Long-range spin wave mediated control of defect qubits in nanodiamonds

At a Glance

Metadata	Details
Publication Date	2017-07-10
Journal	npj Quantum Information
Authors	Paolo Andrich, Charles F. de las Casas, Lanying Li, Hope Bretscher, Jonson R. Berman
Institutions	University of Chicago
Citations	141
Analysis	Full AI Review Included

6CCVD Technical Analysis: Long-Range Spin Wave Mediated Qubit Control

Reference: Andrich, P. et al. npj Quantum Information 3, 28 (2017). Application Focus: Scalable Quantum Sensing, Hybrid Spintronic Architectures, Coherent Qubit Control.

Executive Summary

This research successfully demonstrates highly efficient, long-distance coherent control of diamond nitrogen-vacancy (NV) spin qubits mediated by surface-confined spin waves (SWs) in a Yttrium Iron Garnet (YIG) film. This work has critical implications for developing next-generation, scalable quantum technologies.

Long-Range Coherent Control: Achieved robust, room-temperature coherent driving (Rabi oscillations, CPMG) of NV centers using Damon-Eshbach Spin Waves (DESWs) over distances exceeding 200 µm.
Ultra-Low Power Efficiency: The SW-mediated interaction enhances the local microwave magnetic driving field by a factor of up to >350, enabling qubit control with ultra-low input power down to 1 µW.
Noise Suppression: Demonstrated a specific microwave power regime where coherent SW-NV coupling dominates over the broadband incoherent magnetic noise generated by the ferromagnetic layer.
Surface Confinement Necessity: Results indicate that the strong coupling mechanism relies fundamentally on the surface confinement properties of DESW modes.
Scalability & Sensing: The technique is compatible with commercial nanodiamonds and flexible PDMS matrix transfer methods, supporting the development of high-sensitivity, widefield quantum sensing arrays and low-heat thermometry.
Material Opportunity: The observed coherence times (T_2,CPMG3 = 2.78 µs) highlight the immediate need for higher-quality diamond materials, such as high-purity Single Crystal Diamond (SCD), to maximize the performance potential of this hybrid architecture.

Technical Specifications

The core experimental results and material parameters are summarized below, confirming the feasibility of low-power, long-distance quantum control.

Parameter	Value	Unit	Context
Ferromagnetic Film Material	Yttrium Iron Garnet (YIG)	N/A	Epitaxially grown on GGG substrate
YIG Film Thickness	3.08	µm	Selected for DESW propagation
Nanodiamond (ND) Type	Commercial, ~500 NV centers	per particle	Embedded in PDMS matrix
Microstrip Line (MSL) Metalization	Ti (8 nm) / Au (200 nm)	Stack	Used for SW excitation/detection
Microwave Frequency Range	2.2 to 3.5	GHz	NV center ground state spin resonances
External Magnetic Field (B_ext) Range	0 to 250	G	Used to tune SW resonance
Required Power (SW Driving Regime)	1	µW	Power needed for clear Rabi oscillations
Magnetic Field Enhancement Factor	~100 to >350	Factor	SW-mediated amplification over direct antenna driving
Coherent Interaction Distance	> 200	µm	Distance from MSL for successful coherent control
SW Decay Length (Effective)	> 80	µm	Estimated minimum SW propagation distance
Coherence Time (T_2,Hahn)	1.54	µs	Measured on Nanoparticle NP-Q at 120 G
Coherence Time (T_2,CPMG3)	2.78	µs	Measured on Nanoparticle NP-R at 120 G
Optical Excitation Wavelength	532	nm	Continuous-wave laser

Key Methodologies

The experiment relied on precise material fabrication and advanced spin resonance protocols to integrate the quantum (NV centers) and spintronic (YIG SWs) elements.

Material Integration and Assembly:
- A single-crystal YIG film (3.08 µm thickness) on a Gadolinium Gallium Garnet (GGG) substrate was used as the SW propagation medium.
- Nanodiamonds containing NV ensembles were dispersed in a flexible Polydimethylsilosiloxane (PDMS) strip (~300 µm thick).
- Directed assembly and transfer printing positioned the PDMS/ND layer in direct, conformal contact with the YIG surface, ensuring the NV centers were located optimally for surface-confined DESW coupling.
Microwave Structure Fabrication:
- Microstrip Lines (MSLs) were fabricated on the YIG surface using electron-beam lithography, defining a Ti (8 nm) / Au (200 nm) stack.
- The MSLs were integrated into a coplanar waveguide configuration with ground planes to ensure optimal impedance matching and minimal microwave power loss. MSL separations of 50, 100, and 300 µm were tested.
Spin Wave Excitation and Detection:
- SWs were excited in the YIG film using microwave signals generated by a signal generator and amplified (up to 32 mW used in some scans).
- DESW modes were specifically excited by applying the external magnetic field (B_ext) parallel to the MSLs (θ = 0° case).
- The SW dispersion spectrum was experimentally verified by measuring microwave transmission between two MSLs using a network analyzer (Agilent E8364B).
Optically Detected Magnetic Resonance (ODMR):
- A custom confocal microscopy setup was used for optical addressing (532 nm laser) and Photoluminescence (PL) collection.
- ODMR measured changes in the NV centers’ PL as a function of the applied microwave frequency and magnetic field, identifying SW-NV resonance intersections.
Coherent Control Measurement:
- Pulsed ODMR sequences were employed (e.g., Rabi oscillations, Hahn echo, Carr-Purcell-Meiboom-Gill 3π pulse (CPMG3)) to demonstrate robust, coherent quantum control under ultra-low power (1 µW) conditions.

6CCVD Solutions & Capabilities

This research demonstrates a critical need for high-quality, customizable diamond substrates and precise metalization capabilities—the core expertise of 6CCVD. Our advanced MPCVD diamond solutions enable researchers to replicate this foundational work and extend it toward next-generation quantum devices.

Applicable Materials for Advanced Replication

The current T₂ coherence times (2.78 µs) are limited by the quality of the commercial nanodiamonds. To achieve the long coherence times necessary for practical quantum information processing, 6CCVD recommends transitioning to engineered MPCVD diamond substrates:

Material Grade	6CCVD Recommendation	Rationale & Advantage over Current NDs
High Purity (Electronic Grade) SCD	SCD Substrates (0.1µm - 500µm)	Superior Coherence: Offers isotopically engineered diamond for millisecond-scale T₂ times, overcoming the current material limitations.
Optical Grade SCD	SCD Wafers (Ra < 1nm Polishing)	Surface Quality: Required for precise, non-destructive conformal coupling with the YIG film, ensuring minimal scattering loss and optimal surface DESW interaction.
Large Format PCD	PCD Wafers (Up to 125mm)	Scalability: For large-area widefield sensing arrays where NV centers can be implanted directly into the diamond surface or the PCD used as a robust, high-surface-quality substrate for ND integration.
Boron-Doped Diamond (BDD)	Custom BDD Films	Future Integration: Required if the hybrid system needs electrical contacts or integrated microwave resonators (e.g., superconducting qubits) to complement the NV sensing element.

Customization Potential & Engineering Services

6CCVD provides end-to-end capabilities necessary to accelerate hybrid material integration research, moving from lab demonstration to engineered prototypes.

Precision Metalization for MSLs: The successful excitation of SWs relies on the quality of the metallic MSLs (Ti/Au stack). 6CCVD offers in-house capability for depositing custom metal stacks (Au, Pt, Pd, Ti, W, Cu) with precise control over thickness and adhesion, ensuring optimal performance for on-chip microwave delivery structures.
Custom Dimensions and Etching: We can provide diamond wafers/plates up to 125mm (PCD) or customize smaller SCD pieces via precision laser cutting, ensuring custom device dimensions are met exactly for interfacing with standard YIG/GGG substrates.
Ultra-Smooth Polishing: Achieving strong surface coupling is critical. 6CCVD guarantees ultra-low surface roughness: Ra < 1nm for SCD and Ra < 5nm for Inch-size PCD, ensuring highly conformal contact required for optimal DESW interaction.
Global Logistics: We handle complex global supply chain demands, providing global shipping (DDU default, DDP available) to deliver sensitive materials worldwide quickly and reliably.

Engineering Support

6CCVD’s in-house team of PhD material scientists specializes in optimizing diamond properties for quantum applications. We offer consultation to researchers replicating or extending this Spin-Wave Mediated Qubit Control project:

Substrate Selection: Guidance on selecting the appropriate crystal orientation (e.g., <100> vs. <111>) to align NV centers optimally with the external magnetic field (B_ext) and maximize coupling efficiency to the propagating SWs.
NV Engineering: Assistance in developing optimized NV creation protocols (implantation, annealing) to achieve high-quality NV centers with the longest possible T₂ coherence times in SCD/PCD.

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/s41534-017-0029-z