Detection and control of single proton spins in a thin layer of diamond grown by chemical vapor deposition

At a Glance

Metadata	Details
Publication Date	2020-09-14
Journal	Applied Physics Letters
Authors	Kento Sasaki, Hideyuki Watanabe, Hitoshi Sumiya, Kohei M. Itoh, Eisuke Abe
Institutions	RIKEN Center for Emergent Matter Science, Sumitomo Electric Industries (Japan)
Citations	8
Analysis	Full AI Review Included

Technical Documentation & Analysis: Single Proton Spin Control in CVD Diamond

Reference: Sasaki et al., Detection and control of single proton spins in a thin layer of diamond grown by chemical vapor deposition (arXiv:2006.07761v2, 2020).

Executive Summary

This research demonstrates a critical advancement in nanoscale Nuclear Magnetic Resonance (NMR) and quantum computing by achieving detection and coherent control of a single proton ($^1$H) nuclear spin using a Nitrogen-Vacancy (NV) center in MPCVD diamond as a quantum sensor.

Atomic Scale NMR: The work successfully observes free induction decays (FID) from a single proton, extending high-resolution NMR spectroscopy to the atomic scale.
Quantum Memory Potential: Protons incorporated during the Chemical Vapor Deposition (CVD) growth process are identified as potential built-in quantum memories coupled to the NV center qubit.
Material Requirement: The experiment relies on a high-quality, thin CVD diamond layer grown on a low-strain Type-IIa (100) SCD substrate, emphasizing the need for precise isotopic and nitrogen control.
Coherent Control Achieved: Hyperfine parameters ($A_{||}$, $A_{\perp}$) were determined, and the single proton spin was polarized and coherently rotated (Rabi frequency 57.7 kHz).
CVD Incorporation: The observed protons are confirmed to be incorporated within the diamond matrix during CVD growth, not merely surface termination, highlighting the importance of controlled growth recipes.
Operational Advantage: Utilizing the proton spin offers a higher Larmor frequency compared to the more common $^{13}$C nuclear spin, enabling potentially faster quantum operations.

Technical Specifications

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

Parameter	Value	Unit	Context
Substrate Material	Type-IIa (100) SCD	N/A	HPHT prepared, low N (< 0.1 ppm)
CVD Substrate Temperature	800	°C	MPCVD Growth Parameter
CVD Chamber Pressure	25	Torr	MPCVD Growth Parameter
CVD Microwave Power	750	W	MPCVD Growth Parameter
Methane/Hydrogen Ratio ([CH${4}$]/[H${2}$])	0.5	%	Doped Layer Growth
Nitrogen/Carbon Ratio (N/C)	24	%	NV Incorporation
Proton Larmor Frequency ($f_{H}$)	1.2239	MHz	Measured at $B_{0}$ = 28.7 mT
Parallel Hyperfine Constant ($A_{		}/2\pi$)	-19.0
Perpendicular Hyperfine Constant ($A_{\perp}/2\pi$)	22.9	kHz	NV-Proton Coupling Strength
NV-Proton Distance ($r$)	1.44	nm	Calculated Spatial Coordinate
NV Areal Density	$3 \times 10^{6}$	cm^-2	Estimated from Fluorescence
Nuclear Rabi Frequency	57.7	kHz	Coherent Control of Proton Spin
NV Depth ($d_{NV}$)	10.3	nm	Estimated for NV2 (Ensemble)

Key Methodologies

The experiment relied on highly controlled MPCVD growth combined with advanced quantum sensing protocols:

Substrate Preparation: A Type-IIa (100) Single Crystal Diamond (SCD) substrate, prepared by High Pressure-High Temperature (HPHT) synthesis, was used. The substrate had natural isotopic abundance ($^{12}$C: 98.9%, $^{13}$C: 1.1%).
MPCVD Growth (Isotopic Control): A thin diamond layer was grown using Microwave Plasma Assisted CVD (MPCVD) at 800 °C and 25 Torr. Feed gas was H${2}$ and isotopically purified $^{12}$C CH${4}$ (99.999%).
Layer Structure:
- An undoped buffer layer was grown first ([CH${4}$]/[H${2}$] = 0.025%).
- A doped layer (tens of nanometers thick) was grown subsequently, incorporating Nitrogen (N/C ratio of 24%) to create near-surface NV centers.
Quantum Sensing Setup: Measurements were performed using a homebuilt confocal microscope (515-nm excitation laser) and a single-photon counting module. A static magnetic field ($B_{0}$) of 5-45 mT was applied parallel to the NV symmetry axis.
Spin Control: Microwave (MW) and Radiofrequency (RF) magnetic fields were delivered via a copper wire across the diamond surface to control the NV electronic spin and the proton nuclear spin, respectively.
NMR Spectroscopy: Multipulse sequences (specifically XY16-N) were used to record NMR spectra and determine hyperfine parameters ($A_{||}$, $A_{\perp}$).
Coherent Control & Polarization: Pulsed Dynamic Nuclear Polarization (PulsePol, using PolY/PolX sequences) was used to transfer electron spin polarization to the nuclear spin. Nuclear Rabi oscillations and Free Induction Decay (FID) were measured to confirm coherent control.

6CCVD Solutions & Capabilities

The successful replication and extension of this groundbreaking research—particularly the precise control over NV depth, isotopic purity, and dopant incorporation—is directly dependent on high-specification MPCVD diamond materials and fabrication expertise. 6CCVD is uniquely positioned to supply the necessary components.

Applicable Materials

To replicate or extend the atomic-scale NMR and quantum memory research presented, 6CCVD recommends the following materials:

6CCVD Material	Specification & Relevance	Customization Potential
Optical Grade SCD Substrates	Low-strain, high-purity Type-IIa (100) SCD substrates are essential for minimizing decoherence. We offer substrates up to 10 mm thick.	Custom dimensions and orientation available.
Isotopically Purified SCD/PCD	The paper used 99.999% $^{12}$C methane. 6CCVD specializes in growing SCD and PCD layers with custom isotopic purity (e.g., >99.99% $^{12}$C) to eliminate background $^{13}$C noise, crucial for single-spin detection.	Available for both thin films (0.1 µm) and thick substrates (up to 500 µm).
Controlled-Doping SCD Films	Precise control over the N/C ratio (24% used here) is necessary for achieving the target NV center density ($3 \times 10^{6}$ cm^-2) and depth (10-20 nm). 6CCVD guarantees sub-micron control over doping profiles.	Custom thickness (0.1 µm to 500 µm) and precise depth placement of the NV layer.
Boron-Doped Diamond (BDD)	For future research requiring integrated electrical control or electrochemical sensing alongside quantum sensing, 6CCVD offers highly conductive BDD films.	Available in SCD or PCD formats, with tunable doping levels.

Customization Potential

The experimental setup required precise surface access and RF/MW delivery (via a copper wire). 6CCVD offers integrated solutions to simplify device fabrication:

Custom Dimensions and Polishing: We provide SCD plates with ultra-low roughness (Ra < 1 nm) and PCD plates up to 125 mm (Ra < 5 nm), ensuring optimal surface quality for near-surface NV centers.
Integrated Metalization: The paper used external copper wiring. 6CCVD offers in-house metalization services (Au, Pt, Pd, Ti, W, Cu) for direct deposition onto the diamond surface, enabling integrated microwave striplines and RF antennas for enhanced spin control and signal delivery.
Laser Cutting and Shaping: Custom geometries, including precise laser cutting for chip integration or specific antenna designs, can be accommodated.

Engineering Support

The successful incorporation of protons during CVD growth, leading to built-in quantum memories, opens new avenues for quantum device engineering. 6CCVD’s in-house PhD team specializes in optimizing MPCVD recipes for specific quantum applications.

We offer comprehensive engineering support for projects involving:

Material Selection: Guidance on choosing the optimal SCD or PCD grade based on target coherence times ($T_{2}^{*}$ and $T_{2}$).
Recipe Optimization: Assistance in tuning gas flows, pressure, and temperature to achieve desired NV density and depth for atomic-scale NMR and quantum memory projects.
Device Integration: Consultation on metalization schemes and surface preparation for robust device integration.

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

View Original Abstract

We report detection and coherent control of a single proton nuclear spin using an electronic spin of the nitrogen-vacancy (NV) center in diamond as a quantum sensor. In addition to determining the NV-proton hyperfine parameters by employing multipulse sequences, we polarize and coherently rotate the single proton spin and detect an induced free precession. Observation of free induction decays is an essential ingredient for high resolution proton nuclear magnetic resonance, and the present work extends it to the atomic scale. We also discuss the origin of the proton as incorporation during chemical vapor deposition growth, which provides an opportunity to use protons in diamond as built-in quantum memories coupled with the NV center.

Tech Support

Original Source

DOI: https://doi.org/10.1063/5.0016196

References

2013 - Nanoscale nuclear magnetic resonance with a nitrogen-vacancy spin sensor [Crossref]
2013 - Nuclear magnetic resonance spectroscopy on a (5-nanometer)3 sample volume [Crossref]
2014 - Nuclear magnetic resonance spectroscopy with single spin sensitivity [Crossref]
2015 - Nanoscale nuclear magnetic imaging with chemical contrast [Crossref]
2015 - Nanoscale NMR spectroscopy and imaging of multiple nuclear species [Crossref]
2017 - Nanoscale nuclear magnetic resonance with chemical resolution [Crossref]
2016 - Nuclear magnetic resonance detection and spectroscopy of single proteins using quantum logic [Crossref]
2014 - Magnetic resonance detection of individual proton spins using quantum reporters [Crossref]
2012 - Maurer room-temperature quantum bit memory exceeding one second [Crossref]
2019 - A ten-qubit solid-state spin register with quantum memory up to one minute [Crossref]