Quantum magnetometer based on cross-relaxation resonances in ensembles of NV-centers in diamond
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2022-01-01 |
| Journal | Журнал технической физики |
| Authors | Р. А. Ахмеджанов, Л. А. Гущин, I. V. Zelensky, Kupaev A.V., В. А. Низов |
| Institutions | Institute of Applied Physics |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research details the development and characterization of a novel quantum magnetometer based on Nitrogen-Vacancy (NV) centers in diamond, utilizing cross-relaxation (CR) resonances.
- MW-Free Operation: The core innovation is the elimination of microwave (MW) radiation, a requirement for traditional optically detected magnetic resonance (ODMR) schemes, significantly broadening the applicability of the sensor.
- Demonstrated Sensitivity: A magnetic field sensitivity of 18 nT/Hz1/2 was achieved in the scalar measurement regime using a 300 µm diamond crystal sensor.
- Performance Metrics: The achieved sensitivity is only 1.7 times inferior to the calculated maximum theoretical shot-noise limit (10.7 nT/Hz1/2) for the current optical setup.
- Sensor Material: The sensor utilizes a synthetic HPHT diamond crystal, electron-irradiated (1018 electrons per cm2) and annealed at 800 °C to create a high concentration of NV-centers.
- Detection Method: High-accuracy measurements are enabled by a balanced photodetector scheme and lock-in detection operating optimally at 0.75 kHz.
- Measurement Capability: The system supports both scalar (single projection) and vector (all projections) magnetic field measurements via an iterative procedure tracking the shift of CR resonances.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Achieved Sensitivity (Scalar) | 18 | nT/Hz1/2 | Average noise at frequencies > 0.6 Hz |
| Shot Noise Limit (Theoretical) | 10.7 | nT/Hz1/2 | Maximum possible sensitivity for the setup |
| Sensor Material | Synthetic HPHT | Diamond | Electron irradiated |
| Sensor Size (Crystal) | ~300 | µm | Used for the working model |
| NV-Center Irradiation Dose | 1018 | electrons per cm2 | Post-growth treatment intensity |
| Annealing Temperature | 800 | °C | Post-irradiation treatment |
| Laser Wavelength (Preferred) | 532 | nm | Cobolt 06-91 laser source |
| Optical Fiber Core Diameter | 200 | µm | Used for coupling light to the sensor |
| Numerical Aperture (NA) | 0.5 | - | Optical fiber specification |
| Operating Pump Intensity | 50 | W/cm2 | Limited by adhesive layer thermal stability |
| Optimal Pump Intensity (Contrast) | ~100 | W/cm2 | Intensity maximizing CR resonance contrast |
| Lock-in Detection Frequency (Optimal) | 0.75 | kHz | Alternating magnetic field component |
| Lock-in Detection Amplitude (Optimal) | 0.16 | mT | Alternating magnetic field component |
| CR Resonance Measurement Range | ±200 | µT | Range for each projection in vector regime |
Key Methodologies
Section titled “Key Methodologies”The magnetometer model relies on precise material engineering, optical alignment, and sophisticated electronic control:
- NV-Center Creation: A synthetic HPHT diamond crystal was selected, irradiated with an electron beam at 1018 electrons per cm2, and subsequently annealed at 800 °C to generate a high concentration of NV-centers.
- Sensor Assembly: The 300 µm diamond crystal was glued (using NOA63 optical adhesive) to the end face of a 200 µm core optical fiber (NA 0.5), ensuring the fiber axis aligned approximately with the diamond’s major crystallographic Z-axis ([0, 0, 1]).
- Optical Pumping: A 532 nm laser (Cobolt 06-91) was used for optical pumping. The operating intensity was limited to 50 W/cm2 to prevent overheating and destruction of the adhesive layer.
- Fluorescence Detection: Fluorescence was collected via the same fiber and routed to a PDB450A balanced photodetector. This balanced detection scheme was critical for suppressing residual noise from the laser intensity.
- Magnetic Field Control: A magnetic system consisting of a solenoid (scanning field) and two micro-coils (bias field) was used to apply and adjust the magnetic environment, enabling the tuning of the cross-relaxation resonance conditions.
- Lock-in Detection: An alternating magnetic field component (0.75 kHz, 0.16 mT) was applied to the solenoid. The sensor signal was processed using a custom FPGA board and Raspberry Pi 4 microcomputer to perform synchronous lock-in detection, maximizing the signal-to-noise ratio.
- Field Measurement: Magnetic field determination was achieved using an iterative procedure that measures the shift of the CR resonance centers (where the lock-in signal is zero). This procedure allows for both scalar and vector field determination.
Commercial Applications
Section titled “Commercial Applications”The development of a compact, MW-free, high-sensitivity NV-center magnetometer opens doors for applications previously limited by the need for bulky microwave components or interference concerns.
- Biomedical Imaging and Research: Ideal for magnetometry in biological environments (e.g., in-vivo sensing, magnetocardiography) where MW radiation is undesirable or near conductive tissues that shield RF signals.
- Microscopic Magnetic Sensing: Enables the creation of highly localized, non-invasive probes for measuring magnetic fields in integrated circuits, materials science samples, or small-scale devices.
- Industrial Non-Destructive Testing (NDT): Use in detecting magnetic anomalies or defects in materials without requiring complex RF shielding or large external coils.
- Compact Quantum Sensors: Provides a pathway for developing robust, small-form-factor quantum magnetometers for field use, navigation, or defense applications where size, weight, and power (SWaP) are critical constraints.
- High-Frequency Magnetic Field Measurement: The demonstrated operational frequency range (0.5-10 kHz) is suitable for measuring dynamic magnetic phenomena.
View Original Abstract
We create a working model of a magnetometer of a new type that is based on using cross-relaxation resonances in ensembles of NV-centers in diamond. This type of magnetometer does not require microwave radiation. For a sensor made out of a 300 micron diamond we demonstrate the magnetic field sensitivity of around 18 nT/Hz 1/2 . Keywords: cross-relaxation, NV-center, quantum magnetometer.