Mapping a 50-spin-qubit network through correlated sensing

At a Glance

Metadata	Details
Publication Date	2024-03-05
Journal	Nature Communications
Authors	G. L. van de Stolpe, Damian Kwiatkowski, C. E. Bradley, J. Randall, M. H. Abobeih
Institutions	QuTech, Element Six (United Kingdom)
Citations	27
Analysis	Full AI Review Included

Technical Documentation & Analysis: Mapping Large Spin Qubit Networks in Diamond

Executive Summary

This research demonstrates a significant advancement in solid-state quantum sensing and simulation by successfully mapping a 50-nuclear-spin network surrounding a single Nitrogen-Vacancy (NV) center in diamond.

Core Achievement: Mapping a network of 50 coupled ¹³C nuclear spins, a substantial increase over previous state-of-the-art limits (27 spins), unlocking larger qubit registers for quantum applications.
Methodology: Utilizes novel correlated double-resonance sensing schemes, including concatenated Spin-Echo Double Resonance (SEDOR) sequences, to resolve network connectivity and overcome spectral crowding.
High Resolution: Achieves high spectral resolution (T₂-limited, 1.8 Hz linewidth) for characteristic spin frequencies (hyperfine shifts A_i), enabling unambiguous identification of individual spins.
Material Basis: Experiments rely on high-quality, homo-epitaxially grown CVD diamond substrates with natural 1.1% ¹³C abundance, cleaved along the critical (111) crystal direction.
Application Impact: Provides a crucial foundation for universal quantum control, optimizing quantum memory registers, and advancing high-resolution nano-MRI of complex external spin systems.
6CCVD Value Proposition: 6CCVD provides the necessary high-coherence Single Crystal Diamond (SCD) substrates, custom isotopic engineering, and integrated metalization services required to replicate and scale this foundational quantum research.

Technical Specifications

The following hard data points were extracted from the experimental setup and results:

Parameter	Value	Unit	Context
Mapped Spin Network Size	50	Nuclear Spins	¹³C spins surrounding a single NV center
Diamond Growth Method	Homo-epitaxial	CVD	Cleaved along the (111) crystal direction
¹³C Abundance	1.1	%	Natural abundance
Operating Temperature	3.7	K	Performed in a cryostat
External Magnetic Field (B_z)	403.553	G	Applied along the NV symmetry axis
NV Electron Spin T₂*	4.9(2)	µs	Dephasing time
NV Electron Spin T₂ (Hahn Echo)	1.182(5)	ms	Coherence time
Nuclear Spin T₂ (Hahn Echo)	Up to 0.77(4)	s	For isolated ¹³C spins
High-Resolution Linewidth	1.8	Hz	T₂-limited measurement of hyperfine shift (A_i)
Nuclear-Nuclear Coupling Range (C_ij)	2 - 10	Hz	Strong, resolvable couplings measured
MW Transition Frequencies	1.746666 / 4.008650	GHz	ms = 0 → ms = ±1 transitions
RF Pulse Frequency Range	400 - 500	kHz	Applied via gold stripline

Key Methodologies

The experiment relied on precise material engineering and advanced quantum control sequences:

Material Selection and Preparation: High-quality, homo-epitaxially grown CVD diamond was used. The sample was cleaved along the (111) crystal direction to align the NV center symmetry axis. The NV center was selected based on minimal coupling to nearby ¹³C spins (< 500 kHz).
Cryogenic and Magnetic Environment: Experiments were conducted at 3.7 K. A temperature-stabilized permanent neodymium magnet provided a highly stable external magnetic field (B_z = 403.553 G).
Pulse Delivery Integration: A gold stripline was deposited close to a Solid Immersion Lens (SIL) to deliver high-fidelity Microwave (MW) and Radio-Frequency (RF) pulses necessary for spin control.
Spin Initialization and Polarization: The NV electron spin was initialized and read out optically. The nuclear spin network was polarized using the PulsePol Dynamical Nuclear Polarization (DNP) sequence.
Correlated Sensing Sequences: The core method involved concatenating double-resonance sequences (extensions of SEDOR) to measure chains of coupled spins (up to N=5), directly accessing network connectivity and reducing ambiguity from spectral overlap.
High-Resolution Spectroscopy: An electron-nuclear double-resonance block was inserted into the spin-chain sequence to isolate nuclear spins from quasi-static noise, achieving T₂-limited spectral resolution for distinguishing overlapping spin frequencies (A_i).
Network Reconstruction: A graph search algorithm, complemented by 3D spatial positioning logic, was used to fuse the measured spin chains and pairwise interactions, reconstructing the complete 50-spin network connectivity.

6CCVD Solutions & Capabilities

This research highlights the critical need for ultra-high-quality diamond materials with precise control over crystal orientation and isotopic purity. 6CCVD is uniquely positioned to supply the necessary materials and integrated services to advance this work toward scalable quantum technologies.

Applicable Materials for Quantum Sensing and Simulation

To replicate and extend this research, 6CCVD recommends the following materials:

6CCVD Material	Specification	Application in Research
Optical Grade SCD	SCD plates, Ra < 1nm polishing, Thickness 0.1µm - 500µm.	Essential for hosting high-coherence NV centers and achieving the long T₂ times (up to 0.77 s) required for correlated sensing of distant spins.
Custom (111) SCD Substrates	Single Crystal Diamond wafers cut and polished to specific crystallographic orientations, including (111).	Ensures optimal alignment of the NV center axis with the external magnetic field, maximizing the fidelity of the double-resonance sequences.
Isotopically Engineered SCD	SCD with tailored ¹³C concentration (e.g., < 0.05% for minimal noise, or enriched ¹³C for dense qubit registers).	Allows researchers to precisely control the density and coupling strength of the nuclear spin bath, critical for optimizing quantum memory and simulation registers beyond the natural 1.1% abundance used here.
Polycrystalline Diamond (PCD)	Wafers up to 125mm diameter, substrates up to 10mm thick, Ra < 5nm polishing.	Ideal for scaling up device fabrication, providing large-area platforms for integrating complex arrays of NV sensors or external nano-MRI samples.

Customization Potential

The successful implementation of the correlated sensing sequences relies heavily on the ability to deliver precise MW and RF pulses via integrated structures.

Custom Metalization: The paper utilized a gold stripline. 6CCVD offers in-house, high-precision metalization services, including deposition of Au, Pt, Pd, Ti, W, and Cu. We can pattern these layers to create custom striplines, waveguides, or electrodes directly on the diamond surface, streamlining the integration of pulse delivery systems.
Custom Dimensions and Shaping: 6CCVD provides custom laser cutting and shaping services for both SCD and PCD plates up to 125mm, ensuring the diamond substrate perfectly fits specialized cryogenic or optical setups (e.g., integrating with SILs or cryostat windows).

Engineering Support

6CCVD’s in-house PhD team specializes in the material science of diamond for quantum applications. We offer comprehensive engineering support for projects focused on NV-based Quantum Sensing and Quantum Simulation. Our experts can assist researchers in selecting the optimal isotopic purity, crystal orientation, and surface termination to maximize NV coherence and fidelity for mapping complex spin networks.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. Global shipping (DDU default, DDP available) ensures rapid delivery worldwide.

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41467-024-46075-4