Room-temperature control and electrical readout of individual nitrogen-vacancy nuclear spins

At a Glance

Metadata	Details
Publication Date	2021-07-20
Journal	Nature Communications
Authors	Michal Gulka, Daniel Wirtitsch, Viktor Ivády, Jelle Vodnik, Jaroslav Hruby
Institutions	Imec the Netherlands, Budapest University of Technology and Economics
Citations	54
Analysis	Full AI Review Included

Technical Analysis and Documentation: Electrical Readout of NV Nuclear Spins

This document analyzes the research paper “Room-temperature control and electrical readout of individual nitrogen-vacancy nuclear spins” and maps the material requirements and experimental methodologies to the advanced capabilities offered by 6CCVD (6ccvd.com), an expert supplier of MPCVD diamond materials for quantum technologies.

Executive Summary

This research demonstrates a significant step toward scalable, room-temperature diamond quantum processors by achieving the electrical readout of a single ¹⁴N nuclear spin qubit coupled to a Nitrogen-Vacancy (NV) center.

Core Achievement: Successful room-temperature photoelectric detection and coherent control of a single intrinsic ¹⁴N nuclear spin, mediated by the NV electron spin near the Excited-State Level Anti-Crossing (ESLAC).
Scalability: The Photoelectric Detection of Magnetic Resonance (PDMR) technique limits readout area by inter-electrode distance (3.5 µm gap) rather than the optical diffraction limit, enabling nanoscale integration.
Performance: Achieved high Signal-to-Background Contrast (SBC >65%) at an optimal bias voltage of 8.6 V, utilizing a 561 nm laser to suppress background current from P1 centers.
Resolution Improvement: Electrical imaging demonstrated a threefold improvement in axial spatial resolution (0.9 µm FWHM) compared to conventional optical readout (2.7 µm FWHM).
Material Requirement: The experiment relied on high-purity, low-nitrogen (intrinsic) Single Crystal Diamond (SCD) to ensure long nuclear spin coherence times.
Future Impact: This methodology provides the theoretical and experimental foundation for developing electronic quantum processors based on dipolar interaction of spin-qubits placed at nanoscopic proximity.

Technical Specifications

The following hard data points were extracted from the experimental results, highlighting the critical parameters for device operation.

Parameter	Value	Unit	Context
Operating Temperature	Ambient	°C	Quantum device operation
Optimal Bias Voltage	8.6	V	Highest NV Signal-to-Background Contrast (SBC)
Maximum SBC Achieved	>65	%	Electrical readout performance
Excitation Wavelength	561	nm	Used to reduce P1 center photoionization
Excitation Energy	2.21	eV	Corresponds to 561 nm laser
Laser Power (Operation)	4-6	mW	Applied for high Signal-to-Noise (S/N) ratio
Electrode Gap	3.5	µm	Coplanar interdigitated contacts
NV Center Depth	~2.5	µm	Below diamond surface
ESLAC Magnetic Field	~510	G	Excited-State Level Anti-Crossing condition
Electrical Axial Resolution (FWHM)	0.9	µm	PDMR readout resolution
Optical Axial Resolution (FWHM)	2.7	µm	Conventional optical readout resolution
Nuclear Spin Qubit	¹⁴N	N/A	Intrinsic NV nuclear spin

Key Methodologies

The experiment successfully combined advanced diamond material science with microelectronic fabrication and complex pulsed quantum control sequences.

Material Selection: High-purity, commercial IIa High-Pressure High-Temperature (HPHT) diamond was used, characterized by ultra-low background nitrogen (<10 ppb) to minimize defect noise.
Device Fabrication: Coplanar interdigitated contacts with a 3.5 µm gap were fabricated on the diamond surface using optical lithography, requiring a highly polished substrate.
Photoelectric Detection (PDMR): The spin state was read out electrically by measuring the photocurrent generated by two-photon ionization of the NV center, accelerating charge carriers toward the electrodes under bias voltage.
Excitation Optimization: A yellow-green 561 nm laser was employed instead of the standard 532 nm green laser to reduce background photocurrent induced by photoionization of substitutional nitrogen (P1 centers).
Qubit Initialization: The ¹⁴N nuclear spin was polarized to the |m_I> = |+1> state (>98% polarization) by optical pumping while aligning an external magnetic field (~510 G) with the NV axis (ESLAC condition).
Coherent Control: A modified pulsed lock-in envelope readout technique was used, combining continuous Microwave (MW) driving for electron spin manipulation and Radiofrequency (RF) pulses for coherent nuclear spin rotation.

6CCVD Solutions & Capabilities

6CCVD provides the high-specification MPCVD diamond materials and custom fabrication services necessary to replicate, optimize, and scale the microelectronic quantum devices demonstrated in this research. Our capabilities directly address the need for ultra-high purity, precise geometry, and integrated metalization.

Applicable Materials

Research Requirement	6CCVD Material Recommendation	Technical Justification
Ultra-High Purity Substrate (Intrinsic NV centers, low P1 noise)	Optical Grade Single Crystal Diamond (SCD)	Our MPCVD SCD offers background nitrogen levels significantly lower than the <10 ppb used in the paper (down to <1 ppb available), ensuring maximum intrinsic NV coherence and minimizing background current for enhanced PDMR contrast.
Future Scalability (Extension to ¹³C registers)	Isotopically Pure SCD (¹²C enriched)	To achieve the long coherence times (T₂) required for multi-qubit registers (e.g., ¹³C), 6CCVD supplies SCD with controlled isotopic enrichment, reducing decoherence from lattice nuclear spins.
High-Density Integration	Polycrystalline Diamond (PCD) Wafers	For large-scale integration and high-throughput fabrication, we offer PCD wafers up to 125mm in diameter, providing a cost-effective platform for developing quantum sensors and electronic devices.

Customization Potential

The success of this PDMR device relies heavily on precise microfabrication and surface engineering, areas where 6CCVD offers critical in-house expertise.

Fabrication Requirement	6CCVD Customization Service	Specification Match
Surface Quality (Required for 3.5 µm lithography)	Precision Polishing	SCD surfaces polished to Ra < 1 nm, ensuring high-fidelity lithography, reliable electrode adhesion, and minimal charge carrier scattering.
Electrode Integration (Coplanar contacts)	Internal Metalization Capability	We offer deposition of standard quantum stack metal layers (e.g., Ti/Pt/Au, Ti/W, Cu) directly onto the diamond surface, optimizing ohmic contact for efficient charge carrier collection.
Custom Chip Dimensions (Microelectronic integration)	Custom Laser Cutting & Wafer Sizing	6CCVD supplies SCD plates up to 500 µm thick and offers precision laser cutting to match specific chip sizes and geometries required for integration into microelectronic platforms.
Thickness Control (NV depth optimization)	Precise Thickness Control	We offer SCD wafers with thickness control from 0.1 µm up to 500 µm, allowing researchers to optimize the bulk material properties and subsequent NV implantation depth.

Engineering Support

6CCVD’s in-house PhD team specializes in diamond material optimization for quantum applications. We can assist researchers in extending this work to:

Controlled NV Creation: Advising on post-growth processing (e.g., ion implantation and annealing) to create shallow NV centers with optimized yield and depth control, crucial for enhancing charge collection efficiency.
Material Selection for Sensing: Assisting with the selection of specific SCD grades (e.g., isotopically enriched or high-BDD) for similar Photoelectric Quantum Gate Operations and Nuclear Qubit Register projects.
Device Architecture: Consulting on optimal metalization stacks and surface termination methods to maximize charge carrier mobility and PDMR contrast.

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/s41467-021-24494-x