Simultaneous temperature and magnetic field measurements using time-division multiplexing

At a Glance

Metadata	Details
Publication Date	2022-09-20
Journal	Chinese Optics Letters
Authors	Hao-Bin Lin, Ce Feng, Yang Dong, Wang Jiang, Xuedong Gao
Institutions	University of Science and Technology of China
Citations	4
Analysis	Full AI Review Included

Executive Summary

This research introduces a robust quantum sensing protocol utilizing Nitrogen-Vacancy (NV) centers in diamond for simultaneous and decoupled measurement of magnetic field and temperature.

Core Achievement: Successful implementation of a dual-microwave time-division multiplexing (TDM) protocol combined with Lock-in Amplifiers (LIAs) to directly separate temperature and magnetic field signals in real time.
Decoupling Mechanism: The TDM protocol leverages the distinct spectral shifts caused by temperature (common mode) and magnetic field (differential mode) to isolate the signals into two separate LIA channels.
High Sensitivity: The system demonstrated a magnetic field sensitivity of 3.4 nT/√Hz and a temperature sensitivity of 1.3 mK/√Hz.
Robustness: The method relies on the demodulated amplitude (R) of the LIA output, eliminating the need for complex phase synchronization and making the measurement highly robust against ambient F-noise and mutual coupling effects.
Efficiency: The protocol minimizes the required microwave (MW) resources by combining dual-frequency driving with TDM, achieving simultaneous measurement with fewer MW sources than traditional methods.

Technical Specifications

Parameter	Value	Unit	Context
Magnetic Field Sensitivity	3.4	nT/√Hz	System performance
Temperature Sensitivity	1.3	mK/√Hz	System performance
NV Center Ground State	Spin 1	Triplet State	Electronic ground state
Zero-Field Splitting (D)	2.87	GHz	Resonant MW frequency
ODMR Linewidth	~8	MHz	Measured spectral width
Bias Magnetic Field (DC)	46	Gauss	Applied by permanent magnet
Laser Wavelength	532	nm	Optical excitation source (MGL-N-532A)
Diamond Orientation	[111]	Crystal Plane	Grown via CVD
Diamond Dimensions	200 x 200 x 100	µm	Sample size
Signal Modulation Frequency	2.21	kHz	LIA reference frequency
LIA Time Constant	~15	ms	Signal processing setting

Key Methodologies

The simultaneous and decoupled sensing is achieved through a combination of Optically Detected Magnetic Resonance (ODMR) and a specialized time-division multiplexing (TDM) protocol.

NV Center Preparation: A [111] crystal-oriented diamond sample (200 µm x 200 µm x 100 µm) is used, coupled with a Composite Parabolic Lens (CPC) for efficient light collection.
Optical Excitation: A 532 nm laser is used for spin initialization (to the |0> state) and optical readout. Fluorescence is collected by a balanced photodetector (PDB210A).
MW Spin Control: Resonant MWs near 2.87 GHz are applied via a copper wire antenna to drive transitions between the |0> and |±1> spin states.
Dual-Frequency Driving: The MW frequency is modulated around the maximum slope points (f₁ to f₄) of the ODMR spectrum to maximize signal change per unit physical quantity variation.
- Temperature Measurement: Uses frequencies that suppress magnetic field effects (e.g., f₁ + f₃ or f₁ - f₄).
- Magnetic Field Measurement: Uses frequencies that suppress temperature effects (e.g., f₁ - f₃ or f₁ + f₄).
Time-Division Multiplexing (TDM): The output of the photodetector is routed through two MW switches (SW1, SW2) controlled by a pulse generator (TTL signals). This temporally separates the temperature and magnetic field signals.
Decoupled LIA Demodulation: The switched signals are sent to two separate Lock-in Amplifiers (LIA1 and LIA2) for processing:
- LIA1 measures T_meas (S₁₁ - S₁₂), providing temperature information directly.
- LIA2 measures B_meas (S₂₁ - S₂₂), providing magnetic field information directly.
Robust Readout: The system uses the LIA amplitude (R) value for sensing, ensuring the measurement is independent of the modulation phase and robust against phase mismatch errors common in single-shot experiments.

Commercial Applications

The ability to simultaneously measure and decouple temperature and magnetic fields with high sensitivity makes this technology valuable across several high-tech sectors.

Quantum Sensing and Metrology: Used for characterizing and stabilizing the operating environment of other quantum devices, particularly where laser heating introduces thermal noise.
Biomedical Imaging: High-resolution, localized sensing of magnetic fields and temperature within biological samples, crucial for monitoring drug delivery, magnetic particle imaging, or hyperthermia treatments.
Integrated Circuit (IC) Diagnostics: Non-invasive, high-spatial-resolution mapping of magnetic fields and thermal hotspots in microelectronic devices and ASICs (Application-Specific Integrated Circuits) during operation.
Materials Research: Studying magneto-thermal effects, phase transitions, and localized magnetic domains in novel materials under controlled thermal stress.
Environmental Monitoring: Developing robust, multi-modal sensors for harsh or noisy environments where magnetic and thermal fluctuations must be simultaneously tracked and separated.

View Original Abstract

Nitrogen-vacancy color centers can perform highly sensitive and spatially resolved quantum measurements of physical quantities such as magnetic field, temperature, and pressure. Meanwhile, sensing so many variables at the same time often introduces additional noise, causing a reduced accuracy. Here, a dual-microwave time-division multiplexing protocol is used in conjunction with a lock-in amplifier in order to decouple temperature from the magnetic field and vice versa. In this protocol, dual-frequency driving and frequency modulation are used to measure the magnetic and temperature field simultaneously in real time. The sensitivity of our system is about 3.4 nT/Hz and 1.3 mK/Hz, respectively. Our detection protocol not only enables multifunctional quantum sensing, but also extends more practical applications.

Tech Support

Original Source

DOI: https://doi.org/10.3788/col202321.011201