Electrical-Readout Microwave-Free Sensing with Diamond

At a Glance

Metadata	Details
Publication Date	2022-08-30
Journal	Physical Review Applied
Authors	Huijie Zheng, Jaroslav Hrubý, Emilie Bourgeois, Josef Souček, Petr Siyushev
Institutions	GSI Helmholtz Centre for Heavy Ion Research, Helmholtz Institute Mainz
Citations	5
Analysis	Full AI Review Included

Executive Summary

This research demonstrates a novel, microwave-free method for electron spin resonance (ESR) sensing using Nitrogen-Vacancy (NV) centers in diamond, relying solely on photoelectric current (PC) readout.

Microwave-Free Sensing: The technique eliminates the need for microwave control, addressing a major engineering hurdle related to microwave-induced noise, cross-talk, and integration complexity in conventional NV magnetometers.
Electrical Readout (PDMR): Photoelectric detection of Magnetic Resonance (PDMR) is used to monitor spin dynamics, specifically focusing on the Ground-State Level Anti-Crossing (GSLAC) feature at approximately 102.4 mT.
Enhanced Integration and Resolution: Electrical readout overcomes the spatial resolution limits imposed by optical diffraction, enabling compatibility with nanoscale electrode structures and scalable sensor arrays.
Volume Efficiency: PC detection provides better magnetic sensitivity per unit volume compared to Photoluminescence (PL) detection, as the effective PC interrogation volume is significantly smaller (estimated ratio 1:20 PC:PL).
Defect Characterization: The method successfully extracts ESR spectra for the P1 electronic spin bath in diamond, providing a tool for characterizing optically inactive defects and local spin environments.
Magnetometer Performance: A prototype magnetometer based on PC detection of GSLAC achieved a noise floor of 350 nT/√Hz (compared to 90 nT/√Hz for simultaneous PL detection in this setup).

Technical Specifications

Parameter	Value	Unit	Context
GSLAC Magnetic Field	102.4	mT	Ground-State Level Anti-Crossing point
NV-P1 Cross-Relaxation Field	51.2	mT	Resonance transition field
PC Magnetometer Sensitivity	350	nT/√Hz	Noise floor at GSLAC (Photoelectric Readout)
PL Magnetometer Sensitivity	90	nT/√Hz	Noise floor at GSLAC (Optical Readout)
PC Interrogation Volume Ratio	1:20	Ratio	Effective sensing volume (PC vs PL detection)
PC Signal Origin Depth (90% contribution)	0 to 30	µm	Depth below the diamond surface
Electrode Gap	5	µm	Coplanar Ti/Al electrode spacing
Applied Electrical Potential	17	V	Bias voltage across electrodes
Green Laser Wavelength	532	nm	Optical excitation source
Maximum Laser Power Tested	550	mW	Used for PC/PL power dependence scans
Magnetometer Modulation Frequency	3.3	kHz	Alternating B-field modulation
Magnetometer Modulation Depth	~0.1	mT	Alternating B-field modulation
Diamond Type	HPHT	N/A	High-Pressure High-Temperature single-crystal
Diamond Dimensions	2.1 x 2.3 x 0.65	mm³	Sample size
Initial Nitrogen Concentration	less than 200	ppm	Before irradiation
Electron Irradiation Dose	10¹⁸	cm^-2	14 MeV irradiation for NV creation
Annealing Conditions	700 °C for 3	hours	Post-irradiation thermal treatment

Key Methodologies

The experimental methodology combines advanced diamond material processing with specialized electrical and optical readout techniques.

Diamond Preparation:
- A single-crystal [111]-cut HPHT diamond was used.
- NV centers were created by electron irradiation (14 MeV, 10¹⁸ cm^-2 dose) followed by annealing at 700 °C for three hours.
Electrode Fabrication:
- Coplanar interdigitated Ti/Al electrodes were fabricated on the top surface using optical lithography.
- The metal stack was 20 nm Titanium covered by 100 nm Aluminum, with a 5 µm gap between contacts.
Photoelectric Readout Setup (PDMR):
- A static magnetic field (B_s) was applied along an NV axis using a custom electromagnet.
- A green laser (532 nm) was focused between the electrodes and modulated using an acousto-optic modulator (AOM).
- Photocurrent (PC) generated by photoionization was pre-amplified and detected synchronously using a lock-in amplifier (LIA) referenced to the laser modulation frequency.
Microwave-Free Sensing Protocol (GSLAC Magnetometry):
- The static magnetic field was tuned to the GSLAC working point (~102.4 mT), where the spin state is maximally sensitive to field changes.
- An alternating magnetic field (modulation frequency 3.3 kHz, depth ~0.1 mT) was superimposed on the static field.
- The LIA demodulated the PC signal, yielding a derivative signal proportional to the magnetic field change, which is used for precise magnetometry.
Interrogation Volume Analysis:
- The effective interrogation volume for PC and PL detection was mapped by scanning the laser focus along the z-axis (perpendicular to the surface).
- Modeling confirmed that 90% of the PC signal originates from the top 0-30 µm layer, validating the small sensing volume advantage of electrical readout.

Commercial Applications

The demonstrated microwave-free electrical readout technology is highly relevant for the development of next-generation quantum devices and advanced materials characterization.

Quantum Sensing and Metrology:
- High-Resolution Magnetometry: Enables the creation of compact, robust, and scalable magnetometers for applications in navigation, medical imaging (MRI/MEG), and fundamental physics.
- Hybrid Gradiometers: The sensing volume mismatch between PC (small, high-resolution) and PL (large, background) detection can be leveraged to build hybrid gradiometers.
Integrated Quantum Devices:
- Scalable Sensor Arrays: Electrical readout is compatible with nanoscale electrode fabrication, facilitating the integration of large-scale, dense NV sensor arrays on a chip.
- Quantum Diamond Solutions: Provides a pathway toward fully integrated quantum-diamond devices, overcoming the size and complexity limitations of optical table setups.
Materials Science and Defect Analysis:
- Optically Inactive Defect Probing: The ability to detect cross-relaxation features (like NV-P1) allows for quantitative measurement of photogenerated carriers and characterization of concentrations of various defects, including those that are optically inactive.
- Local Environment Characterization: Offers a tool for determining local spin densities and characterizing the dynamics of the spin environment within the diamond lattice.
Advanced Microscopy:
- Diffraction-Limited Microscopy: The electrical readout method allows for the development of quantum microscopes with spatial resolution potentially superior to existing optical diamond microscopes, as it bypasses the optical diffraction limit.

View Original Abstract

While nitrogen-vacancy (N-V & minus;) centers have been extensively investigated in the context of spin -based quantum technologies, the spin-state readout is conventionally performed optically, which may limit miniaturization and scalability. Here, we report photoelectric readout of ground-state cross-relaxation fea-tures, which serves as a method for measuring electron-spin resonance spectra of nanoscale electronic environments and also for microwave-free sensing. As a proof of concept, by systematically tuning N -V centers into resonance with the target electronic system, we extract the spectra for the P1 electronic spin bath in diamond. Such detection may enable probing optically inactive defects and the dynamics of local spin environment. We also demonstrate a magnetometer based on photoelectric detection of the ground -state level anticrossings (GSLACs), which exhibits a favorable detection efficiency as well as magnetic sensitivity. This approach may offer potential solutions for determining spin densities and characterizing local environment. <comment>Superscript/Subscript Available</comment

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevapplied.18.024079