivotal role in quantum technologies, spanning\napplications in sensing, computation, and secure communication. In this work,\nwe introduce a new approach for efficiently reading populations of hybrid-spin\nstates in the nitrogen-vacancy center of diamond using a single laser pulse,\nwhich utilizes the excited state level anti-crossing mechanism at around 500\nGs. Reading spin state populations through this approach achieves the same\noutcome as traditional quantum state diagonal tomography but significantly\nreduces the experimental time by an order of magnitude while maintaining\nfidelity. Moreover, this approach may be extended to encompass full-state\ntomography, thereby obviating the requirement for a sequence of spin\nmanipulations and mitigating errors induced by decoherence throughout the\nprocedure.\n

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevapplied.21.054041