Broadband microwave detection using electron spins in a hybrid diamond-magnet sensor chip

At a Glance

Metadata	Details
Publication Date	2023-01-30
Journal	Nature Communications
Authors	Joris J. Carmiggelt, Iacopo Bertelli, Roland W. Mulder, A. Teepe, Mehrdad Elyasi
Institutions	Tohoku University, Advanced Institute of Materials Science
Citations	40
Analysis	Full AI Review Included

Technical Documentation & Analysis: Broadband Microwave Detection using Hybrid Diamond Sensors

6CCVD Reference Document: Hybrid Quantum Magnetometry (NV-YIG)

Executive Summary

This research demonstrates a significant advancement in quantum sensing by realizing broadband microwave detection using Nitrogen-Vacancy (NV) centers in a novel hybrid diamond-magnet sensor chip. 6CCVD is uniquely positioned to supply the high-purity, custom diamond materials required to replicate and scale this technology.

Broadband Sensing: Achieved gigahertz (GHz) bandwidth microwave detection at a fixed magnetic bias field, overcoming the narrow-band limitations of conventional NV Electron Spin Resonance (ESR) magnetometry.
Hybrid Platform: The sensor integrates a diamond membrane containing near-surface NV centers with a thin-film Yttrium Iron Garnet (YIG) magnet.
Frequency Conversion: Non-linear spin-wave dynamics in the YIG film act as a mixer, converting target microwave signals ($f_s$) to the fixed NV ESR frequency ($f_{NV}$) using a pump field ($f_p$).
Dual Protocols: Demonstrated two complementary conversion methods: Four-spin-wave mixing (yielding $\sim$1 GHz bandwidth) and Difference-Frequency Generation (enabling detection at multiple GHz detuning).
High Coherence: The converted idler fields exhibit high coherence, enabling high-fidelity, off-resonant Rabi control of the sensor spins and resolving the 3 MHz hyperfine splitting.
Material Requirement: The platform relies on a thin (50 µm) Single Crystal Diamond (SCD) membrane with shallow NV implantation (10-20 nm depth), a specialty of 6CCVD.

Technical Specifications

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

Parameter	Value	Unit	Context
Diamond Membrane Thickness	50	µm	Used for hybrid integration
Diamond Chip Dimensions	2 x 2 x 0.05	mm³	Experimental sample size
NV Center Depth	10 - 20	nm	Near-surface implantation required
Estimated NV Density	10³	/µm²	Sensor density used
YIG Film Thickness	235	nm	Magnetic insulator layer
Diamond-YIG Separation Distance	$\sim$2	µm	Limited by surface particles/dust
NV ESR Zero-Field Splitting (D)	2.87	GHz	Electronic ground state
Detection Bandwidth ($\Delta f$)	$\sim$1	GHz	Achieved via four-spin-wave mixing
Hyperfine Splitting Resolution	3.0(2)	MHz	Coherence measurement (¹⁵N nucleus)
Microwave Drive Power (Max)	14	dBm	Signal and pump power used for mixing
Laser Excitation Wavelength	515	nm	Green laser for initialization

Key Methodologies

The experiment successfully combined advanced material engineering with quantum control protocols to achieve broadband sensing.

Hybrid Sensor Platform Fabrication: A 50 µm thick Single Crystal Diamond (SCD) membrane, containing near-surface NV centers, was positioned onto a 235 nm thick YIG film grown on a 500 µm GGG substrate.
Microwave Excitation: A microstrip line was used to deliver “two-color” continuous-wave (CW) or pulsed signal ($f_s$) and pump ($f_p$) microwave fields, which excited spin waves in the YIG film.
Fixed Magnetic Bias Field: An external magnetic bias field ($B_{NV}$) was applied and aligned along one of the NV orientations to fix the ESR frequency ($f_{NV}$) via the Zeeman interaction.
Four-Spin-Wave Mixing Protocol: This degenerate process ($f_I = 2f_p - f_s$) was used to convert signals within a $\sim$1 GHz bandwidth, enabling off-resonant quantum sensing.
Difference-Frequency Generation Protocol: This process ($f_p - f_s = \pm f_{NV}$) was used for down-conversion of GHz signals to MHz frequencies, enabling detection at multiple GHz detuning from the ESR frequency.
Coherent Spin Control: Pulsed pump fields were used in conjunction with CW signal fields to generate a pulsed idler at $f_{NV}$, successfully driving coherent NV spin rotations (Rabi oscillations) with high fidelity.

6CCVD Solutions & Capabilities

6CCVD provides the specialized MPCVD diamond materials and engineering services necessary to replicate, optimize, and scale this hybrid quantum sensing platform for commercial or advanced research applications.

Applicable Materials

To replicate the high-coherence, shallow-NV platform described in the paper, 6CCVD recommends the following materials:

Optical Grade Single Crystal Diamond (SCD): Required for low-strain environments essential for maintaining long NV spin coherence times and high optical readout efficiency.
Custom Thickness SCD Wafers: The paper utilized a 50 µm thick membrane. 6CCVD routinely supplies SCD material in custom thicknesses ranging from 0.1 µm up to 500 µm, allowing researchers to optimize membrane thickness for mechanical stability and integration efficiency.
Shallow NV Precursors: While NV implantation is typically performed post-growth, 6CCVD provides the high-purity, low-nitrogen SCD material necessary to achieve the required near-surface NV depth (10-20 nm) and density ($10^3/\mu\text{m}^2$) via subsequent processing.

Customization Potential

The success of this hybrid sensor relies heavily on precise material dimensions and integrated microwave components. 6CCVD offers comprehensive customization services:

Requirement in Paper	6CCVD Capability	Optimization Benefit
Custom Dimensions	Plates/wafers up to 125 mm (PCD) and custom laser-cut SCD chips.	Enables scaling from 2x2 mm² lab samples to larger, integrated arrays.
Microwave Delivery	Custom Metalization: Internal capability for depositing Au, Pt, Pd, Ti, W, and Cu films.	Allows for direct fabrication of high-efficiency on-chip microwave structures (e.g., coplanar waveguides or striplines) directly onto the diamond surface, potentially reducing the 2 µm diamond-YIG separation distance and improving spin-wave excitation efficiency.
Substrate Thickness	SCD Substrates available up to 10 mm thick.	Provides robust handling for complex hybrid integration steps before thinning to membrane dimensions.
Surface Quality	Polishing: Achieved surface roughness Ra < 1 nm (SCD).	Crucial for minimizing scattering losses and ensuring optimal coupling when interfacing the diamond membrane with the YIG film.

Engineering Support

6CCVD’s in-house team of PhD material scientists and quantum engineers can assist with material selection and optimization for similar Hybrid Quantum Sensing projects. We offer consultation on:

Optimizing nitrogen concentration in SCD for desired NV density and coherence.
Designing custom metalization stacks for specific microwave frequency ranges.
Selecting appropriate diamond thickness and surface finish for integration with magnetic thin films (YIG, Van der Waals magnets, etc.).

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

View Original Abstract

Abstract Quantum sensing has developed into a main branch of quantum science and technology. It aims at measuring physical quantities with high resolution, sensitivity, and dynamic range. Electron spins in diamond are powerful magnetic field sensors, but their sensitivity in the microwave regime is limited to a narrow band around their resonance frequency. Here, we realize broadband microwave detection using spins in diamond interfaced with a thin-film magnet. A pump field locally converts target microwave signals to the sensor-spin frequency via the non-linear spin-wave dynamics of the magnet. Two complementary conversion protocols enable sensing and high-fidelity spin control over a gigahertz bandwidth, allowing characterization of the spin-wave band at multiple gigahertz above the sensor-spin frequency. The pump-tunable, hybrid diamond-magnet sensor chip opens the way for spin-based gigahertz material characterizations at small magnetic bias fields.

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41467-023-36146-3