Electrical control of coherent spin rotation of a single-spin qubit

At a Glance

Metadata	Details
Publication Date	2020-09-08
Journal	npj Quantum Information
Authors	Xiaoche Wang, Yuxuan Xiao, Chuan-Pu Liu, Eric Lee-Wong, Nathan J McLaughlin
Institutions	University of California, San Diego, Colorado State University
Citations	28
Analysis	Full AI Review Included

Technical Documentation & Analysis: Electrical Control of Coherent Spin Rotation in NV-Magnet Hybrid Systems

This document analyzes the research paper “Electrical control of coherent spin rotation of a single-spin qubit” (npj Quantum Information (2020)6:78) to highlight the critical role of high-quality MPCVD diamond and associated fabrication services offered by 6CCVD.

Executive Summary

This research successfully demonstrates an energy-efficient method for electrically controlling the coherent spin rotation rate ($f_{Rabi}$) of a single Nitrogen-Vacancy (NV) qubit within a hybrid solid-state system.

Core Achievement: Electrical tuning of the NV Rabi oscillation frequency by leveraging spin currents generated via the Spin-Orbit Torque (SOT) effect in an adjacent Platinum (Pt) layer.
Performance Gain: Achieved a significant enhancement of the NV coherent spin rotation rate, increasing $f_{Rabi}$ from a baseline of 0.8 MHz to 9 MHz (over one order of magnitude) at the Ferromagnetic Resonance (FMR) condition of the Yttrium Iron Garnet (YIG) magnet.
Mechanism: The SOT-generated spin currents efficiently tune the magnetic damping of resonant spin waves in the YIG, effectively amplifying the local microwave fields experienced by the NV center.
Material System: The device relies on high-quality diamond nanobeams containing NV centers transferred onto patterned YIG (20 nm or 100 nm) / Pt (10 nm) strips on Gd₃Ga₅O₁₂ (GGG) substrates.
Quantum Coherence: The process preserves excellent quantum coherence, with the measured spin coherent time being comparable to bulk diamond structures, validating the platform’s potential for scalable quantum computing and sensing.
Scalability: This methodology offers a new route for locally addressing individual NV spins in a scalable, energy-efficient manner, overcoming the limitations of conventional microwave striplines.

Technical Specifications

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

Parameter	Value	Unit	Context
YIG Film Thickness (Sputtered)	20	nm	Used for primary device structure
Platinum (Pt) Layer Thickness	10	nm	Used for Spin-Orbit Torque (SOT) generation
Diamond Nanobeam Dimensions	500 x 500 x 10	nm x nm x µm	Equilateral triangular prism shape
YIG Saturation Magnetization (M_s)	1.31 x 10⁵	A/m	Measured for 20 nm YIG film
Baseline Rabi Frequency ($f_{Rabi}$)	0.8	MHz	Measured off-resonance ($f \neq f_{FMR}$)
Enhanced Rabi Frequency ($f_{Rabi}$)	9	MHz	Measured at resonant FMR condition
Rabi Frequency Enhancement	~11.25	N/A	One order of magnitude increase
Applied Current Density ($J_c$)	Up to 1 x 10¹¹	A/m²	Used for electrical tuning via SOT
NV Spin Coherent Time	Comparable to Bulk	N/A	Preserved coherence, 1 order of magnitude > nanodiamonds
Microwave Field Estimate ($h_{rf}$)	0.5	Oe	Estimated from baseline $f_{Rabi}$

Key Methodologies

The experiment relies on precise material synthesis, nanoscale patterning, and advanced quantum measurement techniques:

Substrate and Film Growth: YIG films (20 nm or 100 nm) were deposited on (111)-oriented Gd₃Ga₅O₁₂ (GGG) substrates using magnetron sputtering or liquid-phase epitaxy (LPE).
Device Patterning: Standard photolithography and ion mill etching were used to define YIG/Pt strips (10 µm wide) and Au striplines/CPWs (500 nm thick) for microwave and electrical current delivery.
Diamond Nanostructure Fabrication: Diamond nanobeams containing NV centers were fabricated using a combination of top-down etching and angle-etching procedures.
Nanobeam Transfer: Fabricated diamond nanobeams were picked up and transferred onto the magnetic nanostructures using a tungsten tip under a micromechanical transfer stage, ensuring nanoscale proximity.
NV Initialization and Readout: A scanning confocal microscope was used. NV spin state was initialized using a green laser pulse (3 µs duration) and read out by monitoring the Photoluminescence (PL) generated during the first 600 ns of the readout pulse.
Rabi Oscillation Measurement: Coherent spin rotation was characterized using a sequence of synchronized green laser pulses, microwave pulses (at $f_{FMR}$), and electrical current pulses ($J_c$) applied to the Pt layer to minimize thermal heating.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the foundational diamond materials and advanced processing required to replicate and extend this high-impact research into scalable quantum platforms. Our capabilities ensure superior material quality, precise geometry, and integrated device readiness.

Applicable Materials

To achieve the high coherence times and reliable NV center performance demonstrated in this hybrid system, researchers require the highest quality diamond precursors.

Research Requirement	6CCVD Material Solution	Technical Justification
High-Coherence Qubits	Optical Grade Single Crystal Diamond (SCD)	Provides the lowest strain and highest purity necessary for long $T_2$ coherence times, essential for maintaining quantum fidelity during electrical manipulation.
Nanostructure Precursors	Custom SCD Plates/Wafers	SCD material supplied in thicknesses (0.1 µm to 500 µm) optimized for subsequent top-down etching processes (e.g., creating the 500 nm nanobeams).
Scalable Integration	Polycrystalline Diamond (PCD) Substrates	For future macroscale entanglement efforts, our PCD wafers (up to 125 mm diameter, Ra < 5 nm) offer a robust, large-area platform for integrating complex hybrid devices.
Electrical Control Layers	Boron-Doped Diamond (BDD)	While not used in this specific paper, BDD films can be integrated for on-chip electrical contacts or electrochemical sensing applications, leveraging diamond’s unique electrical properties.

Customization Potential

The success of this hybrid system relies heavily on precise nanoscale geometry and interface engineering. 6CCVD offers comprehensive services to meet these exacting specifications.

Customization Service	Relevance to NV-Magnet Research	6CCVD Capability
Ultra-Low Roughness Polishing	Critical for reliable nanobeam transfer and ensuring nanoscale proximity between the NV center and the YIG/Pt interface, minimizing surface-related decoherence.	SCD polished to Ra < 1 nm. Inch-size PCD polished to Ra < 5 nm.
Custom Metalization Stacks	The device requires precise Pt and Au layers. Future designs may require complex stacks for optimized SOT or microwave delivery.	In-house deposition of Au, Pt, Pd, Ti, W, and Cu layers, allowing for custom adhesion and contact stacks (e.g., Ti/Pt/Au).
Precision Shaping & Dicing	Providing pre-cut or laser-etched SCD pieces optimized for nanobeam fabrication processes, reducing material waste and improving yield.	Custom dimensions and laser cutting services available for plates/wafers up to 125 mm.

Engineering Support

6CCVD’s in-house PhD team specializes in the physics and engineering of diamond quantum materials. We provide authoritative support for researchers developing hybrid solid-state quantum systems and advanced quantum sensing platforms.

We assist clients in optimizing material selection, NV creation methods, and surface preparation to maximize spin coherence and integration efficiency for projects involving:

Spin-wave mediated entanglement.
Electrically controlled quantum gates.
High-sensitivity magnetic field sensing (metrology).

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We offer global shipping (DDU default, DDP available) to ensure rapid delivery of mission-critical materials.

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41534-020-00308-8